LDTP 78-04
Technical Report
Diesel Hydrocarbon Measurement - Series Filter Test
by
Eugene Danielson
March 1978
NOTICE
Technical reports do not necessarily represent the final EPA
decision on regulatory issues. The are intended to present a
technical analysis of an issue and recommendations resulting
from the assumptions and constraints of that analysis. Agency
policy considerations or data received subsequent to the date
of release of this report may alter the recommendations reached.
Readers are cautioned to seek the latest analysis from EPA before
using the information contained herein.
Standards Development and Support Branch
Emission Control Technology Division
Office of Mobile Source Air Pollution Control
Office of Air and Waste Management
U.S. Environmental Protection Agency
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Filters were loaded by driving various cycles (FTP, LA-A and 50 mph SS)
and collecting the particulate material. Wet filters are those on which
particulate was collected and no drying steps were taken. Dry filters
were prepared by baking wet filters at 380°F for one hour.
Two different particulate collection systems were used for loading the
second filter. One was an isokinetic particulate collection device.
designed to collect a large volume of diesel exhaust, and is called a
high volume sampler. The other was the existing Scott filter holder and
heated probe set-up which is used to sample exhaust from the dilution
tunnel.
Results
The graphs attached are reduced reproductions of representative heated
FID traces taken during this testing. Presented on these graphs arc the
level of hydrocarbon in the exhaust passing straight to the heated FID
(dashed line) and the level of hydrocarbon in the exhaust after passing
through the "loaded" filter (solid line). Both are graphed as a func-
tion of time.
The data displayed in Figures 2, 3, and 4 were collected using wet
(unbaked) filters in the second filter holder while Figures 5, 6, and 7
used dry filters in the second holder. The dry filters removed somewhat
more hydrocarbon than wet filters, as might be expected due to a lower
lever-of saturation. No meaningful differences are evident due to the
other variables involved such as driving cycle, probe temperature, and
the holder used to preload the second filter.
From these graphs the following additional observations can be made:
1. The level of hydrocarbon concentration remaining in the exhaust
sample after it passed through the loaded filter (solid line) is
definitely lower than the concentration level in the once filtered
exhaust sample (dashed line). .
2. Hydrocarbons in the exhaust were removed by all combinations of
hot and cold probe, and wet and dry filters.
3. In most cases the particulate indicated a trend toward satura-
tion. However, the particulate remained unsaturated after seven to
ten minutes of exposure to the hydrocarbons (i.e., the filtered HC
concentration never reached the once filtered level of HC). This
is probably due to insufficient time for the gaseous hydrocarbon to
saturate the carbon on the filter at the low concentrations and
flows involved.
These observations form the basis for concluding that carbonaceous
diesel particulate is capable of removing hydrocarbons from a diluted
exhaust sample, and that some or all of the hydrocarbon material exists
in a gaseous form in the tunnel as well as the atmosphere.
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Summary
The intent of the current light-duty diesel hydrocarbon certification
test procedure is to measure total hydrocarbon emissions. Arguments
have been put forth that this intent may not be correct for diesel
hydrocarbon measurements because some of; the heavier hydrocarbons may
appear in the atmosphere as diesel particulate and may be non-reactive
in the atmosphere. Testing has been conducted to determine whether or
not the carbonaceous particulate material collected on diesel exhaust
filters absorbs hydrocarbon material at ambient ("cold") temperatures.
The preliminary results of this testing indicate that the carbonaceous
diesel particulate is capable of removing hydrocarbon from a diluted
exhaust stream sample. The implication of this testing is that some or
all of the hydrocarbon material collected on an unheated filter may
exist in the gaseous rather than the aerosol state in the tunnel as vrell
as in the atmosphere.
Discussion
The current test procedure specifies that light-duty diesel hydrocarbons
are to be measured at a temperature range of 300° to 390°F by the heated
FID system. However, some hydrocarbons measured by this system may not
contribute to the formation of atmospheric photochemical oxidant (i.e.
may be non-reactive). This statement is based on the presumption that
the higher molecular weight hydrocarbons in diesel exhaust would be
particulate material if they were not heated to the temperatures speci-
.fied. Therefore, one of the basic questions that must be answered is
whether or not the carbonaceous material collected on an exhaust filter
has the capability of absorbing hydrocarbon material in a diluted
(i.e., "cold") exhaust stream sample.
Testing has been conducted with the EPA Mercedes 300 D diesel automobile
in order to help answer this basic question. The results of this testing
indicate that the particulate material collected on a diesel exhaust
filter does absorb hydrocarbon material. This in turn implies that at
least part or possibly all of the hydrocarbon material in the dilution
tunnel, and hence in the atmosphere as well, is in a.gaseous state
rather than an aerosol state.
Test Procedure
Two filters were installed in series immediately downstream of the
dilution tunnel sample probe. The sample lines were configured so that
the second filter, which was loaded with diesel particulate from a
previous run, could be quickly switched in and out of the diluted sample
stream. (See Figure 1 attached.) Response of the hydrocarbon to the
loaded filter was measured by direct hot FID reading while the vehicle
was operated in a 50 mph steady state cruise mode. Two series of tests
were conducted; one with the first filter and probe both operated hot
(380°F) and the other with the first filter and probe cold (^ 100°F).
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It should be noted that the exhaust sample was passed through a clean
filter in order to establish that it was in fact the particulate, and
not the filter that was removing hydrocarbon from the exhaust sample.
The clean filtered exhaust gave the same heated FID response as the un-
filtered exhaust. Hence the conclusion v/as that the. carbon particulate
was removing the hydrocarbon from the diluted exhaust.
It should also be noted that the base or once filtered levels are not
constant from test to test. This is considered to be due primarily to
the background hydrocarbon level varying from test to test. However,
this does not affect the conclusion of this testing because they are
based on differences between the once filtered hydrocarbon level and the
twice filtered hydrocarbon level.
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FIGURE 1
SERIES FILTER TEST SET-UP
HF.ID
Second
Filter
First
Filter
Valve
Exhaust
Probe
Exhaust
Dilution Tunnel
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FIGURE 2
Series Filter Test Results
EPA Mercedes (300 D)
50 MPH Cruise u
Second Filter and Probe Data
Loading cycle: FTP
Filter source: Scott & filter holder
Filter condition: Wet (unbaked)
Probe: Cold (unheated)
Test date: 9/21/77
"u
XI-
UJQ
-i
x"1
o
Time - Seconds
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FIGURE 3
Series Filter Test Results
EPA Mercedes (300 D)
.50 MPH Cruise
Second Filter and Probe Data
Loading cycle: FTP
Filter source: High volume sampler
Filter condition: Wet (unbaked)
Probe: Hot
Test date: 9/26/77
prop
HC Concentration
Time - Seconds
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FIGURE A
Series Filter Test Results
EPA Mercedes (300 D)
50 MPH Cruise
Second Filter and Probe Data
Loading cycle: Hot LA-4
Filter source: High volume sampler
Filter condition: Wet (unbaked)
Probe: Hot
Test date: 9/26/77
Once Filtered Level
u:«
r~ '^'
5 5
E-5
So
°z
o
(yOO
Time - Seconds
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FIGURE 5
Series Filter Test Results
.'... EPA Mercedes (300 D)
'K 50 MPH Cruise
Second Filter and Probe Data
Loading cycle: FTP
Filter source: Scott & filter holder
.Filter condition: Dry (baked at 380°F Ihr)
;Probe: Cold (unheated)
Test date: 9/21/77
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FIGURE 6
Series Filter Test Results
EPA Mercedes (300 D)
50 MPH Cruise i :
'. Second Filter and Probe Data
Loading cycle: 50 mph cruise
\Filter source: High volume sampler
-Filter condition: Dry (baked at 380°F
.Probe: Cold (unheated)
;Test date: 9/71/77 . ...,
Ihr)
(o
5
u
oS
x
o
Time - Seconds
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FIGURE 7
Second Filter and Probe Data
Loading cycle: 50 mph cruise
Filter source: High volume sampler
Filter condition: Dry (baked at 380°F
Probe: hot Test date; 9/16/7?
Series Filter Test Results
EPA Mercedes (300 D) <
50 MPH Cruise
lift
Ihr)
Time - Seconds
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