-18-

Iv. References (cont'd)

13. “Technical Progress Report," Bown, Nick, Ricardo

Consulting Engineers, plc.,.EPA Contract No. 68-03-3519, August
2, 1988,

14. “Technical Progress Report," Bown, Nick, Ricardo

Consulting Engineers, plc., EPA Contract No. 68-03-3519, July
18, 1988.

15. "Selee Diesel Particulate Filter," Howitt, John,
Selee Corporation, Hendersonville, NC, presented to EPA by

Selee at the Motor Vehicle Emission Laboratory, February 29,
1988.


-12-

EPA requested that NGK produce a wallflow-type trap made
of silicon carbide or Some other durable conductive ceramic.
The configuration, which we believe lends itself to improved
electrically heating, is a rectangular substrate design with a
diagonal cell orientation relative to two electrical
terminals. This trap configuration is shown in Figure 4. The
idea is to allow uniform current along each cell wall between

the terminals which are Placed on opposite sides of the
rectangular substrate,

Figure 4

Proposed NGK Wallflow Monolith
Si-C Resistive Trap Configuration

-—1
LSSSSSSSSSLL LTT TS
OOOO 06000 00400000005008
LISS 990000 000000005008

NGK has given no indication that they will attempt to
investigate performing this development work in the near term.

H. Corning

Corning reported that it had invested $2 million per year
over the last 10 years on developing the wall flow monolith
(WEM) for Diesel particulate filtration, but it was unlikely
that this rate of investment would continue over the next two
years.{14] Currently their sales of WFMs included Canadian
Mines, who were Successfully using WFMs in mining machinery and
achieving particulate collection efficiencies of 90-95
percent. These machines run at a sufficiently high duty cycle
such that auto regeneration of the filter takes place regularly
and reliably. WFMS are still being supplied to engine
manufacturers for Particulate filtration development, and it
was reported that many manufacturers were conducting tests with
burner regeneration sytems despite the high cost of burners and
control systems and the reliability and safety question marks.


wee

DPF Materies Characterisation Tests
VW1.6) top. One Crlinder Feste “7

%——% Standard 01). SiC Foam - 80 opt - 25 mm Thick
HO Colorail tandard OPF Elenen :
t—-—+ Dur iron Foam with Downstrean Integrei Menbran:

B= Hi-Tech Foan
HmnM Hi-Tech Foam « Reduced Exhoust Gas Flow Rate

16

)
rs

~

~
°o

°

Back Pressure Rise Rate CAPshe
r~)

6

4

2

(6) o-— enn. =
2

0 1 4 5 6
Particulate Loading Rate ( ng/cathr )


-3-

The concept of resistively heated Diesel particulate traps
for improved regeneration efficiency and uniformity has been
evaluated by EPA over the past two years.(5] It was found that
although the regeneration Characteristics can be optimized,
these conditions also must be cyiimized with improved filtering
surface area, and durability. The resistively heated trap
System evaluated was a doped porous silicon carbide tubular
fiber element, produced by the Fogarty Division of Coloroll,
plc. The idea was to have the trapping media be a resistive
element so that when regeneration was desired, the particulate
could be heated directly by resistively heating the trap
media. In this way, intermediate heat transfer losses of
conventional oxidation methods of heating air to heat the
Particulate or heating wires to heat the particulate would be
avoided. This work resulted in the identification of a
resistive material that could both trap Diesel particulate (at
efficiencies of 70 percent) and be uniformly and completely
regenerated. On the downside, rapid backpressure buildup with

this system forced regeneration frequency to occur every 15 to
20 miles.

Among the manufacturers, little has been made public in
the area of resistively heated traps and nothing has been
published. Various manufacturers have, however, reported
results of conventional CTO development programs over the past
year at the SAE Congress and other public forums. On the
light-duty side, FEV and Volvo published a paper this year on
the development of a system for the Volvo 760 turbo-Diesel
vehicle. This system has a conventional honeycomb wallflow
trap, but also and has a modified double-walled manifold,
portliners and intercooler bypasses.(6] With this system, the
Particulate emissions can be lowered below the 0.2 g/mi
standard over the FTP without unacceptable deterioration of
other pollutant emissions and vehicle driveability. Problem
areas which still remain include temperature control and
thermal resistance as they relate to trap durability. At low
temperatures and low speeds during urban cycle testing the
accumulated soot mass in the trap can become too high and cause
cracks and partial melting of the trap subsequently during
accelerations. Also at low temperatures starting problems were
observed. Mercedes-Benz also published a paper of a light-duty
trap development program using their S-cylinder engine.[(7]
This system employs a pressure wave supercharger which shows
advantages in driveability, particular under high altitude
conditions. However, in combination with a particulate trap,
Most of the advantages of the pressure wave supercharging

disappear even with a particulate trap reduced in size by 50
percent.

On the heavy-duty side, the General Motors Corporation
published a report of trap development aimed at meeting the
1991 and 1994 particulate emission standards.{8] The GMC
system is a conventional cordierite ceramic trap with a


V. Appendix


be an engine having Particulate which is Righly organic. This engine seiection will
assist in determining the effects of Significant particulate character differences on
trap effectiveness. The second engine will be one that has an advanced combustion -
chamber cesign, or Perhaps a two-stroke sugine.

This task will Conclude with the successrul design of a particulate trap
medium and trap container that will exhibit acceptable efficiency and short-term
durability on a variety of engines. These engines will be subjected to various
operating conditions. Trap regenerations will be performed using a simple burner.
Regeneration techniques to be used in association with the alternate trap medium
will be examined under a separate task,

2 Task 2 -Trap Durability

After an acceptable trap design bas been developed, the durability of the
trap medium and container will be determined. Two simuitaneous durability
experiments are Proposed. The first experiment vill involve a stationary
dynamometer and a cycle that will resuit in a high-temperature “aging” of the
material. For example, engine speed and torque excursions to achieve high and low
exhaust temperatures will be performed on an isolated trap to determine its long-
term thermal resistance. The trap will be isolated from vibration to examine only
the thermal aspect of trap integrity. Particulate emissions will be used to monitor
trap efficiency, and will therefore serve as an indicator of trap deterioration. Other
pertinent information such as temperature measurements, visual examinations, and
x-ray examinations will be used as required.

The second durability experiment will involve the use of a full-size truck
or bus. This experiment will be concerned primarily with the physical strength of
the trap as it is exposed to vibrational forces during public road operation. The
heavy-duty chassis dynamometer will be used to periodically determine the trap
efficiency and any effects the trap may have on the engine. As in the
aforementioned first durability experiment, Pertinent parameters will be monitored
while the vehicle is on the road and on the dynamometer.

As each durability experiment is being conducted, a controiled, burner-
assisted regeneration will be used to clean the trap. These controlled regenerations
will constitute a third durability experiment (i.e, resistance to multiple
regenerations). Review of data from each durability experiment probably will result
in suggestions to improve a particular aspect of the trap system. These

improvements will be implemented until a satisfactory, durable trap has been
achieved,

3. Task 3 - Trap Regeneration Techniques

This task will invoive experimenting with regeneration techniques that
could be applied to the trap system identified in Task 2. Depending on the
composition of the trap medium, certain regeneration techniques are more
appropriate than others. For example, use of electrical heat is much more
attractive for silicon carbide than for silica due to their differing thermal properties
(thermal diffusivity, thermal conductivity). The electrical heat can he applied

either directly through the silicon Carbide or indirectly via embedded heater
elements.


Ves SBS TS S44 275484 ~~ oo IE

OPF Materiel Cherecterisation Tests
vw 1.6) 102 - One Cylinder Poote
fare St Etderd Q1) SiC Foes - 80 pp! - 25 eam Thick
"9 Coforeil Standard DSF Element
tm-—* Duriron Foam eith Downsteeam Integral Membrane
Ge- Hi-Tech Foam
Hi-Tech Foee - Reduced Exhaust Ges Flow Rate

at/Clean )
ce) N @o

a

w ry

nN

Bock Pressure Ratio ¢ Actu

a

2.4

“O64 0.0 004 0.8 Ied T1670
Particulete Loading ( g )


~16-

backpressure like a conventional trap. The reason for this is
the low material density at 45 ppi. EPA advised Hi-Tech
Ceramics to configure the next samples in 80 to 100 ppi for
improved filtering. It is recognized, however, that the
increase in density will also require an increase in external
energy required to regenerate. Hi-Tech is currently retooling
for these design changes and should also be providing the more

optimized trap samples for EPA evaluation sometime later this
Fall.

c. Equipment Status and Other Material Suppliers

The EPA laboratory is currently functional for all aspects
of Diesel particulate control technology evaluation.
Particulate sampling and analysis systems have been repaired
and improved over the past year and test rigs have been and are
being fabricated to handle a wide variety of test material
configurations. The Mercedes 300D test vehicle has been kept
in proper maintenance and all other instrumentation is set up
and operational. Other material suppliers have been contacted
and may also be providing samples for EPA evaluation. Among
these companies are Brunswick Technetics, Camet, Nippon
Ceramics, Union Carbide, Norton Industrial Ceramics, Cheltenham
Induction Heating, and Mohawk Sintered Alloys, Inc.


-8-

Table 2

Electrical Properties of Heated
Hi-Tech Ceramics Silicon Carbide Foam

Initial Stabilized Heated
Voltage Voltage Current Power Resistance
Test Run (voits) (voits) (amps) (watts) (ohms )
1 21.8 17.7 20.5 363 0.86
2 25.5 20.4 28.7 585 0.71
3 26.5 22.8 38.0 866 0.60
4 28.3 24.4 48.0 1171 0.51
5 29.6 26.8 58.5 1568 0.46
6 18.0 -- 33.5 603 0.51
7 10.3 -- 28.5 465 0.54
8 15.0 -- 27.0 405 0.56
9 14.4 -- 24.5 353 0.58
10 12.0 -- 19.5 234 0.60

Contrary to the initial sample results, the current drift
did not increase with increasing temperature. Also, perhaps
because the sample was deformed as-received, further material
deterioration was observed with continued thermal cycling. The
material glowed orange-hot at current loadings above 30 amps,
but the glow was not uniform and tended to be concentrated
along the cracks in the material. Length-wise cracks developed
on the outer surface of the material, but the sample remained
intact as one piece. The cracking may also have been
exacerbated by the use of a rigid clamp to hold the heater
assembly together rather than a spring loading assembly which
would compensate for the different expansion rates of the
ceramic and metal components. The negative temperature
coefficient (NTC) characteristic of the material is seen by
comparing test 1 with test 10 in Table 2. After the material
had been heated in tests 1 through 9, the low power resistance

was 0.60 ohms compared to 0.86 ohms when the material was
“cold.”

A tubular cracked sample of the Hi-Tech SiC ceramic 45 ppi
foam was shipped to Ricardo for further evaluation. Although
fractured, a sample 75 x 50 x 25 mm was machined from the piece
and characterization tests were carried out.{13] Graphs of
backpressure rise versus loading rate for the Hi-Tech and other
samples, as tested by Ricardo, are contained in the Appendix.
The particulate loading tests showed a collection efficiency of
5-20 percent at the standard engine condition (medium speed and
load) used throughout the Ricardo characterization tests.
Tests at a lower engine speed to reduce the exhaust gas flow
rate through the sample resulted in collection efficiencies of
10 to 30 percent. Backpressure rise rate was insignificant
indicating that particulate was regularly being "blown off"


Tue proposed activity will truly expand our knowledge in particulate trapping and
regeneration by, applying past resuits to the development of a full size
trap/regeneration system. We cre now confident that we are in a better position to
deveiop a workable system that can benefit ail the participants.

Quite frankly, the level of effort to achieve total success is unknown because
the degree of required research is unknown. We do feel, however, that the effort
proposed will contribute significantly to the development of a particulate trap
system that incorporates the findings of our past consortium, and should result in a
prototype device. The more participants joining, the better the chances for success.
We encourage all past consortium participants to support our continued work, and
will actively seek new support.

As mentioned earlier, the target date for starting the project is June 1, 1988,
or earlier. In order for this date to be met, it is essential that we receive your
response to this addendum and associated contract by May 1, 1988, or earlier. By
otfering this additional follow-on study as an "addendum" to a current project, we
hope that your company's internal review process will be simplified. Taose potential
Participants who were not members of the original consortium will be sent the
original proposal and contract (08-2857) along with this addendum (08-2857A).

Please feel free to contact Mr. Bruce Bykowski regarding items of a technical
nature, or Ms. Sharon Rowe for business and contract items. We look forward to
your favorable review and early authorization.

Submitted by: . Approved by:
Bone Aybowsli— Ghat. Ber
Bruce 3. Bykowski Charles T. Hare
Manager, Advanced Technology Director
Department of Emissions Research Department of Emissions Research

ce: Robert Fanick


the higher amount of exhaust flow through the baffle plate
cools the burning filter down below soot ignition
temperatures. A baffle plate with smaller holes, which would
allow only 1 or 2 cfm maximum exhaust flow, may improve
regeneration. ._The basic Coloroll systom still exhibits
problems in not having adequate surface area to lower
regeneration frequency and in unknown durability of the
ceramic-to-metal interface even when intermediates such as
steel wool matting are used.

Cc. Sohio

Sohio Engineered Materials, Ine. (formerly Carborundum)
previously sent EPA several 2-inch thick 5.25-inch diameter
silicon carbide foam “doughnuts” (1.75-inch inside diameter)
for evaluation. These hollow cylinders were quite heavy, over
600 g each (0.95 g/cm?), and as such required too much energy
(over the 2.5 KW power Supply capacity) to heat to regeneration
temperatures. Three doughnuts were sandwiched together in our
test rig for initial EPA evaluation (see Figure 1), to get the
filtering Capacity that these Sohio doughnuts exhibited when
tested previously by Southwest Research Institute.[1l1] EPA was
at first more concerned with the resistance problems which were
anticipated with this design. It was believed that, even when
steel wool intermediates were used between doughnuts, it would
be better to have just one 6-inch thick doughnut to minimize
the number of material interfaces at two. However, in the
interest of also reducing energy requirements, EPA asked Sohio
to significantly increase the inside diameter such that outside
surface area is preserved but the filter mass is reduced. A
drawing of the filter material configuration requested is shown
in Figure 2. Sohio has yet to produce such a sample for EPA
evaluation but is still committed to doing so.

Figure 1

Proposed Sohio Diesel Trap Configuration

SOLD cemmc | |

INSULATORS —— SPRING LOADED

FILTER ASSEMILY

Low — — eansT

5
i

4

U el TRAP CONTAINER
+
SONIA S1LIcaN CARBIDE ————/ STAINLESS STEEL ELECTRICAL LEADS

"DOUGHNUTS"



-4-

burner-bypass system. This system shows promise toward
achieving 290,000-mile durability though only 100K mile
durability was simulated, and the system does not meet both
1991 particulate and NOx emission standards simultaneously. If
the 1991 NOx standard of 5.0 g/BHP-hr is met, the lowest
particulate emission rate achieved is roughly 0.3 g/BHP-hr,
i.e., 20 percent over the 1991 standard and 300 percent over
the 1994 standard. Among other heavy-duty efforts, Cummins is
currently evaluating a resistively heated trap aimed at meeting
the 1991 and 1994 particulate standards, a modified Coloroll
system, and have yet to report their experience with it.
Southwest Research Institute has also proposed an evaluation
(see Appendix) of a modified Sohio silicon carbide or other
high-temperature resistant trap as part of work to be performed
by the Consortium of Heavy-Duty Diesel Manufacturers.[9]

II. Technical Progress

The resistively heated trap material suppliers dealt with
can be sorted into two categories, those who have either sent
EPA material samples for evaluation or have done some
evaluation themselves, and those who have either not shared
with EPA the results of their development work or have not done
much development recently. The "haves" include Coloroll,
Sohio, Duriron, Hi~Tech Ceramics and Aker Industries, and the
“have nots" include NGK, Corning, Matsushita, most heavy-duty
manufacturers and others. Suppliers who plan either
development or evaluation in cooperation with EPA in the future
include Selee, Hi-Tech Ceramics and possibly Sohio, Camet and

Duriron. These latter programs will be discussed in the next
section.

A. Coloroll (Low Density)

A complete description of the first and second generation
Coloroll trap system evaluation is contained in reference [5].
Efficiency tests were run on the new Coloroll filters which are
two-thirds the weight of the original filters (i.e., more
porous). lLoad-up time is about the same since these filters
are still surface loaders (rather than bulk loaders) and more
soot passes through. Baseline 0.45 g/mi particulate was
reduced to 0.23 g/mi for an efficiency of roughly 50 percent.
Regenerations were performed efficiently with similar results
as the previous samples.(10]

B. Coloroll (Bypass Regeneration)

Tests were run with the original Fogarty can equipped with
a baffle plate and dividers to bypass exhaust flow through two
umpowered filters while the third (isolated) filter is
regenerated. No improvements in regeneration efficiency or
regeneration time were obtained. At low speed and idle, very
little heat is available to enhance the burn. At high speeds,
backpressure increases in spite of the regenerating filter, and


-17-

IV. References

se “Mobile Source Emission Summary," Office of Air and
Radiation, U.S. Environmental Protection Agency, March 15, 1987.
2. Automotive News, 1988 Market Data Book Issue, April

1988.
3. Developments in Diesel Particulate Control, SP-735,

Society of Automotive Engineers, International Congress and
Exposition, Detroit, MI, February 29-March 4, 1988.

4. “Fuel and Lubricant Effect on Durability of
Catalytic Trap Oxidizer (CTO) for Heavy-Duty Diesel Engines,"
Saito, Koichi, Yasuo Ikeda. and Shoichi Ichihara, Nippon
Shokubai Kagaku Kogyo Co., SAE Paper 880010, March 1984.

5. “Evaluation of a Resistively Heated Conductive
Ceramic Fiber Diesel Particulate Filter," Bruetsch, Robert I.,

EPA/AA/CTAB-87-04, U.S. Environmental Protection Agency, June
1987.

6. “An Exhaust Gas Aftertreatment System to Reduce
Particulates for Full-Size Passenger Cars," Lepperhoff, George,
Jan Widdershaven, and George Lutkemeyer, FEV Motorentechnik and
Ivan Hedin, Volvo Car Corp., SAE Paper 880003, March 1988.

7. “New Results of Passenger Car Diesel Engines
Pressure Ware Supercharged with and without a Particulate

Trap," Hiereth, Hermann and Gert Withalm, Daimler-Benz AG, SAE
Paper 880005, March 1988.

8. “Development of a Particulate Trap System for a
Heavy-Duty Diesel Engine," MacDonald, J. Scott and Gerald M.
Simon, General Motors Corp., SAE Paper 880006, March 1988.

9. “Addendum No. 1 to SwRI Proposal 08-2857A-:
Development of a High-Temperature Resistant Diesel Particulate
Trap," Bykowski, Bruce B. and Charles T. Hare, Southwest

Research Institute, San Antonio, TX, February 5, 1988.

10. "Status of In-House Electrically Regenerable Diesel

Trap Evaluation," Bruetsch, Robert I., EPA memo to Charles L.
Gray, Jr., June 15, 1988.

1l. Formulation Evaluation of Alternate Diesel
Particulate Trap Media," Bykowski, Bruce B., Southwest Research
Institute, San Antonio, TX, American Society of Mechanical

Engieners Paper No. 87-ICE-36, New York, NY, February 15-20,
1987.

12. “Technical Progress Report," Bown, Nick, Ricardo

Consulting Engineers, plc., EPA Contract No. 68-03-3519, August
8, 1988.


-7-

faces, i.e., oriented for maximum resistance. This level of
resistance was considered to be too low for practical
particulate trap-application (i.e., current requirements for a
given voltage are beyond the capacity of conventional power
supply sources), but hecause of the briefness and simplicity of
the tests, the resistance level measured may not accurately
reflect the inherent material characteristics.

D. Duriron

EPA's initial contact at Duriron retired and his
successors do not appear to be aggressively pursuing any major
development in resistively heating as yet. Initial evaluation
of their material showed a need for improved electrical
Properties. Duriron is currently supplying Ricardo with some
porous (nonconductive) cordierite samples that have solid
conductive silicon carbide coatings.

A sample of the Duriron non-conductive foam with integral
downstream membrane was tested. Resuits showed a particulate
collection efficiency in the region of 40 percent and a back
pressure rise rate between that of the standard Coloroll
element and the Sohio 80 ppi SiC foam. This collection
efficiency may be good for low ppi samples, but not so good for
high ppi samples. The Duriron material is believed to be low
ppi (e.g., about 50 ppi) but the effect of the membrane on
overall porosity and soot collection is unknown at this time.

E. Hi-Tech Ceramics

The Hi-Tech Ceramics material was initially evaluated in a
l-inch thick by 2-inch diameter sample. Their material was
subsequently evaluated for resistive heatability by clamping a
6-inch long sample between two 1/2-inch thick solid stainless
steel disc-shaped electrical leads, which are in turn
sandwiched between two solid ceramic insulators such that all
current is dissipated through the porous SiC sample. Current
and voltage were measured as power was supplied to the heater
assembly. Initially, the sample was_ weighted to determine
material density (equal to 0.285 g/cm3) which is roughly 20
percent less dense than the initial smaller sample.

The evaluation showed that this material displays a
negative temperature coefficient since resistance decreased
with increasing temperature. Exact filter temperature
measurements were not obtained due to lack of an optical
instrument which operates in the range of filter temperatures
experienced during thermal cycling of the sample. Resistance
approached 1.0 ohm at very low power settings and decreased to
roughly 0.5 ohms at power settings over 1500 watts (maximum
current loadings). Current applied to the heater did not
remain stable at a given setting and decreased 1 to 2 amps
before stabilizing. Voltage drifted down 20 to 25 percent from
the preset loading as did the initial sample. The electrical

properties observed through the thermal cycling of the material
are shown in Table 2.


SOUTHWEST RESEARCH INSTITUTE

POST OFFICE DRAWER 28810 © 6220 CULEBRA ROAD © SAN ANTONIO, TEXAS. USA 78284 © (512) 684-5111 © TELEX 244866

February 5, 19283

TO:
ATTN:

SUBJECT: Addendum No. | to SwRI Proposal 08-2857A-, "Development of a
High-Temperature Resistant Diesel Particulate Trap”

L BACKGROUND

This addendum to the subject proposal was prepared as a result of encouraging
experimental data and favorable responses from the consortium participants. The
initial project resulted in the acquisition of significant generic data pertaining to
the regeneration of trapped particulate. Using these data, several approaches to
improve current regeneration techniques, and suggest new ones, were identified.
One of the new approaches identified was to experiment with alternate trap media

intended to withstand the highly exothermic combustion of trapped diesel
particulate.

The alternate trap medium briefly experimented with was a silicon carbide
foam. This foam was evaluated using a heavy-duty diesel engine in a transient test
cell, Based on preliminary tests, trap efficiency was good and the resistance to
regeneration excellent. Several areas require further development. These areas
include trap design considerations, trap efficiency determinations, application of
regeneration techniques, and long-term durability. This addendum outlines a
proposed work effort to investigate the aforementioned areas.

Because of the successful approach of using multiclient sponsorship, this
addendum proposes to continue the previous consortium format. New participants
are able to join this work effort under the same conditions as new participants were
able to join the original consortium. Improvements in the overall management and

direction of the consortium will be implemented based on the suggestions received
from the current participants.

SAN ANTONIO, TEXAS
DALLAS, TEXAS @ DETROIT. MICHIGAN © HOUSTON, TEXAS @ WASHINGTON. OC



EPA/AA/CTAB/88-09

Interim Report: Deveiopment of Resistively
Heated Diesel Particulate Trap/Regeneration Systems

by

Robert I. Bruetsch

August 1988

NOTICE

Technical Reports do not necessarily represent final EPA
decisions or positions. They are intended to present technical
analysis of issues using data which are currently available.
The purpose in the release of such reports is to facilitate the
exchange of technical information and to inform the public of
technical developments which may form the basis for a final EPA
decision, position or regulatory action.

U. S. Environmental Protection Agency
Office of Air and Radiation
Office of Mobile Sources
Emission Control Technology Division
Control Technology and Applications Branch
2565 Plymouth Road
Ann Arbor, Michigan 48105


-10-

Figure 3

Aker Industries Diesel Trap Configuration

4 TURBO EXHAUST

EXHAUST 9 t -_ FLANGE
ANNULUS DM ’
MARMON : CERAMIC LINER
VEE CLAMP 4
SSS): CERAMIC
SG ee [SPACER RING
-- '
, SLECTRIE - - q
TERMINAL :
GLASS SEA. 3 S
WRAZED Cl av
CERAMK FELT
INSULATION EXMAUST
- ——— — mp>-PiPe
REMOVABLE
END PLATE
CERAMIC
CONNECTOR
STRAP LINER
GRouND
TERMINAL pi [~~ FLaNcE
CERAMIC SSS
SPACER YF eae eee
RINGS: eff sw ST oo
CERAMIC FELT
STEEL SHELL DUOCEL SILICON CARBIDE FILTER INSULATION

length of 8 inches. A 10mm diameter silicon carbide fiber was
used in the matted material. Tests were conducted on a
Mercedes-Benz 190D vehicle over 492 miles. An average trapping
efficiency of 91 percent was achieved and roughly 50g of
particulate was collected before each regeneration which was
carried out be placing the filter in a kiln and heating to
980°C (1800°F). Typically pressure drop across the filter
increased from 55 mbar for the cleaned condition to 90 mbar for
the loaded condition. The ratio of mass of particulate
collected at a given backpressure to the mass of the filter was
approximately 1.00 compared with only 0.10 for the Coloroll
material.

Aker Industries are currently working on manufacturing a
silicon carbide non-rigid fiber mat filter of pleated tubular
construction. The filter, 18 inches long, will have an inner
diameter of 5 inches with 1-1/2 inch deep pleats giving a
surface area enhancement factor of 5.2. The filter will be
corrugated in the axial direction and will be supported by
metal rings at various intervals along its length. It was
claimed that the pleated structure would minimize radiative


during the test period. This was readily apparent when a jet
of air directed at the loaded foam sample removed from the test
installation resulted in clouds of particulate dust being
emitted from the sample. Subsequent electrical tests on the
Hi-Tech sample using a typical 12-voit vehicle battery
indicated an electrical resistance of about 6 ohms resulting in
little resistive heating of the sample.

EPA now proposes to build a container for further
evaluation of the Hi-Tech Ceramics material as a Diesel
particle trap/regenerator. The proposed testing apparatus is
similar to the container shown in Figure 1. Testing shall
include determinations of filter efficiency, backpressure rates
and regeneration efficiency on the EPA's Mercedes 300D test
vehicle. If feasible, our Diesel evaluation contractor
(Ricardo) shall fabricate the proposed container and perform
initial evaluations prior to more detailed evaluation of the

final system configuration at the EPA Motor Vehicle Emission
Laboratory.

F, Aker Industries

Aker Industries had recently been formed to exploit
commercial markets for advanced ceramic materials. Dr. Benson,
the CEO, had previously been associated with Energy, Research

and Generation, Inc. (ERG) who supply predominantly defense
establishments with specialized materials.

ERG had been involved with particulate traps in the
mid-1980s and had supplied electrically regenerable silicon
carbide foam traps to various engine manufacturers for
evaluation. Their trap design, shown in Figure 3, included a
foam with a variable density so that electrical terminations
could be made by brazing metal contacts onto solid silicon
carbide.({14] This avoided differential thermal expansion
problems between the metal contact and ceramic, which was
another problem experienced in the previous evaluation of the
Coloroll trap, since the solid silicon carbide and the brazed
metal contact presented insignificant electrical resistance
compared to the main part of the silicon carbide element and
were thus not resistively heated. Tests with this trap design

showed that, with a 100 ppi foam about 40 mm thick, particulate
collection efficiencies were only 30-35 percent.

i

Following this work a non-rigid pleated fiber mat filter
design was developed. A tubular construction was used with an
outside diameter of 6 inches, a 0.02-inch wall thickness and a


-6-

Figure 2

Sohio Resistive Diese! Particulate Filter Element

OPERATING RESISTANCE = 0.3 - 0.5 ohms

5.25"

ee

Particulate collection efficiency and loading tests have
been carried out on the Sohio silicon carbide foam samples.
Silicon carbide foam samples with filter porosities of 45, 60,
80 pores per linear inch (ppi) have been received from Sohio at

Ricardo Consulting Engineers, ple., EPA's Diesel trap
evaluation contractor.

The Sohio silicon carbide foam examples exhibit a
relatively poor maximum collection efficiency of 30 percent,
with the larger pore-sized samples showing signs of particulate
“blow off." Thermogravimetric analysis of the particulate
samples shows that the Sohio Diesel particulate filter element

does not affect the makeup of the filtered particulate carbon
content.[12]

Tests using a typical vehicle 12-volt battery and the
2-inch x 3-inch x 1l-inch Sohio 80 ppi silicon carbide foam
sample shows that a material surface temperature rise of 135°C
(275°F) can be achieved in about 10 seconds. Wire wool and
thin (about 10mm) stainless steel plates were used to make the
electrical terminations. Current measurement was attempted but
the levels involved exceeded the full-scale range of 75 A of
the meter. Further tests using a partially discharged 6-volt
vehicle battery had allowed current measurements to be made and
the electrical resistance of the sample to be determined as
9.055 ohms with electrical contacts on the 2-inch x 1l-inch


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The application of Catalysts and the use of fuel additives will be
investigated to Gxamine their benefits in reducing the temperature requirement for.
regeneration. Adaptation of State-of-the-art burner systems will be performed oniy
if the. consortium Participants request this approach. We feel that the sole
development of a burner system would be redundant with on-going research by
others, but we would research a particular aspect of an available burner system if
its adaptation to our alternate trap system would be beneficial.

The effectiveness and durability of the regeneration technique will be
investigated by designing an experimental test plan to perform repetitive
regeneration cycies on a trap system. These experiments will be performed on an
engine in a transient test cell, During this evaluation phase, improvements in the
regeneration technique will be made until an acceptable approach to regenerate the
trap has been identified. Ag Part of the regeneration technique development, the
controls and sensors required to initiate the regeneration will be identified. These
Sensors and controls include, where applicable, engine backpressure, various
temperatures, bypass valve, etc,

4. Trap/Regeneraticn System Demonstration

After successful completion of Tasks 1 through 3, it is Proposed that a
high-visibility demonstration on a full size truck or bus be a part of this project.
The complete trap/regeneration System will be installed on a selected vehicle and
placed in service. The Purpose of this task is to publically show the successful
development of a Particulate trap System as a result of cooperative research.

OL REPORTS AND REPORTING

Detailed progress reports will be forwarded to each participant in three copies
at the end of each two months. 3 final engineering technical report in five copies
will be prepared and submitted to each Participant within 45 days after the
experimental portion of the Project is complete. This report will include discussion
of the various design considerations as well as summarized data and findings. All
reports and data obtained under this Project are considered proprietary to the
Participants and will be disclosed only to the participants. The EPA wil be kept

abreast of the Project, but will not be given any detailed data uniess the participants
instruct SwRI to do so.

Tt is planned that a one-day project seminar be held in April 1989, and another
one near the end of the Project at Southwest Research Institute. The dates of the
seminars, to review Progress and status of the Project, will be finalized after the
consortium has been formed. The Advisory Group pilus up to two additional
Participants from each member company could attend these seminars, along with
representatives from the EPA and ARB (Air Resources Board), if approved by the

IV. TIME AND Cost ESTIMATES

The minimum level of effort Proposed for this project is $450,000 on a cost
reimbursement basis. The exploratory nature of the specific experiments and the
required flexibility to redirect the technical effort, ii necessary, make a cost
reimbursement contract aDpropriate, In order to begin this program, ten


-2-

Table 1

New Vehicle and Engine Emission Standards

LDV (gpm) LDT (gpm) HD (g/BHP-hr)
HC NOx Part. HC NOx Part. HC NOx Part.
1988-9 0.41 1.0 0.2 0.8 #1.2/1.7(1] 0.26[{2) 1.3 10.7 0.6
1990 0.41 1.0 0.2 0.8 1.2/1.7 0.26 1.3 6.0 0.6
1991-3 0.41 1.0 0.2 0.8 1.2/1.7 0.26 1.3 5.0(3] 0.25(3]/
0.20(4)
1994+ 0.41 1.0 0.2 0.8 1.2/1.7 0.26 1.3 5.0 0.10(S)
(1] Vehicles over 6,000 lbs GVW remain at 2.3 gpm NOx until 1990. Standards of

(2)

(3)

(4)

(s}

1.2 gpm apply to LDTs up to and including 3,750 lbs. loaded weight; 1.7 gpm
standard applies to LDTs equal to and over 3,751 lbs. loaded vehicle
weight. Emissions averaging may be used to meet this standard provided
that trucks produced for sale in California or designated high-altitude
areas may be averaged only within each of those area. Diesel and gasoline-
fueled engine families may not be averaged together.

Emissions averaging may be used to meet this standard provided that trucks
produced for sale in California or designated high-altitude areas may be
averaged only within each of those areas.

Emissions averaging may be used to meet this standard, but these emissions
may not be averaged with HD gasoline engine emissions. Averaging is
restricted to within useful life subclasses (see below). Also, averaging
is restricted regionally--the two regions are California and the other 49
states.

For urban bus engines, the standard is 0.10 g/BHP-hr--particulate averaging
is not allowed with this standard, but emissions from these engines may be
used in NOx averaging.

Emissions averaging may be used to meet this standard. However, averaging
is restricted to within useful life subclasses (see below). Also,
averaging is restricted regionally--the two regions are California and the
other 49 States. Emissions from engines used in urban buses may not be
included in the averaging program.

Full useful life is established for 1985 and later defined as:
Light heavy-duty (under 19,500 lbs. GVWR) = 8 yrs/110,000 miles
Medium heavy-duty (19,500-33,000 lbs. GVWR) = 8 yrs/185,000 miles
Heavy heavy-duty (over 33,000 lbs. GVWR) = 8yrs/290,000 miles


-13-

Corning reported that a typical burner used in these
applications, a Webasto, cost around $5,000 each. It was
Corning's opinion that in a bypass system, two filters would be
needed since raw exhaust would not want to be allowed to bypass
straight to the atmosphere. It was mentioned that development
work was still continuing with the Mercedes-Benz 300 TD filter.

Corning claimed that sufficient studies have been
performed developing regeneration strategies such that
durability problems with Corning WFMs have been overcome. It
was reported that a 15-inch diameter by 15-inch long unit
supplied by Corning has completed 4,000 hours of operation with
no problems. Corning also added that they had had no vehicle
recall claims on three-way catalyst substrates since 1975.

Corning was asked whether any of their current programs
involved the development of electrically regenerable Diesel
particulate filters (DPFs) using electrically conductive
ceramic filter materials. Corning reported that they had
worked with Sohio 10 years ago and had successfully extruded a
silicon carbide WFM; however, sufficient porosity for DPF
applications had not been achieved. There were also thermal
shock resistance concerns with this type of DPF. It was
reported that Corning had discussed the possible application of
a silicon carbide WFM DPF with Ontario Research during the
Proposal stage of the current EPA/Ricardo contract. Corning
also reported that they had made some new developments with
electrically conductive materials which may be of interest for
DPF applications, but would not discuss these until outstanding
patent issues had been resolved, probably later this year.

III. Future Work
A. Selee

John Howitt (formerly of Corning) visited EPA in May 1988
and is fabricating samples of reticulated foam which he claims
can be,. but may not need to be, resistively heated.[15] Selee
will soon be delivering samples of these foams for EPA
evaluation. A picture of the trap configuration initially
envisioned is shown in Figure 5. This trap configuration is in
a “top-hat“ shape such that all particulate must flow through
an enhanced surface area axially and escape through the sides
and outlet end both radially and axially.

Selee has since decided to change this configuration to
the one shown in Figure 6 for ease in fabrication. EPA is
currently fabricating the container shown in Figure 6 to be


-15-

Figure 6

PROPOSED DIESEL TRAP EVALUATION CONTAINER
SS EELLTRAP EVALUATION CONTAINER

EXHAUST FLOW

SPRING ASSEMBLY
WITH SET SCREWS
T
|__SOLID CERAMIC
Ts INSULATING Disc
LLL LLL
q \
P— 5.0" (12.7 cm) —soy
9.0" (22.9 8
. +9 cm) 4 ELECTRICAL TERMINALS
pe
fe
a
/ 1/8" (0.3 cm)
F 7
t a ZA.
bd / ] [— a =
HI-TECH DIESEL TRAP SUBSTRATE SOLID CERAMIC INSULATING RING
cq LS

fee 6.5 (16.5 cn) ——-|


I. Technical Approach and Current Industry Efforts

New vehicle and engine emission standards for future model
years have stimulated the devolopment of advanced control
systems for Diesel particulate emissions from light and heavy
duty Diesel vehicles.(1] The standards which new Diesel

vehicle and engine manufacturers are now challenged to meet are
listed in Table 1.

In past years, development has dealt largely with an
aftertreatment control technology commonly known as the “trap
oxidizer" or the “catalyzed trap oxidizer" (CTO). The common
CTO is a means of trapping or filtering the particulate matter
in Diesel vehicle exhaust and eliminating it in place by
thermal oxidation, commonly referred to as regeneration. These
devices first appeared four years ago on one passenger vehicle
model in the United States. Although production of CTOs is
presently suspended, there are approximately 30,000 trap
oxidizer-controlled Diesel vehicles in customer use. [2]

Heavy-duty trap system development programs are in
progress throughout the world sponsored by almost every Diesel
vehicle and engine manufacturer. Many of these programs are
targeted to meet 1991 and 1994 truck and bus standards, while
others are aimed at retrofit system development for buses and
some off-highway vehicles. Some heavy-duty manufacturers will
conform to the 1991 heavy-duty truck standards without traps,
especially if the sulfur content in Diesel fuel is reduced.
However, trap oxidizers may be used in limited instances in
1991. While almost every manufacturer has a trap development
program, they are also focusing a share of their efforts on
engine modifications, advanced turbocharging and even flow
through catalytic converters.(3]

Durability and packaging problems led to the suspension of
the only production trap systems this past model year. As
such, alternative control systems and improved trap oxidizer
systems are needed for Diesels to meet the current light-duty
and future heavy-duty particulate emission standards. Problems
with the developing traps, which are generally either wallflow
or porous foam ceramic substrates, include inadequate surface
area, quick backpressure buildup and/or nonuniform soot
distribution and regeneration. Proper catalytic coating can
alleviate the regeneration and surface area problems to some

extent, but trapped ashes from lubricating oil can decrease
catalytic activity drastically. [4]


IL STATEMENT OF WORK

This section describes the objectives, approach, aad scope of work proposed.
The scope of work will remain flexible because of the exploratory research nature of
the project.

A. Objective

The primary objective of this addendum will be to design and evaluate a high-
temperature resistant diesei Particulate trap. To meet this primary objective,
several tasks are required, each with its own objective. During the first part of the
Past consortium, the objective was to obtain generic data to better understand
regeneration. This addendum’s activity will be more Specific to hardware design and
development of an actual system.

B. Approach

The approach to meet the Primary objective will include some analytical work,
but principally experimental efforts. Results and conclusions from the past
Consortium activity will be used to assist in the experimental test plan design. For
example, the character of Particulate produced from different engines will be

made to represent the different characters of particulate. The first material that
will be used will be a silicon carbide foam. If the results using the silicon carbide do

not warrant continued development, other alternate materials will be identified and
evaluated.

C. Scope of Work

Southwest Research Institute Department of Emissions Research proposes to
perform the following items of work to meet the principal objective. Because of the
exploratory nature of this Program, detailed test plans will be Prepared as required
for each area of need. Several plans of performance covering specific time periods
will be prepared and submitted during the course of the project.

1.) Task 1 - Trap Design, Engine Selection, and Baseline Tests

The initial design of the silicon carbide foam trap briefly evaluated in
the past consortium’s activity comsisted of an assembly of silicon carbide
"doughnuts." The number of "doughnuts" and the design of the trap container were
selected arbitrarily. After additional engine evaluations, improvements in the trap
container design will be made. The objectives of this phase of the project will be to

be performed on a engine that emits low organic soluble particulate. The
evaluations will be concerned primarily with trap efficiency, trap capacity,
backpressure effects, and effects on engine operation and emissions. The effect of
trap location in the exhaust, as well as engine transient cycle effects, also ‘will be

Several of the tests used to address the aforementioned trap parameters
will be repeated on two additional engines. The first of these additional engines will


Il.

III.

Iv.

Table of Contents

Technical Approach and Current Industry

Techical Progress

A. Coloroll (Low Density)

B. Coloroll (Bypass Regeneration)
Cc. Sohio

D. Duriron

E. Hi-Tech Ceramics

F, Aker Industries

G. NGK

H. Corning ..., . .

Future Work... . ,
A. Selee
B. Hi-Tech Ceramics

Cc. Other Material Suppliers

References

Appendix .....,

Efforts

Page
Number

1l
12
13
13
14
16

17

» A-21l


we

participants, each funding $15,000 a year for two years, are required. Additional
participants will result in an increase in the level of effort at project initiation. The
cost estimate asgumes that engines will be supplied at no charge by the participants
to serve as a particulate generators. All labor, fuels. traps. and auy incidental
expenses are inciuded in the proposed levei of effort. Attached is a copy of the
contract addendum for your review and approval. It is essential that the contract be
approved as is unless there is a substantial problem. In this way, all participants will
have a common agreement with SwRI in the shortest possible time.

The project will require about 24 months to complete, exclusive of the final
report. This estimate is based on obtaining the necessary engine and traps from the
suppliers rapidly. The first 12 to 14 months are allocated to Task 1 - Trap Design,
Engine Selection and Baseline Tests, and Task 2 - Trap Durability. The remainder of
the project (10 to 12 months) will be devoted to Task 3 - Regeneration Techniques,
and one month for Task 4 - Trap/Regeneration System Demonstration. Target date
for project initiation is about June 1, 1988. The project can begin earlier, if
approved before that date.

Vv. PROJECT MANAGEMENT

Article XII of the Consortium Agreement defines the Advisory Committee as
one person from each participating organization and one person from SwRI. The
defined purpose of this committee is to provide liaison, review, and
recommendations related to the project.

One of the first requirements of the Advisory Committee will be to approve
engine selections and assist in their supply to SwRI. If no agreement can be reached
easily on engine selection, SwRI will make such decision and seek to acquire the
engine.

Early in the project, a detailed draft plan of performance will be prepared and
mailed to the Advisory Committee. The Advisory Committee will be asked to
respond quickly with comments, suggestions and recommendations on the plan.
SwRI will attempt to incorporate as much of the input from the Advisory
Committee as possible within time and budget constraints, thereby finalizing the
plan. It is anticipated that due to the wide scope of interests by the participants,
not all ideas for research will be accommodated. In this case, modifications to the
test plan will be at the discretion of SwRI. Final decisions on researca will be the
authority and responsibility of SwRL

The Emissions Researca Department of SwRI will ve in charge of this project,
and the project manager will be Bruce Bykowski. The project leader will be Robert
Fanick. Others lending support to this project will be Charies Hare, Director of the
Emissions Research Department, and Terry Ullman, Senior Research Eagineer.
Several other Institute staff members from other divisions will be used as
consultants in the area of ceramics and electronic controls.

VL SUMMARY
It has been a pleasure to prepare this addendum to the SwRI research activity

pertaining to particulate traps. We have attempted to address the important points
requested by our past consortium members in the preparation of the follow-on study.


-ll-

heat loss during regeneration as heat would mainiy be radiated
from one pleat to another. In addition, Aker Industries
explained that a non-rigid fiber mat construction would not
catastrophically fail by cracking as is the case in a foam
structure which behaves es a monolith in its failure mechcnisms.

Electrical terminations will be similar to those used for
the foam design. Ricardo currently lacks enough EPA contract
funding for purchasing additional material samples for
materials characterization tests. Aker Industries stated that
it would be manufacturing filters for clients later this year

and that it may be possible to supply Ricardo with some sort of
free sample at that time.

Aker Industries described the manufacturing process they
employed for making silicon carbide. A textile precursor is
used to manufacture a vitreous carbon copy which is then
infused with silicon to make a 100 percent dense slightly
silicon rich of stoichiometric beta form of silicon carbide.
This results in a material with a fine grain size giving it
improved durability and a positive electrical resistance
temperature coefficient. By making the fibers 100 percent
dense, oxidation of the material under high temperatures is
reduced to surface oxidation only. Aker Industries noted that
for durability, the temperature of the material during use
should be maintained below 1200°C (2200°F) and that contact
with vanadium and alkali metals should be avoided as these
metals react with the silicon carbide by ion exchange. Aker
also claims that their manufacturing process is much less
costly than the Coloroll process, which utilizes expensive raw
materials. Aker Industries explained that it also has
expertise in manufacturing alumina, silicon-nitride, and
mullite. It has been agreed that Ricardo will keep in contact
with Aker Industries to monitor developments.

G. NGK

Representatives of NGK-Locke, Inc. met with EPA last
February and discussed the possibility of working together on a
cooperative trap development and evaluation program. NGK has
considerable experience in developing wallflow cordierite
honeycomb trap material but has never resistively heated

conductive ceramics. Their cordierite traps have been
evaluated in the EPA laboratory in the past with wire
‘face-heaters. NGK is also capable of producing variable

porosity traps to improve uniformity of soot loading and
regeneration. NGK indicated at this meeting that they had some
experience working with silicon-carbide and other conductive

ceramics, but that they had not as yet produced a trap made of
these materials.


-14-

Figure 5

Proposed Selee Diesel Trap
Evaluation Configuration

QUAUST Flow

S€LEE “Top-nar”
SUBSTRATE CONFIGURATION

used for not only the Selee material, but for other material
configurations as well. It is designed to be easily adaptable
to other trap material configurations that EPA may be
evaluating in the near future. The Selee material is currently
being fabricated in their Switzerland plant and should be
shipped to EPA for evaluation sometime this Fall. Selee is
also attempting to Produce materials which are proprietarily
catalyst coated and made from silicon carbide and other
conductive ceramics in case the initial samples do not show the
filtering or regeneration Characteristics Selee anticipates.

B. Hi-Tech Ceramics
aiztech Ceramics

As mentioned in the Previous section, Hi-Tech Ceramics has
Provided some initial unoptimized samples, EPA has performed
Some preliminary evaluation of this material and it has been
found to be resistively heatable. Ricardo also performed some
filtering efficiency (backpressure buildup) tests on these
samples and have determined that the loading characteristics of
the material are inadequate. In fact, the particulate blows

through the substrate rather than adhering to it and increasing