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| Filtration Products for Air Monitoring and Sampling. Air quality is a concern worldwide due to its known impact on health and environmental issues. Globally, government regulators set standards to control pollution in the air we breathe. Pall began research on the development and production of filters for air sampling and analysis more than 40 years ago. Pall is now one of the world's largest suppliers of membranes and glass fiber filters designed specifically for environmental monitoring and testing. As knowledge about the impact of industrial by-products and the need for monitoring have increased, so has our commitment to supplying products for air analysis. You will find these environmental testing products referenced and recommended by regulatory agencies worldwide for air monitoring and hazardous waste analysis of both organic and inorganic matrices. For the most accurate results in your air analysis, select the membrane or filter media optimized for your application. Choose from the wide selection of complementary products, including filter holders, cassettes, and convenient accessory products. |
Tests show that the Pall Teflo filter, a Teflon® membrane with a poly-methylpentene ring gave the lowest positive artifact mass and the lowest co-efficient of variation in comparison to TX-40 and
other Teflon® membrane filters. As a result of these experiments, a conclusion was to recommend Teflo filters for measurements of PM at the 2007 FTP PM level of 0.01 g/hp-hr. Click to
download the full report.
other Teflon® membrane filters. As a result of these experiments, a conclusion was to recommend Teflo filters for measurements of PM at the 2007 FTP PM level of 0.01 g/hp-hr. Click to
download the full report.
Filtration Products for Air Monitoring and
Sampling. Air quality is a concern worldwide
due to its known impact on health and
environmental issues. Globally, government
regulators set standards to control pollution
in the air we breathe. Pall began research on
the development and production of filters for
air sampling and analysis more than 40 years
ago. Pall is now one of the world's largest
suppliers of membranes and glass fiber
filters designed specifically for
environmental monitoring and testing. As
knowledge about the impact of industrial
by-products and the need for monitoring have
increased, so has our commitment to
supplying products for air analysis. You will
find these environmental testing products
referenced and recommended by regulatory
agencies worldwide for air monitoring and
hazardous waste analysis of both organic
and inorganic matrices.
For the most accurate results in your air
analysis, select the membrane or filter media
optimized for your application. Choose from
the wide selection of complementary
products, including filter holders, cassettes,
and convenient accessory products.
Sampling. Air quality is a concern worldwide
due to its known impact on health and
environmental issues. Globally, government
regulators set standards to control pollution
in the air we breathe. Pall began research on
the development and production of filters for
air sampling and analysis more than 40 years
ago. Pall is now one of the world's largest
suppliers of membranes and glass fiber
filters designed specifically for
environmental monitoring and testing. As
knowledge about the impact of industrial
by-products and the need for monitoring have
increased, so has our commitment to
supplying products for air analysis. You will
find these environmental testing products
referenced and recommended by regulatory
agencies worldwide for air monitoring and
hazardous waste analysis of both organic
and inorganic matrices.
For the most accurate results in your air
analysis, select the membrane or filter media
optimized for your application. Choose from
the wide selection of complementary
products, including filter holders, cassettes,
and convenient accessory products.
SwRI 03.10415
2007 DIESEL PARTICULATE MEASUREMENT
RESEARCH
Project E-66
Executive Summary Report
Prepared by:
Imad A. Khalek, Ph.D.
Prepared for:
Coordinating Research Council, Inc.
U.S. Department of Energy/National Renewable Energy Laboratory
Engine Manufacturers Association
U.S. Environmental Protection Agency
California Air Resources Board
February 2008
DISCLAIMER
The Coordinating Research Council, Inc. (CRC) is a non-profit corporation supported by
the petroleum and automotive equipment industries. CRC operates through the committees
made up of technical experts from industry and government who voluntarily participate. The
four main areas of research within CRC are: air pollution (atmospheric and engineering studies);
aviation fuels, lubricants, and equipment performance; heavy-duty vehicle fuels, lubricants, and
equipment performance (e.g., diesel trucks); and light-duty vehicle fuels, lubricants, and
equipment performance (e.g., passenger cars). CRC’s function is to provide the mechanism for
joint research conducted by the two industries that will help in determining the optimum
combination of petroleum products and automotive equipment. CRC’s work is limited to
research that is mutually beneficial to the two industries involved, and all information is
available to the public.
CRC and the other sponsors of this project make no warranty expressed or implied on the
application of information contained in this report. In formulating and approving reports, the
appropriate committee of the Coordinating Research Council, Inc. has not investigated or
considered patents which may apply to the subject matter. Prospective users of the report are
responsible for protecting themselves against liability for infringement of patents.
SOUTHWEST RESEARCH INSTITUTE®
P.O. Drawer 28510 6220 Culebra Road
San Antonio, Texas 78228-0510
2007 DIESEL PARTICULATE MEASUREMENT
RESEARCH
Project E-66
Executive Summary Report
Prepared by:
Imad A. Khalek, Ph.D.
Prepared for:
Coordinating Research Council, Inc.
3650 Mansell Road, Suite 140
Alpharetta, GA 30022
February 2008
Approved:
Prepared by:
____________________________________
Imad A. Khalek, Program Manager-R&D Jeff J. White, Director
Emissions Research and Development Emissions Research and Development
Department (ER&DD) Department (ER&DD)
ENGINE, EMISSIONS AND VEHICLE RESEARCH DIVISION
This report shall not be reproduced, except in full, without the written approval of Southwest Research
Institute®. Results and discussion given in this report relate only to the test items described in this report.
Exec. Summary Report 03-10415
FOREWORD
Project E-66 was funded by the Coordinating Research Council (CRC), Department of
Energy / National Renewable Energy Laboratory (DOE / NREL), US Environmental Protection
Agency (EPA), Engine Manufacturers Association (EMA), and California Air Resources Board
(CARB). The sponsors were represented by Mr. Brent Bailey and Dr. Chris Tennant from CRC,
Dr. Doug Lawson from NREL, Dr. Bruce Cantrell and Mr. Matt Spears from EPA, Dr. Shirish
Shimpi from Cummins, and Mr. Hector Maldonado from CARB.
The Southwest Research Institute (SwRI) Principal Investigator and Project Manager was
Dr. Imad Khalek, Program Manager-R&D. Technical staff members who largely contributed to
this work were Mr. Daniel Preece, Principal Technician, Mr. Joe Sosa, Senior Technician, Mr.
Robert West, Staff Technician, Ms. Kathy Jack, Research Assistant, Mr. Keith Echtle,
Laboratory Assistant Manager, and Mr. Ernest Kruger, Laboratory Manager.
The work was initiated and reviewed by the E-66 Panel members who are listed below in
alphabetical order. Dr. Steve Cadle was the Chairman and Dr. Shirish Shimpi was the Co-
Chairman of the E-66 Panel. Mr. Brent Bailey and Dr. Chris Tennant from CRC were the Project
Managers representing the sponsors.
Mr. Brent Bailey, CRC
Dr. Ewa Bardasz, The Lubrizol Corp.
Dr. Nick Barsic, Deere & Company
Mr. Mike Bogdanoff, SCAQMD
Dr. Steve Cadle, General Motors Corp.
Dr. Bruce Cantrell, EPA
Mr. King Eng, Shell Global Solution (U.S.), Inc.
Mr. Tim French, EMA
Mr. Rob Graze, Caterpillar, Inc.
Dr. Doug Lawson, NREL
Mr. Hector Maldonado, CARB
Dr. Matti Maricq, Ford Motor Co.
Dr. Mani Natarajan, Marathon Oil Co.
Mr. Adewale Oshinuga, SCAQMD
Dr. Shirish Shimpi, Cummins Inc.
Mr. Matt Spears, EPA
Mr. Joe Suchecki, EMA
Dr. Chris Tennant, CRC
Mr. Bill Trestrail, International Truck and Engine Corp.
Mr. Ken Wright, ConocoPhillips
Exec. Summary Report 03-10415 iii
ACKNOWLEDGMENTS
SwRI thanks the Lubrizol Corp. for providing the engine oil, ConocoPhillips,
ExxonMobil, and BP for the fuel analysis, and Chevron Phillips and Sinclair for providing the
diesel fuel.
SwRI appreciates the assistance of TSI and Dekati in providing their equipment free of
charge during Phase 1 of Project E-66. SwRI also thanks AVL, Cummins, Horiba, Sensors, and
Sierra for providing their partial flow sampling systems that included the SPC, AEI/CUM,
MDLT, MPS, and BG3, respectively, and the personnel listed below, to support Phase 3 of
Project E-66. SwRI also thanks EPA and Caterpillar for the additional support through the
participation of their staff.
AVL North America, Inc.
Mr. Bill Silvis, initial contact and approval to participate in Phase 3
Dr. Shahin Nudehi, SPC setup, calibration, and operation
Mr. Gerald Marek, SPC setup and calibration
Caterpillar, Inc.
Mr. Rob Graze, Sierra BG3 setup and inspection during transient operation in Phase 3
Cummins Engine Co., Inc.
Dr. Shirish Shimpi and Mr. Bill Martin, initial contact and approval to participate in
Phase 3
Mr. Bret Rankin, AEI/CUM system setup, calibration, and operation
Horiba Instruments Ltd
Mr. Neal Harvey, initial contact and approval to participate in Phase 3
Mr. Otsuki Yoshinori, MDLT setup, calibration, and operation
Mr. Dave Laskowski, MDLT setup and calibration
Mr. Ichiro Asano, MDLT setup and supervision
Dr. Qiang Wei, MDLT setup and supervision
Dr. Mike Akard, MEXA-1370 PM (Particle Analysis Instrument) setup, calibration, and
operation
Sensors, Inc.
Mr. Atual Shah, initial contact and approval to participate in Phase 3
Dr. David Booker, MPS setup, calibration, and operation
Sierra Instruments, Inc.
Mr. Del Pier, initial contact and approval to participate in Phase 3
Mr. Gregory Pier, BG3 setup, calibration, and operation
US Environmental Protection Agency
Dr. Bob Giannelli, Sensors MPS setup, calibration, and operation
Exec. Summary Report 03-10415 iv
ACRONYMS
COV Coefficient of Variation
CPC Condensation Particle Counter
CRT-DPF Continuously Regenerative Technology-Diesel Particulate Filter
CVS Constant Volume Sampler
DMM Dekati Mass Monitor
DPF Diesel Particulate Filter
EC Elemental Carbon
EEPS Engine Exhaust Particle Sizer
EMTC Emission Measurement Testing Committee
ET Exhaust Temperature
FFV Filter Face Velocity
FTP Federal Test Procedures
HDD Heavy-Duty Diesel
NRTC Nonroad Transient Cycle
OC Organic Carbon
PDR Primary Dilution Ratio
PEFB Partial Exhaust Flow Bypass
PFSS Partial Flow Sampling System
PM Particulate Matter
PMP Polymethylpentene
PP Polypropylene
QA/QC Quality Assurance/Quality Control
QCM Quartz Crystal Micro-Balance
SDR Secondary Dilution Ratio
SMPS Scanning Mobility Particle Sizer
SPMS Solid Particle Measurement System
SPR Saturation Pressure Ratio
SRT Secondary Residence Time
ST Sampling Time
ULSD Ultra-Low Sulfur Diesel
CARB California Air Resources Board
CRC Coordinating Research Council
DOE Department of Energy
EMA Engine Manufacturers Association
EPA Environmental Protection Agency
ISO International Organization for Standardization
NREL National Renewable Energy Laboratory
US United States
SwRI Southwest Research Institute
Exec. Summary Report 03-10415 v
TABLE OF CONTENTS
Foreword ............................................................................................................................iii
Acknowledgments.............................................................................................................. iv
Acronyms.......................................................................................................................... V
1.0 Background............................................................................................................. 1
2.0 Introduction............................................................................................................. 3
3.0 Objectives ............................................................................................................... 4
4.0 Summary of Main Findings .................................................................................... 6
4.1 PHASE 1 ................................................................................................................. 6
4.1.1 Minimizing Gas Phase Artifact Collection ..................................................... 6
4.1.2 Effect of Filter Media on Quantification of PM Emissions ............................ 6
4.1.3 Variability in PM Emissions Using CRT-DPF with and without Bypass....... 7
4.1.4 Effect of Filter Face Velocity on PM Emissions............................................. 8
4.1.5 Effect of Filter Face Temperature on PM Emissions ..................................... 8
4.1.6 Filter Pre-Baking............................................................................................ 8
4.1.7 Real-Time Particle Instruments and the Filter-based Method ....................... 9
4.1.8 Summary of Phase 1...................................................................................... 10
4.2 PHASE 2 ............................................................................................................... 11
4.2.1
Particle Mass Filtration Efficiency of Teflo Filters...................................... 11
4.2.2
Effect of Sampling Time on PM emissions.................................................... 11
4.2.3
Effect of Dilution Ratio, Residence Time and System History on PM
Emissions Using Real Time Particle Instruments......................................... 12
4.2.4
Summary of Phase 2...................................................................................... 13
4.3
PHASE 3 ............................................................................................................... 14
4.3.1 PFSS Response Time..................................................................................... 14
4.3.2 PFSS as Secondary CVS Dilution Systems ................................................... 14
4.3.3 PFSS Measuring CRT-DPF Emitted PM Directly from Exhaust ................. 15
4.3.4 PFSS with CRT-DPF with Bypass ................................................................ 15
4.3.5 PFSS with Quartz Filters.............................................................................. 16
4.3.6 Summary of Phase 3...................................................................................... 17
5.0 Recommendations................................................................................................. 18
5.1 FILTER MEDIA AND HANDLING.................................................................... 18
5.2 DILUTION PARAMETERS AND FILTER FACE VELOCITY........................ 19
5.3 REAL TIME PARTICLE INSTRUMENTS......................................................... 20
5.4 PARTIAL FLOW SAMPLING SYSTEMS ......................................................... 20
6.0 References............................................................................................................. 21
Exec. Summary Report 03-10415
vi
1.0 BACKGROUND
Since the promulgation of diesel exhaust particulate matter (PM) emissions standards in
1988, the United States (US) Environmental Protection Agency (EPA) has defined diesel exhaust
particulate matter (PM) as the material that collects on a filter in a stream of exhaust that is
cooled and diluted to a temperature of less than or equal to 52°C. Gravimetric analysis of the
filter has been the basis for determining PM emissions from heavy-duty diesel (HDD) engines
for certification and other research and testing activities.
Although PM emissions standards from on-highway HDD engines were reduced by more
than 83 percent from 0.6 g/hp-hr in 1988 to 0.1 g/hp-hr in 1994, the established procedure for
PM collection and quantification was considered to have been adequate for regulatory test
procedural purposes.
In 2007, however, on-highway HDD engines are required to meet a PM emissions
standard of 0.01 g/hp-hr which represents a 90 percent reduction from the 1994 level. In
addition, the exhaust PM composition is expected to change because most engines will require
catalyzed diesel particulate filters (DPFs) to meet the stringent PM emissions standard. PM
composition is expected to consist mainly of volatile and semi-volatile hydrocarbon and sulfuric
acid species derived from unburned and partially burned fuel and lubricating oil. This low level
of volatile PM mass poses a technical challenge for the accurate mass measurement of PM using
the pre-2007 established sampling protocol. Measuring a low quantity of PM mass deposited on
a filter is a major challenge, but several other factors including filter handling, type of filter
media, formation of artifacts, sampling system conditioning, and dilution parameter selection
may also affect PM measurement.
Recognizing some of the PM measurement challenges for 2007, EPA modified the
definition of PM by narrowing the filter face temperature from a peak of below or equal to 52°C
to being continuously maintained in a range between 42°C and 52°C (47°C ± 5°C). EPA also
implemented several changes to the secondary dilution tunnel of the constant volume sampler
(CVS) as well as to the filter media, filter handling, and weighing chamber specifications in
order to improve the quantification of PM mass emissions from engines that meet the 2007
standards [1]. CVS is the EPA-approved system for measuring HDD particulates.
Although the new PM measurement procedures specified by EPA for 2007 were
demonstrated by EPA to achieve less than a 10 percent coefficient of variance (COV) at 0.004
g/hp-hr [2], preliminary data produced by SwRI for EPA, using the 2007 sampling procedures,
gave a COV of 23 percent for four hot-start FTP transient tests at the 0.0034 g/hp-hr level [3].
Although the COV difference between SwRI and EPA may be partially explained by differences
in the sampling and handling methodologies, background particle level, and the variety of engine
and aftertreatment systems tested, these results suggest that additional effort is required to fully
understand the variability present in PM measurement for engines equipped with DPFs.
Exec. Summary Report 03-10415 1 of 21
While the new 2007 sampling methodology is expected to improve quantification of PM
mass and reduce variability in comparison to the current sampling method, improvements were
believed necessary and possible to achieve through further investigation. For example, several
variables likely require more specific definition given the measurement challenges of 2007 PM
emission limits. The objective of E-66 was to explore the benefit of more specific definitions of
several variables on PM mass measurement. Parameter evaluations included:
Secondary dilution tunnel geometry and residence time
Filter face velocity
Dilution air temperature
Means of achieving the 47°C ± 5°C filter face temperature
Primary and secondary dilution ratio requirements
Verification of filter material influence
Filter equilibration time (currently time periods of 30 minutes to 60 hours are allowed)
Primary and secondary dilution air filtration requirements
(Currently, 98% efficient HEPA filtration is required for primary dilution air,
and 99.97 % efficient filtration for secondary dilution air).
In light of these issues, Project E-66, entitled “2007 Diesel Particulate Measurement
Research,” was initiated by the CRC Real World Vehicle Emissions and Emissions Modeling
Group. The primary goal for this project was to investigate the above noted factors with the
intention of improving future PM measurement. Additional investigations compared the PM
emission performance of partial flow sampling system (PFSS) units and real-time PM
measurement instruments to the CVS.
Exec. Summary Report 03-10415 2 of 21
2.0 INTRODUCTION
Project E-66 consists of Final Reports on Phases 1 [4], 2 [5], and 3 [6] submitted to the
project sponsors and is available to the public at the CRC Website (crcao.org). This executive
report summarizes the main conclusions for all three phases of Project E-66. It also includes a set
of recommendations for consideration in future activities requiring PM measurement from diesel
engines.
Exec. Summary Report 03-10415 3 of 21
3.0 OBJECTIVES
Project E-66 was divided into Phases 1, 2, and 3. The same diesel engine was used in all
phases of the project. The engine was a 1998 DDC Series 60 HDD engine equipped with a
continuously regenerative technology diesel particulate filter (CRT-DPF) or a CRT-DPF with a
partial exhaust flow bypass (CRT-DPF with Bypass) to elevate PM emissions to near 70 to 80
percent of the 2007 PM emissions standard. The fuel used for Phases 1 and 2 was an ultra-low
sulfur diesel (ULSD) fuel with a sulfur content of 6.9 ppm. Phase 3 ULSD fuel was from a
different batch with a sulfur content of 3.8 ppm.
The objectives of Phase 1 were to:
Minimize gas phase hydrocarbon adsorption on the filter used for PM
collection from a dilute exhaust sample by using a carbon denuder upstream
of the filter.
Investigate the effect of filter media and filter face velocity on PM collection
and emissions.
Compare the performance of several real time particle measuring
instruments including Engine Exhaust Particle Sizer (EEPS), Scanning
Mobility Particle Sizer (SMPS), Dekati Mass Monitor (DMM), and Quartz
Crystal Microbalance (QCM) with that of the CVS filter-based method that
meets the 2007 PM sampling protocol.
The objectives of Phase 2 were to:
Investigate the effect of filter face velocity (FFV) and sampling time on
solid and volatile particle collection by a Teflon® membrane filter, namely
the Pall Teflo filter.
Examine the effect of dilution conditions, such as the CVS primary dilution
ratio, residence time and temperature, and secondary dilution ratio and
residence time, on particle measurement using the real time particle
instruments listed in Phase 1, and Teflo filters in limited experiments.
Study the effect of exhaust stack and dilution system conditioning history on
particle measurement.
The objectives of Phase 3 were to:
Compare the PM emissions measured from the 1998 DDC Series 60 HDD
engine equipped with a CRT-DPF using six different secondary dilution
systems that were coupled to the full flow CVS. These dilution systems
included one short and one long residence time secondary tunnels from
SwRI that were used only with the full flow CVS, and four partial flow
sampling system (PFSS) units, namely the Cummins AEI/CUM, AVL SPC,
Horiba MDLT, and Sierra BG3. The PFSS units could be either used with
the full flow CVS as secondary dilution systems, or used as independent
dilution systems sampling directly from raw engine exhaust. Engine tests to
generate exhaust species for these particulate measurement system
evaluations consisted of two steady-state (rated speed, 100% and 10% load)
and two transient engine tests, the Federal Test Procedure (FTP) and the
Nonroad Transient Cycle (NRTC).
Exec. Summary Report 03-10415
Compare the PM emissions measured using all the PFSS units mentioned
above on engine exhaust in addition to the Sensors micro-proportional
sampler (MPS) with the PM emissions measured using the CVS. The work
was performed using the CRT-DPF and CRT-DPF with Bypass, as
illustrated in the following figure. The PM was collected on Teflo filters for
all experiments. Quartz filters were used in very limited experiments using
the CRT-DPF with Bypass. These filters were analyzed for PM organic and
elemental carbon and sulfate using the Horiba MEXA-1370.
CRT-DPF
Bypass Valve
Sample Area
Engine
CRT-DPF BYPASS SYSTEM
Exec. Summary Report 03-10415
4.0 SUMMARY OF MAIN FINDINGS
This summary report is intended to present the main findings for Phases 1, 2, and 3 of
Project E-66. For more in-depth information, the reader is referred to Phases 1, 2, and 3 final
reports, which are available at the CRC website.
4.1 Phase 1
This section includes the main findings from Phase 1 of Project E-66. Phase 1 investigated
PM measurement artifacts and variability, filter face velocity, and real time particle instruments.
4.1.1 Minimizing Gas Phase Artifact Collection
Filters used for PM collection are prone to gas phase adsorption that add weight to the
filter during PM collection resulting in “positive artifacts.” The gas phase materials are mainly
volatile hydrocarbon species derived from partially burned and unburned fuel and lube oil. In
Phase 1 of Project E-66, an attempt was made to add a carbon denuder in the PM sample train,
upstream of the filter, to remove volatile hydrocarbon material from the gas phase before
reaching the filter in order to reduce positive artifacts. The performance of the carbon denuder in
adsorbing hydrocarbon was not consistent. Furthermore, the carbon denuder failed to regenerate
after reaching saturation. Thus, it was decided early in the program to discontinue the
development and use of the carbon denuder, and rely on the quality of filter medium itself to
minimize gas phase adsorption.
4.1.2 Effect of Filter Media on Quantification of PM Emissions
Several filter media types were used on this project including:
Filter Media Manufacturer
Initial
Weight,
mg
Material Efficiency,d
%
Thickness,
µm
Pressure Drop,g
inH2O
Teflo Pall 180
PTFEa Membrane, 2 µm pore
size, PMPb ring 99.99 46/508e 30
Teflon® Whatman 143
PTFE Membrane, 2 µm pore
size, PPc ring 99.70 40/ 380e 90
PTFE-PP Donaldson 157
PTFE Membrane, 2 µm pore
size, PPc ring 99.99f 40/508e 78
PTFE-PE Donaldson 119
PTFE Membrane, 2 µm pore
size, PTFE ring 99.99f 40/254e 78
Zefluor Pall 242
PTFE Membrane with PTFE
support 99.99 152 60
TX-40 Pall 91
PTFE Coated Borosilicate Glass
Fiber 99.90 178 30
aPolytetrafluoroethylene (Teflon®)
bPolymethylpentene
cPolypropylene
dFollowing ASTM D 2986-95A 0.3 µm (DOP) at 32 L/min/100 cm2 filter media.
eTotal Ring Thickness
g Approximate pressure drop at 75 cm/sec
Exec. Summary Report 03-10415
For an engine equipped with a CRT-DPF, the reported PM emissions for tests conducted
here ranged from 3% to 23% of the 2007 PM limit. These low PM measurements challenged
the ability of filter weighing procedures that were specified for 2007, therefore, to improve the
understanding of PM measurement capability at the specified 2007 limit, the E-66 investigators
decided to bypass a portion of exhaust around the CRT-DPF to achieve a PM level that was
about 70% of the 2007 limit, rather than the 3% to 23% range obtained with all exhaust passing
through the CRF-DPF.
Performance of Teflon®, Teflo, PTFE-PP, and PTFE-PE filter media was similar, i.e., no
major PM difference was noted among these media. Performance of Pallflex TX-40 filters
differed from the above media as follows: PM indicated by Pallflex TX-40 filters was greater
than Teflon® and Teflo filters by a factor of approximately two when sampling CRT-DPF
exhaust without Bypass at 5% of the 2007 PM limit, and by about 10% when sampling CRTDPF
exhaust with Bypass at 70% of the 2007 PM limit.
These tests showed that the Pall Teflo filter, a Teflon® membrane with a
polymethylpentene ring, gave the lowest positive artifact mass and the lowest coefficient of
variation in comparison to TX-40 and other Teflon® membrane filters. As a result of these
experiments, a conclusion of E-66 was to recommend Teflo filters for future measurements of
PM at the 2007 FTP PM level of 0.01 g/hp-hr.
4.1.3 Variability in PM Emissions Using CRT-DPF with and without Bypass
Forty-six repeat test cycles were generated for the hot-start FTP transient cycle using a
CRT-DPF with an engine emission level at 5 percent of the 2007 PM standard (0.0005 g/hp-hr)
and a coefficient of variation (COV) of 50 percent (0.00025 g/hp-hr). For the rated power
condition, the COV was 35 percent based on 49 repeat test cycles. (These low level PM values
could have been reported as 0.5 mg/hp-hr and 0.25 mg/hp-hr, but since regulations are stated in
units of g/hp-hr, these units were retained although the large number of decimal places may
appear awkward.)
For the CRT-DPF with Bypass at an emission level of 70 percent of the 2007 standard (0.007
g/hp-hr), the COV for the FTP was 8.6 percent (0.0006 g/hp-hr), a measurable improvement
compared to the 50 percent COV without CRT-DPF exhaust Bypass.
If one assumes that the absolute values of the COVs obtained at 5 percent and 70 percent
of the 2007 standard are total measurement errors that are independent of the PM emission level
or the PM mass collected on the filter, one can predict the COV at the standard by dividing those
absolute values over the 2007 PM standard of 0.01 g/hp-hr. Such calculations predict a COV in
the range between 2.5 percent (0.00025/0.01 x 100) and 6 percent (0.0006/0.01x100) at the
standard level of 0.01 g/hp-hr.
4.1.4 Effect of Filter Face Velocity on PM Emissions
For an engine equipped with a CRT-DPF with Bypass, the influence of filter face velocity
at a constant 47°C filter face temperature is as follows:
Engine Test Filter Face Velocity Change PM Decrease
Hot-start FTP 24 cm/sec to 120 cm/sec 25%
Rated rpm, 10% load 60 cm/sec to 120 cm/sec 60%
These reported PM reductions are believed due to the volatile portion of PM as the
following argument outlines, and as also confirmed by experiments performed during Phase 2 of
E-66. Gas phase adsorption on the filter and filter saturation may be responsible for such large
changes in measured PM emissions. For example, the flow volume passing through the filter at
120 cm/sec is about five times larger than the volume sampled at 24 cm/sec. If the filter that is
running at 120 cm/sec reaches its adsorption capacity early during the FTP transient cycle, then
its filter collected PM will not include positive artifact for the later portion of the cycle. In
contrast, the 24 cm/sec filter reaches adsorption capacity toward the FTP cycle end, and is
expected to result in a larger positive artifact.
Diesel particles are composites that consist of solid soot and adsorbed volatile species.
The objective of the subject program is to collect these composite particles, to avoid
accumulating gas phase volatiles onto the filter (positive artifact), and to avoid desorbing the
volatile phase component of the composite particles (negative artifact). In order to minimize
positive artifacts associated with gas phase adsorption on the filter during PM collection, it is
best to reach filter saturation as soon as possible by going to a high filter face velocity. Also,
higher filter face velocity seems to give a better agreement between the filter-based PM mass
emissions and real time particle instruments that are insensitive to positive or negative artifacts.
A filter face velocity that is too high (greater than 100 cm/sec) may result in a negative artifact.
4.1.5 Effect of Filter Face Temperature on PM Emissions
For the case where the engine was equipped with the CRT-DPF with Bypass set to
provide a PM emission rate at 70 percent of the 2007 PM standard, results indicated no
difference in measured PM emissions for the FTP transient cycle between using a Teflo filter
face temperature of 47°C and 25°C. Studies in PM mass collection sensitivity to filter
temperature were not performed at levels below 10% of the 2007 standard (Bypass disabled).
Therefore, the aforementioned conclusions cannot be applied to a CRT-DPF without Bypass.
Further study is required.
4.1.6 Filter Pre-Baking
To avoid contaminants loss from the sample filter during PM collection (negative
artifacts) at a filter face temperature of 47°C ± 5°C, the Teflo filters were first pre-baked in a
vacuum oven for 24 hours at a temperature of 52°C. After pre-baking and conditioning in the
weighing chamber for 24 hours, each pre-baked Teflo filter lost about 5 µg of its original weight
prior to baking. The 5 µg lost are likely to be some unknown volatile contaminant on the filter as
received from the manufacturer.
In order to test whether or not pre-baking the filter is necessary for testing, PM emissions
from a total of 14 repeats of the FTP transient cycle were performed using pre-baked and
unbaked Teflo filters. For an exhaust configuration using CRT-DPF with Bypass at an emission
level of 70 percent of the 2007 PM standard (0.007 g/hp-hr) and a filter weight gain of about 70
µg, no significant difference was observed in PM emissions between using pre-baked and
unbaked filters.
No experiments were performed to compare the PM emissions performance using baked
and unbaked-filter for an exhaust configuration that includes CRT-DPF without bypass, where
the PM emissions level for the FTP is expected to be at 5 percent of the 2007 PM standard
(0.0005 g/hp-hr), with an expected filter weight gain of about 5 µg. Thus, it is not clear whether
or not filter pre-baking will be necessary when testing with CRT-DPF without Bypass. Also, it is
not clear whether or not different filter batches contain more or less contaminant than the one
measured during this work. Thus, as a precaution, it is recommended that filter pre-baking be
used to reduce filter batch to batch variability when using CRT-DPF without Bypass.
4.1.7 Real-Time Particle Instruments and the Filter-based Method
Three real time particulate instruments were compared with simultaneous measurements
of CVS-based PM. These real time instruments were the DMM-230, EEPS and SMPS. The
DMM-230 measures real time particle size and mass and the EEPS measures real time particle
size and number concentration. The SMPS provides particle size and number concentration, but
is limited to steady-state engine operation. If particle density is known, the EEPS and SMPS
results can be converted to mass. A linear regression with a correlation coefficient (R2) of better
than 0.95 at the 95 percent confidence level was obtained for a total of 46 data points. Note that
the observed good linear regression applies only to an exhaust configuration using a CRT-DPF
with Bypass, where solid particles contribute to PM emissions. These results do not guarantee
the same conclusion when using a CRT-DPF without Bypass, where the PM emission is
composed mainly of volatile material.
Another real-time PM instrument, the Quartz Crystal Monitor (QCM) was tested, but
results indicated that more in-depth investigation was required than the E-66 schedule
permitted. In summary, proper operation of the QCM requires firm adhesion of all particles
onto the quartz crystal, thus causing a unique instrument response. A unique response is not
always attained for particles characterized by an agglomerate morphology. Particles that are
attached to other particles, a typical agglomerate character that is true for diesel particulate, do
not exert the same force on the quartz crystal as particles that firmly attach directly to the
crystal. Under circumstances of agglomerates with very low particle deposit, for example, less
than 0.5 micrograms, a QCM may demonstrate a unique response to mass deposit. Non-
agglomerate particles may produce a unique response at higher than 0.5 microgram deposit.
4.1.8
Summary of Phase 1
Minimizing gas phase adsorption on the filter by using a carbon denuder was not
successful due to the difficulty associated with regenerating the denuder after
saturation. Thus, the use of a carbon denuder was discontinued, and minimizing
positive artifacts was achieved by the use of Teflon® membrane filters instead.
Filter pre-baking in a vacuum oven at 52°C for 24 hours did not affect PM
emissions, compared to unbaked filters using the CRT-DPF with Bypass. No
experiments were done to verify the effect of pre-baking filters when using CRTDPF
without Bypass. Because the Teflo filter lost about 5 µg during pre-baking,
an amount similar to filter weight gain for the FTP transient cycle when using
CRT-DPF without Bypass, pre-baking is recommended as a precaution when
using CRT-DPF without Bypass to minimize or avoid negative artifact during PM
collection.
At a PM emission level that is 5 percent of the 2007 standard, all Teflon®
membrane filters such as those made by Pall, Whatman, and Donaldson reported
equivalent PM emission levels at 0.0005 g/hp-hr, however, successive
measurements could vary by approximately half of the mean value. In summary,
a measured value is best reported as 0.0005 ± 0.00025 g/hp-hr. The Pallflex TX40
filter, due to PM volatile artifact, measured a PM emission level that was a
factor of 2 higher than that produced using the Teflon® membrane filters.
At a PM emission level that was 70 percent of the 2007 PM standard, Teflon®
filters measured 0.007 ± 0.0006 g/hp-hr. The PM emission level reported using a
TX-40 filter was about 10 percent higher than the level reported using the Teflon®
membrane filters, likely due to volatile artifact. This artifact (10% of 0.007) was
slightly larger than the Teflon® membrane filter 1s (±0.0006). The Pall Teflo filter
gave the lowest variability (±0.00038 g/hp-hr) along with the lowest pressure
drop among all Teflon® membrane filters tested. This filter was selected for
subsequent E-66 sampling from engines with wall-flow DPFs.
PM measurement coefficient of variation (COV) summary:
At <10 percent of the 2007 PM standard, COV is 50%.
At the 2007 PM standard, COV is expected to be 6%.
Increasing filter face velocity from 24 cm/sec to 120 cm/sec produced a 25
percent reduction in measured PM emissions during the FTP transient cycle.
Controlling filter face velocity to a narrow range may help reduce the variability
in PM measurement.
A linear regression with a correlation coefficient (R2) of better than 0.95 was
obtained for n=46 tests between the CVS filter-based PM mass and PM mass
derived from real time instruments such as the DMM-230, EEPS, and SMPS,
using CRT-DPF with Bypass. Real time instrument vs. CVS correlation was not
evaluated when using CRT-DPF without Bypass
4.2 Phase 2
Phase 2 was performed using the same Phase 1 engine equipped with a CRT-DPF. Teflo
membrane filters were used throughout the entire project phase as the preferred filter medium
unless otherwise specified. Phase 2 investigated filtration efficiency and sampling time when
using Teflo filters. Phase 2 also investigated the effect of dilution ratio and residence time using
real time instruments, and secondary dilution residence time using Teflo filters.
4.2.1 Particle Mass Filtration Efficiency of Teflo Filters
Unlike gaseous emissions that can be reported as a single number, usually concentration,
particle measurement consists of a two-dimensional array involving size and concentration. The
following brief table reports Teflo filter particle mass filtration efficiency and particle size ranges
for 60 to 129 cm/sec filter face velocities. These experiments were performed using diesel
exhaust treated to remove volatiles and thus provide only solid particles to the Teflo filters.
Particle Size Mass Collection Efficiency
7nm to 300nm 99%
<30nm 95%
<10nm 85%
This work showed that the filtration efficiency of solid exhaust PM mass is high, over 99
percent within the range of 60 to 129 cm/sec filter face velocity. It also demonstrated that the
effect of filter face velocity on PM mass collection observed in Phase 1 was mainly due to
volatile PM and not solid PM.
4.2.2 Effect of Sampling Time on PM emissions
At rated speed, 100 percent load, changing sampling times and face velocities resulted in
the following observations:
Sample Time Increase
20 min. to 50 min.
60 min. to 150 min.
Filter Face Velocity
125 cm/sec
30 cm/sec
Decrease in PM Reported
40%
70%
These results are for an exhaust aerosol that was about 5 percent of the 2007 PM emission
standard. It is important to note that the effects of filter face velocity and sample time on filter-
based PM emissions are not independent of each other. High filter face velocity and short sample
time may be equivalent to low filter face velocity and long sample time only if the flow volume
is the same, and particle phase volatile material depositing on the filter is stable. In case the
aerosol is unstable and subject to evaporation, the long sample time may bias the results to lower
PM emissions due to negative artifacts.
In order to reach filter gas phase saturation as quickly as possible, a high filter face
velocity is desired. In order to minimize negative artifacts, a short sample time is desired, but in
order to minimize positive artifact a long sample time is desired. However, in most engine
testing, the sample time is dictated by the length of the cycle to be run. Thus, the only means of
minimizing positive artifact is by going to a high filter face velocity within the upper limit
defined by EPA at 100 cm/sec.
In cases where the length of testing is not predefined, one tends to increase filter face
velocity and sample time to maximize PM loading on the filter, particularly when the PM
emission level is well below the 2007 PM standard. While increasing filter face velocity and
sample time minimizes positive artifact collection relative to the total particle mass, it may lead
to negative artifacts; this practice presents a challenge for filter media to accurately evaluate PM
emissions at an emission level well below the 2007 PM standard.
4.2.3
Effect of Dilution Ratio, Residence Time and System History on PM Emissions Using
Real Time Particle Instruments
The SMPS, EEPS, DMM-230, and QCM were used to study the effect of dilution
parameters on PM emissions. With some of these real time instruments, a large matrix of
different dilution parameters such as primary and secondary CVS dilution ratio and residence
times were investigated. Teflo filters were only used later to determine the effect of secondary
residence time on PM emissions for comparison with that observed using real time instruments.
Depending upon the engine operating condition, increasing the primary dilution ratio from
4 to 9 while holding the secondary dilution ratio at two resulted in 5 to 20 fold increase in PM
emissions using SMPS, EEPS, DMM-230 and QCM. Since these four instruments employed
three different physical measurement principles, some differences in particle mass were
expected, however, all of these instruments reported similar response to dilution ratio, namely,
higher dilution ratio increased the indicated PM. Increasing the secondary dilution ratio from 1.5
to 4.5 while holding the primary dilution ratio at two resulted in two-fold PM mass increase.
Primary dilution ratio changes have greater influence on particle mass than secondary dilution
ratio changes, within the range of dilution ratios investigated here, thus lab to lab comparisons at
2007 particle emission levels need to coordinate primary dilution ratios more carefully than
secondary dilution ratios, but the factor of two influence of secondary dilution ratio is not to be
viewed as unimportant.
The secondary dilution residence time had a very significant influence on particle mass
emissions. A long residence time of 10 to 30 seconds showed an increase in PM mass emissions
by more than two orders of magnitude, compared to a residence time of less than one second,
using data obtained from the real time particle instruments. During Phase 3, this phenomenon
was also demonstrated using Teflo filters, but the increase in PM emissions was a factor of three.
This was likely due to the use of a different ULSD fuel in this part of the study with about half
the sulfur content and 1/10th the aromatic content of the fuel originally used with the real time
instruments.
Results during E-66 indicated that engine history, DPF, and dilution systems influenced
the reported particle mass emissions from engines due to storage and release phenomenon of
volatile and semi-volatile exhaust species. These observations have also been reported by other
investigators, and indicate the importance of adhering to clearly defined testing protocol to
ensure test to test and lab to lab repeatability.
The use of real time instrumentation in this phase of E-66 provided insight into diluted
exhaust particle formation sensitivity. This limited study suggests that the details of dilution air
conditioning and dilution system dynamics specific to mixing and mixture aging may have
effects of varying significance on PM measured, regardless of the measurement technique
applied (real time or gravimetric). In this study, it was observed that PM emissions from one
DPF-equipped engine were measured to be as low as 5 percent of the 2007 PM standard or as
high as the standard, depending on the dilution parameter combination and real time instrument
selected, however, the magnitude of this sensitivity is likely to vary between engines and
aftertreatment systems. It is believed that a strong interdependence exists between exhaust
constituency (sulfate and organics content in combination with remaining soot), dilution mixing
characteristics (including residence time) and dilution air properties, including temperature and
humidity. It must be recognized that a complete understanding of the mechanics of particle
formation and growth under real–life dilution system conditions is well beyond the scope of E-66
and does not as yet exist.
4.2.4 Summary of Phase 2
•
The change in filter face velocity did not have much influence on solid particle
filtration efficiency using a Teflo filter. The filtration efficiency remained over 99
percent for filter face velocities between 60 cm/sec and 130 cm/sec. Thus, the
influence of filter face velocity on particle mass collection that was observed during
Phase 1 is mainly due to the presence of volatile PM.
Longer PM sampling time led to a reduction in the reported PM emissions.
Increasing the PM sampling time reduces the contribution of positive artifact
collected by the filter relative to the total PM mass collected, but also contributes to
the negative artifact evaporation loss of volatile PM material collected by the filter.
Thus, long sampling time is not recommended unless the advantages of avoiding
positive artifact outweigh the disadvantages of negative artifact.
The influence of primary and secondary dilution ratio on particle mass
measurement was demonstrated using the real time instruments. The primary
dilution ratio had a strong influence on particle emissions. Changing the primary
dilution ratio from 4 to 9 resulted in a factor of 5 to 20 PM mass increase. Changing
the secondary dilution ratio did not have as much influence as changing the primary
dilution ratio using a CRT-DPF without bypass.
Increasing the secondary dilution residence time from the usual <1 second to a
range of 10 to 30 seconds increased the reported particle mass emissions by two
orders of magnitude, as determined by the real time instruments. The influence of
secondary residence time was also demonstrated using Teflo filters, but only a
particle mass increase by a factor of three was observed. Further investigation of
reasons for the observed order of magnitude vs. factor of three difference is
recommended.
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4.3 Phase 3
In light of the EPA 2007 PM sampling protocol and the improvement made by the PFSS
manufacturers relative to response time, the CRC Real World Vehicle Emissions and Emissions
Modeling Group initiated the work under Phase 3 of Project E-66 to investigate the performance
of PFSS compared to the full flow CVS using the 2007 PM sampling protocol with a diesel
engine that meets the 2007 PM standard.
The main objective of Phase 3 was to evaluate several different partial flow sampling
systems (PFSSs) used as either secondary dilution systems coupled to the full flow CVS, or as
stand-alone systems to sample directly from an exhaust pipe and perform the entire task of
exhaust dilution. The logic of implementing Phase 3 as the last phase of Project E-66 was to
conduct the experiments in the best possible way using recommendations and practices learned
in Phases 1 and 2 of the project.
Phase 3 was performed using CRT-DPF and CRT-DPF with Bypass. Although some
results of Phase 3 may be compared with those of Phases 1 and 2, note the following fuel
differences. Compared to fuel of Phases 1 and 2, the Phase 3 fuel had a factor of 10 lower
aromatic compounds, and a factor of 1.8 lower sulfur. The Phase 3 fuel differed since the Phase 1
and 2 fuels had been depleted.
4.3.1 PFSS Response Time
The response time of all PFSS units was better than 200 milliseconds with excellent
proportionality to exhaust flow changes during transient operations. Evaluation of previous
PFSS versions concluded that response time performance required major improvements because
PFSS sample flow did not correspond to changes in exhaust flow, thus violating proportional
sampling requirements of a PFSS. In contrast, the present versions of BG3, SPC, MDLT,
AEI/CUM and MPS demonstrated excellent proportionality between exhaust flow and sample
flow. The correlation coefficient of exhaust to sample flow was 99 percent or better for the BG3,
AEI/CUM, MDLT, and SPC; and better than 97 percent for the MPS. The standard error relative
to the average was generally below five percent, except for the MPS where the standard error
was about 7 percent for the FTP and 13 percent for the NRTC. It is important to note that the
correlation was based on all data points collected; however, CFR Part 1065 allows for the
removal of five percent of the data collected for this correlation which would improve the
correlation coefficient and standard error reported above for all the PFSS units. The exhaust
flow sampling proportionality performance of these PFSS units complied with the CFR Part
1065 requirements that were in place during this investigation (Part 1065 is not final as of this
publication date).
4.3.2 PFSS as Secondary CVS Dilution Systems
The BG3, SPC, MDLT, and AEI/CUM, when used as secondary dilution systems on the
full flow CVS, measured similar average PM emission levels as the CVS (near 0.0005 g/hp-hr)
with mean values that differed from each other within the CVS repeatability on the FTP ( ±
0.00025 g/hp-hr). The CVS repeatability of 0.00025 g/hp-hr and differences among PFSS of
0.00025 appear to be high. However, note that the PM emissions comparison was performed at
PM emission levels below 10 percent of the 2007 standard. Also note that this comparison was
with an exhaust configuration that did not include the CRT-DPF Bypass. Furthermore, the PM
Exec. Summary Report 03-10415 14 of 21
emission levels obtained were approximately the same magnitude as the PM level obtained using
a tunnel blank filter without engine operation. The very low PM level at or below 10 percent of
the 2007 PM standard presents a laboratory challenge. Although all of today’s best laboratory
practices were performed, the similarity of tunnel blanks and engine results is evidence of that
challenge and suggests that additional effort may be appropriate to refine present laboratory
procedures. This is presently being investigated by EPA and engine manufacturers.
4.3.3
PFSS Measuring CRT-DPF Emitted PM Directly from Exhaust
The BG3, SPC, MDLT, and AEI/CUM, when used as partial flow systems measured
similar average PM emission levels with mean values (near 0.0006 g/hp-hr) that differed from
each other within the CVS repeatability on the FTP (+/- 0.00025 g/hp-hr). The CVS
repeatability of 0.00025 g/hp-hr and differences among PFSS at 0.00025 appear to be high,
however, as noted for these comparisons as secondary dilution systems, the mean values were
very low, only 6% of the 2007 PM limit. The AEI/CUM reported PM emissions were 50 to 70
percent lower than those reported by the CVS. The MPS reported PM emissions about four times
higher than a CVS filter measurement. For the AEI/CUM, it is likely that using 47oC dilution air
temperature resulted in lower PM collection on the filter, compared to the CVS method, which
used a secondary dilution air temperature of about 27oC. For the MPS, it was not clear why the
reported PM emission level was higher than the CVS method. It is noteworthy that these results
were measured by the CVS at 0.0006 g/hp-hr, which was 6% of the required 2007 PM limit of
0.01 g/hp-hr.
4.3.4
PFSS with CRT-DPF with Bypass
Three observations or factors suggested that E-66 should consider testing at 70% rather
than 6% of the 2007 PM regulated limit. These were:
•
+400% to -70% variation of PFSS from CVS when using direct sampling of
CRT-DPF exhaust at only 6% of the 2007 regulated PM limit
The same magnitude results for CVS-sampled engine data and tunnel blanks
observed in Phase 1 when measuring exhaust at 6% of the 2007 PM limit
The potential for actual PM levels at 70% of the 2007 PM limit that could be
observed when 2010 NOx aftertreatment is required.
The 70% PM limit testing was achieved with a bypass loop around the CRT-DPF. As
noted above, this hardware configuration was termed CRT-DPF with bypass. PFSS performance
when sampling the bypass exhaust mix resulted in improved ability to measure PM. For
example, except for one PFSS that later evaluation resolved, most of the PFSS for steady-state
engine operation demonstrated improved performance characterized by agreement within +/-30%
of the CVS, a major improvement compared to the previously noted +400% to -70% differences.
Results for transient testing were even better, with differences between CVS and PFSS ranging
from 1% to 30% with one exception. These results indicated that improvement was achieved and
suggested that attempting to measure filter-based PM emissions at <10% of the 2007 limit is a
significant challenge.
As noted above, PFSS performance improvement resulted when exhaust PM
concentration was increased through the use of a bypass. Opportunity remains for further
improvement through examination of other variables related to particle physics. For example,
additional work with the SPC showed that when the residence time, dilution ratio, and dilution
air temperature were matched with that of the CVS, the difference in PM emission results at
rated speed, 100 percent load, narrowed significantly. Thus, future work should focus on
comparing the PFSS with the CVS under very tightly defined dilution parameters. However,
there should also be a recognition that the dilution processes of CVS and PFSS are different, and
they may not agree under all engine exhaust conditions or with changes in engine technology. At
present, EPA requires verification of equivalence between CVS and PFSS for transient cycle-
based certification.
4.3.5 PFSS with Quartz Filters
Relative to the work with quartz filters using CRT-DPF with Bypass, the results were
qualitative in nature due to the low level of PM collection on the filter and the possible elemental
carbon (EC) artifact formation by pyrolysis during the OC portion of the PM analysis using the
MEXA 1370 PM. When using the MEXA 1370 for quartz filter analysis, a stream of nitrogen is
first introduced over the filter at a temperature of 980oC to desorb all OC material deposited on
the filter. During this process, some of the OC may decompose and form EC on the filter.
Typically, an optical method is used to correct for the EC artifact, but, in the case of MEXA1370-
PM no artifact correction is implemented. Thus, some of the EC usually reported using this
method may be an artifact.
The AVL SPC showed higher emissions at rated engine power, not only relative to EC,
but also relative to organic carbon (OC) and sulfate. The observed results particularly relative to
the increase in OC and sulfate support the data obtained when the dilution parameters between
the SPC and CVS were matched. The EC results, however, do not support the agreement
obtained between the CVS and the SPC as a result of changing the dilution parameters,
suggesting a potential EC artifact due to the method used for PM analysis or some other
unknown behavior with the instrument that is not well understood.
The Sensors MPS seemed to underestimate EC in comparison to all other systems. This
indicates that particle losses could be a problem with this system, or the analytical technique used
for EC analysis is not accurate due to the very low level of EC collected with the MPS. At any
rate, it will be useful to conduct a particle loss experiment with the MPS to better understand
particle losses in the sample train.
The AEI/CUM that used a 47oC dilution air temperature seemed to minimize the collection of
sulfate on the filter. This temperature may play a role in reducing the potential nucleation and
growth of particles because the diluted exhaust never sees a temperature below 47oC during the
dilution and cooling of the raw exhaust stream. Hence, using 47ºC instead of 25°C dilution air
temperature may suppress particle formation or condensation/adsorption during the dilution
process, resulting in less PM mass collection by the filter. It is suspected that particle nucleation
and growth and evaporation may not be totally reversible and may have some amount of
hysteresis that inadvertently prevents material from going back into the gas phase. Thus, using a
dilution air temperature of 47°C ± 5°C and maintaining a filter face temperature of 47°C ± 5°C,
as was practiced in the AEI/CUM PFSS, seemed to result in less volatile hydrocarbon and sulfate
PM deposit on the filter, compared to a dilution air temperature of 25°C±°C and a filter face
temperature of 47°C ± 5°C, which is the currently adapted and recommended practice.
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4.3.6
Summary of Phase 3
The main objective of Phase 3 was to evaluate several different partial flow sampling
systems (PFSSs) used as either secondary dilution systems coupled to the full flow CVS, or as
stand-alone systems to sample directly from an exhaust pipe and perform the entire task of
exhaust dilution.
PFSS (BG3, SPC, MDLT, AEI and MPS) evaluated in Project E-66 demonstrated
their ability to follow a transient test with better than 200 ms response, and with
97% to 99% proportionality between exhaust flow and sample flow, and
demonstrating compliance with 40 CFR Part 1065 as described at the time of
these tests.
As the secondary dilution system on the full flow CVS, these PFSS (BG3, SPC,
MDLT and AEI) yielded similar PM results to a system consisting of a full flow
CVS and a secondary dilution system.
•
When applied as PFSS sampling directly from an exhaust pipe that delivered PM
at 6% of the 2007 regulated limit, several of these systems were equivalent to a
CVS within measurement variability, while two others ranged from 400% high to
70% low.
•
When PM levels were 70 percent of the 2007 PM standard, with one exception,
these PFSS units improved from the +400% to -70% deviation from CVS (when
measuring at 6% of the PM limit) to +/- 30% deviation from a CVS.
•
Additional studies with quartz filters and other studies with dilution ratio and
dilution air temperature variations explained some of the measurement differences
among PFSS units.
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5.0 RECOMMENDATIONS
5.1 Filter Media and Handling
The recommendations in this section include discoveries made during Project E-66 and
SwRI laboratory practices known to be effective for HDD particle measurement.
•
Teflo membrane filters are recommended for PM emission measurement due to their
low affinity for artifact formation. In case chemical analysis of the PM sample is
required, it is recommended that the feasibility of using the Donaldson-manufactured
Teflon® membrane filter with the Teflon® ring be explored because of the inert
nature of the ring support.
•
Performing at least three consecutive filter weights before and after testing best
determines an average weight gain. This practice was performed throughout Project
E-66 and was very beneficial in obtaining a robust filter weight before and after
testing.
•
To prevent an electrostatic charge buildup, it is recommended that filters be placed
on a pair of polonium 210 radioactive strips for at least 30 seconds before weighing
and tweezers used to handle filters must be grounded.
•
Condition clean filters for at least 24 hours in the weighing chamber before first
weighing. After 24 hours of conditioning a stable filter weight was obtained with
various filter media tested under Project E-66.
•
Project E-66 did not show a difference in PM emission performance between a pre-
baked and unbaked Teflo filter media, using the CRT-DPF with Bypass. Thus, it is
recommended that filter pre-baking in a vacuum oven for 24 hours at 52°C becomes
optional for CRT-DPF with Bypass or similar configurations of engine-out particle
concentration. It is still recommended that filters be baked when using a DPF
without Bypass. The Teflo filter typically loses about 7 micrograms after pre-baking
for 24 hours. Different filters obtained from different lots may yield different
responses to the filter baking protocol.
These results suggest that current test and filter handling protocol for PM mass
measurement is challenging, and may be replaced in the future if an alternative is identified. The
use of filters for PM collection using current methods is not practical, particularly when the PM
emission level is well below the 2007 PM standard. Attempting to overcome a low filter weight
challenge by using artificially low overall dilution ratio is not recommended. E-66 testing
indicated that dilution ratio exerted a measurable influence on the PM reported; therefore forcing
a test at low dilution to achieve a minimum net filter mass to improve weighing accuracy may
distort the overall result.
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5.2 Dilution Parameters and Filter Face Velocity
To reduce variability of PM mass measurement, it is recommended that PM sampling
protocol in 40 CFR Part 1065 be reexamined. The following parameters must be narrowly
defined in order to produce consistent and repeatable results:
1.Filter Face Velocity
2.Secondary dilution residence time
3.Secondary dilution ratio
4.Secondary dilution air temperature
5.CVS primary dilution ratio
6.CVS primary dilution residence time
7.CVS primary and secondary tunnel dilution air temperature.
Discussions on tightening some of these parameters are already underway as a part of
EMA’s Emission Measurement and Testing Committee (EMTC) that is composed of EMA, EPA
and CARB members and includes other stakeholders such as testing facilities and instrument
manufacturers. Based on the latest EMTC discussions, the following modifications have been
proposed for Part 1065. They apply to both partial flow sampling systems (PFSSs) and CVS,
unless otherwise specified.
a.Maximize the filter face velocity as much as practically possible but not to exceed
100 cm/sec.
b.Set the secondary dilution residence time to at least 0.5 sec but not to exceed 5
seconds (not applicable to PFSS).
c.Set the total dilution residence time to at least 1 second but not to exceed 5 seconds.
d.Set the primary dilution ratio to at least 2 at the maximum exhaust flow rate
expected during a transient cycle.
e.Set the total dilution ratio to a value between 5 and 7 at the maximum exhaust flow
rate expected during a transient cycle.
f.Set the dilution air temperature to 25°C +/- 5°C anywhere upstream of the mixing
point, but the closer the better.
g.Set the transfer tube length between the exhaust pipe internal wall and the point of
mixing to no more than 26 cm (applicable only to PFSS).
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5.3
Real Time Particle Instruments
Results of E-66 suggest that a steering committee be established to design, verify, and
implement a standard operating protocol for real time particle instruments that may be used as
substitutes for the filter-based method or may be used for onboard PM measurement. Some of the
needs are to:
Evaluate particle loss within instruments and sampling systems
Define zero, span and linearity check for different concentration levels
Define instrument accuracy determination
Define a calibration protocol
Specify calibration particle material
Define an instrument performance comparison method; e.g., compare to filters or
some other accepted method
Define a standard operating procedure.
5.4
Partial Flow Sampling Systems
Project E-66 evaluated PFSSs at a time when production versions of most were available,
except for the MPS, which was a prototype. The response time and mechanical operation of the
production versions are capable of correctly determining a proportional sample mass flow rate on
a real time basis from measured exhaust mass flow values produced during USEPA on- and off-
road diesel engine transient cycles, extracting said proportional exhaust sample from the exhaust
stack and diluting the raw sample for gravimetric PM measurement as defined in 40CFR Part
1065. All remaining correlation issues are related to PM emissions differences between PFSSs,
or between PFSSs and CVS or between CVS systems. However, with the proposed tightening of
dilution parameters and filter face velocity being considered by EMA, EPA, CARB and other
stakeholders in the Emission Measurement and Testing Committee (EMTC), the differences may
be reduced to an acceptable level within and among laboratories.
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6.0 REFERENCES
1.Code of Federal Regulations (CFR) 40, Part 86, 86.1310.2007.
2.Spears, Matt, “EPA’s Heavy-Duty Diesel PM Changes and Other Mass
Measurement Research,” CRC Workshop on Vehicle Exhaust Particulate
Emission Measurement Methodology, San Diego, CA, Oct. 2002.
3.Khalek, I.A., “Particulate Mass Measurement of Heavy-Duty Diesel Engine
Exhaust Using 2007 CVS PM Sampling Parallel to QCM and TEOM,” SwRI
Final Report to EPA, Project 08.06129, September 2003.
4.Khalek, I.A., “2007 Diesel Particulate Measurement Research,” CRC Project E-66
Phase-1, CRC Website at crcao.org, 2006.
5.Khalek, I.A., “2007 Diesel Particulate Measurement Research,” CRC Project E-66
Phase-2, CRC Website at crcao.org, 2007.
6.Khalek, I.A., “2007 Diesel Particulate Measurement Research,” CRC Project E-66
Phase-3, CRC Website at crcao.org, 2007.
Exec. Summary Report 03-10415
2007 DIESEL PARTICULATE MEASUREMENT
RESEARCH
Project E-66
Executive Summary Report
Prepared by:
Imad A. Khalek, Ph.D.
Prepared for:
Coordinating Research Council, Inc.
U.S. Department of Energy/National Renewable Energy Laboratory
Engine Manufacturers Association
U.S. Environmental Protection Agency
California Air Resources Board
February 2008
DISCLAIMER
The Coordinating Research Council, Inc. (CRC) is a non-profit corporation supported by
the petroleum and automotive equipment industries. CRC operates through the committees
made up of technical experts from industry and government who voluntarily participate. The
four main areas of research within CRC are: air pollution (atmospheric and engineering studies);
aviation fuels, lubricants, and equipment performance; heavy-duty vehicle fuels, lubricants, and
equipment performance (e.g., diesel trucks); and light-duty vehicle fuels, lubricants, and
equipment performance (e.g., passenger cars). CRC’s function is to provide the mechanism for
joint research conducted by the two industries that will help in determining the optimum
combination of petroleum products and automotive equipment. CRC’s work is limited to
research that is mutually beneficial to the two industries involved, and all information is
available to the public.
CRC and the other sponsors of this project make no warranty expressed or implied on the
application of information contained in this report. In formulating and approving reports, the
appropriate committee of the Coordinating Research Council, Inc. has not investigated or
considered patents which may apply to the subject matter. Prospective users of the report are
responsible for protecting themselves against liability for infringement of patents.
SOUTHWEST RESEARCH INSTITUTE®
P.O. Drawer 28510 6220 Culebra Road
San Antonio, Texas 78228-0510
2007 DIESEL PARTICULATE MEASUREMENT
RESEARCH
Project E-66
Executive Summary Report
Prepared by:
Imad A. Khalek, Ph.D.
Prepared for:
Coordinating Research Council, Inc.
3650 Mansell Road, Suite 140
Alpharetta, GA 30022
February 2008
Approved:
Prepared by:
____________________________________
Imad A. Khalek, Program Manager-R&D Jeff J. White, Director
Emissions Research and Development Emissions Research and Development
Department (ER&DD) Department (ER&DD)
ENGINE, EMISSIONS AND VEHICLE RESEARCH DIVISION
This report shall not be reproduced, except in full, without the written approval of Southwest Research
Institute®. Results and discussion given in this report relate only to the test items described in this report.
Exec. Summary Report 03-10415
FOREWORD
Project E-66 was funded by the Coordinating Research Council (CRC), Department of
Energy / National Renewable Energy Laboratory (DOE / NREL), US Environmental Protection
Agency (EPA), Engine Manufacturers Association (EMA), and California Air Resources Board
(CARB). The sponsors were represented by Mr. Brent Bailey and Dr. Chris Tennant from CRC,
Dr. Doug Lawson from NREL, Dr. Bruce Cantrell and Mr. Matt Spears from EPA, Dr. Shirish
Shimpi from Cummins, and Mr. Hector Maldonado from CARB.
The Southwest Research Institute (SwRI) Principal Investigator and Project Manager was
Dr. Imad Khalek, Program Manager-R&D. Technical staff members who largely contributed to
this work were Mr. Daniel Preece, Principal Technician, Mr. Joe Sosa, Senior Technician, Mr.
Robert West, Staff Technician, Ms. Kathy Jack, Research Assistant, Mr. Keith Echtle,
Laboratory Assistant Manager, and Mr. Ernest Kruger, Laboratory Manager.
The work was initiated and reviewed by the E-66 Panel members who are listed below in
alphabetical order. Dr. Steve Cadle was the Chairman and Dr. Shirish Shimpi was the Co-
Chairman of the E-66 Panel. Mr. Brent Bailey and Dr. Chris Tennant from CRC were the Project
Managers representing the sponsors.
Mr. Brent Bailey, CRC
Dr. Ewa Bardasz, The Lubrizol Corp.
Dr. Nick Barsic, Deere & Company
Mr. Mike Bogdanoff, SCAQMD
Dr. Steve Cadle, General Motors Corp.
Dr. Bruce Cantrell, EPA
Mr. King Eng, Shell Global Solution (U.S.), Inc.
Mr. Tim French, EMA
Mr. Rob Graze, Caterpillar, Inc.
Dr. Doug Lawson, NREL
Mr. Hector Maldonado, CARB
Dr. Matti Maricq, Ford Motor Co.
Dr. Mani Natarajan, Marathon Oil Co.
Mr. Adewale Oshinuga, SCAQMD
Dr. Shirish Shimpi, Cummins Inc.
Mr. Matt Spears, EPA
Mr. Joe Suchecki, EMA
Dr. Chris Tennant, CRC
Mr. Bill Trestrail, International Truck and Engine Corp.
Mr. Ken Wright, ConocoPhillips
Exec. Summary Report 03-10415 iii
ACKNOWLEDGMENTS
SwRI thanks the Lubrizol Corp. for providing the engine oil, ConocoPhillips,
ExxonMobil, and BP for the fuel analysis, and Chevron Phillips and Sinclair for providing the
diesel fuel.
SwRI appreciates the assistance of TSI and Dekati in providing their equipment free of
charge during Phase 1 of Project E-66. SwRI also thanks AVL, Cummins, Horiba, Sensors, and
Sierra for providing their partial flow sampling systems that included the SPC, AEI/CUM,
MDLT, MPS, and BG3, respectively, and the personnel listed below, to support Phase 3 of
Project E-66. SwRI also thanks EPA and Caterpillar for the additional support through the
participation of their staff.
AVL North America, Inc.
Mr. Bill Silvis, initial contact and approval to participate in Phase 3
Dr. Shahin Nudehi, SPC setup, calibration, and operation
Mr. Gerald Marek, SPC setup and calibration
Caterpillar, Inc.
Mr. Rob Graze, Sierra BG3 setup and inspection during transient operation in Phase 3
Cummins Engine Co., Inc.
Dr. Shirish Shimpi and Mr. Bill Martin, initial contact and approval to participate in
Phase 3
Mr. Bret Rankin, AEI/CUM system setup, calibration, and operation
Horiba Instruments Ltd
Mr. Neal Harvey, initial contact and approval to participate in Phase 3
Mr. Otsuki Yoshinori, MDLT setup, calibration, and operation
Mr. Dave Laskowski, MDLT setup and calibration
Mr. Ichiro Asano, MDLT setup and supervision
Dr. Qiang Wei, MDLT setup and supervision
Dr. Mike Akard, MEXA-1370 PM (Particle Analysis Instrument) setup, calibration, and
operation
Sensors, Inc.
Mr. Atual Shah, initial contact and approval to participate in Phase 3
Dr. David Booker, MPS setup, calibration, and operation
Sierra Instruments, Inc.
Mr. Del Pier, initial contact and approval to participate in Phase 3
Mr. Gregory Pier, BG3 setup, calibration, and operation
US Environmental Protection Agency
Dr. Bob Giannelli, Sensors MPS setup, calibration, and operation
Exec. Summary Report 03-10415 iv
ACRONYMS
COV Coefficient of Variation
CPC Condensation Particle Counter
CRT-DPF Continuously Regenerative Technology-Diesel Particulate Filter
CVS Constant Volume Sampler
DMM Dekati Mass Monitor
DPF Diesel Particulate Filter
EC Elemental Carbon
EEPS Engine Exhaust Particle Sizer
EMTC Emission Measurement Testing Committee
ET Exhaust Temperature
FFV Filter Face Velocity
FTP Federal Test Procedures
HDD Heavy-Duty Diesel
NRTC Nonroad Transient Cycle
OC Organic Carbon
PDR Primary Dilution Ratio
PEFB Partial Exhaust Flow Bypass
PFSS Partial Flow Sampling System
PM Particulate Matter
PMP Polymethylpentene
PP Polypropylene
QA/QC Quality Assurance/Quality Control
QCM Quartz Crystal Micro-Balance
SDR Secondary Dilution Ratio
SMPS Scanning Mobility Particle Sizer
SPMS Solid Particle Measurement System
SPR Saturation Pressure Ratio
SRT Secondary Residence Time
ST Sampling Time
ULSD Ultra-Low Sulfur Diesel
CARB California Air Resources Board
CRC Coordinating Research Council
DOE Department of Energy
EMA Engine Manufacturers Association
EPA Environmental Protection Agency
ISO International Organization for Standardization
NREL National Renewable Energy Laboratory
US United States
SwRI Southwest Research Institute
Exec. Summary Report 03-10415 v
TABLE OF CONTENTS
Foreword ............................................................................................................................iii
Acknowledgments.............................................................................................................. iv
Acronyms.......................................................................................................................... V
1.0 Background............................................................................................................. 1
2.0 Introduction............................................................................................................. 3
3.0 Objectives ............................................................................................................... 4
4.0 Summary of Main Findings .................................................................................... 6
4.1 PHASE 1 ................................................................................................................. 6
4.1.1 Minimizing Gas Phase Artifact Collection ..................................................... 6
4.1.2 Effect of Filter Media on Quantification of PM Emissions ............................ 6
4.1.3 Variability in PM Emissions Using CRT-DPF with and without Bypass....... 7
4.1.4 Effect of Filter Face Velocity on PM Emissions............................................. 8
4.1.5 Effect of Filter Face Temperature on PM Emissions ..................................... 8
4.1.6 Filter Pre-Baking............................................................................................ 8
4.1.7 Real-Time Particle Instruments and the Filter-based Method ....................... 9
4.1.8 Summary of Phase 1...................................................................................... 10
4.2 PHASE 2 ............................................................................................................... 11
4.2.1
Particle Mass Filtration Efficiency of Teflo Filters...................................... 11
4.2.2
Effect of Sampling Time on PM emissions.................................................... 11
4.2.3
Effect of Dilution Ratio, Residence Time and System History on PM
Emissions Using Real Time Particle Instruments......................................... 12
4.2.4
Summary of Phase 2...................................................................................... 13
4.3
PHASE 3 ............................................................................................................... 14
4.3.1 PFSS Response Time..................................................................................... 14
4.3.2 PFSS as Secondary CVS Dilution Systems ................................................... 14
4.3.3 PFSS Measuring CRT-DPF Emitted PM Directly from Exhaust ................. 15
4.3.4 PFSS with CRT-DPF with Bypass ................................................................ 15
4.3.5 PFSS with Quartz Filters.............................................................................. 16
4.3.6 Summary of Phase 3...................................................................................... 17
5.0 Recommendations................................................................................................. 18
5.1 FILTER MEDIA AND HANDLING.................................................................... 18
5.2 DILUTION PARAMETERS AND FILTER FACE VELOCITY........................ 19
5.3 REAL TIME PARTICLE INSTRUMENTS......................................................... 20
5.4 PARTIAL FLOW SAMPLING SYSTEMS ......................................................... 20
6.0 References............................................................................................................. 21
Exec. Summary Report 03-10415
vi
1.0 BACKGROUND
Since the promulgation of diesel exhaust particulate matter (PM) emissions standards in
1988, the United States (US) Environmental Protection Agency (EPA) has defined diesel exhaust
particulate matter (PM) as the material that collects on a filter in a stream of exhaust that is
cooled and diluted to a temperature of less than or equal to 52°C. Gravimetric analysis of the
filter has been the basis for determining PM emissions from heavy-duty diesel (HDD) engines
for certification and other research and testing activities.
Although PM emissions standards from on-highway HDD engines were reduced by more
than 83 percent from 0.6 g/hp-hr in 1988 to 0.1 g/hp-hr in 1994, the established procedure for
PM collection and quantification was considered to have been adequate for regulatory test
procedural purposes.
In 2007, however, on-highway HDD engines are required to meet a PM emissions
standard of 0.01 g/hp-hr which represents a 90 percent reduction from the 1994 level. In
addition, the exhaust PM composition is expected to change because most engines will require
catalyzed diesel particulate filters (DPFs) to meet the stringent PM emissions standard. PM
composition is expected to consist mainly of volatile and semi-volatile hydrocarbon and sulfuric
acid species derived from unburned and partially burned fuel and lubricating oil. This low level
of volatile PM mass poses a technical challenge for the accurate mass measurement of PM using
the pre-2007 established sampling protocol. Measuring a low quantity of PM mass deposited on
a filter is a major challenge, but several other factors including filter handling, type of filter
media, formation of artifacts, sampling system conditioning, and dilution parameter selection
may also affect PM measurement.
Recognizing some of the PM measurement challenges for 2007, EPA modified the
definition of PM by narrowing the filter face temperature from a peak of below or equal to 52°C
to being continuously maintained in a range between 42°C and 52°C (47°C ± 5°C). EPA also
implemented several changes to the secondary dilution tunnel of the constant volume sampler
(CVS) as well as to the filter media, filter handling, and weighing chamber specifications in
order to improve the quantification of PM mass emissions from engines that meet the 2007
standards [1]. CVS is the EPA-approved system for measuring HDD particulates.
Although the new PM measurement procedures specified by EPA for 2007 were
demonstrated by EPA to achieve less than a 10 percent coefficient of variance (COV) at 0.004
g/hp-hr [2], preliminary data produced by SwRI for EPA, using the 2007 sampling procedures,
gave a COV of 23 percent for four hot-start FTP transient tests at the 0.0034 g/hp-hr level [3].
Although the COV difference between SwRI and EPA may be partially explained by differences
in the sampling and handling methodologies, background particle level, and the variety of engine
and aftertreatment systems tested, these results suggest that additional effort is required to fully
understand the variability present in PM measurement for engines equipped with DPFs.
Exec. Summary Report 03-10415 1 of 21
While the new 2007 sampling methodology is expected to improve quantification of PM
mass and reduce variability in comparison to the current sampling method, improvements were
believed necessary and possible to achieve through further investigation. For example, several
variables likely require more specific definition given the measurement challenges of 2007 PM
emission limits. The objective of E-66 was to explore the benefit of more specific definitions of
several variables on PM mass measurement. Parameter evaluations included:
Secondary dilution tunnel geometry and residence time
Filter face velocity
Dilution air temperature
Means of achieving the 47°C ± 5°C filter face temperature
Primary and secondary dilution ratio requirements
Verification of filter material influence
Filter equilibration time (currently time periods of 30 minutes to 60 hours are allowed)
Primary and secondary dilution air filtration requirements
(Currently, 98% efficient HEPA filtration is required for primary dilution air,
and 99.97 % efficient filtration for secondary dilution air).
In light of these issues, Project E-66, entitled “2007 Diesel Particulate Measurement
Research,” was initiated by the CRC Real World Vehicle Emissions and Emissions Modeling
Group. The primary goal for this project was to investigate the above noted factors with the
intention of improving future PM measurement. Additional investigations compared the PM
emission performance of partial flow sampling system (PFSS) units and real-time PM
measurement instruments to the CVS.
Exec. Summary Report 03-10415 2 of 21
2.0 INTRODUCTION
Project E-66 consists of Final Reports on Phases 1 [4], 2 [5], and 3 [6] submitted to the
project sponsors and is available to the public at the CRC Website (crcao.org). This executive
report summarizes the main conclusions for all three phases of Project E-66. It also includes a set
of recommendations for consideration in future activities requiring PM measurement from diesel
engines.
Exec. Summary Report 03-10415 3 of 21
3.0 OBJECTIVES
Project E-66 was divided into Phases 1, 2, and 3. The same diesel engine was used in all
phases of the project. The engine was a 1998 DDC Series 60 HDD engine equipped with a
continuously regenerative technology diesel particulate filter (CRT-DPF) or a CRT-DPF with a
partial exhaust flow bypass (CRT-DPF with Bypass) to elevate PM emissions to near 70 to 80
percent of the 2007 PM emissions standard. The fuel used for Phases 1 and 2 was an ultra-low
sulfur diesel (ULSD) fuel with a sulfur content of 6.9 ppm. Phase 3 ULSD fuel was from a
different batch with a sulfur content of 3.8 ppm.
The objectives of Phase 1 were to:
Minimize gas phase hydrocarbon adsorption on the filter used for PM
collection from a dilute exhaust sample by using a carbon denuder upstream
of the filter.
Investigate the effect of filter media and filter face velocity on PM collection
and emissions.
Compare the performance of several real time particle measuring
instruments including Engine Exhaust Particle Sizer (EEPS), Scanning
Mobility Particle Sizer (SMPS), Dekati Mass Monitor (DMM), and Quartz
Crystal Microbalance (QCM) with that of the CVS filter-based method that
meets the 2007 PM sampling protocol.
The objectives of Phase 2 were to:
Investigate the effect of filter face velocity (FFV) and sampling time on
solid and volatile particle collection by a Teflon® membrane filter, namely
the Pall Teflo filter.
Examine the effect of dilution conditions, such as the CVS primary dilution
ratio, residence time and temperature, and secondary dilution ratio and
residence time, on particle measurement using the real time particle
instruments listed in Phase 1, and Teflo filters in limited experiments.
Study the effect of exhaust stack and dilution system conditioning history on
particle measurement.
The objectives of Phase 3 were to:
Compare the PM emissions measured from the 1998 DDC Series 60 HDD
engine equipped with a CRT-DPF using six different secondary dilution
systems that were coupled to the full flow CVS. These dilution systems
included one short and one long residence time secondary tunnels from
SwRI that were used only with the full flow CVS, and four partial flow
sampling system (PFSS) units, namely the Cummins AEI/CUM, AVL SPC,
Horiba MDLT, and Sierra BG3. The PFSS units could be either used with
the full flow CVS as secondary dilution systems, or used as independent
dilution systems sampling directly from raw engine exhaust. Engine tests to
generate exhaust species for these particulate measurement system
evaluations consisted of two steady-state (rated speed, 100% and 10% load)
and two transient engine tests, the Federal Test Procedure (FTP) and the
Nonroad Transient Cycle (NRTC).
Exec. Summary Report 03-10415
Compare the PM emissions measured using all the PFSS units mentioned
above on engine exhaust in addition to the Sensors micro-proportional
sampler (MPS) with the PM emissions measured using the CVS. The work
was performed using the CRT-DPF and CRT-DPF with Bypass, as
illustrated in the following figure. The PM was collected on Teflo filters for
all experiments. Quartz filters were used in very limited experiments using
the CRT-DPF with Bypass. These filters were analyzed for PM organic and
elemental carbon and sulfate using the Horiba MEXA-1370.
CRT-DPF
Bypass Valve
Sample Area
Engine
CRT-DPF BYPASS SYSTEM
Exec. Summary Report 03-10415
4.0 SUMMARY OF MAIN FINDINGS
This summary report is intended to present the main findings for Phases 1, 2, and 3 of
Project E-66. For more in-depth information, the reader is referred to Phases 1, 2, and 3 final
reports, which are available at the CRC website.
4.1 Phase 1
This section includes the main findings from Phase 1 of Project E-66. Phase 1 investigated
PM measurement artifacts and variability, filter face velocity, and real time particle instruments.
4.1.1 Minimizing Gas Phase Artifact Collection
Filters used for PM collection are prone to gas phase adsorption that add weight to the
filter during PM collection resulting in “positive artifacts.” The gas phase materials are mainly
volatile hydrocarbon species derived from partially burned and unburned fuel and lube oil. In
Phase 1 of Project E-66, an attempt was made to add a carbon denuder in the PM sample train,
upstream of the filter, to remove volatile hydrocarbon material from the gas phase before
reaching the filter in order to reduce positive artifacts. The performance of the carbon denuder in
adsorbing hydrocarbon was not consistent. Furthermore, the carbon denuder failed to regenerate
after reaching saturation. Thus, it was decided early in the program to discontinue the
development and use of the carbon denuder, and rely on the quality of filter medium itself to
minimize gas phase adsorption.
4.1.2 Effect of Filter Media on Quantification of PM Emissions
Several filter media types were used on this project including:
Filter Media Manufacturer
Initial
Weight,
mg
Material Efficiency,d
%
Thickness,
µm
Pressure Drop,g
inH2O
Teflo Pall 180
PTFEa Membrane, 2 µm pore
size, PMPb ring 99.99 46/508e 30
Teflon® Whatman 143
PTFE Membrane, 2 µm pore
size, PPc ring 99.70 40/ 380e 90
PTFE-PP Donaldson 157
PTFE Membrane, 2 µm pore
size, PPc ring 99.99f 40/508e 78
PTFE-PE Donaldson 119
PTFE Membrane, 2 µm pore
size, PTFE ring 99.99f 40/254e 78
Zefluor Pall 242
PTFE Membrane with PTFE
support 99.99 152 60
TX-40 Pall 91
PTFE Coated Borosilicate Glass
Fiber 99.90 178 30
aPolytetrafluoroethylene (Teflon®)
bPolymethylpentene
cPolypropylene
dFollowing ASTM D 2986-95A 0.3 µm (DOP) at 32 L/min/100 cm2 filter media.
eTotal Ring Thickness
g Approximate pressure drop at 75 cm/sec
Exec. Summary Report 03-10415
For an engine equipped with a CRT-DPF, the reported PM emissions for tests conducted
here ranged from 3% to 23% of the 2007 PM limit. These low PM measurements challenged
the ability of filter weighing procedures that were specified for 2007, therefore, to improve the
understanding of PM measurement capability at the specified 2007 limit, the E-66 investigators
decided to bypass a portion of exhaust around the CRT-DPF to achieve a PM level that was
about 70% of the 2007 limit, rather than the 3% to 23% range obtained with all exhaust passing
through the CRF-DPF.
Performance of Teflon®, Teflo, PTFE-PP, and PTFE-PE filter media was similar, i.e., no
major PM difference was noted among these media. Performance of Pallflex TX-40 filters
differed from the above media as follows: PM indicated by Pallflex TX-40 filters was greater
than Teflon® and Teflo filters by a factor of approximately two when sampling CRT-DPF
exhaust without Bypass at 5% of the 2007 PM limit, and by about 10% when sampling CRTDPF
exhaust with Bypass at 70% of the 2007 PM limit.
These tests showed that the Pall Teflo filter, a Teflon® membrane with a
polymethylpentene ring, gave the lowest positive artifact mass and the lowest coefficient of
variation in comparison to TX-40 and other Teflon® membrane filters. As a result of these
experiments, a conclusion of E-66 was to recommend Teflo filters for future measurements of
PM at the 2007 FTP PM level of 0.01 g/hp-hr.
4.1.3 Variability in PM Emissions Using CRT-DPF with and without Bypass
Forty-six repeat test cycles were generated for the hot-start FTP transient cycle using a
CRT-DPF with an engine emission level at 5 percent of the 2007 PM standard (0.0005 g/hp-hr)
and a coefficient of variation (COV) of 50 percent (0.00025 g/hp-hr). For the rated power
condition, the COV was 35 percent based on 49 repeat test cycles. (These low level PM values
could have been reported as 0.5 mg/hp-hr and 0.25 mg/hp-hr, but since regulations are stated in
units of g/hp-hr, these units were retained although the large number of decimal places may
appear awkward.)
For the CRT-DPF with Bypass at an emission level of 70 percent of the 2007 standard (0.007
g/hp-hr), the COV for the FTP was 8.6 percent (0.0006 g/hp-hr), a measurable improvement
compared to the 50 percent COV without CRT-DPF exhaust Bypass.
If one assumes that the absolute values of the COVs obtained at 5 percent and 70 percent
of the 2007 standard are total measurement errors that are independent of the PM emission level
or the PM mass collected on the filter, one can predict the COV at the standard by dividing those
absolute values over the 2007 PM standard of 0.01 g/hp-hr. Such calculations predict a COV in
the range between 2.5 percent (0.00025/0.01 x 100) and 6 percent (0.0006/0.01x100) at the
standard level of 0.01 g/hp-hr.
4.1.4 Effect of Filter Face Velocity on PM Emissions
For an engine equipped with a CRT-DPF with Bypass, the influence of filter face velocity
at a constant 47°C filter face temperature is as follows:
Engine Test Filter Face Velocity Change PM Decrease
Hot-start FTP 24 cm/sec to 120 cm/sec 25%
Rated rpm, 10% load 60 cm/sec to 120 cm/sec 60%
These reported PM reductions are believed due to the volatile portion of PM as the
following argument outlines, and as also confirmed by experiments performed during Phase 2 of
E-66. Gas phase adsorption on the filter and filter saturation may be responsible for such large
changes in measured PM emissions. For example, the flow volume passing through the filter at
120 cm/sec is about five times larger than the volume sampled at 24 cm/sec. If the filter that is
running at 120 cm/sec reaches its adsorption capacity early during the FTP transient cycle, then
its filter collected PM will not include positive artifact for the later portion of the cycle. In
contrast, the 24 cm/sec filter reaches adsorption capacity toward the FTP cycle end, and is
expected to result in a larger positive artifact.
Diesel particles are composites that consist of solid soot and adsorbed volatile species.
The objective of the subject program is to collect these composite particles, to avoid
accumulating gas phase volatiles onto the filter (positive artifact), and to avoid desorbing the
volatile phase component of the composite particles (negative artifact). In order to minimize
positive artifacts associated with gas phase adsorption on the filter during PM collection, it is
best to reach filter saturation as soon as possible by going to a high filter face velocity. Also,
higher filter face velocity seems to give a better agreement between the filter-based PM mass
emissions and real time particle instruments that are insensitive to positive or negative artifacts.
A filter face velocity that is too high (greater than 100 cm/sec) may result in a negative artifact.
4.1.5 Effect of Filter Face Temperature on PM Emissions
For the case where the engine was equipped with the CRT-DPF with Bypass set to
provide a PM emission rate at 70 percent of the 2007 PM standard, results indicated no
difference in measured PM emissions for the FTP transient cycle between using a Teflo filter
face temperature of 47°C and 25°C. Studies in PM mass collection sensitivity to filter
temperature were not performed at levels below 10% of the 2007 standard (Bypass disabled).
Therefore, the aforementioned conclusions cannot be applied to a CRT-DPF without Bypass.
Further study is required.
4.1.6 Filter Pre-Baking
To avoid contaminants loss from the sample filter during PM collection (negative
artifacts) at a filter face temperature of 47°C ± 5°C, the Teflo filters were first pre-baked in a
vacuum oven for 24 hours at a temperature of 52°C. After pre-baking and conditioning in the
weighing chamber for 24 hours, each pre-baked Teflo filter lost about 5 µg of its original weight
prior to baking. The 5 µg lost are likely to be some unknown volatile contaminant on the filter as
received from the manufacturer.
In order to test whether or not pre-baking the filter is necessary for testing, PM emissions
from a total of 14 repeats of the FTP transient cycle were performed using pre-baked and
unbaked Teflo filters. For an exhaust configuration using CRT-DPF with Bypass at an emission
level of 70 percent of the 2007 PM standard (0.007 g/hp-hr) and a filter weight gain of about 70
µg, no significant difference was observed in PM emissions between using pre-baked and
unbaked filters.
No experiments were performed to compare the PM emissions performance using baked
and unbaked-filter for an exhaust configuration that includes CRT-DPF without bypass, where
the PM emissions level for the FTP is expected to be at 5 percent of the 2007 PM standard
(0.0005 g/hp-hr), with an expected filter weight gain of about 5 µg. Thus, it is not clear whether
or not filter pre-baking will be necessary when testing with CRT-DPF without Bypass. Also, it is
not clear whether or not different filter batches contain more or less contaminant than the one
measured during this work. Thus, as a precaution, it is recommended that filter pre-baking be
used to reduce filter batch to batch variability when using CRT-DPF without Bypass.
4.1.7 Real-Time Particle Instruments and the Filter-based Method
Three real time particulate instruments were compared with simultaneous measurements
of CVS-based PM. These real time instruments were the DMM-230, EEPS and SMPS. The
DMM-230 measures real time particle size and mass and the EEPS measures real time particle
size and number concentration. The SMPS provides particle size and number concentration, but
is limited to steady-state engine operation. If particle density is known, the EEPS and SMPS
results can be converted to mass. A linear regression with a correlation coefficient (R2) of better
than 0.95 at the 95 percent confidence level was obtained for a total of 46 data points. Note that
the observed good linear regression applies only to an exhaust configuration using a CRT-DPF
with Bypass, where solid particles contribute to PM emissions. These results do not guarantee
the same conclusion when using a CRT-DPF without Bypass, where the PM emission is
composed mainly of volatile material.
Another real-time PM instrument, the Quartz Crystal Monitor (QCM) was tested, but
results indicated that more in-depth investigation was required than the E-66 schedule
permitted. In summary, proper operation of the QCM requires firm adhesion of all particles
onto the quartz crystal, thus causing a unique instrument response. A unique response is not
always attained for particles characterized by an agglomerate morphology. Particles that are
attached to other particles, a typical agglomerate character that is true for diesel particulate, do
not exert the same force on the quartz crystal as particles that firmly attach directly to the
crystal. Under circumstances of agglomerates with very low particle deposit, for example, less
than 0.5 micrograms, a QCM may demonstrate a unique response to mass deposit. Non-
agglomerate particles may produce a unique response at higher than 0.5 microgram deposit.
4.1.8
Summary of Phase 1
Minimizing gas phase adsorption on the filter by using a carbon denuder was not
successful due to the difficulty associated with regenerating the denuder after
saturation. Thus, the use of a carbon denuder was discontinued, and minimizing
positive artifacts was achieved by the use of Teflon® membrane filters instead.
Filter pre-baking in a vacuum oven at 52°C for 24 hours did not affect PM
emissions, compared to unbaked filters using the CRT-DPF with Bypass. No
experiments were done to verify the effect of pre-baking filters when using CRTDPF
without Bypass. Because the Teflo filter lost about 5 µg during pre-baking,
an amount similar to filter weight gain for the FTP transient cycle when using
CRT-DPF without Bypass, pre-baking is recommended as a precaution when
using CRT-DPF without Bypass to minimize or avoid negative artifact during PM
collection.
At a PM emission level that is 5 percent of the 2007 standard, all Teflon®
membrane filters such as those made by Pall, Whatman, and Donaldson reported
equivalent PM emission levels at 0.0005 g/hp-hr, however, successive
measurements could vary by approximately half of the mean value. In summary,
a measured value is best reported as 0.0005 ± 0.00025 g/hp-hr. The Pallflex TX40
filter, due to PM volatile artifact, measured a PM emission level that was a
factor of 2 higher than that produced using the Teflon® membrane filters.
At a PM emission level that was 70 percent of the 2007 PM standard, Teflon®
filters measured 0.007 ± 0.0006 g/hp-hr. The PM emission level reported using a
TX-40 filter was about 10 percent higher than the level reported using the Teflon®
membrane filters, likely due to volatile artifact. This artifact (10% of 0.007) was
slightly larger than the Teflon® membrane filter 1s (±0.0006). The Pall Teflo filter
gave the lowest variability (±0.00038 g/hp-hr) along with the lowest pressure
drop among all Teflon® membrane filters tested. This filter was selected for
subsequent E-66 sampling from engines with wall-flow DPFs.
PM measurement coefficient of variation (COV) summary:
At <10 percent of the 2007 PM standard, COV is 50%.
At the 2007 PM standard, COV is expected to be 6%.
Increasing filter face velocity from 24 cm/sec to 120 cm/sec produced a 25
percent reduction in measured PM emissions during the FTP transient cycle.
Controlling filter face velocity to a narrow range may help reduce the variability
in PM measurement.
A linear regression with a correlation coefficient (R2) of better than 0.95 was
obtained for n=46 tests between the CVS filter-based PM mass and PM mass
derived from real time instruments such as the DMM-230, EEPS, and SMPS,
using CRT-DPF with Bypass. Real time instrument vs. CVS correlation was not
evaluated when using CRT-DPF without Bypass
4.2 Phase 2
Phase 2 was performed using the same Phase 1 engine equipped with a CRT-DPF. Teflo
membrane filters were used throughout the entire project phase as the preferred filter medium
unless otherwise specified. Phase 2 investigated filtration efficiency and sampling time when
using Teflo filters. Phase 2 also investigated the effect of dilution ratio and residence time using
real time instruments, and secondary dilution residence time using Teflo filters.
4.2.1 Particle Mass Filtration Efficiency of Teflo Filters
Unlike gaseous emissions that can be reported as a single number, usually concentration,
particle measurement consists of a two-dimensional array involving size and concentration. The
following brief table reports Teflo filter particle mass filtration efficiency and particle size ranges
for 60 to 129 cm/sec filter face velocities. These experiments were performed using diesel
exhaust treated to remove volatiles and thus provide only solid particles to the Teflo filters.
Particle Size Mass Collection Efficiency
7nm to 300nm 99%
<30nm 95%
<10nm 85%
This work showed that the filtration efficiency of solid exhaust PM mass is high, over 99
percent within the range of 60 to 129 cm/sec filter face velocity. It also demonstrated that the
effect of filter face velocity on PM mass collection observed in Phase 1 was mainly due to
volatile PM and not solid PM.
4.2.2 Effect of Sampling Time on PM emissions
At rated speed, 100 percent load, changing sampling times and face velocities resulted in
the following observations:
Sample Time Increase
20 min. to 50 min.
60 min. to 150 min.
Filter Face Velocity
125 cm/sec
30 cm/sec
Decrease in PM Reported
40%
70%
These results are for an exhaust aerosol that was about 5 percent of the 2007 PM emission
standard. It is important to note that the effects of filter face velocity and sample time on filter-
based PM emissions are not independent of each other. High filter face velocity and short sample
time may be equivalent to low filter face velocity and long sample time only if the flow volume
is the same, and particle phase volatile material depositing on the filter is stable. In case the
aerosol is unstable and subject to evaporation, the long sample time may bias the results to lower
PM emissions due to negative artifacts.
In order to reach filter gas phase saturation as quickly as possible, a high filter face
velocity is desired. In order to minimize negative artifacts, a short sample time is desired, but in
order to minimize positive artifact a long sample time is desired. However, in most engine
testing, the sample time is dictated by the length of the cycle to be run. Thus, the only means of
minimizing positive artifact is by going to a high filter face velocity within the upper limit
defined by EPA at 100 cm/sec.
In cases where the length of testing is not predefined, one tends to increase filter face
velocity and sample time to maximize PM loading on the filter, particularly when the PM
emission level is well below the 2007 PM standard. While increasing filter face velocity and
sample time minimizes positive artifact collection relative to the total particle mass, it may lead
to negative artifacts; this practice presents a challenge for filter media to accurately evaluate PM
emissions at an emission level well below the 2007 PM standard.
4.2.3
Effect of Dilution Ratio, Residence Time and System History on PM Emissions Using
Real Time Particle Instruments
The SMPS, EEPS, DMM-230, and QCM were used to study the effect of dilution
parameters on PM emissions. With some of these real time instruments, a large matrix of
different dilution parameters such as primary and secondary CVS dilution ratio and residence
times were investigated. Teflo filters were only used later to determine the effect of secondary
residence time on PM emissions for comparison with that observed using real time instruments.
Depending upon the engine operating condition, increasing the primary dilution ratio from
4 to 9 while holding the secondary dilution ratio at two resulted in 5 to 20 fold increase in PM
emissions using SMPS, EEPS, DMM-230 and QCM. Since these four instruments employed
three different physical measurement principles, some differences in particle mass were
expected, however, all of these instruments reported similar response to dilution ratio, namely,
higher dilution ratio increased the indicated PM. Increasing the secondary dilution ratio from 1.5
to 4.5 while holding the primary dilution ratio at two resulted in two-fold PM mass increase.
Primary dilution ratio changes have greater influence on particle mass than secondary dilution
ratio changes, within the range of dilution ratios investigated here, thus lab to lab comparisons at
2007 particle emission levels need to coordinate primary dilution ratios more carefully than
secondary dilution ratios, but the factor of two influence of secondary dilution ratio is not to be
viewed as unimportant.
The secondary dilution residence time had a very significant influence on particle mass
emissions. A long residence time of 10 to 30 seconds showed an increase in PM mass emissions
by more than two orders of magnitude, compared to a residence time of less than one second,
using data obtained from the real time particle instruments. During Phase 3, this phenomenon
was also demonstrated using Teflo filters, but the increase in PM emissions was a factor of three.
This was likely due to the use of a different ULSD fuel in this part of the study with about half
the sulfur content and 1/10th the aromatic content of the fuel originally used with the real time
instruments.
Results during E-66 indicated that engine history, DPF, and dilution systems influenced
the reported particle mass emissions from engines due to storage and release phenomenon of
volatile and semi-volatile exhaust species. These observations have also been reported by other
investigators, and indicate the importance of adhering to clearly defined testing protocol to
ensure test to test and lab to lab repeatability.
The use of real time instrumentation in this phase of E-66 provided insight into diluted
exhaust particle formation sensitivity. This limited study suggests that the details of dilution air
conditioning and dilution system dynamics specific to mixing and mixture aging may have
effects of varying significance on PM measured, regardless of the measurement technique
applied (real time or gravimetric). In this study, it was observed that PM emissions from one
DPF-equipped engine were measured to be as low as 5 percent of the 2007 PM standard or as
high as the standard, depending on the dilution parameter combination and real time instrument
selected, however, the magnitude of this sensitivity is likely to vary between engines and
aftertreatment systems. It is believed that a strong interdependence exists between exhaust
constituency (sulfate and organics content in combination with remaining soot), dilution mixing
characteristics (including residence time) and dilution air properties, including temperature and
humidity. It must be recognized that a complete understanding of the mechanics of particle
formation and growth under real–life dilution system conditions is well beyond the scope of E-66
and does not as yet exist.
4.2.4 Summary of Phase 2
•
The change in filter face velocity did not have much influence on solid particle
filtration efficiency using a Teflo filter. The filtration efficiency remained over 99
percent for filter face velocities between 60 cm/sec and 130 cm/sec. Thus, the
influence of filter face velocity on particle mass collection that was observed during
Phase 1 is mainly due to the presence of volatile PM.
Longer PM sampling time led to a reduction in the reported PM emissions.
Increasing the PM sampling time reduces the contribution of positive artifact
collected by the filter relative to the total PM mass collected, but also contributes to
the negative artifact evaporation loss of volatile PM material collected by the filter.
Thus, long sampling time is not recommended unless the advantages of avoiding
positive artifact outweigh the disadvantages of negative artifact.
The influence of primary and secondary dilution ratio on particle mass
measurement was demonstrated using the real time instruments. The primary
dilution ratio had a strong influence on particle emissions. Changing the primary
dilution ratio from 4 to 9 resulted in a factor of 5 to 20 PM mass increase. Changing
the secondary dilution ratio did not have as much influence as changing the primary
dilution ratio using a CRT-DPF without bypass.
Increasing the secondary dilution residence time from the usual <1 second to a
range of 10 to 30 seconds increased the reported particle mass emissions by two
orders of magnitude, as determined by the real time instruments. The influence of
secondary residence time was also demonstrated using Teflo filters, but only a
particle mass increase by a factor of three was observed. Further investigation of
reasons for the observed order of magnitude vs. factor of three difference is
recommended.
Exec. Summary Report 03-10415
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4.3 Phase 3
In light of the EPA 2007 PM sampling protocol and the improvement made by the PFSS
manufacturers relative to response time, the CRC Real World Vehicle Emissions and Emissions
Modeling Group initiated the work under Phase 3 of Project E-66 to investigate the performance
of PFSS compared to the full flow CVS using the 2007 PM sampling protocol with a diesel
engine that meets the 2007 PM standard.
The main objective of Phase 3 was to evaluate several different partial flow sampling
systems (PFSSs) used as either secondary dilution systems coupled to the full flow CVS, or as
stand-alone systems to sample directly from an exhaust pipe and perform the entire task of
exhaust dilution. The logic of implementing Phase 3 as the last phase of Project E-66 was to
conduct the experiments in the best possible way using recommendations and practices learned
in Phases 1 and 2 of the project.
Phase 3 was performed using CRT-DPF and CRT-DPF with Bypass. Although some
results of Phase 3 may be compared with those of Phases 1 and 2, note the following fuel
differences. Compared to fuel of Phases 1 and 2, the Phase 3 fuel had a factor of 10 lower
aromatic compounds, and a factor of 1.8 lower sulfur. The Phase 3 fuel differed since the Phase 1
and 2 fuels had been depleted.
4.3.1 PFSS Response Time
The response time of all PFSS units was better than 200 milliseconds with excellent
proportionality to exhaust flow changes during transient operations. Evaluation of previous
PFSS versions concluded that response time performance required major improvements because
PFSS sample flow did not correspond to changes in exhaust flow, thus violating proportional
sampling requirements of a PFSS. In contrast, the present versions of BG3, SPC, MDLT,
AEI/CUM and MPS demonstrated excellent proportionality between exhaust flow and sample
flow. The correlation coefficient of exhaust to sample flow was 99 percent or better for the BG3,
AEI/CUM, MDLT, and SPC; and better than 97 percent for the MPS. The standard error relative
to the average was generally below five percent, except for the MPS where the standard error
was about 7 percent for the FTP and 13 percent for the NRTC. It is important to note that the
correlation was based on all data points collected; however, CFR Part 1065 allows for the
removal of five percent of the data collected for this correlation which would improve the
correlation coefficient and standard error reported above for all the PFSS units. The exhaust
flow sampling proportionality performance of these PFSS units complied with the CFR Part
1065 requirements that were in place during this investigation (Part 1065 is not final as of this
publication date).
4.3.2 PFSS as Secondary CVS Dilution Systems
The BG3, SPC, MDLT, and AEI/CUM, when used as secondary dilution systems on the
full flow CVS, measured similar average PM emission levels as the CVS (near 0.0005 g/hp-hr)
with mean values that differed from each other within the CVS repeatability on the FTP ( ±
0.00025 g/hp-hr). The CVS repeatability of 0.00025 g/hp-hr and differences among PFSS of
0.00025 appear to be high. However, note that the PM emissions comparison was performed at
PM emission levels below 10 percent of the 2007 standard. Also note that this comparison was
with an exhaust configuration that did not include the CRT-DPF Bypass. Furthermore, the PM
Exec. Summary Report 03-10415 14 of 21
emission levels obtained were approximately the same magnitude as the PM level obtained using
a tunnel blank filter without engine operation. The very low PM level at or below 10 percent of
the 2007 PM standard presents a laboratory challenge. Although all of today’s best laboratory
practices were performed, the similarity of tunnel blanks and engine results is evidence of that
challenge and suggests that additional effort may be appropriate to refine present laboratory
procedures. This is presently being investigated by EPA and engine manufacturers.
4.3.3
PFSS Measuring CRT-DPF Emitted PM Directly from Exhaust
The BG3, SPC, MDLT, and AEI/CUM, when used as partial flow systems measured
similar average PM emission levels with mean values (near 0.0006 g/hp-hr) that differed from
each other within the CVS repeatability on the FTP (+/- 0.00025 g/hp-hr). The CVS
repeatability of 0.00025 g/hp-hr and differences among PFSS at 0.00025 appear to be high,
however, as noted for these comparisons as secondary dilution systems, the mean values were
very low, only 6% of the 2007 PM limit. The AEI/CUM reported PM emissions were 50 to 70
percent lower than those reported by the CVS. The MPS reported PM emissions about four times
higher than a CVS filter measurement. For the AEI/CUM, it is likely that using 47oC dilution air
temperature resulted in lower PM collection on the filter, compared to the CVS method, which
used a secondary dilution air temperature of about 27oC. For the MPS, it was not clear why the
reported PM emission level was higher than the CVS method. It is noteworthy that these results
were measured by the CVS at 0.0006 g/hp-hr, which was 6% of the required 2007 PM limit of
0.01 g/hp-hr.
4.3.4
PFSS with CRT-DPF with Bypass
Three observations or factors suggested that E-66 should consider testing at 70% rather
than 6% of the 2007 PM regulated limit. These were:
•
+400% to -70% variation of PFSS from CVS when using direct sampling of
CRT-DPF exhaust at only 6% of the 2007 regulated PM limit
The same magnitude results for CVS-sampled engine data and tunnel blanks
observed in Phase 1 when measuring exhaust at 6% of the 2007 PM limit
The potential for actual PM levels at 70% of the 2007 PM limit that could be
observed when 2010 NOx aftertreatment is required.
The 70% PM limit testing was achieved with a bypass loop around the CRT-DPF. As
noted above, this hardware configuration was termed CRT-DPF with bypass. PFSS performance
when sampling the bypass exhaust mix resulted in improved ability to measure PM. For
example, except for one PFSS that later evaluation resolved, most of the PFSS for steady-state
engine operation demonstrated improved performance characterized by agreement within +/-30%
of the CVS, a major improvement compared to the previously noted +400% to -70% differences.
Results for transient testing were even better, with differences between CVS and PFSS ranging
from 1% to 30% with one exception. These results indicated that improvement was achieved and
suggested that attempting to measure filter-based PM emissions at <10% of the 2007 limit is a
significant challenge.
As noted above, PFSS performance improvement resulted when exhaust PM
concentration was increased through the use of a bypass. Opportunity remains for further
improvement through examination of other variables related to particle physics. For example,
additional work with the SPC showed that when the residence time, dilution ratio, and dilution
air temperature were matched with that of the CVS, the difference in PM emission results at
rated speed, 100 percent load, narrowed significantly. Thus, future work should focus on
comparing the PFSS with the CVS under very tightly defined dilution parameters. However,
there should also be a recognition that the dilution processes of CVS and PFSS are different, and
they may not agree under all engine exhaust conditions or with changes in engine technology. At
present, EPA requires verification of equivalence between CVS and PFSS for transient cycle-
based certification.
4.3.5 PFSS with Quartz Filters
Relative to the work with quartz filters using CRT-DPF with Bypass, the results were
qualitative in nature due to the low level of PM collection on the filter and the possible elemental
carbon (EC) artifact formation by pyrolysis during the OC portion of the PM analysis using the
MEXA 1370 PM. When using the MEXA 1370 for quartz filter analysis, a stream of nitrogen is
first introduced over the filter at a temperature of 980oC to desorb all OC material deposited on
the filter. During this process, some of the OC may decompose and form EC on the filter.
Typically, an optical method is used to correct for the EC artifact, but, in the case of MEXA1370-
PM no artifact correction is implemented. Thus, some of the EC usually reported using this
method may be an artifact.
The AVL SPC showed higher emissions at rated engine power, not only relative to EC,
but also relative to organic carbon (OC) and sulfate. The observed results particularly relative to
the increase in OC and sulfate support the data obtained when the dilution parameters between
the SPC and CVS were matched. The EC results, however, do not support the agreement
obtained between the CVS and the SPC as a result of changing the dilution parameters,
suggesting a potential EC artifact due to the method used for PM analysis or some other
unknown behavior with the instrument that is not well understood.
The Sensors MPS seemed to underestimate EC in comparison to all other systems. This
indicates that particle losses could be a problem with this system, or the analytical technique used
for EC analysis is not accurate due to the very low level of EC collected with the MPS. At any
rate, it will be useful to conduct a particle loss experiment with the MPS to better understand
particle losses in the sample train.
The AEI/CUM that used a 47oC dilution air temperature seemed to minimize the collection of
sulfate on the filter. This temperature may play a role in reducing the potential nucleation and
growth of particles because the diluted exhaust never sees a temperature below 47oC during the
dilution and cooling of the raw exhaust stream. Hence, using 47ºC instead of 25°C dilution air
temperature may suppress particle formation or condensation/adsorption during the dilution
process, resulting in less PM mass collection by the filter. It is suspected that particle nucleation
and growth and evaporation may not be totally reversible and may have some amount of
hysteresis that inadvertently prevents material from going back into the gas phase. Thus, using a
dilution air temperature of 47°C ± 5°C and maintaining a filter face temperature of 47°C ± 5°C,
as was practiced in the AEI/CUM PFSS, seemed to result in less volatile hydrocarbon and sulfate
PM deposit on the filter, compared to a dilution air temperature of 25°C±°C and a filter face
temperature of 47°C ± 5°C, which is the currently adapted and recommended practice.
Exec. Summary Report 03-10415 16 of 21
4.3.6
Summary of Phase 3
The main objective of Phase 3 was to evaluate several different partial flow sampling
systems (PFSSs) used as either secondary dilution systems coupled to the full flow CVS, or as
stand-alone systems to sample directly from an exhaust pipe and perform the entire task of
exhaust dilution.
PFSS (BG3, SPC, MDLT, AEI and MPS) evaluated in Project E-66 demonstrated
their ability to follow a transient test with better than 200 ms response, and with
97% to 99% proportionality between exhaust flow and sample flow, and
demonstrating compliance with 40 CFR Part 1065 as described at the time of
these tests.
As the secondary dilution system on the full flow CVS, these PFSS (BG3, SPC,
MDLT and AEI) yielded similar PM results to a system consisting of a full flow
CVS and a secondary dilution system.
•
When applied as PFSS sampling directly from an exhaust pipe that delivered PM
at 6% of the 2007 regulated limit, several of these systems were equivalent to a
CVS within measurement variability, while two others ranged from 400% high to
70% low.
•
When PM levels were 70 percent of the 2007 PM standard, with one exception,
these PFSS units improved from the +400% to -70% deviation from CVS (when
measuring at 6% of the PM limit) to +/- 30% deviation from a CVS.
•
Additional studies with quartz filters and other studies with dilution ratio and
dilution air temperature variations explained some of the measurement differences
among PFSS units.
Exec. Summary Report 03-10415
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5.0 RECOMMENDATIONS
5.1 Filter Media and Handling
The recommendations in this section include discoveries made during Project E-66 and
SwRI laboratory practices known to be effective for HDD particle measurement.
•
Teflo membrane filters are recommended for PM emission measurement due to their
low affinity for artifact formation. In case chemical analysis of the PM sample is
required, it is recommended that the feasibility of using the Donaldson-manufactured
Teflon® membrane filter with the Teflon® ring be explored because of the inert
nature of the ring support.
•
Performing at least three consecutive filter weights before and after testing best
determines an average weight gain. This practice was performed throughout Project
E-66 and was very beneficial in obtaining a robust filter weight before and after
testing.
•
To prevent an electrostatic charge buildup, it is recommended that filters be placed
on a pair of polonium 210 radioactive strips for at least 30 seconds before weighing
and tweezers used to handle filters must be grounded.
•
Condition clean filters for at least 24 hours in the weighing chamber before first
weighing. After 24 hours of conditioning a stable filter weight was obtained with
various filter media tested under Project E-66.
•
Project E-66 did not show a difference in PM emission performance between a pre-
baked and unbaked Teflo filter media, using the CRT-DPF with Bypass. Thus, it is
recommended that filter pre-baking in a vacuum oven for 24 hours at 52°C becomes
optional for CRT-DPF with Bypass or similar configurations of engine-out particle
concentration. It is still recommended that filters be baked when using a DPF
without Bypass. The Teflo filter typically loses about 7 micrograms after pre-baking
for 24 hours. Different filters obtained from different lots may yield different
responses to the filter baking protocol.
These results suggest that current test and filter handling protocol for PM mass
measurement is challenging, and may be replaced in the future if an alternative is identified. The
use of filters for PM collection using current methods is not practical, particularly when the PM
emission level is well below the 2007 PM standard. Attempting to overcome a low filter weight
challenge by using artificially low overall dilution ratio is not recommended. E-66 testing
indicated that dilution ratio exerted a measurable influence on the PM reported; therefore forcing
a test at low dilution to achieve a minimum net filter mass to improve weighing accuracy may
distort the overall result.
Exec. Summary Report 03-10415
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5.2 Dilution Parameters and Filter Face Velocity
To reduce variability of PM mass measurement, it is recommended that PM sampling
protocol in 40 CFR Part 1065 be reexamined. The following parameters must be narrowly
defined in order to produce consistent and repeatable results:
1.Filter Face Velocity
2.Secondary dilution residence time
3.Secondary dilution ratio
4.Secondary dilution air temperature
5.CVS primary dilution ratio
6.CVS primary dilution residence time
7.CVS primary and secondary tunnel dilution air temperature.
Discussions on tightening some of these parameters are already underway as a part of
EMA’s Emission Measurement and Testing Committee (EMTC) that is composed of EMA, EPA
and CARB members and includes other stakeholders such as testing facilities and instrument
manufacturers. Based on the latest EMTC discussions, the following modifications have been
proposed for Part 1065. They apply to both partial flow sampling systems (PFSSs) and CVS,
unless otherwise specified.
a.Maximize the filter face velocity as much as practically possible but not to exceed
100 cm/sec.
b.Set the secondary dilution residence time to at least 0.5 sec but not to exceed 5
seconds (not applicable to PFSS).
c.Set the total dilution residence time to at least 1 second but not to exceed 5 seconds.
d.Set the primary dilution ratio to at least 2 at the maximum exhaust flow rate
expected during a transient cycle.
e.Set the total dilution ratio to a value between 5 and 7 at the maximum exhaust flow
rate expected during a transient cycle.
f.Set the dilution air temperature to 25°C +/- 5°C anywhere upstream of the mixing
point, but the closer the better.
g.Set the transfer tube length between the exhaust pipe internal wall and the point of
mixing to no more than 26 cm (applicable only to PFSS).
Exec. Summary Report 03-10415
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5.3
Real Time Particle Instruments
Results of E-66 suggest that a steering committee be established to design, verify, and
implement a standard operating protocol for real time particle instruments that may be used as
substitutes for the filter-based method or may be used for onboard PM measurement. Some of the
needs are to:
Evaluate particle loss within instruments and sampling systems
Define zero, span and linearity check for different concentration levels
Define instrument accuracy determination
Define a calibration protocol
Specify calibration particle material
Define an instrument performance comparison method; e.g., compare to filters or
some other accepted method
Define a standard operating procedure.
5.4
Partial Flow Sampling Systems
Project E-66 evaluated PFSSs at a time when production versions of most were available,
except for the MPS, which was a prototype. The response time and mechanical operation of the
production versions are capable of correctly determining a proportional sample mass flow rate on
a real time basis from measured exhaust mass flow values produced during USEPA on- and off-
road diesel engine transient cycles, extracting said proportional exhaust sample from the exhaust
stack and diluting the raw sample for gravimetric PM measurement as defined in 40CFR Part
1065. All remaining correlation issues are related to PM emissions differences between PFSSs,
or between PFSSs and CVS or between CVS systems. However, with the proposed tightening of
dilution parameters and filter face velocity being considered by EMA, EPA, CARB and other
stakeholders in the Emission Measurement and Testing Committee (EMTC), the differences may
be reduced to an acceptable level within and among laboratories.
Exec. Summary Report 03-10415
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6.0 REFERENCES
1.Code of Federal Regulations (CFR) 40, Part 86, 86.1310.2007.
2.Spears, Matt, “EPA’s Heavy-Duty Diesel PM Changes and Other Mass
Measurement Research,” CRC Workshop on Vehicle Exhaust Particulate
Emission Measurement Methodology, San Diego, CA, Oct. 2002.
3.Khalek, I.A., “Particulate Mass Measurement of Heavy-Duty Diesel Engine
Exhaust Using 2007 CVS PM Sampling Parallel to QCM and TEOM,” SwRI
Final Report to EPA, Project 08.06129, September 2003.
4.Khalek, I.A., “2007 Diesel Particulate Measurement Research,” CRC Project E-66
Phase-1, CRC Website at crcao.org, 2006.
5.Khalek, I.A., “2007 Diesel Particulate Measurement Research,” CRC Project E-66
Phase-2, CRC Website at crcao.org, 2007.
6.Khalek, I.A., “2007 Diesel Particulate Measurement Research,” CRC Project E-66
Phase-3, CRC Website at crcao.org, 2007.
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