EPA-AA-LDTP 78-14
Technical Report
November, 1978
Particulate Measurement - Dilution Tunnel Stablization
by
Eugene Danielson
NOTICE
Technical reports do not necessarily represent final EPA decisions
or positions. They are intended to present technical analysis of
isues using data vhich 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.
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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Summary
Particulate testing was conducted to determine the number of
hot-start UDDS (LA-4) cycles that must be driven to stabilize a
clean 18-inch diameter dilution tunnel. The results of this
investigation indicate that valid particulate measurments can be
obtained with a clean dilution tunnel; i.e., essentially no LA-4
cycles are required to stabilize the dilution tunnel with respect
to particulate material. This conclusion is based on the obser-
vation that slightly higher than average particulate levels (taken
with stabilized tunnel) were measured during the first (actually
first two) LA-4 test after tunnel cleaning. If particulate mater-
ial is being lost to the dilution tunnel walls it is minimal and
not significant compared to normal test variability.
Test Procedure
This test program was designed to quantify the number of hot-start
UDDS cycles required to stabilize a clean 18-inch dilution tunnel
with respect to particulate material. A 1975 EPA owned Mercedes
300 D was selected for this evaluation primarily because: (1) this
vehicle had a well established UDDS baseline (standard deviation of
+ 5.1 %) from which particulate stabiliation could be measured; and
T2) its level of particulate production is representative of the
majority of light-duty diesel vehicles currently being manufac-
tured.
«! -.-•
Initial preparation of the study required that the dilution tunnel
be cleaned. This was accomplished by disassembling the tunnel and
washing each section. After cleaning and reassembling the tunnel,
particulate measurements began.
The procedure used to measure the particulate emissions was similar
to the procedure specified in the "Draft Recommended Practice for
Measurement of Gaseous and Particulate Emissions from Light-Duty
Diesel Vehicles" March 1978. Therefore, only highlights of this
procedure will be indicated.
Particulate measurements were made by isokinetically removing a
sample of dilute exhaust from the 18-inch diameter dilution tunnel,
and then passing the sample flow through a 47 mm fluorocarbon
coated glass fiber filter. The weight of particulate material
collected is considered to be the net weight difference between the
clean filter (stabilized with respect to humidity) and the loaded
filter (also stabilized).
Discussion of Results
The attached graph, Figure 1, presents the individual UDDS particu-
late measurement results of this study (presented in the. order
taken) along with a summary of the baseline level of particulate
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emissions (measured with a stabilized tunnel). Theoretically,
if substantial tunnel deposition were taking place during the
stabilization process, each successive particulate measurement
taken after tunnel cleaning would be slightly higher than the
previous measurement, with the limiting value being equal to
the stabilized tunnel average. However, a comparison of the
individual data points to the previously established hot-start UDDS
particulate baseline indicates that the level of measured particu-
late material for the first hot-start test was slightly.higher than
the baseline. Further testing did not indicate any trend toward
substantial increases in measured particulates.
Although the average particulate level from the seven tests per-
formed after the tunnel was cleaned was 4.8 percent higher than the
previous baseline, the increased level was within the normal test
variation experienced with this vehicle. No significant difference
in measured hydrocarbon was observed after the tunnel was cleaned.
It is concluded from these data that no preconditioning is neces-
sary to stabilize the dilution tunnel with respect to particulate
material. Hence, as stated in the Summary, it is also concluded
that the amount of particulate material lost to dilution tunnel
walls is very small (i.e., within measurement capabilities), and
therefore valid particulate measurements can be made with a clean
dilution tunnel.
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Figure 1 - Dilution Tunnel Stabilization
18-Inch Tunnel
CVS.Flow Rate 535 SCFM
Mercedes 300D, 4000 #
0.5
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^ — JL V^*1^ iSr T
. If ^^"
Stabilized tunnel baseline + 5.1% standard deviation *^"^
m
A Data collected after cleanlnjj the dilution tunnel.
Points are graphed in the order measured. Ave of
7 points = 0.44 gm/mile. Standard deviation =
4.7%.
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0 123 45 67
Test Number
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