EPA-AA-SDSB-79-15
Technical Report
March, 1979
Particulate Measurement - Evaluation of the Equivalency
of the Three-Bag and Four-Bag
LA-4 Dynamometer Test Procedures
by
Eugene Danielson
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, positon or regulatory action.
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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Abstract
An evaluation of the equivalency of particulate measurements taken
with the three-filter/coId-start/simulated hot-start (3-bag) dynamometer
procedure and measurements taken with the two-filter/cold-start/hot-
start (4-bag) dynamometer procedure has been completed. Two different
light-duty diesel vehicles were used in this evaluation. Data from each
of these vehicles indicate that the corrected mass of total suspended
particulate material with either of the procedures are equal.
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Introduction
Substantial concern was generated over the dynamometer procedure
specified for particulate emissions in the "Draft Recommended Practice
for Measurement of Gaseous and Particulate Emissions from Light-Duty
Diesel Vehicles," issued in March, 1978. This document specified that
a 4-bag LA-4 based driving cycle must be used for particulate measure-
ments instead of the 3-bag LA-4 based driving cycle used for gaseous
emissions measurements. The concern centered around the fact that this
4-bag procedure could be potentially costly not only because of the
extra dynamometer time required, but also because it would require
substantial computer reprogramming.
The exact procedure specified for particulate measurements con-
sisted of a cold-start drive over the LA-4 cycle (first two bags)
followed by a complete hot-start drive over the LA-4 cycle (second two
bags). A single proportional particulate filter sample was taken during
each LA-4 cycle so that the cold/hot FTP weighted particulate mass could
be determined. This dynamometer procedure is referred to as the 2-
filter/4-bag procedure, and is different from the common 3-bag dynamo-
meter procedure used for gaseous emissions measurements in which the
hot-start is simulated; i.e., the hot-start terminates after the first
505 seconds of the second LA-4 cycle (bag 3) because gaseous measure-
ments that would have been taken during the remainder of the hot cycle
(bag 4) are assumed to be identical to those taken during the same
remaining period of the cold-start cycle (bag 2). A similar assumption
for particulate emissions could not be made at the time the Recommended
Practice was issued, and hence, the 2-filter/4-bag procedure was specified.
However, as noted previously, the 2-filter/4-bag procedure could be
potentially costly, and therefore, it is desirable to sample particulates
during a 3-bag FTP test. This 3-bag test would also have to be a three
filter test (one for each bag) in order to properly weight each part of
the cycle. This procedure is referred to as the 3-filter/3-bag proce-
dure, and could only be used for diesel particulates if shown to be
equivalent to the 2-filter/4-bag test.
Objective of Experiment
This study was conducted in order to evaluate the equivalency
between the 2-filter/4-bag dynamometer procedure and the 3-filter/3-bag
dynamometer procedure for light-duty diesel particulates.
Test Procedure
A specific particulate collection procedure was followed for
determining the FTP weighted particulate mass for each dynamometer
procedure. For the 2-filter/4-bag test, the sequence specified in the
"Draft Recommended Practice for Measurement of Gaseous and Particulate
Emissions from Light-Duty Diesel Vehicles" dated March, 1978, was fol-
lowed. The important concepts of this procedure are diagrammed in
Figure 1 below.
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Figure 1
2-Filter/4-Bag Particulate Procedure
Cold Start
Filter No. 1
tBag 1 >L Bag 2 ^
^505 sec.'P 871 sec. ^
Weight Factor = 0.43
10 min.
soak
Change
Filters
Hot Start
Filter No. 2
^Bag 3 J
505 sec.
Weight Fa
c Bae 4 .,
871 sec.
ctor =0.57
Weighted Mass
0.43 x Net Weight of filter #1 + 0.57 x Net Weight of
filter #2
In the 3-filter/3-bag test sequence, the above procedure was
modified such that a filter was taken during each of the first three bag
sample periods; the bag 4 sample was eliminated. In this sequence it is
assumed that the particulate emissions that would have been measured
during bag 4 is the same as that measured during bag 2. This results in
a weighting factor for each filter that is identical to the correspon-
ding bag weighting factor. The important concepts of this procedure are
diagrammed in Figure 2 below.
Figure 2
3-Filter/3-Bag Particulate Procedure
Cold Start
Filter No. 1
«Bag 1 „
505 sec.
Weight Factor=0.43
Filter No. 2
it-Bag 2
871 sec.
Weight Factor=1.00
10 min.
soak
Change
Filter
Hot Start
Filter No. 3
3
505 sec.
Weight Factor=0.57
Instantaneous
Filter Change
Besides the test sequences described above, some other important
factors should be noted with respect to the Test Procedure. In both
sequences, particulates were collected by isokinetically removing a
sample of exhaust from an 18 inch dilution tunnel. The sample was then
passed through a 47 mm Pallflex filter (Teflon coated glass fiber) which
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removed all of the particulate material. The weight of the particulate
collected is considered to be the net weight difference between the
clean filter, which has been stabilized with respect to humidity and
temperature, and the loaded filter, which again has been stabilized with
respect to humidity and temperature.
Results
Two different light-duty diesel vehicles were used in evaluating
the equivalency of the dynamometer procedures. The individual FTP
weighted particulate mass measurements for each vehicle and each pro-
cedure are presented in Table I attached. From this data it was con-
cluded that the two dynamometer procedures are equivalent.
This conclusion was based on a test of the hypothesis that the aver-
age 3-filter/3-bag FTP weighted particulate mass was equal to the
average 2-filter/4-bag FTP weighted particulate mass against the alter-
native that the particulate masses are unequal. The test was made at
the 5% level of significance; i.e., if the procedures were equivalent,
this would be determined with 0.95 probability. .Moreover, if the pro-
cedures were unequal (i.e., differed by two standard deviations or
more), the hypothesis would be rejected with the risk of making an
incorrect decision not exceeding 0.15 with six samples. The criteria
for acceptance of the hypothesis was met by both vehicles. Hence, it
was concluded that the two dynamometer procedures are equivalent.
Attachment
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ATTACHMENT
Table I
Dynamometer Test Procedure Evaluation
FTP Weighted Particulate Results *> Gm/Mi
Peugeot 504D
Oldsmobile 350D
3-filter/3-bag
0.353
0.359
0.378
0.383
0.380
0.367
Ave. 0.370 (+ 3.3%)
2-filter/4-bag
0.366
0.351
0.382
0.387
0.357
0.376
0.370 (+ 3.9%)
3-filter/3-bag
1.035
1.001
0.961
0.934
0.956
1.006
0.982 (+ 3.9%)
2-filter/4-bag
0.949
0.928
0.958
0.923
0.909
0.969
0.939 (+ 2.4%)
Diff =0.0%
Diff =4.6%
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