HDV 78-06
Technical Report
June, 1978
A Preliminary Examination of the Repeatability of
the Heavy-Duty Transient Dynamometer Emission Test
by
William B. Clemens
NOTICE
Technical Reports do not necerssarily 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 tech-
nical information and to inform the public of technical develop-
ments 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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The purpose of this report is to briefly examine the repeat-
ability of the new Heavy-Duty (HD) transient test procedure based
upon the limited test experience gained to date.
The first two HD 1969 baseline engines have been tested on the
proposed 1983 MY transient test procedure. This procedure involves
the use of a modified DC electric dynamoiater at the EPA Motor
Vehicle Emissions Laboratory in Ann Arbor, Michigan. Emissions
were analyzed by the CFV-CVS (constant flow venturi - constant
volume sampler) technique. The CVS was rated at 1500 SCFM.
The heavy-duty transient procedure is a new test procedure,
and a preliminary estimate of the accuracy of the test results
gathered to date (April 28, 1978) were of paramount interest in
evaluating the test procedure. The accuracy of these results would
be subject to two basic types of errors. Errors due to lack of
precision, commonly referred to as repeatability, and errors due to
offset, usually considered bias errors. As shown in Table 1, the
precision errors appear to be quite good for the complexity of
the test procedure, and the amount of experience with the equip-
ment. The bias errors are mainly equipment calibration errors, and
are not quite as good as the precision errors. However, the
accuracy of the data presented is considered adequate for the
initial stages of the baseline program. An ongoing effort will
attempt to minimize both precision and bias errors during the
baseline program.
Table 1
Average Coefficient of Variation
HD Tests Typical LDV
(g/BHP-hr) REPCA (g/mile)
HC 13.4% 5.7%
CO 6.5% 6.0%
NOx 4.4% 4.4%
The specific coefficients of variation are listed in Table 2.
As shown, the variability of the HD transient procedure compares
favorably with results obtained on the LDV transient procedure,
which is quite pleasing this early in the program. However, it
should be emphasized that these values are only average values, and
in some instances the variation for an individual engine or vehicle
can be quite high.
In order to investigate the source of the variability, the
coefficients of variation for the hot start portion of the heavy-
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Table 2
Coefficient of Variation
(s/x)
A. HD Cold Soak Emission Test (g/BHP-Hr)
(cold start + hot start)
BHP-hr BSHC BSCO BSNOx
1. 225 CID
Dyno cal. "A" 1.5% 9.6% 5.5% 4.1%
Dyno cal. "B" 3.9% 4.8% 6.4% 4.9%
2. 392 CID
Dyno Cal. "B" 6.2% 25.9% 7.7% 4.2%
B. HD Hot Portion (g/BHP-Hr)
(hot start only)
BSHC BSCO BSNOx
1. 225 CID
Dyno cal. "A" 9.8% 5.1% 4.5%
Dyno cal. "B" 3.6% 5.6% 4.9%
2. 392 CID
Dyno Cal. "B" 27.6% 9.2% 3.5%
C. LDV FET (g/nile)
HC C0_ NOx
1. Production Catalyst Vehicle
Dyno A 5.9% 47.3% 3.3%
Dyno B 6.1% 26.2% 4.1%
Dyno C 10.0% 31.1% 5.1%
2. REPCA Non-Catalyst Vehicle
Dyno A 5.6% 5.9% 4.1%
Dyno B 6.3% 5.5% 4.6%
Dyno C 5.3% 6.5% 4.4%
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duty test were computed. These data (Table 2A and B) indicate that
there is essentailly no difference in terms of emission variability
between the hot portion and the total test. This result is not
surprising since the weighting factor for the hot start portion
for these tests was 0.875 versus 0.125 for the cold start por-
tion.* Therefore, it is assumed that most of the variability can
be attributed to. the repeatability of each segment. It is sus-
pected that the starting segment of each portion has the greatest
variability. A more detailed analysis may be undertaken in the
future to verify this assumption.
The emission measurement accuracy discussed so far, deals only
with errors due to random variability for a given set of condi-
tions. Another source of errors in emission results are bias
errors. An example of a bias error would be the testing of an LDV
with an incorrect power absorber setting. It would be expected
that the emission results would have equivalent variability regard-
less of the power absorber setting, but, only one group of data
would be correct, the data taken with the correct power absorber
setting.
This analogy applies to the heavy-duty transient test as well.
Only, the heavy-duty test has many more parameters that must be
measured to assure the correct power setting. As in the light-duty
test, most bias errors can be corrected with proper calibration.
During these tests, two different calibrations were used. The
difference between calibration "A" and calibration "B" was that the
engine operating speed was increased from the values in calibration
"A" to values slightly over the reference speed in the test cycle.
The control system was adjusted in this manner because calibration
"A" generally had a negative error in speed which resulted in a
measured cycle horsepower-hour approximately 10% below the refer-
ence horsepower-hour. The speed adjustment was overcompensated
slightly, and the change resulted in calibration "B" operating the
engine approximately 14% above the reference or correct horse-
power-hour. Although this change did not significantly affect the
repeatability, it did affect the emission levels (see Table 3).
Based on the difference between calibration "A" and "B" in
inegrated BHP-Hr over cycle, the following observation can be
stated; for the tests on the 225 CID Chrysler engine, every 1%
change in cycle BHP-Hr resulted in approximately a 2% change in
* Note: Since this report was prepared, the hot/cold weighting
factor has been changed based upon final analysis of the CAPE-21
data base - see EPA Technical Report No. HDV 78-04, "Transient
Cycle Arrangement for Heavy-Duty Engine and Chassis Emissions
Testing", by C. France, June 1978.
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Table 3
Test Results
Cold Start Weighting = .125
Hot Start Weighting = .875
Cold Soak Emission Test
BHP-hr BSHC BSCO BSNOx
1. 225 CID
Dyno Cal. "A" 10.95 6.68 52.24 9.66
Dyno Cal. "B" 13.96 3.96 47.59 8.58
2. 392 CID
Dyno Cal. "B" 19.39 11.83 206.17 3.91
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BSHC, a 0.375% change in BSCO, and a 0.5% change in BSNOx.
Although no similar LDV data are available for REPCA at MVEL in Ann
Arbor for comparison, the variation in emissions relative to BHP-Hr
changes from this HD engine seem acceptable.
The International Harvester 392 CID engine was operated only
with speed calibration "B". However, the IHC engine had more
difficulty in following the torque cycle than the Chrysler engine.
Thus, the cycle power developed by the IHC engine was approximately
6% below the reference power. Because the IHC engine did not meet
the statistical criteria for torque, it is most likely that that
engine will be retested.
From this discussion of bias errors, it is obvious that bias
errors do occur during testing. The effect of these bias errors
influence the emission test results in two important ways.
Initially, the engine is operated at an incorrect power setting.
The magnitude and direction of the error in the engine emissions
due to operating the engine at an incorrect power setting would
generally be unknown. Possibly more important though, is that the
test results in grams/horsepower-hour would be computed with a
horsepower-hour value that is different than the reference or cycle
horsepower-hour. The magnitude and direction of this effect is
easily computed by knowing the operating horsepower-hour and the
reference horsepower-hours.
To some degree bias erros due to operating the engine at an
incorrect power setting, and bias errors due to dividing by a
different horsepower-hour value must be accepted. No machine will
ever be perfect. However, errors of this type can be minimized by
continuing to emphasize accurate calibration of the equipment.
The actual emission results from each individual test on the
two engines are given in Tables 4 and 5. Additional examination of
the repeatability of the HD transient dynamometer emission test
will be performed as more test data become available.
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Table 4
Engine Description;
MFC: Chrysler
CID: 225
Type: L-6
Cold Start Weighting
Hot Start Weighting
S/N: FW225R2994032
Rated BHP: 94
Rated RPM: 3556
.125
.875
Maintenance Requirements/Problems;
Tune-up prior to BLT-1
Rebuild Carburetor After BLT-7
10-Hour Cold Soak Test Results:
Test No.
BLT-1
BLT-2
BLT-4
BLT-5
BLT-7
BLT-8
BLT-9
BLT-11
x"
s
Dyno Cal. HC
"A" 6.08
"A" 6.31
"A" 6.77
"A" 7.54
"B" 5.12
"B"* 3.74
"B"* 4.05
"B"* 4.08
A B*
6.68 3.96
.64 .19
4-Hour Cold Soak Test Results
Test No.
BLT-3
BLT-6
BLT-1 0
Dyno Cal. HC
"A" 6.17
"A" 6.83
"B"* 4.23
(g/BHP-Hr)
CO
55.61
49.04
50.95
53.34
50.00
46.33
45.50
51.04
A B*
52.24 47.59
2.86 3.02
•
•
CO
48.11
51.75
49.74
(Ib /BHP-Hr)
NOx
10.00
9.74
9.23
—
9.12
9.00
8.57
8.16
A B*
9.66 8.58
.39 .42
NOx
9.19
9.36
9.20
BSFC
.821
.655
.650
.627
.597
.574
.554
.576
BSFC
.640
.618
.591
BHP-Hr
10.767
10.894
10.967
11.154
13.551
14.488
14.011
13.394
BHP-Hr
11.016
11.110
14.140
* plus carburetor rebuild.
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Table 5
Engine Description;
MFC: IHC
CID: 392
Type: V-8
Cold Start Weighting
Hot Start Weighting
S/N: V392 658417
Rated BHP: 159
Rated RPM: 3527
.125
.875
Maintenance Requirements/Problems;
Tune-up prior to BLT-1
Replaced faulty coil wire after BLT-4
10-Hour Cold Soak Test Results:
Test No. Dyno Cal. HC
BLT-1
BLT-3
BLT-5
BLT-7
BLT-8
c
s
"B"
"B"
"B"
"B"
"B"
15.96
—
12.22
8.93
10.22
11.83
3.07
(g/BHP-Hr)
CO
200.30
191.86
203.87
228.64
206.17
15.81
(Ib/BHP-Hr)
NOx BSFC BHP-Hr
3.68 .795 21.153
4.02
4.04
3.89
3.91
.17
.825
.819
.868
18.941
18.958
18.506
4-Hour Cold Soak Test Results:
Test No. Dyno Cal.
BLT-2 "B"
BLT-4 "B"
BLT-6 "B"
HC
8.80
8.41
CO
172.10
193.90
NOx
4.02
4.29
.817
BHP-Hr
19.805
19.098
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