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
^*>^ ^^ ^^r"^
^ — 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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