Trap-Oxidizer Feasibility Study
March 1982
Standards Development and Support Branch
Emission Control Technology Division
Office of Mobile Source Air Pollution Control
Office of Air, Noise and Radiation
U.S. Environmental Protection Agency
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Trap-Oxidizer Feasibility Study
March 1982
Standards Development and Support Branch
Emission Control Technology Division
Office of Mobile Source Air Pollution Control
Office of Air, Noise and Radiation
U.S. Environmental Protection Agency
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CHAPTER I
EXECUTIVE SUMMARY
This study analyzes the technological feasibility of
trap-oxidizers and the 1985 light-duty diesel particulate
standards. The 1985 particulate standards were promulgated on
March 5, 1980, and were set at 0.2 gram per mile for
diesel-powered light-duty vehicles and 0.26 gram per mile for
diesel-powered light-duty trucks. EPA acknowledged the
technology-forcing nature of these standards at the time of
promulgation, but projected that trap-oxidizers would be
successfully developed iti time to permit compliance with the 1985
particulate standards.
The feasibility of the 1985 particulate standards has
continued to be a source of controversy within the automotive
industry and EPA has monitored the research of vehicle
manufacturers throughout the last two years in order to assess the
progress of trap-oxidizer development. On June 17, 1981, EPA
announced that it would prepare this study, and invited interested
parties to submit any new data or information not considered
during the original rulemaking, and to respond to specific
questions about their trap-oxidizer research programs. This study
is based predominantly on the submissions received from trap and
vehicle manufacturers, as well as data from EPA's own test
programs.
Trap-oxidizer research has been concentrated primarily on two
distinct designs. One involves a porous ceramic honeycomb
monolith material similar to the monolith substrate used for
catalytic converters on many gasoline-fueled vehicles. These
monoliths have had alternate channels blocked in order to maximize
particulate filtering. To this point most ceramic monolith traps
have not utilized catalytic material. Corning and NGK have been
the leading suppliers of prototype ceramic monolith traps. The
second design utilizes compacted alumina-coated wire mesh as the
filter and storage medium. Johnson Matthey has been the primary
supplier of catalyzed wire mesh trap prototypes while Texaco has
produced many non-catalyzed wire mesh traps•
This study analyzes the most important issues involved in
trap-oxidizer development. The largest part of the report
summarizes the current status of trap-oxidizer development and
evaluates the overall feasibility of the technology. The study
also analyzes the various leadtime issues and determines when
trap-oxidizers will be available for production application.
The state of trap-oxidizer development has advanced
significantly, over the last two years. Particulate collection
efficiencies of new trap-oxidizers are quite high, ranging from 70
to 90 percent for ceramic monolith traps and 50 to 80 percent for
wire mesh traps. Zero-mile backpressure levels are acceptable for
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the various trap designs. More importantly, there is a
near-consensus among researchers that high efficiency and low
backpressure can be maintained throughout repetitive regenerations
for all trap designs when regeneration can be properly
controlled. The conditions necessary for regeneration of
non—catalyzed traps were found to be temperatures in the range of
500°C to 650°C and oxygen levels of 3 to 4 percent maintained for
2 to 10 minutes. It is also necessary to control the maximum
temperatures in the trap to prevent uncontrolled regeneration and
possible trap failure.
Several systems to initiate and maintain regeneration
conditions have been investigated. Some of these designs, such as
fuel burners and electrical heating, appear workable but involve
higher relative cost or the need for greater vehicle
modifications. Other systems, such as intake air throttling and
exhaust stroke fuel injection, would likely be simpler and less
expensive but are further from being proved feasible on in-use
vehicles. Research is continuing in an effort to identify and
optimize the most promising regeneration mechanism.
Probably the most undefined area of development involves the
sensors, controls, and control logic which would be necessary
parts of any regeneration system. Ideal sensors for the
initiation of the regeneration process would be trap loading or
backpressure sensors, but at this time such sensors are not
commercially available and alternatives such as engine revolution
and mileage counters, in combination with temperature sensors, are
being examined. Integrating the proper sensors, controls, and
system logic within a total regeneration system and onto vehicles
is the last major technical problem in trap-oxidizer development.
Trap durability is dependent upon the success of regeneration
system design. It appears that, with sufficient control over the
regeneration process, trap durability is sufficient.
Manufacturers have reported several on-road vehicle tests and
dynamometer simulations where traps have survived upwards of
30,000 miles, and many of these tests occurred in 1979 and 1980.
Johnson Matthey has successfully completed a 50,000-mile
durability test with its catalyzed wire mesh trap. The durability
testing utilized a first-generation regeneration system, and thus
did not demonstrate a production-ready overall design, but it did
prove the general durability of the trap's filter structure,
catalyst and washcoat formulation, and mounting system. Based on
the information submitted to EPA, this study concludes that
regeneration is the most significant remaining technical problem
and that there is a high likelihood that manufacturers will be
able to design a successful trap-oxidizer system.
The determination of when trap-oxidizers could be ready for
integration with production vehicles requires a projection of the
amount of time still needed for development purposes, as well as
an analysis of "production" leadtime issues such as a.ssurance
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testing, tooling, and certification. In view of the significant
progress that has been achieved.during the last four years and the
determination that only regeneration initiation and control
remains unresolved, this study projects that manufacturers will be
able to optimize trap systems and begin assurance testing by
January 1983. Because trap-oxidizers are a new technology, EPA
believes it important to allow time for field assurance testing.
The first phase of assurance testing should take 7 to 9 months.
At this point, manufacturers will be able to make initial tooling
commitments. EPA projects that a total of 18 to 24 months will be
necessary for tooling. If necessary, manufacturers will be able
to carry out a second phase of assurance testing concurrently
during the initial stages of the tooling period. Certification
should take approximately 12 months to complete, but this can
likewise take place during the extended period available for
tooling. Thus, the critical path for leadtime involves the first
phase of assurance testing and tooling, and EPA estimates that
trap-oxidizer systems could be available for use on production
vehicles within 25 to 33 months after a successful prototype
system had been developed.
Assuming a successful trap prototype design by January 1983,
traps would be available for production application sometime
between February 1985 and September 1985. 1986 model year
production would begin in July/August 1985, so the shorter
leadtime projection could result in 1986 model year introduction,
but the longer leadtime projection would not allow introduction
until the 1987 model year. Because of this range of leadtime
projections, and the technical and economic risks inherent in the
introduction of new technologies, the study concludes that
trap-oxidizers will not be feasible on production vehicles until
the 1987 model year. The fact that this conclusion is based on
several conservative production leadtime assumptions is balanced
by the uncertainty inherent in the development leadtime analysis,
i.e., it is possible that unforeseen difficulties might occur in
the final stages of trap development.
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CHAPTER II
INTRODUCTION
The emission of particulate matter from diesel vehicles has
been a major concern to EPA for several years. Research into the
environmental impacts of diesel particulate emissions began in the
late 1970s when it became known that several passenger car
manufacturers were seriously considering manufacturing large
numbers of diesel vehicles. This work culminated in a Notice of
Proposed Rulemaking (44 Federal Register 6650), published on
February 1, 1979, which proposed particulate standards of 0.6 g/mi
in 1981 and 0.2 g/mi in 1983 for both diesel passenger cars and
light trucks. Thirty-two oral and written submissions were
received on the proposed regulations from automotive
manufacturers, federal agencies, environmental groups,
Congressmen, and private citizens during the public comment period
which ended on April 19, 1979. After reviewing these comments and
reanalyzing the environmental and economic impacts and
technological feasibility of the proposed standards, EPA published
a Final Rule (45 Federal Register 14496), on March 5, 1980. The
Final Rule delayed the implementation dates for the particulate
standards. It established a standard of 0.6 g/mi for all 1982
through 1984 diesel passenger cars and light trucks. The 1985
standards were set at 0.2 g/mi for diesel passenger cars and 0.26
g/mi for diesel light trucks. EPA identified the 1985 standards
as "technology-forcing," i.e., while EPA could not show that the
1985 standards were technically feasible at the time of
promulgation, EPA projected that the standards would be achievable
by the 1985 model year. EPA's technical projection was based on
the expectation of successful development . of trap-oxidizers by
1985. It is this projection of trap-oxidizer feasibility which
has been disputed by automotive manufacturers, and which is the
subject of this study.
The only other EPA rulemaking action affecting light-duty
diesel particulate regulation was a Notice of Proposed Rulemaking
(46 Federal Register 62608) issued on December 24, 1981, which
proposed to allow light-duty diesel manufacturers to meet the 1985
particulate standards by averaging the emissions of their diesel
engine families. EPA has not yet made a final determination with
respect to averaging.
General Motors petitioned EPA for reconsideration of the
Final Rule on May 5, 1980, in part on the basis that the 1985
standards were infeasible. EPA denied this petition on June 27,
1980 (45 Federal Register 48133). In the spring of 1980 General
Motors, joined by other diesel vehicle manufacturers, sued to
overturn the Final Rule. Oral arguments were heard on October 28,
1980 before the United States Court of Appeals for the District of
Columbia Circuit. The Court of Appeals upheld the Final Rule in
its entirety on April 22, 1981. General Motors petitioned the
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United States Supreme Court for certiorari review of the Court of
Appeals decision on July 31, 1981; this petition was denied on
November 2, 1981.
Because the feasibility of the 1985 particulate standards was
dependent upon a projected rate of technological development, EPA
was prepared to review the progress the industry was making in
trap-oxidizer development. EPA published a Request for
Information (46 Federal Register 31677) on June 17, 1981, which
announced that EPA would be undertaking this study of the
feasibility of trap-oxidizers and the 1985 particulate standards,
as well as three other unrelated studies. The request notice
included a list of questions concerning trap-oxidizer development
(see Appendix A). EPA invited interested parties to submit any
new data or information not considered during the original
rulemaking, as well as direct responses to the questions listed.
EPA asked that all comments be submitted by October 1, 1981 to EPA
Docket A-81-20.
EPA received a total of 21 submissions from 15 different
parties during the time period from September 9, 1981, to November
23, 1981. Since November 23, three commenters have updated their
original submissions. The Agency's policy has been to accept all
submissions, even those received while the study was in progress.
Parties which submitted comments, the dates of the submissions,
and the corresponding EPA docket identification numbers are all
given in Table II-l.
The rest of this study is divided into two chapters. Chapter
III, Stage of Development, will summarize the current status of
trap-oxidizer development and will make an overall evaluation of
the ultimate feasibility of trap-oxidizers. Chapter IV, Leadtime,
will determine the model year when traps will be available for
production application. This will involve projecting how much
additional development leadtime is necessary to optimize
trap-oxidizer design as well as determining the amount of leadtime
necessary for the vehicle manufacturers to integrate traps with
vehicle production.
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Table II-l
Commenters to the Trap-Oxidizer Feasibility Study
(EPA Docket A-83-32)
EPA IH Ho.
II-D-1
II-D-2
II-D-3
II-D-4
II-D-5
II-D-6
II-D-7
II-D-8
II-D-8a
II-D-9
II-D-10
II-D-11
II-D-12
II-D-13
II-D-14
II-D-15
II-D-16
II-D-17
II-D-18
II-D-19
II-D-20
II-D-21
II-D-22
II-D-23
II-D-28
II-D-31
Commenter
Renault USA
National Automobile Dea2ers Assoc.
Volkswagen of America, Inc.*
Toyota Motor Co., Ltd.
Chrysler Corporation*
Johnson Matthey, Inc.*
Ford Motor Company
Texaco Inc.*
Texaco Inc.*
Nissan Motor Company, Ltd.
Natural Resources Defense
Council, Inc.
U.S. Technical Research Company
(Peugeot)**
BMW AG***
General Motors Corporation*
General Motors Corporation*
Johnson Matthey, Inc.*
Hogan and Hartson
(Daimler-Benz AG)
Volkswagen of America, Inc.*
General Motors Corporation*
Chrysler Corporation*
Johnson Matthey, Inc.*
Corning
Johnson Matthey, Inc.*
General Motors Corporation*
Johnson Matthey, Inc.*
Johnson Matthey, Inc.*
Date of Comment
September
October 1,
September
September
October 1,
October 1,
October 2,
October 2,
October Ik
October 1,
October 13
9, 1981
1981
30, 1981
29, 1981
1981
1981
1981
1981
, 1981
1981
, 1981
October 12, 1981
October 23, 1981
September 30, 1981
October 20, 1981
October 29, 1981
November 1, 1981
November 16
November 5,
November 25
October 8,
November 23
December 2,
December 15
January 25,
February 12
.1981
1981
1981
1981
, 1981
1981
, 1981
1982
» 1982
* This commenter submitted more than one document.
** This submission included confidential material which could
not be used in the study.
*** This entire submission was confidential and could not be used
in the study.
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CHAPTER III
STAGE OF DEVELOPMENT
A. Different Trap Designs
Conceptually the diesel trap-oxidizer can be considered to be
somewhat analogous to the oxidation catalytic converter now used
on gasoline-fueled passenger cars. The oxidation catalytic
converter consists of a supporting structure (such as alumina
pellets or a ceramic honeycomb monolith) coated with a thin layer
of catalytically active material (platinum, palladium), providing
a large surface area for the oxidation of exhaust gas hydrocarbons
(HC) and carbon monoxide (CO) to water and carbon dioxide.
Particulate matter, composed primarily of solid carbonaceous
soot, cannot be oxidized as easily as gases such as HC and CO.
This problem is further exacerbated by the lower exhaust gas
temperatures of diesel vehicles relative to gasoline-fueled
vehicles. Thus, continual oxidation of diesel particulate is
impossible, and the alternative solution is a mechanism which
collects the particulate on a filter structure and periodically
oxidizes the collected particulate when proper conditions (high
exhaust gas temperature, sufficient oxygen content) are reached.
Thus, the trap-oxidizer utilizes filter/oxidation/filter/oxidation
cycles to reduce particulate emissions while the catalytic
converter utilizes continual and near-instantaneous oxidation to
reduce HC and CO emissions.
Since trap-oxidizer development began in the mid-1970's, many
different designs have been investigated. The most fundamental
parameter of trap-oxidizer design is the filter material. Nearly
all work in this area is now focused on two materials—ceramics
and alumina-coated wire meshes. These materials will be discussed
in turn with specific designs described in some depth.
1. Ceramic Traps
Although several manufacturers have stated that they are
focusing their development programs on ceramic trap designs,[1, p.
5; 2, p. 6] Corning Glass Works was the only manufacturer of
ceramic traps to submit information to EPA and the following
description relies heavily on Coming's own discussion of their
trap. [3, p. 2] Coming's trap is very similar to its support
structure for catalytic converters for gasoline-fueled vehicles,
which is a square, cell-shaped honeycomb with parallel channels
running the length of the unit. The structure is basically a
porous cordierite (2MgO - 2AI2O3 - 5Si02) material and is
shown in Figure III-ld.[8, p. 42] As shown in Figure III-2[4, p.
19], the trap filter concept involves blocking alternate cell
channel openings in "checkerboard" fashion on both the front and
rear faces of the monolith, with the plugs on the front face one
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Figure III-l
a.'Alumina Coated
Metal Mesh
c. Foam Filter
bi Alumina Coated
Steel Wool
d.i Honeycomb Filter
Configuration of Various Trap Materials
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Figure III-2
P 4r-'S5
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cell displaced from the plugs on the rear face. Therefore, each
channel is blocked either at the front or rear face, and as Figure
III-2 shows, exhaust gas cannot flow directly through any one
channel and must pass through one of the porous walls of the
honeycomb in order to exit through an adjacent channel. The
forcing of the exhaust gas through the ceramic walls is the
primary filtering mechanism of the trap. At first, the very small
diesel particles (typically smaller than 1 micrometer in diameter)
are trapped in the internal pores of the porous cell walls. As
particulate continues to be collected, it begins to form a layer
on the surface of the ceramic wall. It is fairly typical for
collection efficiency to increase as this particulate "blanket"
forms as there are more obstructions to the flow. Of course,
there is a limit to how much particulate can be trapped before
backpressure levels become prohibitive, and the trap must be
regenerated before that point.
Based on a fairly comprehensive characterization program,
Corning identified a candidate filter material, designated EX-47,
for further testing by themselves and vehicle manufacturers. The
EX-47 design includes 100 cells per square inch, a 0.017 inch wall
thickness, a mean pore size of 12 to 13 micrometers, 50 percent
porosity, and an overall honeycomb dimension of 5.66 inches in
diameter and 12 inches in length. [3, p. 9] Many of the test
results which will be discussed later in this report will be with
the Corning EX-47 trap, but variations in cell density, wall
thickness, pore size, porosity, and overall dimensions have been
tested as well. The ceramic can be, and has been, coated with
catalytic material as well. Corning has produced nearly 2,000
prototype units of various sizes and shapes and has supplied traps
to "[vjirtually every automaker in the world who has or expects to
have a diesel engine option in 1985."[5, p. 1]
A number of vehicle manufacturers commented on the Corning
trap in particular, or else on ceramic honeycomb monoliths in
general. (It should be noted that NGK. Insulators, Ltd. has also
supplied traps of this basic design.) There is a consensus that
ceramic honeycomb monoliths provide high collectiar. efficiency and
that, accordingly, their primary drawback is relatively high
backpressure. (4 j p. 6; 6, p. 3; 7, p. 3; 8, p. 6] These issues
will be discussed in later sections.
Other ceramic designs besides the honeycomb monoliths have
been built and tested though no trap, manufacturer submitted
information on them. Probably the most promising of these other
designs is the ceramic foam filter, shown in Figure III-lc, which
relies on "tortuous path" impaction for particulate removal. At
least two vehicle manufacturers have tested ceramic foam
filters.[8, p. 5; 9, p. 7] Also, ceramic fiber filters and porous
ceramic tube elements have been tried, though again few specifics
are known about their construction.[6> p. 2; 7t p. 3; 9, p. 8]
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2.
Wire Mesh Traps
The second general type of trap-oxidizer utilizes
alumina-coated wire mesh as the filtering mechanism (see Figure
Ill-la) • Johnson Matthey, Inc. and Texaco, Inc. both make wire
mesh traps and both reported on their developments to EPA.
Johnson. Mattheyfs original development work was with a trap
that could be placed in the exhaust manifold as shown in Figure
III-3.[10, p. 40] It is referred to as the JM4 trap. The JM4
trap is a long, cylindrical wire mesh filter with a hollow central
core. The flow through the filter is radial, that is, the exhaust
gas enters on the outside of the cylindrical filter but must pass
through the wire mesh to exit through the hollow core. The
structure of the wire mesh yields a random path for the exhaust
gas to follow. Particulate filtration is due primarily to
impingement on the mesh fibers. ¦ Inherent in the Johnson Matthey
concept is a catalytic coating which lowers the temperature
necessary for oxidation of the collected particulate matter.[10,
p. 2]
Johnson Matthey has performed considerable development
testing which resulted in a "second-generation" trap, the JM13.
The JM13 is similar to the JM4 described above but involves a
graduated wire mesh bulk density and a graduated surface-to-volume
ratio. Thus, the exhaust gas first enters a relatively low
density, low surface-to-volume ratio section of wire mesh but,
closer to the corej the density and surface-to-volume ratio of the
wire mesh both increase. Thus, larger particulate tends to be
trapped on the outer section of the filter and finer particulate
is trapped on the inner sections. The JM13 design has also been
adapted for placement in the exhaust system underneath the
vehicle, similar to where catalytic converters are placed on
gasoline-fueled vehicles. The underfloor trap, shown in Figure
III-4[10, p. 43J with two wire mesh filters instead of one (two
filters may be necessary only on the largest vehicles), resembles
a conventional muffler in shape. The trap inlet has baffles to
force the exhaust gas to flow around the perimeter of the can,
through the mesh filter, and out through the hollow central
core.[10, pp. 12-14]
Finally, Johnson Matthey has developed a "third-generation
trap," the JM41. The JM41 differs from the JM13 in that it would
be somewhat easier to mass produce. Thus, data on Johnson Matthey
traps will involve JM4, JM13, and JW41 designs.
Whether traps will ultimately be installed in the exhaust
manifold or underneath the vehicle will be decided by the vehicle
manufacturers. The primary advantage of exhaust manifold
placement is that the exhaust gas temperature is higher, making
trap regeneration somewhat easier. Placing the trap farther back
in the exhaust system, underneath the vehicle, is simpler to
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Figure III-3
Schematic of a JM Manifold System
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— J. J —
Figure III-4
Schematic of a
Large Capacity JM
Underfioor System
Inlet
i
i
/
\
\
/
/
\
\
/
\ H
\
/
/
\
\
\V
}/
,N /
I
Exhaust
i
}
i
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integrate with the vehicle, however, and may be absolutely
necessary on some vehicles due to space limitations in the
manifold.
Johnson Matthey has continued to optimize its trap-oxidizer
design, and "numerous testing programs are underway with most of
the major diesel automobile manufacturers throughout the
world."[10, p. 32] Several commenters specifically discussed
Johnson Matthey's design. The distinguishing characteristic of
the trap is Johnson Matthey's catalytic coating. The primary
advantages of the coating are a reduction of the minimum
"light-off" temperature and lower HC and CO emissions; the primary
disadvantage is greater sulfate emissions.[9, p. 7,20; 6, p. 2)
The second alumina-coated wire mesh design for which EPA
received information is the Texaco trap-oxidizer. As shown in
Figure III-5,[H, p. 5] the Texaco design consists of a
muffler-type container packed with alumina-coated metal wool or
wire. Unlike the Johnson Matthey design, the Texaco trap permits
exhaust flow straight through the filter although there is a "gas
spreader" to force the flow over the entire filter face. Texaco
stated that their traps have been constructed in a wide range of
sizes and shapes from 16-inch diameter round units to exhaust
manifold-packed units.[11, p. 1] Only one commenter mentioned the
Texaco trap by name, reporting it to have moderately low
backpressure and backpressure rise rates, but expressing a concern
about its physical integrity and high thermal mass.[6, p. 1]
Now that we have described the two general types of
trap-oxidizers and a few specific designs, we can turn to the
important technical parameters of trap operation—efficiency,
backpressure, regeneration, and durability. These will be
discussed in the following sections. Some vehicle manufacturers
identified their prototype traps by name (e.g., Corning, Johnson
Matthey, Texaco, etc.), others did not. Whenever possible, we
will identify the trap manufacturers in the following discussions,
but often it will be possible only to name the general design
involved.
B. Efficiency and Backpressure
Efficiency and backpressure are two of the most basic
trap-oxidizer performance parameters. Efficiency is a measure of
the particulate reduction capability, which is the driving force
for trap usage. The effect of traps on exhaust gas backpressure
is a fundamental concern as the trap filter medium is an
"artificial" obstruction in the exhaust system and excessive
backpressure can adversely impact engine performance and fuel
consumption. The determination of the efficiency and backpressure
of a filter material when new is an appropriate first step toward
analyzing a trap design. Thus, much data has been generated
concerning zero-mile efficiency and backpressure levels. But,
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Figure III-5
TYPICAL TEXACO DIESEL EXHAUST FILTER DESIGN
ALUMINA-COATED METAL WOOL
SUBSTRATE
INSULATION
INLET
GAS
PERFORATED
BAFFLES AND
RETAINERS
GAS
SPREADER
OUTLET
^ 6AS
Ln
I
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just as critical, and far more time consuming, is determining
whether the trap material can maintain acceptable efficiency and
backpressure over the lifetime of the vehicle on which it is
used. Accordingly, this section will examine the data on trap
efficiency and backpressure in two sections—at zero-mile
conditions and after significant mileage accumulation.
1. Zero-Mile Efficiency and Backpressure
It has been known for some time that filter materials are
available which, when new, can significantly reduce diesel
particulate emissions without raising exhaust gas backpressure to
unacceptable levels.[12, pp. 48-49] Table III-l summarizes
zero-mile efficiency and backpressure data which were submitted by
vehicle and trap manufacturers for this study. Unless otherwise
noted, the efficiency data were all generated over EPA's Urban
Dynamometer Driving Schedule, under either the Federal Test
Procedure or hot start LA-4 conditions. The backpressure data
were generated in various ways and, where stated by the
commenters, are also listed in Table III-l.
Except for Johnson Matthey and Texaco, which design metal
mesh traps, every commenter listed in Table III-l reported data on
ceramic monolith traps. Most of the ceramic monolith data are for
the Corning design, with the remaining data unidentified by
manufacturer. It is clear that the ceramic monolith design is a
very effective particulate trap when new—the reported data range
from General Motors' 60 to 80 percent to Daimler-Benz' 86
percent. EPA has recently tested a Corning ceramic monolith trap
and found efficiency to be 90 percent when new. [27, p. 3] No
vehicle manufacturer has stated that zero-mile trap collection
efficiency is a problem, and it is likely that it is the ceramic
monolith's high efficiency that has made it a favorite candidate
trap for many vehicle manufacturers.
Backpressure is a somewhat more complex issue. The first
issue to be resolved must be the determination of "acceptable"
backpressure. EPA did not specifically ask commenters to address
this issue, and none did so directly. However, a few commenters
did shed some light on this issue. In its development testing of
its ceramic monolith prototype traps, Corning used a trap pressure
drop of 103 mm Hg as the endpoint for trap filtering. This value
was suggested by the manufacturer of the engine Corning was using
(Oldsmobile 5.7-liter V-8 diesel) as .the maximum tolerable
pressure drop.[3, p. 3] Ford, in its initial testing of the
Corning ceramic monolith, apparently decided that a 75 mm Hg
pressure drop at 40 mph was the limit.[13, p. 8] Johnson Matthey,
in its trap development work, regenerates its trap when the
pressure drop across the trap reaches about 41 mm Hg.[10, p. 24]
Thus, there apppears to be quite a range of values for
"acceptable" backpressure levels.
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Table III-l
Zero-Mile Efficiencies and Backpressures for Various Trap Designs
Commenter (Reference)
Type of Trap
Daimler-Benz[2, pp. 6-8] Ceramic monolith
Corning[3, p. 5] Ceramic monolith
Volkswagen[A, pp. 21-22] Alumina-coated wire
mesh with catalyst
Ceramic monolith
Ceramic monolith
with catalyst
Ford[6, p. 5]
Nissan[7, pp. 9-10]
Toyota[8, pp. 7-8]
Alumina-coated wire
mesh
Alumina-coated wire
mesh
Porous ceramic tubes
Ceramic monolith
Steel wool
Ceramic monolith
Ceramic fiber
Ceramic-coated steel
wool
Alumina-coated metal
mesh
Alumina-coated steel
wool
Ceramic monolith
with catalyst
Ceramic foam
Manufacturer of Trap
Corning
Corning
Zero-Mile
Efficiency*
(%)
86
Zero-Mile
Backpressure
Increase
( mm Hg)
80 7.5
(steady-state) (steady—state)
Johnson Matthey (JM13) 51-61
Corning
Corning with catalyst
Texaco
Johnson Matthey
NGK
Corning/NGK
77
78
115 (maximum, LA-4)
185 (maximum, LA-4)
23-71
21-58
77
80
53
(steady-s tate)
72-74
69
60
48
55
80
55
15 {40 mph)
26 (40 mph)
249 (40 mph)
26 (40 mph)
20 (55 mph)
170 (45 mph)
30 (maximum, LA-4)
Remarks
VI
I
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Table III-l (cont'd)
Zero-Mile Efficiencies and Backpressures for Various
Trap Designs
Commenter (Reference)
General Motors
[9 pp. 5,9)
Johnson Matthey
[10, pp. 17,34-37,44,
50,86-87)
Type of Trap
Texaco[ll, p. 2]
Metal mesh
Ceramic monolith
Ceramic foam
Ceramic fiber
Alumina-coated metal
mesh with catalyst
Alumina-coated metal
mesh with catalyst
Alumina-coated metal
mesh with catalyst
Alumina-coated metal
mesh with catalyst
Alumina-coated metal
mesh with catalyst
Alumina-coated metal
mesh with catalyst
Alumina-coated metal
mesh with catalyst
Alumina—coated wire
mesh
Manufacturer of Trap
Johnson
Johnson
J ohnson
Johnson
Johnson
Johnson
Johnson
Matthey
Matthey
Matthey
Matthey
Mat they
Matthey
Matthey
Texaco
(JM13)
(JM13)
(JM13)
(JM13)
(JM41)
(JM41)
(JM41)
Zero-Mile
Efficiency*
(%)
45-65
60-80
45-55
40-80
73
80
55
51
68
58-80
Zero-Mile
Backpressure
Increase
( mm Hg)
0.15
27
41
18
13 (60 mph)
38 (60 mph)
8 (60 mph)
84 (60 mph)
145 (60 mph)
31 (60 mph)
38-79 (40 mph)
Remarks
EPA testing
NA - Underfloor
NA - Underfloor
NA - Manifold
TC - Underfloor
NA - Underfloor
NA - Manifold
TC - Underfloor
Efficiency data reported for FTP or LA-4 testing unless noted otherwise.
-------
-18-
It ¦ can be seen in Table I1I-1 that the zero-mile incremental
backpressure values for the non-catalyzed ceramic monolith traps
were 7.5 mm Hg (Corningj under steady-state conditions), 26 mm Hg
(Ford., 40 taph), 27 mm Hg (General Motors), and 115 mm Hg
(Volkswagen, maximum pressure drop during LA-4 cycle). Only the
VW figure is high enough to warrant discussion. It is important
to keep in mind that "acceptable" backpressure is very dependent
on the vehicle being considered * For example, the 115 nun Hg
pressure drop for the ceramic monolith trap reported by VW
resulted in an approximate doubling of the total exhaust
backpressure. But, as "Volkswagen stated in its comment, "[t]he
exhaust gas backpressure at a level of two times higher than
normal does not yet essentially affect the fuel economy, EC
emissions, or engine power output".[4, p. 22] Thus, on this
vehicle at least, VW did not consider a 115 nun Eg pressure drop
increase to be unacceptable. Daimler-Benz, which reported very
high efficiency for the ceramic monolith trap, stated that the
backpressure of the trap "seems to be acceptable when the filter
is new."(2, p. 7] Thus, the data reported to EPA indicate that
the zero-mile uncatalyzed ceramic monolith trap is very efficient
arid produces acceptable backpressure levels.
Zero-mile backpressure data in Table 111-1 for catalyzed
ceramic monolith traps are less positive—185 mm Hg (Volkswagen,
maximum during LA-4 cycle) and 170 mm Hg (Toyota, 45 mph)• VW did.
not comment on this backpressure level while Toyota claimed that
the 170 cm Hg pressure drop would result in a 10 percent fuel
economy penalty. One reason for this apparent discrepancy between
the two manufacturers is that the VW value is the maximum obtained
over the LA.-4 driving cycle while the Toyota value was taken at 45
mph operation and might well have been much higher at some point
during LA-4 operation. Incremental backpressures near 200 mm Hg
would likely not be acceptable for most vehicles and thus the use
of a catalyst for ceramic monolith traps does not now appear to be
a promising option. However, this conclusion is based on very
limited data and it is quite possible that further research will
produce a successful way of catalyzing ceramic monolith traps.
Only a sparse data base was reported for other types of
ceramic traps. Toyota and GM reported efficiencies between 45 and
55 percent and incremental backpressures of between 30 end 41 ram
Hg for ceramic foam traps at zero-mile. Nissan and GM reported
zero-mile efficiencies between 40 and 80 percent for ceramic fiber
traps, with GM reporting a zero-aile backpressure increase of 18
mm Hg. These data warrant further consideration of ceramic foam
and fiber traps; thus far their development has lagged behind
ceramic monoliths. Ford was the only manufacturer to report on
porous ceramic tubes; their efficiency was quite good at 77
percent but the incremental backpressure of 249 mm Kg was very
high. This backpressure would have to be reduced for this trap to
be successful.
-------
-19-
Most commenters also reported data for alumina-coated metal
mesh traps. There were considerable data reported on the Johnson
Matthey catalyzed metal mesh trap. Johnson Matthey submitted
detailed data on their various trap designs and some of them are
summarized in Table III-l. An attempt was made to categorize the
Johnson Matthey data by basic design (JM13 vs. JM41), trap
placement (manifold vs. underfloor), and by whether the trap was
used on a naturally-aspirated or turbocharged vehicle.
(Considerable concern has been expressed in the past regarding the
additional complexity of utilizing trap-oxidizers on turbocharged
vehicles. It is noteworthy that both Volkswagen and Daimler-Benz
reported trap data for turbocharged vehicles and neither discussed
any particular problems with such applications.) It can be seen
in Table III-l that Johnson Matthey reported zero-mile collection
efficiencies of between 50 and 80 percent for their traps under
various conditions. EPA testing of an underfloor JM13 trap on a
1978 Fiat 131 diesel passenger car resulted in a 73 percent
particulate reduction.
Two vehicle manufacturers also reported data on the Johnson
Matthey design. Volkswagen reported zero-mile efficiencies of
between 51 and 61 percent and Ford listed efficiencies of between
21 and 58 percent for the Johnson Matthey design. Finally, GM
reported efficiencies of 45 to 65 percent for metal mesh traps,
and GM tested several Johnson Matthey traps. Based on the weight
of these data, we can conclude that the Johnson Matthey
trap-oxidizer is capable of 50 to 80 percent collection efficiency
when new. -
Johnson Matthey and Ford were the only commenters to submit
information on zero-mile incremental backpressure levels for the
former's trap design. As shown in Table III-l all of the reported
backpressure levels were less than 40 mm Hg except for the JM41
design on naturally-aspirated vehicles. Even these higher
values—84 and 145 mm Hg at 60 mph—might be acceptable (see
discussion above), but the large discrepancy in incremental
backpressure levels between the JM13 and JM41 traps on
naturally-aspirated vehicles suggests that improvements in the
latter's design are likely. Based on the data in Table III-l, we
conclude that the Johnson Matthey trap provides good collection
efficiency with acceptable incremental backpressure levels under
zero-mile conditions.
Texaco and Ford reported test data for Texaco's non-catalyzed
wire mesh trap. Texaco reported efficiencies of between 58 and 80
percent and Ford reported efficiencies of 23 to 71 percent for the
former's design. Texaco reported backpressure increases of 38 to
79 mm Hg while Ford realized a 15 mm Hg increase. Toyota and
General Motors also reported data on wire-based traps without
elaborating on the traps on which the data were collected. Toyota
reported efficiencies of 48 to 55 percent and GM 45 to 65 percent,
all at relatively low backpressure increases. These data are not
-------
-20-
significantly different than the results discussed above for the
Johnson Matthey catalyzed design which indicate that the
fundamental collection efficiency characteristics of the wire mesh
filters ,are very similar and that, unlike ceramic traps, the use
of a catalyst does not appear to significantly affect wire mesh
backpressure levels.
In conclusion, it can be confidently stated that ceramic
monolith traps are 70 to 90 percent efficient and wire mesh traps
are 50 to 80 percent efficient when new. Both designs have
acceptable backpressure increases at zero-miles.
2. Efficiency and Backpressure After Mileage Accumulation
Having determined in the previous section that both ceramic
monolith and alumina-coated wire mesh trap-oxidizers are capable
of providing high collection efficiencies with acceptable
backpressure increases at zero-mile levels, the issue becomes
whether a trap-oxidizer can maintain these characteristics over
the useful life of the vehicle. As no trap-oxidizer has been
developed which can continuously oxidize particulate matter, a
trap reaches a point after mileage accumulation where the amount
of particulate contained in the filter medium becomes excessive
and backpressure increases to unacceptable levels. It is at this
point that the trap has to be regenerated, with the goal being to
return the efficiency and backpressure to as close to zero-mile
levels as possible.
Several vehicle manufacturers commented on the ability of
ceramic monolith traps to return to zero-mile efficiency and
backpressure levels. General Motors stated that "[i]n general the
collection efficiencies and backpressure levels return to
zero-mile levels after repeated regeneration.... Only in cases of
incomplete regeneration, trap deterioration, or where additives
have been used which collect on the trap, have we seen increasing
backpressure levels with repeated regeneration."[9, p. 21) To
illustrate its point, GM submitted a series of graphs showing the
particulate emission levels and backpressure levels during 180
hours of dynamometer testing of a vehicle equipped with a Corning
ceramic monolith trap. Two of these graphs have been reproduced
as Figures III-6 and III-7. Figure 6 shows that during the first
12 hours of testing (involving 6 regenerations) the vehicle
emitted between 0.09 and 0.12 g/mi particulate and had
post-regeneration backpressure levels of between 36 and 41 mm Hg.
Figure III-7 gives data for the same vehicle at hours 142 to 160.
It shows that the vehicle was then emitting between 0.07 and 0.12
g/mi particulate with post-regeneration backpressure levels of 25
to 38 mm Hg. The data between hours 12 and 142 were in similar
agreement. Thus, during the 180 hours of testing, which simulated
approximately 7000 miles of driving at 40 mph and which included
approximately 80 regenerations with a manifold burner, the ceramic
monolith trap maintained its zero-mile efficiency and backpressure
characteristics following regeneration.
-------
Figure .111-6
"Cfell 6
H Olcls Y-
^t-O mph!R,L.
8> Jl 80'
-------
Figure III-7
I'M
: ' >
i ¦
' : i
" ¦ r"
¦ i 1 1
:!ii
.Mi
|-T
!|
j !
rt-
i i
rr
i
t:
rr
i ! i !
i. I.L
» I
lit-
i > i
; i
l!'
! i1
in--
r ¦
-U-
11
4
i:
i''
'!' H"
1 : I
i ;
1 i
Tt
I
-1-
Loaded at AO MPH, Regenerated at 25 MPH
: I
4'
i : :
! I
V! t
! i I
I
: I
; I : : II
Li.;.;. |.|
"iTi!
Jl!.!.
Jii.i.
I
i
: i
lt"T
i
~C£LL C fi/\
, .AT/V-ArOZ/O.
i!
I
.±
I
I ( !
}{^ap:
-------
-23-
Ford reports a similar conclusion—"With adequate
regeneration temperatures and time intervals, backpressure levels
can be returned to levels very close to the clean trap
backpressure levels for the ceramic honeycomb trap, likewise,
collection efficiency only slightly decreases with
regeneration."[6, p. 8] Ford's position is supported in Figure
III-8 which shows efficiency and backpressure data for a test
vehicle equipped with a Corning ceramic monolith trap. The
vehicle was driven on the road for over 10,000 miles and the trap
underwent approximately 100 regenerations before the test was
ended due to trap failure. Figure III-8 shows a very slight
increase in post-regeneration backpressure levels and a slight
decrease in collection efficiency over the 10,000 miles, though
these trends are subject to data scatter, especially with respect
to efficiency.
Other vehicle manufacturers' data on ceramic monolith traps
support the conclusions made by GM and Ford. Nissan reported
results for the ceramic monolith trap with two different methods
of regeneration. Using a burner to initiate regeneration, it
reported virtually no change in efficiency or clean trap
backpressure over a testing period of 500 miles. Nissan also
modified engine operating conditions so that the exhaust gas
temperature would be sufficient for regeneration. This resulted
in the ceramic monolith trap maintaining its clean-trap efficiency
and backpressure performance throughout a 5000-mile testing period
involving 54 regenerations.[7, pp. 23-24] Toyota regenerated a
ceramic monolith trap after approximately 100 miles of operation
and found that the trap collection efficiency actually stabilized
at a somewhat higher level than at zero-mile while the clean trap
backpressure returned to the zero-mile level.[8, p. 15J EPA
testing of a Corning ceramic monolith trap also supports the
thesis that zero-mile collection efficiency can be maintained.
Testing at 5,000, 10,000, and 15,000 miles has resulted in the
same 90 percent collection efficiency that existed at
zero-miles.[27, p. 3]
Volkswagen was the only manufacturer to state that it could
not return efficiencies and backpressure levels of ceramic
monolith traps to zero-mile levels. It commented that
"[p]otential trap collection efficiencies and backpressure levels
never return to zero-mile levels following use and
regeneration.... Ricardo has determined that at filter
temperatures of 700°C approximately 4 percent of the particulate
material collected remains in the filter. This applies to
ceramic-type filter elements with high pore density."[4, p. 31]
Volkswagen also supported its conclusion with data showing that
the air flow through catalyzed and non-catalyzed ceramic monoliths
never returned to zero-mile levels even after external flame
regeneration and reverse air blasting. The fact that 4 percent of
the particulate matter remained in the filter medium should not
necessarily affect backpressure significantly and could actually
-------
6o
50
1+0
30
20
10
0
00
80
6o
l+o
20
0
BACKPRESCtiRE g C-1+0 mph
AFTER TRAP REGENERATION
R106
• » »
5 i »
* r
3-3 in Hg/100 Mi @ CbO mph
109 Mi Interval Average
' R122
10
12
MILES (X10 3)
DURABILITY TRAP - D1
119 cu.in. Corning Ceramic Honeycomb
2.3L Opel Diesel Vehicle
O
o_
o
o
o o
CVS-C/H
o SVL
^'ETL
O
Limited Durability
MILES (X10 3)
— AVG.E7F. 81.6;"!-
°v 10,337 mi.
Ther!r:?.l
Shock
: Failure
AMA Durability
-------
-25-
improve collection efficiency. The air flow results are the more
significant and deserve some examination. VW did perform the
regeneration and air flow tests after 180 miles of operation,
which is a fairly high testing period for the efficient ceramic
monolith trap. The trap would have been loaded very heavily.
Regeneration after a short mileage interval might have produced
different results. Otherwise,' no explanation is readily available
as to why the other vehicle manufacturers which directly measured
efficiencies and backpressure levels for ceramic monolith found
post-regeneration levels to be at or near the zero-mile levels,
while Volkswagen, using more indirect analytical methods, found
otherwise. Given the near consensus of data from the vehicle
manufacturers, especially those data which involve direct
measurement of efficiency and backpressure, it can be concluded
that ceramic monolith traps are capable of maintaining high
collection efficiencies and acceptable backpressure levels through
repetitive regenerations.
The only commenters to submit information on wire mesh traps
were Johnson Matthey and Texaco. The nature of trap-oxidizer
research has been that the vehicle manufacturers perform most of
the vehicle/trap integration work. Since no vehicle manufacturer
reported on the ability of wire mesh traps to maintain acceptable
efficiencies and backpressures throughout mileage accumulation and
repetitive regenerations, the data base for metal mesh traps is
much more sparse.
Johnson Matthey submitted much information on the collection
efficiencies of its catalyzed wire mesh trap designs during
mileage accumulation.[10, pp. 46-49, pp. 52-57] Its data
generally show that its trap designs maintain, and in some cases
improve, zero-mile collection efficiency with mileage. Figure
III-9 is a graphical illustration of the efficiency of a JM13
manifold trap over 1000 miles of hot-start LA-4 operation. There
is some data scatter, but most of the efficiencies are between 65
and 75 percent and there is no discernible negative trend with
mileage accumulation. These data are representative of the data
base for efficiency which Johnson Matthey provided.
Johnson Matthey also provided data on the backpressure levels
of its traps with mileage accumulation. Its most comprehensive
data are shown in Figures 111-10 and III-ll [10, p. 123, p. 125]
which give the backpressure levels for the first 11,000 miles of
Johnson Matthey's durability testing at Southwest Research
Institute (which will be discussed in more detail later). Figure
111-10 shows that the trap had to be externally regenerated only 3
times during the 11,000 miles, at 6310, 8125, and 9220 miles. The
zero-mile backpressure level of the test vehicle was 21 mm Hg at
40 mph. After the first regeneration at 6310 miles the
backpressure was 27 mm H.g (Figure 111-10), after the second
regeneration at 8125 miles it was 26 mm Hg (Figure III-ll), and
after the third regeneration at 9220 miles it was approximately 32
-------
Figure III-9
Vehicle GF101 Manifold JM13
Miles
-------
Figure III-1Q
JM13/11 Durability Test
Back Pressure vs Mileage
First 10,000 Miles
On Board Pressure Measurement
Vehicle GW101
lO-i
1st Reqenoralion
6310 Miles
Daclc Pressure
In H20
At 40 MPH
2nd Regeneration
0125 Miles
I
ho
I
3rd Regeneration
9220 Miles
i i i \ i i i i i i r
1000 2000 3000 4000 5000 6000 7000 6000 9000 10000 11000
Mileage
-------
Figure III-ll
JM13/II Durability Test
Stabilized Back Pressure vs Mileage
1000 Mile Detail
On Board Pressure Measurement
Vehicle GW101
-------
-29-
mm Hg (Figure XII-10). Recently Johnson Matthey reported the
final data on the 50,000-mile durability vehicle. Over the 50,000
miles the trap was externally regenerated 37 times. After
regeneration the vehicle backpressure ranged from 24 mm Hg to 39
mm Hg with all but two of the levels between 24 mm Hg and 32 mm
Hg.[28, p. 27] There was very little increase in
post-regeneration vehicle backpressure levels and no upward trend
with mileage over the 50,000-mile durability test.
Texaco reported on two durability tests with its
non-catalyzed wire mesh trap-oxidizer—one was an on-highway
program which achieved 10,000 miles before trap failure and the
second was a steady-state dynamometer program which lasted 30,000
miles before trap failure. In both cases, Texaco's data indicate
that collection efficiencies were maintained at levels very near
to zero-mile levels while clean-trap backpressure levels tended to
stablize somewhat above zero-mile levels.[3, pp. 6-7]
Based on the foregoing discussion, it can be stated that,
given a successful on-vehicle regeneration system, trap-oxidizers
are now available which can maintain high collection efficiencies
at acceptable backpressure levels throughout mileage accumulation
and repetitive regeneration cycling. This conclusion is most
supportable for ceramic monolith traps, as there is a near
consensus from the vehicle manufacturers on this issue. There is
a much smaller data base with respect to metal mash traps, though
Johnson Harthey1s data strongly support this conclusion.
C. Regeneration
1. The Need for Regeneration
Because of the lower exhaust gas temperatures of diesel
vehicles and the more difficult physical task of particulate
matter oxidation, the trap-oxidizer cannot continually oxidize
particulate emissions. But the need for periodic oxidation of the
collected particulate or regeneration of the trap is clear. For
example, the Corning ceramic monolith trap tested by Ford, which
was 5 inches in diameter and 9 inches long and which contained 100
cells per square inch with a wall thickness of 0.017 inches, has
43.4 cubic inches of void space within the filter for particulate
storage. Assuming an average particle density of 0.92 grams per
cubic inch, this trap would only be able to store a maximum of
approximately 40 grams of particulate matter before simply running
out of space within the trap. If this trap collected particulate
at 80 percent efficiency on a vehicle which emitted 0.40 g/mi,
then the trap storage volume would be completely filled after
approximately 125 miles of vehicle operation for this specific
trap design and size. [13, p. 8] Trap-oxidizers could be made to
be bigger with correspondingly larger storage volumes, but it can
be easily seen that regeneration is ultimately necessary simply
from a physical standpoint.
-------
-30-
A second factor which affects the need for trap regeneration
is exhaust gas backpressure. As greater amounts of particulate
matter collect on the filtering medium, the exhaust gas stream
must pass through more material and exhaust gas backpressure
rises. Excessive backpressure can worsen fuel economy and engine
performance. Third, the amount of particulate collected is a
strong determinant of the maximum temperatures reached in the trap
during the regeneration process. The greater the amount of
particulate collected, the greater the temperature reached during
regeneration. Both backpressure and regeneration temperature
characteristics can result in regeneration interval requirements
even more stringent than those which would be defined by total
trap storage space. Thus, there are several benefits of frequent
trap regeneration.
Alternatively, there are reasons why the number of
regenerations should be minimized. Since the regeneration process
involves high-temperature oxidation during relatively short
periods of time, it would be expected that the greatest physical
stresses on the trapping materials (filter medium, filter/canning
interface, etc.) would exist during regeneration. Thus, it has
been hypothesized that trap durability is not so much a function
of mileage accumulation as it is the number of regeneration cycles
it must survive.[3, p. 3] Thus, the fewer regeneration cycles the
better. Also, most methods being investigated for regeneration
initiation and control involve some deleterious effects (increased
fuel consumption, power loss) during the regeneration cycle which
would be minimized by maximizing regeneration intervals.
2. Factors Affecting Regeneration Frequency
The optimum regeneration intervals for any specific
vehicle/trap combination will be a function of all of the above
parameters and must be determined by the vehicle manufacturers.
Generally, it seems reasonable to project that most vehicle
manufacturers will choose to minimize the number of regenerations
while not allowing excessive backpressure or particulate
loadings.
Several commenters reported information concerning which
factors were most critical in defining trap regeneration intervals
for various trap/vehicle combinations. A brief survey of these
comments will summarize the latest data on trap regeneration
frequency. Host of the specific comments regarding the "critical
loading" and frequency of trap regeneration concern ceramic
monolith traps. These comments will be discussed, first followed
by comments concerning other trap designs.
Two manufacturers, Nissan and General Motors, stressed the
primary importance of limiting the particulate trap loading in
controlling the maximum trap temperatures reached during
regeneration. Figure 111-12 shows graphs from Nissan which give
-------
-31-
Figure 111-12
• Regenerated by Burner
^Engine : LD 2 S
•1400- r--
• 12 00
-1000-
]
-600
- - 6 0 0
_.-400-.
o-
C e r am i c" Coa t'e d ' S t ee 1 Woo! Filter
10
20
30
40
.Particulate Loading ( grams)
1400-r
¦1200 •
1000 ¦
-6 00-
-600 ¦
thermal stack-rwtsrffnt Limit
¦ 400
Ceramic Monolith Filler
t
10 20 30 40
Particulate LondLnq ( qrtimi )
-------
-32-
the maximum trap regeneration temperatures for various particulate
loadings for both ceramic coated steel wool and ceramic monolith
traps.[7, p. 32] It can be seen that there is a definite
relationship between maximum trap temperature and particulate
loading. Based on their concerns, Nissan stated that regeneration
should take place about every 50 miles and General Motors
commented that regenerations should occur at 40- to 100-mile
intervals.[7, p. 28; 9, p. 32] Nissan and General Motors also
stated that on some trap designs excessive backpressure might also
mandate regeneration, but they did not elaborate as to the types
of traps or operating conditions for which backpressure would be
the critical parameter.
The rest of the manufacturers which commented on ceramic
monolith traps all reported that exhaust gas backpressure levels
were the most critical factor in determining the need for
regeneration, with increased fuel consumption being the primary
result, although impaired engine performance and driveability were
also frequently mentioned. Suggested regeneration intervals
ranged from 30 to 50 miles for Toyota, approximately 90 miles for
Ford, and from 60 to 100 miles for Volkswagen.[8, p. 17; 13, p. 8;
4, p. 34] It can be concluded from these comments that the mass
of particulate collected and exhaust gas backpressure are the two
most important factors defining when ceramic monolith trap
regeneration must occur and that with most current trap/vehicle
combinations the regeneration interval would be approximately 50
to 100 miles.
Fewer data were reported to EPA on this issue for wire mesh
trap-oxidizers. Texaco reported that it is the maximum
regeneration temperature which limits the amount of particulate
which can be collected in its non-catalyzed alumina-coated metal
mesh trap. With the engines Texaco used in its development
programs, typical regeneration intervals were 150 to 200
miles.[11, p. 4] Johnson Matthey's catalyzed metal mesh trap
design appears to oxidize particulate much more frequently during
normal vehicle operation. General Motors has reported the melting
of several Johnson Matthey traps, and it would seem plausible that
overloading in the trap might have been a serious problem,
especially for those traps which were designed to be
self-regenerating and which had no external regeneration
mechanism. In its recent durability testing Johnson Matthey has
utilized an external regeneration system which is manually
operated when backpressure rises to a certain level. Johnson
Matthey has only found it necessary to utilize the regeneration
mechanism approximately once every 1,350 miles, though the
regeneration frequency increased with mileage accumulation.[28, p.
27] This interval is much longer than for any other trap design,
though the fact that the vehicle used for the durability testing,
a Volkswagen Rabbit, has low engine-out particulate levels
certainly contributes to the long regeneration interval. Given
the rather scarce data base, it can only be tentatively concluded
-------
-33-
that the temperature resulting from regeneration is the primary
limit on the particulate loading for wire mesh traps as well, and
that regeneration intervals for mesh traps will likely be
considerably longer than for ceramic monolith traps.
3. Conditions Necessary for Regeneration
There are two conditions which must exist in order for
trap-oxidizer regeneration to occur: the exhaust gas temperature
must be high enough and there must be sufficient oxygen in the
exhaust to initiate and sustain particulate oxidation. A third
important factor is time. Both the temperature and oxygen content
of the exhaust must be maintained for an adequate length of time
in order for complete (or as near complete as feasible)
regeneration to occur.
The first issue is the exhaust gas temperature necessary for
trap regeneration. Table II1-2 summarizes the statements of the
commenters on this issue. It can be seen that for non-catalyzed
ceramic monolith traps, the minimum ignition temperatures range
from 500°C to 650°C. It would be expected that by impregnating
the trap-oxidizer with catalytic material the minimum ignition
temperature of the ceramic monolith trap could be lowered.
However, the only data reported for such an attempt, by Ford, do
not support this thesis. Ford impregnated ceramic monolith traps
with both platinum and lead catalysts and found' that neither
material lowered the temperature required for regeneration. Ford
stated, "Since the catalyst was impregnated into the ceramic trap
material, only the first layer of particulate material was in
contact with the catalyst.... Since successive layers of collected
particulate material were not in contact with the catalyst,
significant advantages from an impregnated catalyst would not be
expected. Methods to improve contact between the catalyst and a
larger amount of the particulate material may have the potential
to reduce the particulate ignition temperature."[13, p. 12] Thus,
at this time it is not clear how successful catalytic material
would be in reducing ignition temperatures for ceramic monolith
t.raps.
Table III-2 reports minimum ignition temperature data for
other ceramic trap designs as well. Two manufacturers reported
data on ceramic foam traps, with and without catalytic treatment.
The non-catalyzed ceramic foam traps needed temperatures in the
500°C to 550°C range while catalyzed versions regenerated at 300°C
to 500°C« Thus, the catalyst material does appear to have an
effect on ceramic foam traps. Two points should be made in this
regard. First, the structure of the ceramic foam trap, being a
"tortuous path" design similar to wire mesh designs, might well be
simply better suited for effective catalytic treatment. Second,
it should be noted that both of the manufacturers which reported
ceramic foam trap data, Toyota and General Motors, noted that
while significant particulate oxidation occurred at lower
-------
Table III-2
Minimum Temperatures Necessary for Regeneration
of Various Trap Designs as Reported by Commenters
Commenter (Reference)
Renault[14, p. 2]
Texaco[ll, p. 9]
Corning[3, p. 8]
Johnson Matthey
[10, p. 30]
Daimler-Benz[2, p. 8]
Volkswagen[4, p. 27]
Toyota[8, p. 13]
Type of Trap
Alumina-Coated Wire Mesh w/o Catalyst
Ceramic Monolith w/o Catalyst
Alumina-Coated Wire Mesh w/o Catalyst
Alumina—Coated Wire Mesh w/Catalyst
Ceramic Monolith w/o Catalyst
Ceramic Monolith w/o Catalyst
Alumina-Coated Wire Mesh w/Catalyst
Ceramic Monolith w/o Catalyst
Ceramic Foam w/o Catalyst
Ceramic Foam w/Catalyst
Manufacturer
of Trap
Texaco
Corning
Johnson Matthey
Corning
Johnson Matthey
Minimum Temperature
Required for Ignition
°_C
600
540
540
600
350
500-650
500
350
600
500
300-500
Nissan[7, p. 20] — — 550
Ford[13, pp. 9,12] Ceramic Monolith w/o Catalyst Corning 500
Ceramic Monolith w/Catalyst — 500
General Motors Ceramic Monolith w/o Catalyst — 600
[9, p. 20] Alumina-Coated Wire Mesh w/o Catalyst — 580
Alumina-Coated Wire Mesh w/Catalyst — 310
Ceramic Foam w/o Catalyst — 550
Ceramic Foam w/Catalyst — 420
Ceramic Fiber w/o Catalyst — 600
Ceramic Fiber w/Catalyst — 450
-------
-35-
regeneration temperatures with the catalyzed traps, complete
regeneration required temperatures in the 500°C to 700°C range
regardless of whether catalytic material was present.[8, p. 13; 9,
p. 16] With ceramic foam traps the overall evaluation of catalyst
effectiveness may depend upon whether "complete" regeneration is
essential or whether something less is acceptable in terms of
backpressure, efficiency, etc.
General Motors also reported minimum ignition temperature
data for ceramic fiber traps. The non-catalyzed version required
a temperature of 600°C while the catalyzed trap needed 450°C.
Again, GM reports that the catalyst did not significantly reduce
the temperature necessary for complete regeneration.
Three manufacturers reported data on alumina-coated wire mesh
traps without catalysts. All found the minimum temperatures for
regeneration to be between 540°C and 600°C, regardless of the
manufacturer of the trap. Three manufacturers also provided such
information on catalyzed wire mesh traps, with two of the
manufacturers identifying the Johnson Matthey trap by name. All
three reported the minimum ignition temperature for the catalyzed
wire mesh trap to be in the range of 310°C to 350°C. Again, GM
qualifies its data by pointing out that complete regeneration does
not occur at these temperatures. Nevertheless, the catalyst seems
to be successful in lowering the necessary temperature for
significant particulate oxidation in metal mesh traps.
In summary, we can conclude from the data in Table III-2 that
non-catalyzed traps, whether ceramic or wire mesh based, require
minimum ignition temperatures of 500°C to 650°C. Catalyzed traps
appear to promote particulate oxidation at temperatures of 300°C
to 500°C, with the catalytic material more effective on "tortuous
path" trap designs like foam or wire designs than on ceramic
monolith designs. In addition, it seems to be generally accepted
that complete regeneration requires temperatures on the order of
600°C to 700°C, whether catalysts are used or not. The need for
complete regeneration, as opposed to nearly complete regeneration,
may not be absolutely essential, but cannot be firmly concluded at
this time.
A second condition which must exist for regeneration to occur
is that sufficient oxygen must be available in the exhaust gas
stream. Two trap suppliers, Texaco and Corning, submitted graphs
indicating the requisite exhaust oxygen levels for regeneration at
various exhaust gas temperatures for non-catalyzed traps.[11, p.
9; 3, p. 8] The two graphs are essentially identical and Texaco's
graph is reproduced as Figure 111-13. At a temperature of
approximately 550°C there must be at least 4-1/2 percent oxygen
for regeneration to occur, but at 600°C only 3-1/2 percent oxygen
is required. Coming's submission extrapolated its own results to
higher temperatures and hypothesized that at 700°C only 2 percent
oxygen would be required for oxidation.
-------
Figure 111-13
DEF REGENERATION CONDITIONS
*5
12
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-
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O DEF REGENERATED
A DEF DID NOT REGENERATE-
900 1000 1100
EXHAUST TEMPERATURE, °F
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I
1200
-------
-37-
The third requirement for trap regeneration is that the
requisite exhaust gas temperature and oxygen content be maintained
for a sufficient length of time. It had been hypothesized by some
researchers that once trap-oxidizer "light-off" occurred, the
particulate oxidation process would be self-sustaining. Several
commenters have found that this is not true, however, and that the
temperature and oxygen content necessary for particulate ignition
must be maintained throughout the regeneration cycle in order for
regeneration to continue to completion. [ 2, p. 10; 4, p. 27] Eow
long regeneration takes depends on the temperature and oxygen
content of the exhaust flow, as well as on the amount of
particulate to be oxidized. Generally, the commenters' data do
not address the latter. Typical of the commenters' responses were
those of Texaco and Ford. Texaco stated that exhaust at 600°C
containing 7 percent oxygen required less than 3 minutes to
regenerate its non-catalyzed wire mesh trap, while lowering the
temperature of the exhaust to 540°C raised the regeneration time
to 3-1/2 minutes.[11, p. 4] Ford reported that complete
regeneration of the Corning ceramic monolith trap at 540°C with
sufficient oxygen took over 10 minutes, while at 600°C it took
less than 2 minutes.[6, p. 7] Nissan, Toyota, and General Motors
all reported regeneration times of from 2 to 10 minutes.[7, p. 30;
8, pp. 22-24; 9, p. 33]
From the above discussion, it can be concluded that
successful trap regeneration requires maintaining exhaust gas
temperatures of between 500°C and 650°C for non-catalyzed traps
(possibly as low as 300°C for some catalyzed traps, depending on
the need for complete regeneration) and oxygen levels of at least
3 to 4 percent for between 2 and 10 minutes.
4. Attaining Regeneration Conditions In-Use
Having defined the exhaust gas temperature and oxygen content
conditions necessary for successful trap regeneration, the issue
becomes whether such conditions can be attained on light-duty
diesel vehicles and trucks in use. It would be most desirable to
fulfill the requirements for particulate oxidation without having
to design additional hardware for the diesel vehicle.
Unfortunately, the commenters were nearly unanimous in
stating that in-use diesel vehicle exhaust gas temperatures are
too low to allow for successful trap-oxidizer regeneration. Table
III-3 summarizes typical exhaust gas temperature ranges for
different diesel vehicles and testing conditions as reported by
various commenters. Very few vehicles ever reach temperatures of
500°C, the minimum particulate ignition temperature for
non-catalyzed traps, and those that do exceed it do so only for
short periods of time. Even temperatures of 300°C to 350°C, which
seem capable of significant regeneration for some catalyzed trap
designs, are not reached by some- of the vehicles listed and
clearly would not be maintained for the lengths of time necessary
-------
-38-
Table III-3
Exhaust Gas Temperatures for Various
Diesel Vehicles as Reported by Commenters
Exhaust Gas
Commenter (Reference)
Vehicle/Engine
Test
Conditions
Temperatures
°C
General Motors
[9, p. 19]
Mercedes 300D
Opel Rekord
Olds 88
Isuzu Chevette
VW Rabbit
Isuzu Gemini
10-55 mph
10-55 mph
10-55 mph
10-55 mph
10-55 mph
10-55 mph
200-400
125-320
180-260
190-360
190-290
180-340
Volkswagen
[A, pp. 27,29]
1.6-liter, naturally aspirated
FTP
"City"
"Highway
160-360
130-320
260-440
Johnson Hatthey
[10, p. 80]
Turbocharged vehicle
Engine Mapping
100-350
Daimler-Benz
[2, p. 8]
—
FTP
100-500
(median-200)
T oy ot a
[8, p. 14]
2.2-liter Toyota
FTP
100-650
(mean-250)
Ford
2.3-liter Opel
FTP
100-500
[13, p. 10]
-------
-39-
for successful regeneration for most of the vehicles listed. It
is this fundamental problem of low diesel exhaust gas temperatures
which has convinced most of the commenters that some form of
"positive" regeneration, i.e., some method of specifically
creating the requisite exhaust gas conditions for regeneration, is
needed.
Besides the temperature requirements discussed above, the
exhaust gas must also contain at least 3 to 4 percent oxygen in
order for regeneration to occur. Because the diesel engine
utilizes very high air-fuel ratios, there is normally considerable
oxygen in diesel exhaust. However, there is the likelihood that
at certain operating modes, such as hill climbing in low gear or
at high altitude, there might not be sufficient excess oxygen for
regeneration. No commenter expressed much concern about oxygen
levels in general. Clearly, the primary concern has been
attaining and maintaining the requisite exhaust gas temperatures
in the trap-oxidizers.
In addition to having to raise exhaust gas temperatures and
oxygen levels to minimum levels so that particulate oxidation can
be initiated and maintained, it is also necessary to limit the
maximum temperatures reached during trap regeneration in order to
prevent melting and/or thermal fracture of the trapping material.
Vehicle manufacturers reported that they have experienced maximum
regeneration temperatures of 1400°C to 1500°C.[2, p. 11; 6, p. 13;
9, p. 33] The melting point of the cordierite material used in
ceramic traps is reported to be approximately 1300°C to 1400°C,
while metal mesh traps are thought to have lower melting
temperatures. [2, p. 11; 6, p. 10; 7, p. 30; 9, p. 33]
Accordingly, to prevent trap failure, General Motors stated that
its design goal is to limit the maximum regeneration temperatures
to 900°C for wire mesh traps and 1100°C for ceramic traps. [9, p.
33] Nissan believes that 900°C is an appropriate design goal for
ceramic traps. [7, p. 30] In addition to the possibility of trap
melting, rapid and uncontrolled temperature rises in ceramic traps
also raise the possibility of trap fracture from thermal stresses
induced by thermal gradients within the filter itself.
Fortunately, those actions implemented to prevent trap melting
should also help ameliorate thermal gradients in the trap as well.
The maximum temperature reached during trap regeneration is a
function of several parameters. The particulate loading in the
trap is very important, as the greater the amount of oxidizing
particulate the greater the amount of energy released and thus the
higher the temperature within the trap. The exhaust flow rate is
relevant as a high flow rate is able to withdraw excessive heat
out through the exhaust system much more effectively than a low
flow rate. The exhaust gas temperature and oxygen content
initiating regeneration are also important since moderate levels
can produce a relatively controlled regeneration process while
much higher levels can promote rapid and uncontrolled oxidation.
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-40-
A worst-case scenario would involve a heavily loaded trap which is
exposed to exhaust that is very hot but devoid of much excess
oxygen (such as during hill-climbing or high-altitude operation);
under such conditions the particulate would get very hot but would
not oxidize. Then, upon a change in engine/vehicle operation
which would produce much excess oxygen, the hot particulate could
undergo very rapid oxidation with a high probability of trap
damage.[6, pp. 10-11]
Thus, it can be seen that not only must exhaust gas
temperature and oxygen content be maintained above minimum levels
so that the regeneration process can be initiated and sustained,
but these levels, as well as total particulate loading and exhaust
gas flow rate, must also be controlled so as to avoid excessive
maximum regeneration temperatures and resultant trap damage. It
can be concluded that a satisfactory regeneration system should be
able to do all the following. It must be able to initiate
regeneration with satisfactory frequency so that the particulate
trap loadings do not become excessive. It must have the ability
to maintain a sufficiently high, but not excessive, exhaust gas
temperature for the time necessary to complete regeneration.
Finally, it must be able to provide sufficient oxygen to the trap
both to sustain the regeneration process and to avoid
oxygen-deficient particulate heating which can lead to trap
failure. These are the design goals that any successful
regeneration system would have to achieve in-use.
5. Specific Regeneration Mechanisms
Now that we have identified the relevant parameters in the
trap-oxidizer regeneration process, we can examine the various
regeneration mechanisms which have been investigated by the
vehicle and trap manufacturers. Most of the systems discussed
below have the primary goal of raising the temperature of the
exhaust in the trap to the extent that regeneration occurs. As
was discussed earlier, there must also be adequate oxygen in the
exhaust and the temperature/oxygen conditions must be maintained
for a sufficient length of time. However, researchers in this
area have found that generating the requisite exhaust gas
temperature is the most challenging technical problem. The issues
of oxygen content and regeneration time are still important,
however, and will be considered at various points in the following
discussion. Six regeneration mechanisms will be considered in
turn: engine parameter changes, intake throttling, fuel burner,
exhaust stroke fuel injection, electrical heating, and fuel
additives.
Several manufacturers considered the possibility of modifying
certain engine parameters as the means of increasing exhaust gas
temperature and initiating regeneration. Such a mechanism might
have the advantage of requiring no major new hardware. The design
change mentioned most frequently was injection timing retard, but
-------
-41-
both Daimler-Benz and Volkswagen have noted that the retard
necessary for the requisite exhaust gas temperature increases
would significantly impair fuel economy and performance.[2, p. 3;
4, p. 37] The silence of other commenters on this possibility
lends credence to the conclusion that modifying engine parameters
is an unacceptable way of initiating trap regeneration.
Intake air throttling has probably been investigated as much
or more than any other regeneration mechanism. Throttling reduces
the overall air flow to the engine and thus reduces the air-fuel
ratio of the mixture in the combustion chambers. This lower
air-fuel ratio in turn results in higher average combustion gas
temperatures and subsequently higher exhaust gas temperatures.
The primary advantages of throttling are its relative simplicity
and low expense compared to other regeneration systems. However,
there were three primary concerns expressed about throttling.
First, and most important, was simply whether throttling alone
could provide the certainty of reaching regeneration conditions
with sufficient frequency so as to avoid excessive particulate
accumulation in the trap. GM implied that this was a concern, but
did not elaborate.[9, p. 34] Ford determined that utilizing
throttling on a 2.3-liter Opel diesel still required relatively
high speed/high load operation to reach the necessary exhaust
temperatures to regenerate non-catalyzed ceramic monolith traps.
For example, at steady-state operation the minimum vehicle speed
that resulted in regeneration of the ceramic trap was 55 mph.[13,
p. 14] Since ceramic traps might have to be regenerated as often
as every 50 miles, there would be much concern over whether such
high speed/high load operation could be counted on to occur before
the buildup of excessive particulate loadings in the trap. The
success of throttling might well hinge on the success of catalytic
coatings. As discussed previously, some catalyzed traps at least
partly regenerate at temperatures in the 300°C to 350°C range.
Throttling would almost certainly produce temperatures in this
range for any but the lowest speed/load operations. Thus, to the
extent that catalysts can be successfully utilized to lower the
necessary exhaust gas temperatures, and assuming that other
problems discussed below are solved, throttling should continue to
be investigated as a possible regeneration mechanism.
A second primary concern with throttling is that by its very
nature it reduces the oxygen content in the exhaust gas. This
raises the possibility of major trap failure when large amounts of
hot particulate which had been exposed to heavily-throttled and
oxygen-deficient exhaust is then quickly exposed to hot,
oxygen-rich exhaust resulting in uncontrolled oxidation. Clearly
this must not be allowed to happen. This concern is so strong
that Johnson Matthey, whose catalyzed trap appears to regenerate
at temperatures of 300°C to 350°C, commented that throttling is
"unacceptable."[ 10, p. 23] The issue may not be so clear-cut,
however. Ford hypothesized that the maximum amount of throttling
should be limited to an exhaust oxygen concentration of no lower
-------
-42-
thar. 2 percent as a way to avoid such a problem.[13, pp. 14-15]
In additioiij avoiding excessive particulate accumulation in the
trap would reduce the likelihood of uncontrolled oxidation.
Finally, the possibility of adding additional oxygen to the trap
at heavy throttle conditions is a possibility, if it could be done
while still maintaining temperatures sufficient for regeneration.
Third3 several commenters deplored the loss of driveability
during heavy throttling conditions-[4, p. 36; 9, p. 34; 10, p.
23] But no commenter supported its position with any data or
analysis and we are unable to deal with this issue. It is likely
that trap-oxidizers will generally be utilized on those diesel
vehicles with the highest particulate emission rates, the most
powerful engines, and the highest performance levels; such
vehicles would be more capable of overcoming a slight power loss
during throttling than small displacement, less powerful diesel
vehicles.
Another regeneration system which has received wide attention
is the external fuel burner. The concept is to actually ignite an
air-fuel mixture near the trap inlet whenever regeneration is
required. The combustion raises the exhaust gas temperature to
the necessary level. Ford has described two types of fuel
burners, air-fed and exhaust-fed burners.[13, pp. 16-17] The
air-fed burner utilizes an injector to provide fuel, a pump to
supply combustion air, and a glow plug or spark plug to ignite the
mixture, all placed just upstream of- the trap inlet. With this
design the burner air flow and fuel flow must be carefully
controlled to ensure adequate exhaust temperatures for
regeneration. The advantages of a burner system are the clear
ability to raise exhaust gas temperatures to necessary levels and
the lack of any adverse effect on engine performance. But the
drawbacks of burner systems are very cleaT—of all the
regeneration systems considered the external fuel burner would
easily be the most complex and expensive system due to . the
additional hardware and controls which would be necessary for
successful burner operation. At this time the fuel burner is
General Motors' preferred regeneration system.[20]
In an attempt to simplify burner operation, Ford also
evaluated an exhaust-fed burner. The exhaust-fed burner would be
the same as the air-fed burner discussed above except that,
instead of utilizing atmospheric air for combustion, the process
would rely on the excess air inherent in diesel exhaust. This
simplifies the process by removing the need for the supply and
control of air for the burner. Since there is much more excess
oxygen in diesel exhaust at low speed/low load conditions,
regeneration becomes possible even under these conditions. It
appears that this type of burner is also workable, but it still
retains most of the complexity and expense of any burner system.
Of course, all burner systems result in some increased fuel
consumption.
-------
-43-
A fourth type of regeneration system has been proposed by
Johnson Matthey and can be termed "exhaust stroke fuel
injection." The concept is to create the diesel equivalent of a
misfire, with the resulting hydrocarbons lighting-off the
catalytic material in the trap and providing sufficient
temperature in the trap for regeneration. Johnson Matthey
suggests injecting additional fuel into one cylinder at the end of
the combustion stroke before bottom dead center and the start of
the exhaust stroke. This fuel is cracked into smaller
hydrocarbons by the heat and pressure which still exist in the
combustion cylinder. These hydrocarbons are then exhausted on the
piston upstroke and burned when they reach the catalyst in the
trap. This raises the trap temperature and initiates
regeneration.[10, p. 23]
Johnson Matthey has stated that the exothermic reaction of
the hydrocarbons/catalyst light-off produces a temperature rise of
approximately 150°C to 200°C. Since their trap begins to oxidize
particulate at approximately 350°C, the system can regenerate at
exhaust temperatures as low as 200°C. This temperature is reached
frequently by all diesel vehicles. It must be noted that the
150°C to 200° C temperature rise would likely not be sufficient
for non-catalyzed trap designs.
Johnson Matthey utilized a "first generation" version of this
system on its recent 50,000-mile durability vehicle that was
tested at Southwest Research Institute. A backpressure sensor was
used with a read-out placed in the driver's compartment. When the
backpressure reached a certain level, the driver operated a manual
lever which injected additional fuel into one combustion chamber
and initiated the regeneration process. Johnson Matthey attempted
46 regenerations during the course of the durability test, the
system did not function completely nine times.[28, p. 15]
Johnson Matthey believes that this system deserves serious
consideration. Volkswagen was the only vehicle manufacturer to
address this system; it stated that "this system shows some
promise but as yet is only a system which will cause regeneration
to begin."[4, p. 36] Unfortunately, little development work has
been done with this concept. The most important requirement would
be to automate the system. It is possible that modifications
could be made to the injection pump so that when regeneration was
desired the pump would automatically inject extra fuel into one
cylinder. Two signals would be necessary to initiate the
process. First, there would have to be some way of determining
when regeneration was required. Johnson Matthey utilized a
backpressure sensor in its initial work and this continues to be a
possibility. Although backpressure devices of sufficient
durability are not now available, alternatives are now being
considered. One promising alternative would be an engine
revolution counter. A worst-case scenario could be defined to
determine the minimum number of revolutions which would require
-------
-44-
regeneration, and then regeneration could be initiated whenever
that level was reached. Even with the Johnson Matthey trap,
however, the temperature of the normal exhaust must be at least
200°C, and so the injection pump would also require a signal that
the temperature of the exhaust was above 200°C before injecting
additional fuel. Finally, some control over the duration of the
special fuel injection would be necessary. As Volkswagen pointed
out, it is necessary not only to initiate regeneration but also to
sustain it. Thus, the pump should continue to inject additional
fuel until the oxidation process is completed. • Yet, continuing
the extra injection after the regeneration had concluded would
simply be wasting fuel. Thus, some standard duration of injection
or some measure of the completeness of the regeneration would be
necessary.
The primary advantage of this regeneration concept is that,
like the fuel burner, it can create the conditions necessary for
regeneration with certainty throughout almost all " vehicle
operating modes (of course this is true only for traps which can
successfully utilize catalyzed material) while avoiding much of
the complexity and expense of the fuel burner. If indeed the
injection pump can be modified to handle the extra injection, the
only new hardware needed would be in the sensors and controls
discussed above. This is in marked contrast to the fuel burner
which would require an additional injector, fuel lines, a spark or
glow plug, possibly an external air supply and possibly an exhaust
bypass. Volkswagen was the only vehicle manufacturer to comment
on the Johnson Matthey system and it concluded its discussion of
the concept by stating, "Work is continuing on systems which will
monitor criteria indicating the need for regeneration and trigger
the activity of this system."[4, p. 37] Clearly, the primary
question about this system is whether it can be successfully
integrated with injection pump design.
A fifth regeneration mechanism which has been investigated is
electrical heating. This would involve the placement of an
electrical resistance heating element at the trap inlet which
would be powered by the vehicle's electrical system and would be
able to raise the temperature inside the trap to the proper
regeneration level. The advantages of electrical heating are that
it can be a relatively simple system without requiring any engine
design changes and without requiring any additional fuel
combustion. The primary difficulty is its rather large power
requirement. In its response of April 1979 to the light-duty
diesel particulate NPRM, General Motors stated that without any
assistance from any other method, '8.5 kilowatts of power would be
necessary to raise the total exhaust of a test vehicle at 25 mph
to the 480°C it then believed was necessary for regeneration. GM
found that by utilizing a dual path trap, where a flap valve would
route only a small part of the total exhaust flow to the path of
the trap being regenerated, it could lower the maximum power
requirements to 500 watts. Still, GM stated that "such a load is
-------
-45-
still near the limit of the capabilities of a vehicle electrical
system."[15, pp. 116, 119] GM reaffirmed its concern over the
necessary power requirements in its recent submission, but did not
present any details.[9, p. 34] Volkswagen stated that electrical
heating would "probably not be feasible" considering the power
requirements.^, p. 37] Toyota, the onl}' other commer.ter to
discuss electrical heating, did not express concern about power
requirements,[8, p. 23] Given the scarcity of comments concerning
electrical heating, it is difficult to judge its potential as a
regeneration mechanism. At mini-mum, because of its relative
simplicity, it seems to be a "fall-back" option, though it would
likely require a more powerful (and thus more expensive) vehicle
electrical supply system.
Finally, Ford and General Motors both discussed the
possibility of utilizing a fuel additive to aid the regeneration
process. Ford found that by adding one gram of lead (as
tetraethyl lead) to one gallon of diesel fuel, the temperature
necessary to regenerate its Corning trap was reduced by over
150°C. The advantage of using a catalyst in the fuel itself is
that the catalytic material is distributed on the carbon particles
and can have the intimate contact with the particulate which is
necessary for maximum ignition temperature reduction. From the
standpoint of the vehicle manufacturers, fuel additives are the
simplest regeneration mechanisms available since they might not
affect vehicle or engine design whatsoever and would likely not
add to vehicle cost. But additives have not been shown to be
reliable for regeneration under all vehicle operating conditions.
The use of additives would raise several as yet unanswered
concerns about their effects on engine, trap, and fuel injection
system durability. Most important, the use of additives could
raise very significant environmental concerns. Lead, for example,
is widely recognized as a dangerous environmental contaminant and
is one of the six pollutants for which EPA has promulgated
Rational Ambient Air Quality Standards. It is possible that
other, less objectionable additives could be developed.
Regardless of which regeneration system is adopted by vehicle
manufacturers to raise exhaust gas temperatures to necessary
levels, two other issues must be addressed with respect to the
regeneration systems — 1) oxygen supply and 2) sensors and
controls. As has been mentioned several times earlier, hot
temperature, low oxygen content exhaust can result in uncontrolled
regeneration and catastrophic trap failure. Due to the extremes
of real-world vehicle operation such conditions would likely take
place, for example, during high-altitude or hill-climbing
operation. The simplest way to avoid such problems would be to
ensure an adequate oxygen supply under hot exhaust temperature
conditions. Such a solution should not be difficult, as it is
very analogous to the need for extra oxygen in oxidation catalytic
converters on gasoline-fueled cars. Johnson Matthey has suggested
two ways to ensure sufficient oxygen in the trap. One system uses
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-46-
a gasoline engine air pump to inject air in front of the trap. A
diverter valve coupled to the throttle activates the air stream at
two-thirds power. This way the extra air is provided only under
conditions where high temperature, low oxygen content conditions
might occur and is not supplied when it is unnecessary and would
only serve to lower the temperature of the exhaust. Johnson
Matthey also suggests the possibility of using a simple venturi in
the exhaust system to pull in extra air.[10, p. 22] If workable,
the venturi would be simpler and cheaper than an air pump. The
only vehicle manufacturer to address this concern was Volkswagen,
which stated that the "development of a durability system which
would add additional air to the exhaust system under high load
conditions is necessary."[4, p. 35]
It will also be necessary to utilize sensors and controls as
part of the regeneration process, regardless of what type of
system is ultimately adopted. The most obvious requirements are
those which would be used to initiate, the oxidation process.
Toyota reported the most research on this subject.[8, pp. 19-20]
Given the importance of backpressure on fuel economy and
performance, and its direct relationship to trap loading, a
backpressure sensor would be an important part of an ideal
regeneration system. Unfortunately, pressure sensors available
today have insufficient durability and reliability for this
usage. This fact has caused researchers to examine other control
mechanisms. Both mileage counters and engine revolution counters
have been considered as methods of determining regeneration
•frequency. Neither is as direct a measure of trap loading as
backpressure, but both types of counters are available and
durable. General Motors has considered a "particulate loading
sensor" but did not describe how such a sensor worked or whether
it was successful.[9, p. 32] At this time, it would seem that the
mileage and engine revolution counters are most workable. The
latter is probably preferable because it would better deal with
idle conditions, as the mileage counter would not account for
idle. All of these mechanisms are ones which would only signal
when a regeneration ought to occur, they would not indicate
whether a regeneration was possible. For many regeneration
systems, such as throttling or exhaust stroke fuel injection,
regeneration can still take place only when the exhaust gas stream
is at a certain temperature before the operation of the
regeneration mechanism. Thus, there would also have to be a
signal when the exhaust gas temperature was high enough for the
regeneration process to begin. This would require a temperature
sensor in the exhaust. This should not be a technical problem.
Whether or not these initiation and control mechanisms can be
handled mechanically or whether they will have to be
electronically controlled is not yet clear. Volkswagen believes
that "an electronic control system which can interpret an exhaust
backpressure map relating engine speed, load, and power" will be
required. [4, p. 47] GM also mentioned the need for electronic
controls under the burner regeneration scenarios.[9, p. 44] Given
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-47-
the sophistication of electronics systems which have been
developed for three-way-catalyst, closed-loop systems on
gasoline-fueled cars, it would not seem overly difficult to
develop electronic controls over exhaust gas temperature, engine
revolutions, mileage, etc. and possibly over backpressure and
particulate loading as well.
In conclusion, several regeneration systems have been
investigated though few were described in depth to EPA. Two
regeneration mechanisms, fuel burners and electrical heating, are
definitely workable, but the former is both complex and costly and
the latter would likely require more powerful and expensive
electrical supply systems. They may be necessary for
non-catalyzed traps. Intake air throttling is well understood,
and may be feasible if catalyst systems can lower the necessary
exhaust gas temperatures and if adequate oxygen can be maintained
during throttling. For catalyzed traps, Johnson Matthey's exhaust
stroke fuel injection system is promising and deserves further
investigation. The likelihood of utilizing fuel additives or
engine parameter modifications as the primary regeneration
mechanism is small. No matter what regeneration system is
ultimately adopted, an adequate oxygen level must be maintained at
high temperature operation. This will likely require either an
air pump or venturi in the exhaust. Finally, sensors will be
required to initiate and control the regeneration process with
temperature, engine revolution, and possibly backpressure sensors
being of most importance. Electronic control of these parameters
may be necessary.
D. Durability
During the original particulate rulemaking, EPA considered
durability to be the most critical unresolved technical issue with
respect to trap-oxidizer development.[16, p. 14498] At that time
the best durability that had been reported was 12,800 miles by
General Motors for a metal mesh trap.[12, p. 51] EPA's position
at that time was that the primary reason there were few positive
durability results was that few resources had been expended on
durability testing while other more basic issues had been the
focus of trap development programs.[16, p. 14498] Clearly
trap-oxidizers must be durable for the useful life requirements
for light-duty vehicles and light-duty trucks. Several
manufacturers have submitted information on the durability of
various trap designs, and the following discussion will again be
divided into sections on ceramic and wire mesh trap designs. We
will not -attempt to summarize, the histories of all of the
trap-oxidizers which have been submitted to EPA for two reasons.
Frist, it would simply be too burdensome. Second, and more
importantly, such an analysis would not be particularly helpful.
In the development of any new technology, there will likely be
many failures before success is achieved. Multiple failures do
not prove that success is impossible, yet positive demonstrations
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-48-
tend to indicate that success is probable. There have been many
trap failures during durability testing as well as many promising
results. In identifying the most probable trap designs, the
successful tests are most relevant. The failures will be
discussed only if their examination aids the analysis of a
particular design.
1. Ceramic Traps
Three manufacturers reported on the durability of ceramic
monolith traps in some depth—Daimler-Benz, General Motors, and
Ford. Other manufacturers had either not seriously undertaken
durability testing of ceramic monolith traps or else had not yet
reached the point in their programs where durability testing was a
priority.
Daimler-Benz has reported the most promising durability data
for ceramic monolith traps. [2, p. 7] They were able to achieve
over 33,500 miles of durability accumulation on an unidentified
vehicle equipped with a Corning ceramic monolith trap. The
emission levels for this vehicle/trap system at various points
during the mileage accumulation are shown in Figure III-14[2, p.
7] taken from Daimler-Benz1 submission. The data corresponding to
the ceramic monolith trap are identified by x's. As can be seen,
the particulate emissions for this vehicle were consistently
maintained around 0.05 g/mi, and the NOx emissions were generally
well below 1.0 g/mi, the level that, barring changes in the Clean
Air Act, diesel passenger cars will have to meet in 1985. Also
worthy of note is that the graph supplied' by Daimler-Benz was
dated November 26, 1979, well over two years ago.
Daimler-Benz reports several qualifications with respect to
the use of this data. First, the standard AMA durability cycle
was not used in the mileage accumulation; instead, Daimler-Benz
used a "special driving cycle" which they did not describe.
Second, Daimler-Benz retarded injection timing (in order to raise
the exhaust gas temperatures for regeneration) to a degree that it
considers unacceptable for production vehicles. Finally, and most
importantly, Daimler-Benz was not able to duplicate the positive
results discussed above with "other vehicles equipped with
basically identical trap-oxidizers." For example, they report
that a second trap was "mechanically destroyed " at approximately
3,000 miles and a third trap was "thermically destroyed" at
approximately 3,700 miles. A fourth trap lost its collection
efficiency after less than 1,000 miles.
The fact, that one trap survived 33,500 miles in Daimler-Benz'
testing is an important indicator that such traps have some
potential of lasting 50,000 and 100,000 miles. The fact that this
trap was so durable over 2 years ago is also impressive.
Unfortunately, Daimler-Benz has not stated whether the testing of
the successful trap continued, failed, or was simply halted. It
-------
..•¦•A (••«« »• ¦!
Figure 111-14
• •*»««l»**»t •••'• •••••••ft. ••••.•!•••» .••••*••• • ••»••?«•. • t •« M ^ I
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••:••"!¦—
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• 4 : ' ¦ 1 : 1 • • • • » : 1 : »- :
?—t—i—: ; ' • i ¦:.. LJ-' : i i i •
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¦ : { : f : T : | : ' • ¦ ¦
4- :• •:..j j—L_-
ft
• i
"' •; /: —
• • • X ¦
For assessment of these results it has to be..rioted .thati
; i ; ; (
- Special Driving Cycle (not AMA-Cycle) vith-fp;dsitive z-e-j-j
generation of the soot filter: City 80 # +.-;Autobihn 20#.'
with the following schedule: k days city delving,'_.l day...;
" I m * : • • ' «
Autobahn
Drawbacks of the system used:
i:
PH—0v6-i
(g/ki-- ;¦•
* I '
-7-O.iH
Retarded begin of injection necessary, thus•worsened • - j-
combustion Li i—. .;I. i
higher noise . i 5 : i ; '
w .<••••• • • • • • —»
worsened cold start characteristics ' . ! i
risk of damage for cylinder head gasket ~j !
increase of back press, up to>1 bar caused by soot
accumulation resulting in deteriorated combustion j ¦«
pover loss, may lead to stalling j. 1
risk of mechanical damages
wlch
' ¦ Fiihr
Ceiamfc
\kh
I—~ I— —I
..S...L.1.32 r »i 18 H2U-: - 30
• I -' » * t
•42
Running Distance
Durability test results with sand-
wich and ceramic soot filter
VINA. 26.11.79
-------
-50-
also has not reported any more recent durability data in the two
years that have passed, except to describe a test program in
Denver the results of which have not been submitted to EPA. The
only conclusion that can be drawn is that one ceramic monolith
trap survived at least 33,500 miles over two years ago.
Before continuing our discussion of ceramic monolith trap
durability, we must address one other feature in Figure 111-14,
which was taken directly from Daimler-Benz' submission to this
study. We have just discussed the ceramic monolith durability
data indicated in Figure 111-14 by the x's. But it can also be
seen that there are data for a "sandwich filter," most likely a
wire mesh trap, indicated by small squares. It appears that this
trap accumulated over 55,000 kilometers (or over 34,000 miles) of
durability testing as of late 1979. Yet Daimler-Benz does not
mention these data anywhere in its submission. We regret that we
will not be able to include these data in the discussion on wire
mesh traps.
General Motors reported durability testing with ceramic
monolith traps.[9, p. 10] Its most impressive data involved
dynamometer testing. GM states that ceramic monoliths have
survived simulated mileages up to 37,200 miles on dynamometers.
GM points out that "these were performed under controlled
laboratory conditions. The simulated AMA duty cycle was not as
rigorous or unpredictable as real-life driving, the traps were not
subjected to the vibration and temperature extremes encountered in
a vehicle, and the system could be shut down automatically if any
of the monitored parameters indicated a potential problem."[9, p.
10]
GM points out further that no ceramic monolith has survived
past 1860 miles in its vehicle testing, and that during a recent
Denver test program no ceramic trap survived the entire trip and
18 traps failed.[9, p. 10] From an examination of GM's subsequent
submission of test data sheets it appears that the trap failures
GM experienced were generally due to regeneration occurring with
too much particulate in the trap or due to operation at high
altitude.[17, p. 9B] We have discussed earlier the likelihood of
trap failure when the trap is overloaded. Similarly, GM does not
mention whether precautions were taken to avoid low oxygen
conditions which could lead to uncontrolled regeneration. At high
altitude the low oxygen problem is even more likely to occur.
Despite these problems, GM does report successful ceramic monolith
operation on at least one vehicle in Denver. The vehicle was an
Oldsmobile Omega with the new 4.3-liter, V-6 engine. The
regeneration system was an inline fuel burner. Quoting GM:
"After three early (50-100 km each) trap failures on a Denver test
trip, modifications were made which resulted in successful
operation in Denver and at altitudes up to 11,000 feet."[17, p.
10A]
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-51-
GM's problems with obtaining good durability with ceramic
monolith traps may actually be a problem with regeneration
control. No trap can survive uncontrolled regenerations due to
particulate overloading or oxygen deficient/oxygen rich
conditions. GM's 37,200-mile dynamometer test shows that ceramic
monoliths can survive several hundred regenerations if those
regenerations are controlled properly. As discussed in a
preceding section, no manufacturer has yet been able to control
on-board regenerations successfully.
Ford tested a 2.3-liter Opel diesel equipped with a Corning
ceramic monolith trap. A total of 10,000 miles was accumulated
with normal highway usage. Ford regenerated the trap every 100
miles on-board by operating under high speed/high load
conditions. After 10,000 miles had been reached, Ford began using
the AMA durability cycle for mileage accumulation, continuing to
use high speed/high load operation to regenerate the trap every
100 miles. Early in this process the trap cracked and failed.
Ford attributes the failure to thermal shock.[6, p. 6] No
explanation was offered as to why the trap failed so soon after
AMA testing began when it had been performing well before. It is
possible that some on-board regeneration was naturally occurring
during the course of the highway operation, thus slowing the
loading of the trap under those conditions, while during the AMA
testing such was not occurring and the trap was overloaded prior
to regeneration.
EPA is in the process of durability testing a Corning ceramic
monolith trap on a Mercedes 300 SD. As of February 10, 1982, the
trap had maintained 90 percent collection efficiency through
15,000 miles of durability testing. Throttling is being utilized
for regeneration and no difficulties have arisen during the first
18,000 miles of operation.[27, pp. 1-3]
In summary, the vehicle durability testing by Daimler-Benz
and Ford and the ongoing EPA testing indicate that with control
over the regeneration mechanism the ceramic monolith trap has the
potential to survive the vehicle environment for thousands of
miles. The dynamometer testing by General Motors supports this
thesis. Alternatively, the vehicle testing by General Motors
shows that the durability of ceramic monolith traps is very poor
in real-world operation with imperfect controls over the
regeneration process. Clearly the durability of a trap-oxidizer
is very dependent on the efficiency of its regeneration system.
2. Wire Mesh Traps
The two wire mesh traps which have been discussed in this
study—the Johnson Matthey and Texaco designs—have had durability
results reported to EPA. Since all of the wire mesh durability
data reported to EPA have identified the trap manufacturers by
name, the Johnson Matthey and Texaco designs will be discussed in
turn.
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-52-
The first durability testing reported for a Johnson Matthey
trap design was on a JM4 trap in a program involving
Volkswagen.[4, p. 25] This trap' was successfully operated on the
road for approximately 12,500 miles during 1979. At 12,500 miles
the trap was reducing particulate levels by 52 percent, and HC and
CO levels by 60 percent. [10, p. 7] At this point, the trap sat
dormant for approximately 4 months. When testing resumed another
10,000 miles were accumulated before testing proved that the
catalyst material had failed. Particulate levels had increased
throughout the latter 10,000-mile accumulation, and analysis
determined that these increased levels were due to the catalyst
washcoat becoming brittle and flaking off of the wire mesh.
Despite the fact that the JM4 trap ultimately failed, Johnson
Matthey was encouraged by the results and continued its
optimization program. This culminated in their JM13 design, .which
involves a graduated wire mesh bulk density, a graduated
surface-to-volume ratio, and an improved washcoat formulation. By
the spring of 1981 Johnson Matthey was confident that their trap
design was sufficiently optimized to attempt a 50,000-mile
durability test. The program was initially described to EPA in
Johnson Matthey's original submission to this studj'.[10s p. 24]
This 50,000-mile testing was completed in January 1982 and Johnson
Matthey has reported the results to EPA in a letter to the
Administrator dated January 25, 1982.[18, p. 1]
Johnson Matthey contracted with the Southwest Research
Institute, an independent facility, to perform the durability
testing and emission tests were performed per Federal Register
requirements. The vehicle used was a 1981 Volkswagen Rabbit, with
a 1.6-liter, 4-cylinder engine. The car was tested by Southwest
as delivered with the only changes being the addition of the JM13
trap and the modifications necessary for Johnson Matthey's
prototype exhaust stroke fuel injection regeneration system.
Johnson Matthey has described the vehicle changes: "The trap
itself, 14 inches long and 5 1/2 inches in diameter, was easily
mounted in the exhaust pipe next to the gear shift linkage in the
existing floor hump. Insulation was wrapped around the car and
all piping back to the exhaust manifold. An air pump and diverter
valve were installed using a mechanical link up to a microswitch
to activate the valve allowing air into the exhaust at two-thirds
throttle or higher. The regenerator, in this case manually
operated by a lever in the car, was installed. A check valve and
ball valve were installed on tees between the injector lines for
cylinders two (2) and four (4)."[10, p. 24] The fuel used during
the testing conformed to EPA durability specifications for diesel
fuel.
The durability trap/vehicle system successfully completed the
50,000-mile AMA durability cycle testing. Tables II1-4 and III-5
were provided to EPA by Johnson Matthey and summarize the
emissions and fuel economy results for the baseline and trap
-------
-JJ-
Table III-4
DURABILITY TEST RESULTS AT SOUTHWEST RESEARCH INSTITUTE
VEHICLE ~ VOLKSWAGEN RABBIT
CATALYST - JM-13/II UNDERFLOOR
FEDERAL TEST PROCEDURE
CONDITION
NOMINAL
MILEAGE
PARTICULATE
G/MILE
HC
G/MILE
CO
G/MILE
NOx
G/MILE
SULFATE
G/MILE
FUEL ECONOMY
MPG
BACK
FRESSUR
MM HG
1985 Standard
0.20
0.41
3.4
1.0
-
Baseline
0
0.225
0.24
1.01
0.90
0.0036
37.9
19
Baseline
5,000
0.259
0.19
0.82
0.89
0.0055
36.2
Baseline
10,000
0.211
0.19
0.84
0.90
0.0137
37.7
3aseline
15,000
0.227
0.23
0.92
0.81
0.0110
38.1
Baseline
20,000
0.275
0.19
0.79
1.00
0.0124
36.9
Baseline
25,000
0.220
0.21
0.87
0.81
0.0086
38.5
Baseline
40,000
0.213
0.17
0.85
0.85
0.0021
37.1
Baseline
50,000
0.277
0.22
0.92
1.04
0.0093
38.3
MEAN
37.6
Catalyst
0
0.113
0.05
0.16
0. 79
0.0018
37.6
21
Catalyst
5,000
0.135
0.05
0.18
0.89
0.0073
35.6
41
Catalyst
10,000
0.129
0.06
0.24
0.94
0.0110
35.7
41
Catalyst
15,000
0.111
0.10
0.31
0.79
0.0095
37/6
34
Catalyst
20,000
0.111
0.05
0. 27
0.87
0.0048
35.1
34
Catalyst
25,000
0.114
0.11
0.48
0.87
0.0032
37.9
32
Catalyst
30,000
0.144
0.13
0.49
0.82
0.0098
38.4.
52
Catalyst
35,000
0.174
0.07
0.45
0.83
0.0244
37.9
50
Catalyst
40,000
0.099
0.10
0.49
0.92
0.0017
35.5
24
Catalyst
45,000
0.153
0.11
0.56
0.94
0.0066
34.3
60
Catalyst
50,000
0.167
0.10
0.55
0.86
0.0045
36.5
41
Cat. Repeat
50,000
0.163
0.10
0.57
0.97
0.0039
35.3
41
MEAN 36.5
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-54-
Table III-5
DURABILITY TEST RESULTS AT SOUTHWEST RESEARCH INSTITUTE
VEHICLE - VOLKSWAGEN RABBIT
CATALYST - JM-I3/II UNDERFLOOR
HIGHWAY FUEL
ECONOMY
TEST
CONDITION
MILEAGE
PARTICULATE
G/MILE
HC
G/MILE
CO
G/MILE
NOx
G/MILE
SULFATE
G/MILE
FUEL ECONOMY
MPG
Baseline
0
0.137
0.16
0.48
0.60
0.0030
51.7
Baseline
5,000
0.166
0.06
0.37
0.62
0.0594
48.5
Baseline
10,000
0.151
0.08
0.40
0.61
0.0151
49.7
Baseline
15,000
0.143
0.08
0.43
0.55
0.0101
49.3
Baseline
20,000
0.161
0.08
0.39
0.66
0.0112
45.4
Baseline
25,000
0.132
0.08
0.40
0.56
0.0093
50.1
Baseline
40,000
0.144
0.07
0.39
0.65
0.0029
49.0
Baseline
50,000
0.171
0.10
0.49
0.70
0.0102
MEAN
51.0
49.3
Catalyst
0
0.107
0.02
0.02
0.55
0.0100
50.2
Catalyst
5,000
0.187
0.01
0.05
0.58
0.0215
48.2
Catalyst
10,000
0.267
0.02
0.10
0.63
0.0383
'45.1
Catalyst
15,000
0.150
0.02
0.26
0.56
0.0328
50.1
Catalyst
20,000
0.200
0.02
0.06
0.63
0.0411
50.2
Catalyst
25,000
0.077
0.03
0.13
0.58
0.0097
49.6
Catalyst
30,000
0.096
0.03
0.18
0.62
0.0167
49. 4
Catalyst
35,000
0.124
0.03
0.16
. 0.62
0.0059
49.2
Catalyst
40,000
0.060
0.02
0.15
0.67
0.0048
47.0
Catalyst
45,000
0.124
0.04
0.21
0.62
0.0022
45.1
Catalyst
50,000
0.105
0.06
0.21
0.66
0.0123
MEAN
48.7
48.4
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-55-
testing over the Federal Test Procedure and Highway Fuel Economy
Test.[18, pp. 4-5] Particulate reductions over the FTP ranged
from 39 percent at 10,000 miles to 60 percent at 20,000 miles; the
trap was 40 percent efficient at the end of the 50,000 miles.
These efficiencies are not very high, but because of the low
engine-out particulate levels of the Rabbit, Johnson Matthey only
designed the trap to be 50 percent efficient.[10, p. 24] As Table
II1-4 shows, with the trap the vehicle never exceeded the 0.2 g/mi
level which was the design goal of the system. The particulate
results for the highway test were not as encouraging. At the
0-mile and 50,000-mile test points, the trap particulate levels
were somewhat lower than the baseline levels. But at several
interim test points the trap levels were actually higher. This is
a source of concern and is undoubtedly due in part to the higher
sulfate levels with the catalyzed trap.
The successful completion of the Johnson Matthey
trap-oxidizer system is very important. It shows that the basic
JM13 design can survive the vehicle environment for 50,000 miles
if regeneration is successfully controlled. It proved the general
durability of the Johnson Matthey filter structure, catalytic
coating, and mounting system and brings the process forward to the
point where vehicle manufacturers can seriously attempt to
integrate traps and on-board regeneration systems into their
diesel vehicles.
General Motors received 11 Johnson Matthey traps for testing
during the period from October 1980 to April 1981. None of these
traps performed satisfactorily with the longest durability trap
lasting only 1,290 miles.[9, p. 17] Six of these traps were
intended to be self-regenerating traps, i.e., requiring nothing
more than high vehicle speeds and loads for regeneration. Given
the difficulties in assuring regeneration without the aid of
additional heat or hydrocarbons, it may not be surprising that
these traps ultimately failed. Johnson Matthey has even come to
the conclusion that it is necessary to have some form of positive
regeneration system to inhibit trap overloading. The other five
Johnson Matthey traps were to be regenerated by intake air
throttling. As has been discussed above, one primary problem with
throttling is that it tends to starve the exhaust of excess oxygen
just when the trap requires it for regeneration. Accordingly, at
first particulate can get very hot but not oxidize due to lack of
oxygen, leading to uncontrolled oxidation when oxygen rich exhaust
enters the hot trap. GM does not offer enough information for us
to determine exactly what the failure modes were for each of the
traps regenerated with throttling, but there was one trap failure
for which some information was provided. Referring to trap
JM-13-1 in their original submission.[9, p. 17] GM's subsequent
submission of data sheets states the following: "This trap would
not regenerate in early testing, even at speeds up to 88 km/hr.
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-56-
After accumulated particulate increased backpressure to about 8
kPa, regeneration would occur, but still required speeds of 80
km/hr or higher. In attempts to regenerate at lower speeds,
particulates continued to accumulate, overloading the trap and
increasing backpressure. When regeneration did finally occur, the
heat of combustion of the particulates melted the trap (at about
1,240 miles)."[17, p. 5F-1] Thus, at least in this case of a
trap/throttling system, GM agrees that the primary problem was
regeneration with an overloaded trap. Thus, again, the problem is
not so much the durability of the trap material and design itself
but with the inability to control the regeneration conditions to
acceptable levels.
The only two commenters to address the durability of Texaco's
wire mesh trap design were Texaco and General Motors. Texaco
reported the results of two trap durability programs.[11, pp.
2-3] The first involved a Texaco trap in the exhaust system of a
dynamometer-mounted 5.7-liter Oldsmobile diesel engine.
Particulate was collected under 40 mph steady-state conditions.
The trap survived for the equivalent of 30,800 miles before being
damaged during a regeneration. This trap was regenerated every
200 miles so the trap successfully underwent approximately 150
regenerations before failing. Texaco offered no analysis of the
failure. This trap maintained its collections efficiency over the
entire test while exhaust gas backpressure rose slightly with
mileage.
Texaco's second durability program also involved a Texaco
trap and a 5.7-liter Oldsmobile engine, but in this case, the
vehicle was driven on the road at 50 to 55 mph to accumulate
mileage. After approximately 2,500 miles one filter cartridge of
the two-cartridge trap was replaced with a slightly different
design in order to eliminate filter matrix compaction. The trap
survived a total of 10,000 miles before a portion of the filter
was damaged during regeneration. This trap was regenerated every
150 miles, so it survived approximately 65 regenerations. Again,
the trap maintained its collection efficiency throughout the test
except for one incomplete regeneration which temporarily decreased
efficiency.[11, p. 6]
General Motors reported on the durability testing of a Texaco
wire mesh trap coated with a catalyst material to aid
regeneration. [9, p. 14; 17, p. 3A] This trap was placed in the
exhaust manifolds of a 5.7-liter Oldsmobile vehicle. No positive
regeneration system was utilized on the vehicle. Quoting GM:
"This system would regenerate on the standard AMA test cycle, but
it would not regenerate on a modified cycle from which the more
demanding modes were deleted. After 19,000 miles, the trap was
loaded so heavily that it had to be removed from the vehicle and
"regenerated" in an oven before the durability test of the metal
mesh could be continued. Because it had been anticipated that
regeneration would not occur without some demanding driving modes,
-------
-57-
this system was never intended as a candidate for production, but
it was a means of evaluating durability of metal mesh as a
trapping material without the need for a complicated regeneration
system."[9, p. 14] This trap accumulated 34,100 miles before
failing due to disintegration of part of the wire mesh, resulting
in "excessive backpressure and poor performance."[17, p. 3A]
Two points should be made with respect to this durability
test. Most important, the fact that the trap became overloaded at
19,000 miles and had to be regenerated in an oven is not a problem
with trap durability; clearly it was due to the lack of a positive
regeneration system. As GM stated, the system, lacking any
positive regeneration method, was never intended as a production
system, but rather was simply a means for evaluating wire mesh
durability. However, the fact that the trap did survive 34,000
miles without a positive regeneration system indicates that with
such a system the trap might well have lasted 50,000 miles or
more. It is also worthwhile to note that this durability testing
ended in October of 1980,[17, p. 3A-24) thus 1-1/2 years have been
available with which to continue work with this design.
Both the Texaco and General Motors durability testing
indicates that the Texaco trap design is capable of surviving many
thousands of miles of on-road operation. The GM results, i.e.,
the trap surviving 34,000 miles with no positive regeneration
system and having to take the trap off the vehicle just once to
externally regenerate it, are the most promising.
E. Overall Evaluation
The previous sections of this chapter have examined the most
important technical issues with respect to trap-oxidizers—
efficiency, backpressure, regeneration, and durability. This
section will summarize the conclusions from the preceding analyses
and will provide an overall evaluation of the current status of
trap-oxidizer development.
The particulate collection efficiencies of new traps are
quite good. The consensus of many commenters was that zero-mile
ceramic monolith traps are approximately 70 to 90 percent
efficient and that zero-mile wire mesh traps are 50 to 80 percent
efficient, regardless of whether either trap design is catalyzed
or not. The efficiencies of both types of traps can be varied by
the sizes of the traps and by the relative porosities of ceramic
monolith traps and the relative mesh densities of wire mesh
traps. Generally, the zero-mile backpressure levels of the
various trap designs were found to be acceptable to the vehicle
manufacturers, with the one possible exception being catalyzed
ceramic monolith traps. A very limited data base indicates that
catalyzing can significantly increase zero-mile backpressure
levels of ceramic monolith traps. Generally, the wire mesh traps
-------
-58-
exhibited lower zero-mile backpressure increases than ceramic
monolith designs.
Even more important, there was a near consensus among the
commenters that the zero-mile efficiency and backpressure
characteristics of the various trap designs could be maintained
throughout repetitive regenerations. General Motors, Ford, and
Nissan all provided strong evidence supporting this conclusion for
ceramic monolith traps, and Johnson Matthey and Texaco both
provided similar data for wire mesh designs. Volkswagen was the
only dissenter on this point. Its position was based on air flow
tests as opposed to actual trap/vehicle tests which the other
manufacturers relied on.
The submissions were in fair agreement on the conditions
necessary for the initiation of trap regeneration. Non-catalyzed
traps, regardless of design, require minimum exhaust gas
temperatures of 500°C to 650°C while some catalyzed traps only
require temperatures in the 300*0 to 500°C range. Oxygen levels
in the exhaust must be 3 to 4 percent or greater, and the
re-quisite temperatures and oxygen levels must be maintained for 2
to 10 minutes for sufficient regeneration to occur. The comments
were also consistent on the need to control the maximum
temperatures reached in the trap during regeneration. The trap
inlet exhaust gas temperature and oxygen content, total trap
particulate loading, and exhaust gas flow rate must be controlled
such that excessive regeneration temperatures are avoided.
(General Motors suggested maximums of 1100cC for ceramic monolith
traps and 900°C for wire mesh designs.)
Several possible regeneration systems have been identified.
Research continues on the development of a catalytic treatment
which could significantly reduce the exhaust gas temperature
required for regeneration, but at this time all trap designs need
some form of positive regeneration mechanism. Two concepts, fuel
burners and electrical heating, appear to be technically feasible
but are relatively complex and would likely involve costly vehicle
modifications. They may be the best candidates for non-catalyzed
traps which need relatively high exhaust gas temperatures. There
are' problems with utilizing intake air throttling as a
regeneration initiation mechanism, but it might yet prove to be
acceptable for catalyzed traps where the lower requisite exhaust
gas temperatures would reduce the need for excessive throttling.
Johnson Matthey's exhaust stroke fuel injection, if it can be
achieved through internal injection pump modificationsj may well
be the most promising mechanism for catalyzed traps which only
require moderate exhaust gas temperature increases.
Regardless of which regeneration system is used, sufficient
oxygen levels must be maintained in the trap during periods of
high exhaust gas temperatures. This may well require an air pump
or some other mechanism for oxygen addition to the trap. Except
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for Johnson Matthey's recent suggestion, all of the regeneration
systems described above have been considered for several years now
and are well understood. Probably the most undefined area of
research involves the sensors and controls which would be an
integral part of any regeneration system. The ideal sensors for
the initiation of the regeneration process would be trap loading
or backpressure sensors. At this time such sensors are not
available, however, and engine revolution and mileage counters are
being examined instead. Temperature sensors would also be
required, but these should not pose any great technical problems.
Integrating proper sensors and controls within a total
regeneration system onto vehicles is the last major technical
problem in trap-oxidizer development.
Many promising durability data were reported to EPA.
Daimler-Benz submitted information on a ceramic monolith trap
which accumulated 33,500 miles of on-vehicle durability as of late
1979. Daimler-Benz did not state whether the trap testing
continued, failed, or was simply halted. Ford ran a ceramic
monolith trap on a vehicle for 10,000 miles before trap failure.
EPA has an ongoing ceramic monolith durability program with 18,000
miles of successful operation as of February 1982. General Motors
simulated over 37,000 miles on a ceramic monolith trap under
dynamometer testing, though it has not achieved good durability on
vehicles on the road.
Johnson Matthey reported the first successful 50,000-mile
durability demonstration of trap technology. This demonstration
proved the general durability of Johnson Matthey's wire mesh
filter structure, catalyst and washcost formulation, and mounting
system. It did not involve an entire vehicle system as
regeneration was initiated by the driver and involved a very
crude, first-generation design. Nevertheless, the program showed
that durability can be achieved if regeneration is properly
controlled.
General Motors recorded over 34,000 miles on a Texaco trap
with a catalyst coating before the trap failed. The trap had to
be externally regenerated at 19,000 miles; it is likely that both
the 19,000-mile regeneration and the ultimate failure were due to
overloading since no positive regeneration system was used during
the testing. Texaco reached 30,000 miles on a non-catalyzed trap
in a dynamometer simulation and 10,000 miles during vehicle
testing.
Despite the fact that nearly all of the durability testing
reported to EPA resulted in trap failures, it appears that trap
durability is not the primary problem so much as is control over
the regeneration process. It has been shown that both ceramic
monolith and wire mesh trap designs can survive the vehicle
environment for tens of thousands of miles, and up to 50,000 miles
for the Johnson Matthey design, if the regeneration process is
properly controlled.
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In conclusion, the data submitted to EPA are encouraging and
indicate that substantial progress has been made in the last two
years. Efficiency and backpressure are no longer serious problems
even after repetitive regenerations.. The evidence indicates that
the durability of various trap designs may be acceptable if
regeneration can be adequately controlled, though improvements are
both possible and likely being made. The most important area of
ongoing research is regeneration initiation and control. This is
the most significant remaining technical problem.
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CHAPTER IV
LEADTIHE
A. Development Leadtime
The previous chapter summarized the current status of
trap-oxidizer development. It concluded that trap-oxidizers hold
significant promise but that technical improvements must still be
made. The issue this section will address is how much leadtime is
still required for the vehicle manufacturers to optimize
trap-oxidizer systems to the point where assurance testing of the
most promising trap system concepts can begin.
Projection of future technical advances is admittedly a
difficult task. Yet the determination of achievable emission
reductions is an integral part of motor vehicle emission
regulation and Congress has generally delegated such
determinations to EPA. Uncertainty and lack of proof are inherent
in predicting technical improvements. If technological progress
could indeed be proven, then the improvements would not be true
"progress" so much as simply application of existing technology.
Given the data which have been submitted to EPA, and our
experience in motor vehicle emission technology issues, we believe
that vehicle manufacturers are near the stage where the most
promising trap-oxidizer systems can be identified and can begin to
be integrated into overall engine and vehicle designs. This
position is based on the following considerations.
Most importantly, trap-oxidizers are at a very advanced stage
of development. Trap and vehicle manufacturers have been
performing research and development of traps for over four years
and have resolved most of the basic technical issues. As was
shown in Chapter III, significant advances have been achieved with
respect to trap-oxidizer efficiency, backpressure, and durability
for both ceramic monolith and wire mesh trap designs. The
efficiency and backpressure characteristics of traps have advanced
to the stage where they are not only acceptable at zero-mile
levels but are also able to be maintained throughout mileage
accumulation and repetitive regenerations. Durability was a major
concern when the original particulate final rule was published; at
that time the best durability that EPA was aware of was 12,800
miles.[12, p. 51] Since that time, manufacturers have reported
several on-road vehicle tests and dynamometer simulations where
traps have .survived upwards of 30,000 miles, and it is significant
to note that many of these durability tests were performed in late
1979 and early 1980 and that much time has passed for even further
improvements. Johnson Matthey has produced a trap design which,
in combination with a rather crude regeneration system, has
completed a 50,000-mile durability test. It is clear that
significant progress has been made with respect to trap
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durability, and that the primary concern with durability is
whether a regeneration system can be designed with sufficient
control so as to maintain trap durability.
As concluded in Chapter III, the primary technical task
facing vehicle (and trap) manufacturers is the development of
positive regeneration systems, including accompanying sensors and
controls, which can be successfully integrated with diesel engine
and vehicle design. Although no one regeneration system has yet
been developed which is workable, simple, and inexpensive, the
conditions and controls necessary for successful trap regeneration
have been defined. Several candidate regeneration systems have
been identified and tested. Some systems, such as fuel burners
and electrical heating, appear quite workable with their primary
drawbacks being higher cost and/or the need for greater vehicle
modifications. Other systems, such as intake air throttling and
exhaust stroke fuel injection, are much more promising but as yet
are not completely proven. Still, all of these concepts are now
well understood, and the hardware necessary for their utilization
is generally available. For example, a fuel burner system would
require an injector, a fuel pump, an air pump, a glowplug or
sparkplug, and possibly an exhaust bypass, along with the
requisite controls. Throttling would require a throttling motor
with the necessary controls. Basically, these hardware items are
all available off-the-shelf today. Probably the most undefined
area involves the sensors and controls which would be used with
any regeneration system. Even here manufacturers have identified
many possibilities, and the experience with electronic controls on
gasoline-fueled vehicles should be of great assistance. Now that
more basic concerns such as efficiency, backpressure, and
durability have been resolved, vehicle manufacturers will be able
to concentrate their efforts on optimizing and integrating
regeneration systems. Based on the solid progress of the last
four years in trap-oxidizer development, and the narrowing of the
technical areas where research need be concentrated, we believe it
is quite reasonable to expect progress to continue and solutions
for on-board regeneration initiation and control to be found in
the near future.
Once complete regeneration systems are developed, the vehicle
manufacturers can proceed with assurance testing in the field in
order to comprehensively evaluate the entire trap/regeneration
system design in-use. It is not necessary that the manufacturers
have production-ready trap systems available for the assurance
testing fleets, since assurance testing is itself a part of the
final evaluation process. Rather, the manufacturer must select
the most promising trap design/regeneration system combination(s)
so that the assurance testing process may begin. The manufacturer
may need to include more than one concept in its assurance testing
if it is unable to identify one most promising concept, or if it
wants to be "safe" in case of failure of any particular design.
Our analysis of the time necessary for assurance testing leaves
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the manufacturer enough latitude to perform the testing in two
separate phases, so improvements may be made in the midst of the
program.
The technical advances which still need to be achieved do not
appear overly formidable or unreasonable in light of the technical
capability of the automotive industry in other areas of
engineering. One commenter quotes a top General Motors engineer
as saying that the company is now able to produce a different
engine model from scratch in two years.[19, p. 18] GM has stated
that its first two diesel engines, the 5.7-liter and 4.3-liter
(which has since been replaced by a newer 4.3-liter design)
engines introduced in 1978 and 1979, respectively, both took only
three years to develop.[15, pp. 129-130] Finally, and most
analogous to the issue at hand, it is' important to consider the
requisite trap-oxidizer improvements in light of the achievements
manufacturers have made with respect .to emission control on
gasoline-fueled passenger cars. Beginning with most passenger
cars sold in California in 1980 and extending to nearly all
passenger cars nationwide in 1981, the vehicle manufacturers have
integrated sophisticated electronics on-board in order to maintain
tight control over the air-fuel ratio based on the oxygen level in
the exhaust and other engine parameters. This precise control of
air-fuel ratio is necessary for successful operation of
three-way-catalysts to oxidize HC and CO and reduce NOx
simultaneously. Control over the initiation and extent of
particulate oxidation during regeneration may or may not entail
similar levels of electronics and overall sophistication, but in
any case the experience the manufacturers have gained in
electronic controls on . gasoline-fueled vehicles should aid their
work on trap regeneration systems. This experience should
indicate that it is highly likely that success will soon be
achieved.
Given that 1) trap-oxidizer development has advanced to the
stage where only regeneration remains as a major technical
problem, 2) that significant progress has taken place during the
last four years in all areas of trap design and that research may
now be concentrated on the issue of regeneration, and 3) that the
necessary technical improvements are not unrealistic given the
technical capabilities of the automotive manufacturers with
respect to engine design and emission control, the EPA technical
staff projects that another one and one-half years of development
leadtime is sufficient for the vehicle manufacturers to identify
and optimize regeneration systems for the beginning of assurance
testing. Since the data reported to EPA by the vehicle
manufacturers were generally inclusive up to about the summer of
1981, the one and a half years of development leadtime projection
would result in assurance testing beginning in January 1983.
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Th e . only vehicle manufacturer to comment directly on the
issue of development leadtime was General Motors. GM reported
that a "product design development program" of 24 months was
underway which, if successful, could result in a production
design.[9, p. 44] Subsequent communication with General Motors
disclosed that this 24-month program began in September 1981.[20]
Applying GM's timetable, a design would not be available for
assurance testing until . September 1983. Unfortunately, GM
provided no details as to the specifics of the program or why it
would take 2 years to complete. Thus, we cannot analyze GM's
position in any detail, but we believe it may be too pessimistic
in view of the discussion above.
In addition, past experience has shown that the automotive
industry has often been too pessimistic in terms of its technical
capabilities for emission control. Since the benefits of emission
control equipment and lower pollutant levels are realized by
society as a whole and not by . individual vehicle purchasers, the
marketplace does not provide an incentive for vehicle
manufacturers to develop and install pollution control equipment.
In fact, since emission controls often increase vehicle prices,
there is actually a marketplace disincentive for emission control
improvements, which encourages the industry to downplay its
technical capabilities.[19, p. 11] It was concern about this
tendency for the automotive industry to be pessimistic about
technological improvements in emission control which guided
Congress in its development of the motor vehicle provisions of the
Clean Air Act of 1970 and subsequent amendments.
Inherent in the motor vehicle provisions of the Act is the
concept of technology-forcing, i.e., setting standards which
cannot be met at the time of promulgation but which reasoned
technical analysis projects can be met by the time the standards
take effect. Technology-forcing has proved to be the most
effective strategy available to encourage the research and use of
better emission control systems. Technology-forcing was utilized
in our original particulate rulemaking and because of its
application the automotive industry is now very close to a
production trap design. Trap manufacturers have stated that much
of their trap-oxidizer research would net have been funded if the
particulate standards had not been in place.[22]
The tendency for the automotive industry to be pessimistic
with respect to emission control development was demonstrated in
the early 1970's when the feasibility of catalytic converters and
the 197 5 statutory emissions standards were being debated. In
March and April, 1972, five motor vehicle manufacturers filed for
suspension of the 1975 statutory standards on the basis that the
development of catalytic converters was insufficiently advanced
for successful use in the field. On April 11, 1973, the
Administrator granted a one-year suspension of the 1975 statutory
standards and promulgated a set of interim standards which he
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believed would require catalytic converters only on California
vehicles* Nevertheless, over 85 percent of all 1975 model
passenger cars successfully employed catalytic converters. One
other fact involving the catalyst analogy should be noted. Even
though catalytic converters were ultimately used on 1975
production, the first successful 50,000-mile durability
demonstration of a catalyst did not take place until the spring of
1973, only 1 1/2 years before 1975 production.[22] Alternatively,
there has already been a successful 50,000-mile trap—oxidizer
durability test as of January 1982.
The only other parties which have commented on development
leadtime requirements have been the trap manufacturers. Johnson
Matthey has stated that "our experience shows that the
trap-oxidizer can be integrated into a given vehicle system within
four months" and that "[mjore than adequate time remains to carry
out the necessary steps to ensure that effective control systems
are properly integrated on 1985 model year production
vehicles."[21, p. 2] Other trap manufacturers have projected that
additional development leadtime is needed, resulting in
introduction on 1986 or 1987 production vehicles.[22] We believe
these statements generally support our development leadtime
projections.
In summary, EPA projects that one and a half years of
development leadtime is sufficient for the vehicle manufacturers
to identify and optimize regeneration systems. This projection
would allow assurance testing to begin by January 1983.
B. Assurance Testing
After successful trap-oxidizer prototypes have been
developed, the vehicle manufacturers must then undertake a program
of "assurance testing." This will begin when the manufacturers
identify the physical specifications for the prototype
trap-oxidizer model(s) for each vehicle family, and these
prototype traps are fabricated by the suppliers. The desired trap
model(s) are installed on the vehicles and the testing program can
begin.
Assurance testing allows the vehicle manufacturer to evaluate
the trap-oxidizer models available in actual operating conditions
on its own vehicles, identify specific improvements which could be
made to optimize the engine/trap-oxidizer system for its vehicles,
and to develop greater confidence in the performance of
trap-oxidizer systems. The ultimate goal of assurance testing is
to further prove and optimize the prototype design in an effort to
provide the necessary degree of particulate control over the
useful life at the lowest cost. Factors such as production
economies of scale and potential warranty implications will also
impact the choice of trap-oxidizer systems and the direction of
the assurance testing program. For example, if one trap-oxidizer
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system will work successfully on all of a manufacturer's vehicle
families, this could be preferable to developing a specific system
optimized for each family.
In testing such as this there are several factors which must
be considered. Here, we are primarily interested in the factors
bearing on the amount of assurance testing deemed necessary. The
scope of a manufacturer's assurance testing program will vary
according to factors such as; 1) the number of vehicle/engine
configurations being evaluated, 2) the degree of experience with
light-duty diesels, 3) the number of specific trap-oxidizer models
being evaluated, and A) other concerns such as testing in various
climatic regions, geographical areas, and special applications.
These will be discussed further below.
It is clear that the amount of assurance testing required
will vary with the number of vehicle/engine configurations being
evaluated. A manufacturer planning to certify several size
passenger cars and light-duty trucks will have a much larger job
and much more to gain than a smaller manufacturer. The task will
be- especially important because of the potential economic jeopardy
of an unsuccessful program and the potential, cost-saving gains
associated with minimizing the number of systems certified.
A manufacturer's degree of experience with light-duty diesel
vehicles/engines will also impact the scope of the program.
Manufacturers with limited experience in diesel engine technology
will probably require more assurance testing than their
experienced counterparts. This need for more testing would arise
from a lack of historical data and vehicle performance experience
on which to base judgments.
In sotae cases a manufacturer may choose to evaluate both wire
mesh and ceramic trap-oxidizer designs. In this case, the scope
of the testing program would expand, but it is most likely that
the initial evaluations being conducted on current prototypes
would allow the manufacturers to choose between the two basic
designs prior to the beginning of assurance testing. However, it
is likely that manufacturers could choose to evaluate more than
one configuration of the same basic trap-oxidizer design, for
example, trap-oxidizers of different volume, trapping material
density, or shape. Also, evaluations of different regeneration
systems or trap-oxidizer placements could occur.
Often a manufacturer's assurance testing program will be
broad enough to also cover operations in different areas of the
country and special applications. For example, manufacturers may
choose to send fleets to specific areas in hot or cold climates or
send fleets to operate in high-altitude areas. Another
possibility is to place fleets in applications which are extremes
from the operating norm. For example, a fleet could operate in
all urban or all inter-city driving to determine performance in
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more rigorous operational environments.
What is desired in an assurance testing program will be based
on a manufacturer's specific goals. As was stated above, the
program should ultimately lead to recommendations for
trap-oxidizer specifications so that commitments leading to
production and tooling can be made. However, it is not certain to
what point each manufacturer must go to reach this decision, and
this point is likely to be different for each manufacturer.
Given this discussion on assurance testing, what is a
reasonable time period for manufacturers to complete the
anticipated program? There are several factors which will affect
the time required.
As was mentioned above, the degree of assurance desired by a
manufacturer will have an influence on the amount of time
necessary to complete the program. This will vary according to
the manufacturer's policy, the manufacturer's experience with
diesels, and the manufacturer's degree of experience with
trap-oxidizer systems. Obviously these factors are different for
each manufacturer.
The length of time to complete assurance testing would also
depend on the number of vehicle/engine-system models to be
evaluated (size of the program). When practical, the best use of
time would require these models to be evaluated concurrently such
that they are completed at about the same time, but this may not
be practical for other reasons as will be discussed below.
The characteristics of the assurance program will also affect
its length. This includes the manner of mileage accumulation
(test track versus over the road), the amount of mileage desired
per vehicle, and the amount of emissions testing and maintenance.
EPA expects these programs will be quite similar to the current
durability testing procedure for certification, with the exception
of those cases where a manufacturer may choose to place a fleet in
a special application.
One final aspect which needs consideration is the current
financial condition of the auto industry. Manufacturers may not
have the resources to conduct concurrent evaluations of their
entire product lines. Instead, they may be forced to evaluate
worst case configurations first, make modifications and
improvements, and then evaluate the remainder of the models. This
could be a.more financially conservative approach but would likely
require more time. Financial considerations may also limit the
scope of the manufacturers' test programs in various geographic
areas, climatic regions, and rigorous applications. This may be
partially compensated for through in-house dynamometer simulation
testing.
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As will be discussed below, EPA now estimates that an
adequate assurance testing program would require approximately
10-14 months. The actual length of time would vary as described
earlier, so this estimate uses somewhat conservative assumptions.
As shown in Table IV-1, Phase I of the program would require 3 1/2
to 5 months for mileage accumulation, maintenance, and testing.
The amount of mileage which could be accumulated in this period
would depend upon the daily mileage accumulation rate. Based on
past EPA analyses, in 3 1/2 to 5 months manufacturers could
accumulate 50,000 miles operating one shift per day and 100,000
miles operating two shifts.[25, p. 28] After Phase I is
completed, the results of the program are analyzed, the
vehicle-engine/trap oxidizer system is evaluated, and further
improvements and optimizations can be recommended. EPA believes a
thorough engineering analysis of these results plus development of
recommended changes in design or hardware would take 3-4 months.
In some cases manufacturers may choose to conduct a follow-up
(Phase II) program for further evaluation of the refined systems.
For other manufacturers Phase II may consist of special
applications testing as described above. Some manufacturers may
choose to completely forego Phase II testing. This program may be
of greater or lesser scope than Phase I, but should be achievable
within a similar timeframe. In any event, after Phase I and the
analysis of the results, most manufacturers will have adequate
information to make initial commitments for production tooling.
EPA's estimate of 10-14 months provides adequate time for
assurance testing even if a manufacturer's plans on how to conduct
assurance testing are substantially different than outlined
above. EPA's time estimate is supported by those provided by
GM[9, p. 45] and Toyota[8, p. 36] which both stated that one year
would be sufficient for assurance testing.
C. Preparation for Trap-Oxidizer Production
Once the manufacturers have trap-oxidizer basic designs and
specifications which can be committed to production, the actual
preparation for mass production is a relatively straightforward
process. This step is far more straightforward because no
technological advances are necessary as in the developmental
phase. Depending on the anticipated production volumes and the
number of different sizes and models to be built, trap-oxidizer
suppliers must procure facilities, make any necessary facility
modifications, and install tooling and other equipment. Some
components and materials may be procured from other production
facilities but others may have to be produced from the basic
specifications.
Decisions must also be made with regards to which components
will be produced internally and which will be purchased from
sub-contractors. Sub-contractors in turn must prepare their own
facilities and equipment. Many of these initial facility,
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Table IV-1
Time to Complete Fleet Assurance Testing
Phase I (50,000 miles) 3.5-5 months
Supplemental data analysis 3-4 months
and system refinement/
optimization
Phase II (5.0,000 miles) 3.5-5 months
10-14 months
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tooling, and equipment actions can be taken before the
manufacturers have their final trap-oxidizer specifications (after
the completion of Phase I but before the completion of Phase II of
assurance testing).
Once these final specifications have been received, any final
tooling or equipment can be purchased and any last minute
modifications can be made. After production personnel have been
hired and received some initial training, production dry runs can
be conducted for additional training, improvements in the
production process, and quality control.
Even though all of the components needed in the final product
have their own separate leadtime requirements, the composite
leadtime necessary to supply the final trap-oxidizer system is the
controlling leadtime determinant.
Although almost all of the commenters addressed the leadtime
topic, few specifically addressed the manufacturing component of
the leadtime. These comments are summarized below.
Johnson Matthey, Inc.: "Johnson Matthey could be producing
these diesel trap-oxidizers 12-18 months upon receipt of an
order."[10, p. 1]
Corning Glass; "Corning plans development and building of
prototype process equipment by 1982, transfer to a production
plant by 1983 1/2 and production beginning in 1984."[5, p. 2]
Daimler-Benz: "The final version of a trap-oxidizer vehicle
system ready for series production will require four years after a
system meeting the design and regeneration requirements has been
found."[2, p. 20]
Ford Motor Co. ; "Upon successful completion of the
demonstration of a feasible research prototype, five additional
years are required to bring the components into production."[6, p.
24]
Toyota Motor Co.; "Examination for manufacturing and
assurance of reliability will take approximately 3 years."[8, p.
36]
Volkswagen; "Once a workable system has been developed, it
will take 3 years to put into production."[ 4, p. 58] An earlier
submission by VW estimated a manufacturing leadtime of 18-24
months.[23, p. 40]
General Motors; GM requires 24 months to validate the
product design (including EPA certification) and to design, build,
and try out facilities for mass producing the design.[9, p. 44]
In an earlier comment GM estimated 2 1/2 to 3 years production
leadtime after an acceptable method is defined.[23, p. 41]
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Clearly the leadtime estimates provided by the commenters are
not directly comparable. Each estimate incorporates different
aspects of the total leadtime picture. Johnson Matthey's estimate
of 12-18 months is the manufacturing leadtime. Coming's
statement can be interpreted to estimate a leadtime of about 2
years for manufacturing. VW's earlier submission estimated a
manufacturing leadtime of 18-24 months.
If it is assumed that Toyota and VW would conduct their
assurance testing and then make their initial tooling commitments,
a period of 1 1/2 to 2 years would be anticipated for
manufacturing leadtime. GM estimated 24 months for this phase,
but their estimate also included certification.
Comments from Ford and Daimler-Benz were not detailed enough
to be useful in this portion of the leadtime analysis. These will
be considered when the total leadtime estimate is examined.
Taking the useful comments en masse, it would appear that
most commenters anticipated manufacturing leadtime requirements of
18-24 months. This period would begin when the vehicle
manufacturers place their initial orders and end when the first
production trap-oxidizers are constructed.
This estimate of 18-24 months is corroborated well by
manufacturers' comments in a recent EPA rulemaking of a similar
nature, "Gaseous Emission Regulations for 1984 and Later Model
Year Heavy-Duty Engines." The emission standards promulgated in
that rulemaking required oxidation catalysts for heavy-duty
gasoline-powered trucks and buses which were to be uniquely
designed and built for the heavy-duty operating environment. GM
estimated a tooling leadtime of 15 months (assuming substantial
component carry across from light-duty), International Harvester
estimated 21 months and Ford estimated 26 months.[24, p. 177]
Given the general agreement in the commenters' manufacturing
leadtime estimates and the corroboration of these estimates by the
heavy-duty engine oxidation catalyst comments, EPA agrees that a
manufacturing leadtime of 18-24 months is reasonable.
D. Vehicle/Engine Modifications
Both vehicle and engine modifications will be likely as a
result of trap-oxidizer technology. These will be related to the
trap-oxidizer system itself and the ' regeneration system(s)
utilized.
Any vehicle modifications will be related to changes in the
underfloor area to accommodate the trap-oxidizer system and
potential engine compartment changes primarily caused by the
regeneration system. Since most diesel-powered vehicles are also
sold with gasoline-fueled engines, they could accommodate
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trap-oxidizer systems with no major vehicle modifications by
placing the trap-oxidizer system in approximately the same
location as the catalytic converter.
The situation with engine modifications is more complex.
Engine modifications may be required by the trap-oxidizer itself
and the regeneration system. The trap-oxidizer is likely to
require exhaust manifold modifications for proper and efficient
operation. Stainless steel exhaust pipes may also be required to
help ensure the effective operation of the trap-oxidizer system
over the vehicle's useful life.
Since only potential regeneration systems have been
identified, it is difficult to precisely identify these engine
modifications. Potential areas for regeneration system-related
engine modifications include the fuel system, the addition of a
fuel burning system, a throttling mechanism, an air injection
system, electronic engine controls, and/or other sensing devices.
No submissions to the study specifically address the time
required for any vehicle or engine modifications. EPA recognizes
that these modifications will need to be made. However, these
tooling and equipment changes can be made in parallel with tooling
for the traps themselves. Since the 18-24 months allotted for
tooling for trap-oxidizer production should be more than enough to
accommodate these engine/vehicle modifications, this should not
directly affect the necessary leadtime requirements.
E. Certification
In order for a vehicle manufacturer to introduce new vehicles
into the consumer market, it must first describe these vehicles in
a prescribed format and then show that representative vehicles
meet EPA emission standards. The process of obtaining EPA
approval of the vehicles for release to the consumer market is
called the certification process. The certification process is
essentially the same for both passenger cars and light-duty trucks
whether they are gasoline or diesel-powered. Differences between
the two lie in the emission and fuel economy standards which must
be met, and in the details of the test procedures.
At the same time, all new vehicles introduced to the market
must be labeled with a fuel economy rating. In this case also,
the vehicles are described in a prescribed format, and fuel
economy ratings are determined by tests of representative
vehicles. Certification and fuel economy approvals apply for one
model year only. Although the model year may begin any time, it
ends on the last day of the same calendar year. Any vehicles
manufactured after that are considered to be new models. New
certification and fuel economy approvals are needed. If there' are
no changes, there are provisions for carryover which greatly
simplify the recertification and relabeling process.
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The certification procedure for the manufacturer now follows
an abbreviated procedure whereby the manufacturer completes all
of the paper work and testing before any formal application is
made to EPA. Previous procedures required interfacing with, and
receiving approval from, EPA at a number of steps in the process.
The entire process for the manufacturer consists of
completing an application with detailed information about the
particular engine family-exhaust emission control system
combination for which a certificate is being sought. It must
demonstrate, with actual data, the lifetime emission control
durability of the various components by conducting a 50,000-mile
vehicle test. It must also demonstrate with actual data that all
variations of the emission control systems do, indeed, control
exhaust and evaporative emissions so that they do not exceed the
applicable standards. This is done by conducting 4,000-mile
vehicle tests and applying deterioration factors determined in the
durability test. All substantiating data must be submitted with
the application.
The most time-consuming part of the process is the durability
demonstration. One durability test vehicle must be run for each
engine displacement-system combination. The test is conducted by
actually driving the vehicle the equivalent of a 50,000-mile
distance. At specified periods, the driving is stopped and tests
are conducted to determine the emission levels of the system at
that point. A deterioration factor is determined by statistically
analyzing the changes in the emission levels at each of these test
points over the 50,000-mile test run.
At the rate of driving 500 miles per work shift, it can be
seen that such a test can take more than four months at one shift
per day. Of course, double shifts and overtime can speed the
process at increased expense to the manufacturer. Time must also
be allowed for other factors. Driving is stopped to conduct each
required periodic test. Maintenance on the vehicle must be
performed as would be expected of the consumer-owner. Unscheduled
maintenance problems occur which sometimes require that EPA review
the situation to determine whether or not the vehicle might have
to be rejected as unrepresentative, and a new test vehicle be
started. Also, it is not unusual that the periodic tests indicate
that the emissions are increasing to the point where they will
exceed the standards further along in the test, and invalidate the
particular engine family-emissions control system combination. If
this situation develops, a new test vehicle must be initiated with
a modification in the emission control system. Often, a
manufacturer will run one or two backup durability vehicles which
are designated as representing different families.
The emission data test vehicles which are run for 4,000 miles
are not tested until the durability engine test has been completed
and deterioration factors have been established. The emissions
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from the emission data test vehicles are measured at the end of
the 4,000 miles. Then the deterioration factors are applied to
the test data so that a prediction can be made as to what the
emissions would be after a 50,000-mile run. These are the results
that must meet the emission standards.
In a program of about the same length and scope as the
emission data vehicle requirements, manufacturers must also
demonstrate the fuel economy performance of their vehicles and
trucks. These results are used for the fuel economy label and are
a necessary component of the Department of Transportation's
Corporate Average Fuel Economy (CAFE) program.
After all of this testing is completed, detailed information
and test data are submitted to EPA for review and evaluation. At
this stage, EPA may accept the data as is or call for confirmatory
testing at EPA. Confirmatory testing at EPA can involve several
weeks due to scheduling considerations and potential testing
complications. Should the test vehicle fail to meet emission
standards under EPA testing, the vehicle data will not be
accepted. Modifications must be made to the emissions control
system and data from a new 4,000-mile vehicle must be submitted.
Similar confirmatory testing is sometimes done on fuel economy
vehicles and trucks.
After all the data is accepted by EPA, the manufacturer may
now complete the certification application and submit it. A
certificate of conformity is issued shortly thereafter.
At this point it would be useful to review the steps involved
in the formal emissions and fuel economy certification processes
and to estimate the time required using current certification
procedures.
In this analysis we will first view the process considering
the time requirements for a manufacturer's entire product line and
from that draw an estimate of the time required to certify its
light-duty diesel vehicles and light-duty diesel trucks.
Intermediate milestones in the process will be determined
presuming that the manufacturers require their certificates of
conformity by the August prior to new model introduction. All
time periods will be measured back from that date, which will be
referred to as the desired certificate date.
Based on EPA experience with the process, the certification
of a manufacturer's entire product line would roughly follow the
schedule shown in Table IV-2. Using this schedule, EPA
anticipates that a manufacturer would require about 14 months to
complete a given model year's certification program. This, of
course, would vary by manufacturer and would depend on factors
such as the size of the product line and the resources a
manufacturer wishes to expend.
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Table IV-2
Product-Line Certification Schedule
Period Prior to
Desired Certification Date
Event
Beginning Ending
Intention to certify
14
months 13 months
Certification application preparation
13
months 2 months
Durability vehicles
13
months 3 months
Emission-data vehicles
7
months 2 months
Fuel economy vehicles
6
months 1 month
Confirmatory testing
(if necessary)
1
month 0 month
Table IV-3
Engine Family Certification
Schedule
Event
Time Required
for Completion
Durability Testing and
Application Preparation
6 months
Emission Data Vehicle
1 month
Fuel Economy Vehicle
1 month
Confirmatory Testing
1 month
Application Processing
1 month
10 months
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Intent to certify would be submitted 13-14 months prior to
the desired certificate date and work on durability vehicles would
begin immediately. Development of each family's durability
vehicles together with mileage accumulation and testing would take
about 6 months per engine family. During durability testing the
certification application would be prepared. As durability
testing ends manufacturers will be identifying their emission-data
vehicle requirements and preparing vehicles for emission-data
testing. For the earliest durability fleets, emission-data
vehicle testing could begin about 7 months prior to the desired
certificate date- and would require approximately 1 month per
vehicle. An additional month would also be required to finalize
the application and processing at EPA. Fuel economy certification
could begin as emission-data testing is completed and would also
take approximately 1 month.
Given this information, EPA estimates that a vehicle/truck
family could move through the certification process in
approximately 10 months (see Table IV-3). This would allow 6
months for durability testing, 1 month each for emission data and
fuel economy testing, and 1 month for possible confirmatory
testing. In addition, it is reasonable to allow an extra month
for items such as manufacturer and EPA processing of the
certification application, confirmatory testing for both emissions
and fuel economy, or perhaps other, as of yet unidentified, delays.
Under the schedule outlined above, manufacturers would have
to begin the light-duty diesel vehicle and truck certification
processes about 10 months prior to the desired certificate date.
In an analysis such as this it is reasonable to consider that
manufacturers must schedule their light-duty diesel certification
as only one part of their total certification process. As a
result, manufacturers may not always be able to give light-duty
diesel certification top priority. Since it is estimated that the
certification of a manufacturer's entire product line would take
approximately 14 months and certification of any one family would
require about 10 months, it is reasonable to allow a leeway of an
additional 2 months to allow for potential scheduling and priority
conflicts. Therefore, EPA considers 12 months a comfortable
period for certification of a manufacturer's light-duty diesel
vehicle and light-duty diesel truck families.
F. Estimate of Total Leadtime Requirements
Having determined the leadtime requirements for trap-oxidizer
development, assurance testing, production tooling and
certification, it is now possible to determine the total leadtime
still required before trap-oxidizer systems can be used on
production vehicles.
As discussed above, EPA now estimates that the development of
workable trap-oxidizer prototypes will require until January
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1983. This basically requires the manufacturers to identify their
choices of trapping material, determine the models/sizes of
trap-oxidizers which could be used, and identify one or more
successful trap-oxidizer regeneration mechanisms. The major
effort still required lies in the third area.
Once the workable prototype systems have been developed,
vehicle manufacturers can begin assurance testing. This will
allow vehicle manufacturers to determine the operational success
of these prototype systems on their own vehicles/engines. After
Phase I assurance testing is complete, manufacturers will be able
to identify any needed refinements or optimizations on the
trap-oxidizer system, engine, or vehicle. At this point, which
should take approximately 9 months, manufacturers will be able to
make initial commitments for tooling and other equipment necessary
for suppliers to produce the trap-oxidizer system. Some
manufacturers may choose to conduct a second phase of assurance
testing (Phase II) to further evaluate the refinements and
optimizations or to test vehicles in more extreme climatic,
geographic, or operating environments. It is probably not
necessary to complete Phase II testing (5 months) before
committing a design to initial tooling. After completion of Phase
II testing manufacturers can supply final details on system
specifications so any remaining tooling actions can be finalized.
Tooling and equipment for trap-oxidizer system production
including production dry runs and employee training would take
18-24 months after initial tooling commitments are made. During
this period production lines would be developed to: 1) build the
components of the trap-oxidizer system (including the regeneration
mechanism) and 2) assemble the complete trap-oxidizer. This 18-24
months would also allow time for the vehicle manufacturers to
assess any vehicle or engine modifications required and to plan
for such changes during normal model year changeover.
Finally as described above, vehicle manufacturers would
require 12 months to certify their light-duty diesels for
emissions and fuel economy.
To determine the required total leadtime we must identify the
critical path within the different components of the leadtime
picture. Figure IV-1 shows the critical path timeline for total
leadtime. The solid lines represent the critical path. The
broken lines represent other time necessary but not on the
critical path.
As can be seen in Figure IV-1, the critical path is first
dependent on the development leadtime assumed to require until
January 1983. Vehicle manufacturers will then require at most 9
months to complete Phase I assurance testing and analysis of the
results of such testing. After this, initial tooling commitments
can be made. Tooling and equipment preparation for mass
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JAN 1982
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Ul
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TTTT
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. . , Figure IV-1
Trap-Oxidizer Leadtime
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Certification
i 1
i x-
Tooling/Equipment
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Phase jl Phase II
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Agsurartce Testing !
Development .
i I
j- - ; :•: ' y: '¦ ! :
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ill;
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if
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lit
i i
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JAN 1985
t
JAN 1986
H-j ;
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H 1986 MYh : • :
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-79-
production of trap-oxidizer systems and preparation for
vehicle/engine modifications will require another 18-24 months.
Theoretically, certification could begin any time after completion
of Phase II assurance testing, and is therefore not a critical
path item.
Based on this analysis, EPA estimates that trap-oxidizer
systems could be available for use on production-line vehicles and
trucks 25-33 months after a successful prototype system has been
developed.
Using first the shorter total leadtime estimate, if a
successful prototype is available by the end of 1982, 25 months of
additional leadtime would allow trap-oxidizer systems to be
available on production vehicles and trucks by February 1985.
Under this scenario, trap-oxidizers could be used on 1986 model
year light-duty diesel vehicles and trucks. Job 1 for the 1986
model year would begin in late July-early August of 1985.
With the longer total leadtime estimate (33 months)
trap-oxidizer systems would be available during September 1985.
This would miss the 1986 model year by 2-3 months, so under these
conditions, trap-oxidizers could be used on 1987 model year
light-duty diesel vehicles and trucks.
In making the choice of which model year is preferable for a
possible deferral of the 1985 particulate standards there are
several other factors which deserve consideration. The technology
development still required cannot be "scheduled" but must proceed
at its own pace. Economic pressures bearing on the automotive
industry and its suppliers could slow the pace of the entire
process. In addition, as mentioned previously, manufacturers
entering the light-duty diesel market in the mid-eighties might
require a little more time to develop their vehicles/trap-oxidizer
systems than their more experienced counterparts. And, of course,
there is the real economic risk of a manufacturer not being able
to certify and sell one or more engine families in 1986 if its
efforts are unsuccessful. Considering all of these factors, plus
the fact that the longer range in the leadtime estimates brings us
early into the 1987 model year, it would probably be wiser to
choose the more conservative 1987 model year.
Most of the comments related to the achievable model year
were keyed to the development of a successful prototype. If one
assumes that a successful prototype and' regeneration system are
achieved by the end of 1982, then the comments received can be
used to conclude the following model years as achievable;
VW 1986 [A, p. 58]
D-B 1987 [2, p. 20]
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GM
1987
[9, p. 45]
Ford
1988
[6, p. 24]
NAS
1988
[26, p. 35]
VW's estimate supports our 1986 model year conclusion, and both
D-B's and GM's estimates support EPA's more conservative 1987
model year conclusion. Neither Ford nor NAS included any data to
justify the need for five years leadtime beyond a successful
prototype so EPA can neither affirm nor refute their estimates.
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References
1. "Petition to Suspend Application of 1985 Diesel
Particulate Standards," Submitted to EPA by General Motors
Corporation on September 30, 1981 (EPA Docket A-81-20, II-D-31).
2. "Submission of Daimler-Benz A.G. on the Technological
Feasibility of the 1985 Light-Duty Diesel Particulate Standard,"
October 21, 1981, Submitted to EPA by Hogan and Hartson on
November 2, 1981 (EPA Docket A-81-20, II-D-37).
3. "Cellular Ceramic Diesel Particulate Filter," John S.
Howitt and Max R. Montierth, Corning Glass Works, SAE Paper 810114.
4. "Comments on the Technological Feasibility of the 1985
Light-Duty Diesel Particulate Standard," November 1981, Submitted
to EPA by Volkswagen of America, Inc., on November 16, 1981 (EPA
Docket A-81-20, II-D-46).
5. Letter from John S. Howitt, Corning Glass Works to Jeff
Alson, EPA, Concerning the Trap-Oxidizer Feasibility Study,
November 23, 1981 (EPA Docket A-81-20, II-D-64).
6. "Study of the 1985 Light-Duty Diesel Particulate
Standard," Submitted to EPA by Ford Motor Company on October 2,
1981 (EPA Docket A-81-20, Il-D-24).
7. "The Technological Feasibility of 1985 Light-Duty
Diesel Particulate Standard," October 1981, Submitted to EPA by
Nissan Motor Co., Ltd., on October 1, 1981 (EPA Docket A-81-20,
II-D-26).
8. "The Technological Feasibility of the 1985 Light-Duty
Diesel Particulate Standard," Submitted to EPA by Toyota Motor
Co., Ltd., on September 29, 1981 (EPA Docket A-81-20, II-D-20).
9. "General Motors Response to EPA Questions on
Feasibility of 1985 Light-Duty Diesel Particulate Standards,"
October 1981, Submitted to EPA by General Motors Corporation on
October 20, 1981 (EPA Docket A-81-20, II-D-32).
10. "Control of Particulate, Hydrocarbon, and Carbon
Monoxide Emissions from Diesel Engines," Submitted to EPA by John-
son Matthey, Inc., on October 1, 1981' (EPA Docket A-81-20,
II-D-22).
11. Letter from Richard K. Meyers, Texaco, Inc., to EPA
Public Docket No. A-81-20 Concerning the Trap-Oxidizer Feasibility
Study, October 2, 1981 (EPA Docket A-81-20, II-D-25).
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12. "Regulatory Analysis of the Light-Duty Diesel
Particulate Regulations for 1982 and Later Model Year Light-Duty
Diesel Vehicles," EPA, OANR, OMSAPC, February 20, 1980 (EPA Docket
OMSAPC-7 8-3).
13. "Diesel Particulate Trap Regeneration Techniques," W.
R. Wade, J. E. White, and J. J. Florek, Ford Motor Company, SAE
Paper 810118.
14. "Renault's Comments Regarding EPA Studies on Light Duty
Diesel Particulate Requirements for 1985," Submitted to EPA by
Renault USA on September 9, 1981 (EPA Docket A-81-20, II-D-16).
15. "General Motors Response to EPA Notice of Proposed
Rulemaking on Particulate Regulation for Light-Duty Diesel
Vehicles," Submitted to EPA on April 19, 1979 (EPA Docket
OMSAPC-78-3).
16. "Standard for Emission of Particulate Regulation for
Diesel-Fueled Light-Duty Vehicles and Light-Duty Trucks," 45
Federal Register 14496, March 5, 1980.
17. "Addendum to General Motors October 20, 1981,
Submission on Technology for Controlling Particulates from
Light-Duty Diesels," Submitted to EPA on December 15, 1981 (EPA
Docket A-81-20, II-D-66).
18. Letter from, B. E. Enga, Johnson Matthey, Inc., to Anne
M. Gorsuch, Administrator, EPA, Concerning the 1985 Light-Duty
Diesel Particulate Standards, January 25, 1982 (EPA Docket
A-81-20, II-D-75).
19. "Memorandum in Opposition to General Motors' Petition
for Suspension of the 1985 Diesel Particulate Standards,"
Submitted to EPA by the Natural Resources Defense Council, Inc.,
on October 13, 1981 (EPA Docket A-81-20, II-D-27).
20. Personal Communication Between John Nolan, General
Motors, and Jeff Alson, EPA, January 29, 1982.
21. Letter from Dr. George McGuire, Johnson Matthey, Inc.,
to Anne M. Gorsuch, Administrator, EPA, Concerning the 1985 Light-
Duty Diesel Particulate Standards, October 8, 1981 (EPA Docket
A-81-20, Il-D-63).
22. Memo from Maureen D. Smith, EPA. to the Record, "Record
of January 27., 1982 Meeting with the Manufacturers of Emission
Controls Association (MECA) on Trap-Oxidizers," February 24, 1982
(EPA Docekt A-81-20, II-E-2).
23. "Summary and Analysis of Comments on the Notice of
Proposed Rulemaking for the Control of Light-Duty Diesel
Particulate Emissions from 1981 and Later Model Year Vehicles,"
EPA, OANR, OMSAPC, October 1979 (EPA Docket 0MSAPC-78-3).
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24. "Summary and Analysis of Comments to the NPRM: 1983
and Later Model Year Heavy-Duty Engines, Proposed Gaseous Emission
Regulations," EPA, OANR, OMSAPC, December 1979 (EPA Docket
OMSAPC-78-4).
25. "Summary and Analysis of Comments on the Notice of
Proposed Rulemaking for Gaseous Emission Regulations for 1983 and
Later Model Year Light-Duty Trucks," EPA, OANR, OMSAPC, May 1980
(EPA Docket OMSAPC-79-2).
26. "Diesel Cars - Benefits, Risks and Public Policy,"
Final Report of the Diesel Impacts Study Committee, National
Research Council, 1981 (EPA Docket A-81-20, II-A-2).
27. "Light-Duty Diesel Organic Material Control Technology
Investigation Program," Southwest Research Institute, EPA Contract
No. 68-03-2873, Monthly Progress Report No. 28 for the period of
January 1 through January 31, 1982, dated February 10, 1982 (EPA
Docket A-81-20, II-B-1).
28. "Final Report on 50,000 Volkswagen Rabbit Durability
Test," (Preliminary Draft) June 1981 to January 1982, B. E. Enga,
Johnson Matthey, Inc., and B. B. Bykowski, Southwest Research
Institute, submitted to EPA by Johnson Matthey, Inc., on February
12, 1982 (EPA Docket A-81-20, II-D-78).
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