EPA-AA-SDSB-82-09
Technical Report
Testing of the Cummins VTB-903 at EPA/MVEL
By
Alex Azary
May 1982
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,
position 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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Table of Contents
Page
I. Summary 1
II. Introduction 2
III. Testing Results from EPA and Correlation 2
With Other Test Laboratories
A. Test Results 2
B. Variability at EPA 3
C. Correlation 3
IV. Conclusions 5
V. Recommendations 5
VI. Tables 6
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I. Summary
The Cummins VTB-903 heavy-duty diesel engine was tested at
EPA as part of the EMA/EPA correlation program. The purpose of
this program is to analyze lab-to-lab variability in emissions
measurements and to assess whether or not the large amount of
transient emissions data generated at the Southwest Researach
Institute (SwRI) was repeatable at other laboratories. This
particular engine was first tested at Cummins Engine Company
(Cummins) and then at SwRI. This engine was tested next at the
MVEL during August 1981, then sent to Detroit Diesel Allison
(DDA). It was returned to the MVEL for retesting in February
1982, after which it was sent back to Cummins for the final test
in the series.
The initial testing of this engine at the MVEL from August
17th to September 9th resulted in highly variable HC and
particulate emissions; however, NOx, C02, and CO emissions data
were consistent. Inspection of the HC and particulate data from
this phase of the testing indicated that there was a serious
start-up problem resulting from the manner in which fuel was
delivered to the engine. Fuel was pumped from a Flowtron fuel
measuring device to the engine fuel pump and through the engine
fuel solenoid valve. There was a constant pressure of 6 psig
maintained in the fuel line from the Flowtron to the fuel pump.
At times the fuel pump solenoid valve was left open during a soak
period resulting in fuel (being under pressure) leaking into the
cylinders, thus causing start-up problems. There were other, more
general problems also associated with this method of fuel delivery
since the fuel pump would not see a positive pressure in-use.
After correcting for this problem consistent transient and steady
state emission results were obtained.
A summary of EPA's initial results together with Cummins',
SwRI's and DDA's are reported in Table 1A. It is evident that
EPA's HC and particulate results did not correlate well with the
other labs. During DDA's testing of this engine (subsequent to
EPA's testing), a turbocharger oil leak was accidentally detected
by DDA personnel when oil was seen dripping from the turbocharger
exhaust/tailpipe connection. After installing a new turbocharger,
DDA retested the engine and their results agreed with Cummins' and
SwRI's results. DDA also conducted 4 tests with the leaky
turbocharger and found that their particulate emissions were 13
percent higher than EPA's and their HC emissions were 36 percent
lower than EPA's. For both pollutants the emissions were much
higher with the leaky turbocharger than without. EPA retested the
engine with the new turbocharger during February 1982 and the
results are summarized in Table IB. As can be seen, the overall
variability for transient composite NOx, CO and particulate is
very good, 7.8, 3.5 and 2.9 percent, respectively; while HC
variability was good, 11.6 percent. EPA's emission measurements
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also correlate very well with those of the other laboratories; all
transient composite and 13-mode measurements are within 7 percent
of the mean measurements of all the laboratories, except for the
13-mode particulate measurement, which was 10 percent higher than
the mean. This is a characteristic offset for particulates, which
has been discussed in previous reports.
II. Introduction
This report discusses the results of testing the Cummins
VTB-903 at EPA. This engine was tested as part of the EMA/EPA
cooperative test program designed to analyze lab-to-lab
variability in emissions measurements. The standard test program
followed by all labs consists of: 1) two sets of EPA transient
tests, each consisting of one cold start test followed by six hot
start tests, 2) two 13-mode steady-state tests, and 3) two
measurements of particulate emissions over modes 6 and 11 of the
13-mode test. In addition to being tested at EPA, this engine was
also tested at Cummins, SwRI and Detroit Diesel (DDA).
It should be noted that there were three phases of testing
conducted at EPA. Inconsistent data were obtained from the first
phase as a result of an improper fuel delivery system to the
engine. These data will not be presented in this report. The
second phase of testing was performed after correction of this
problem, but which is now suspect due to the discovery of a
defective turbocharger by DDA. The third phase of testing was
necessary to provide data after the replacement of the defective
turbocharger. In this report, EPA's testing results from both the
second and third phases will be presented and compared with
Cummins, DDA's and SwRI's results. A review of the problems
encountered during all three phases of testing and an examination
of variability in particulate results will conclude this report.
III. EPA Test Results and Correlation with Other Laboratories
A. Test Results
Table 1A presents data from the second phase of testing with
EPA data excluded from calculations of "x. NOx data were not
available during the second phase of testing, as the NOx probe was
used for single dilution particulate results to aid in the
discovery of the causes of high variability and high particulate
measurements relative to other manufacturers. The 13-mode data
was actually obtained during the initial phase of testing of the
engine; time constraints did not allow 13-mode testing during the
second testing phase.
The results from the third phase of testing are presented in
Table IB, again with the data from Cummins, SwRI, and DDA. This
table shows that transient emissions results from all labs agree
well for particulate, CO and NOx emissions; whereas the
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differences in HC measurements are somewhat higher. Inspection of
the coefficients of variation for emission results obtained from
the three laboratories shows that the emission measurements at
each laboratory were very repeatable.
Variability for 13-mode and mode-6 particulate was 13.3 and
9.9 percent, respectively; while mode-11 variability was very low,
3.7 percent. Variability for 13-mode HC and NOx emissions was 7.9
and 5.0 percent, respectively.
B. Variability at EPA
Twenty-nine transient tests were conducted during the first
phase of testing with inconsistent HC and particulate emission
results. The primary reason for the large number of tests is that
the instantaneous HC strip charts were ignored; these readings
would have indicated a problem during the first few tests.
The HC variability problem was solved by noting that HC
emissions during the first 5-minute portion of the transient test
were extremely high. Noticeably high variability in HC levels was
still occuring into the "Bag 3" portion of the test which
indicated that the engine was taking over 10 minutes to reach
independence from initial start-up. Therefore, a series of tests
was designed to analyze the effect of fuel delivery method on
initial HC emissions. It was determined that our fuel delivery
method was the cause of the variability. Discussions with
Cummins' engineers confirmed this. After modification of our fuel
delivery system, repeatable results were obtained. Correction of
this problem reduced emissions by up to 3 g/BHP-hr of HC and over
1 g/BHP-hr of particulate.
The initial fuel delivery configuration involved pumping fuel
to the engine fuel pump. There was a constant pressure of about 6
psig on the engine fuel pump. Whenever the engine fuel pump
solenoid valve was mistakenly left open during a soak period or
overnight, fuel would leak into the cylinders and cause high
initial HC's. During one cold start a thick cloud of white smoke
was visible in the test cell, caused by the excess fuel. The
modified fuel delivery system simply allows the engine fuel pump
to do all the work in drawing fuel from the fuel tank. This, is
identical to the "on road" fuel delivery method.
The initial fuel delivery configuration had been used on all
previous engines tested at MVEL including the Cummins NH-250 and
NTC-290, which were not sucessfully tested. Of the engines tested
at MVEL only the Cummins' engines were sensitive to our fuel
delivery system. This is because their engines' fuel injection
systems are based on different design concepts than those of the
other manufacturers.
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C. Correlation
During the second phase of testing, after correcting the fuel
delivery problem, it soon became apparent that there was still a
correlation problem between EPA, SwRI and Cummins. During this
time, it was not known that there was a turbocharger oil leak and
EPA had no reason to suspect any engine problems. Therefore, the
EPA test cell and equipment were investigated to determine the
correlation problem.
Since EPA's repeatability was acceptable, the investigation
focused on inter-lab differences. An important point appeared to
be that both HC's and particulate were significantly higher than
those from the other two labs and that the difference for HC was
the greater of the two. It was postulated that the reason for the
high particulate may be the high HC level. This was further
confirmed when comparing filter efficiencies from EPA and SwRI for
transient tests.
EPA SwRI
Cold 85 90
Hot 92 95
The fact that EPA had lower efficiencies could indicate that EPA's
filters were experiencing higher hydrocarbon concentrations, based
on the hypothesis that the non-volatile HC's soak the back-up
filter, causing the measured inefficiency. With previous engines,
EPA's filter efficiencies were always greater than 95 percent.
In comparing EPA's HC emissions with those from Cummins and
SwRI for the hot start portion of the cycle, it appeared that
EPA's hydrocarbons were approximately twice as high as the other
labs. When the hot start HC emissions from all three labs were
subdivided into "bag 1-4" portions (each "bag" consists of the
hydrocarbon emissions of a 5-minute segment of the 20-minute
cycle), it was found that any given bag represented the same
fraction of total hydrocarbons for each lab. These results are
presented in Table 2. This implied that the additional
hydrocarbons being generated by EPA were appearing throughout the
cycle and indicated the presence of a miscalibration somewhere in
the system.
EPA's HC system was then analyzed thoroughly. Both software
and hardware were inspected. A known amount of HC was injected
into the dilution tunnel and compared with the real-time value.
Both values were nearly the same, which indicated that our HFID
was not the problem. Numerous other parameters were
investigated. Cummins was contacted and the calculation procedure
was discussed with them. No differences were found in the
calculation procedures. Cummins' real time emissions data was
sent to EPA and inspected. EPA's idling HC level was abcut twice
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that of Cummins, again indicating a constant percentage offset
throughout the test. All three labs use the same Beckman 402 HFID
analyzer. However, each lab has slightly different response times
and sample line lengths.
Both DBA and SwRI correlated well on HC and particulate on a
previous DDA engine and EPA had correlated reasonably well with
SwRI on HC emissions on four baseline engines. Thus, we were
confident that the DDA tests would reveal where the problem lay.
Since this investigation had not turned up the problem and
further effort promised little results, it was decided discontinue
any further testing of the engine and to ship it to DDA. Their
results would confirm whether or not the engine had shifted or
been damaged, or if there was a problem with the EPA HC system.
As has been noted elsewhere in this report, a turbocharger
oil leak was discovered at DDA and the turbocharger was replaced.
The subsequent test results confirmed the contention that the high
measurements observed during earlier tests at EPA were indeed
engine related, and not a function of defective equipment or
procedures.
IV. Conclusions
The Cummins VTB-903 heavy-duty diesel engine has been tested
at EPA as part of the EMA/EPA testing program. Four labs have
tested this engine; Cummins, SwRI, DDA and EPA, with Cummins and
EPA testing the engine twice. Valid data accumulated during tests
at the above labs has shown that variability for transient
combined (one cold start with one hot start) NOx, CO, and
particulate emissions was very good, 7.8, 3.5, and 2.9 percent,
respectively; while HC variability was good, 11.6 percent. Steady
state test results also showed a simiilar correlation.
Variability for 13-mode HC, NOx, and particulates was, 7.9, 5.0,
and 13.3 percent, respectively; and mode-6 and mode-11 particulate
variabilty was, 9.9 and 3.7 percent, respectively.
VII. Recommendations
Recommendations regarding the test program and procedures are
outside the scope of this report, and will be covered in detail in
the Technical Report prepared at the end of the test program.
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Table 1A.
Cummins VTB-903 Emission Results, g/BHP-hr
Transient Testing
Testing
Laboratory
Cummins
SwRI
EPA
DDA
*x
Cummins
SwRI
EPA
DDA
Cummins
SwRI
EPA
DDA
HC
1.69+3.
2.24+5.
3.46+3.
1.91+6.
1.95+14
1.50+3.
1.87+5.
3.04+3.
1.61+6.
2.79
4.42
5.95+5.
3.41
NOx
3 5.63+2.7
0 5.57+3.9
9 4.9+9.2
8 4.87+2.6
.2** 5.36+7.9
3 5.63+2.7
0 5.7+3.92
7 4.95+8.6
8 5.01+2.6
5.68
4.95
6 4.65+12.9
4.74
Composite
Particulate
0.67+8.1
0.67+2.9
0.99+4.2
0.65+8.6
0.66+1.7
Hot Start
0.63+8.12
0.61+2.9
0.88+3.2
0.58+8.6
Cold Start
1.02
1.02
1.65+10.5
0.96
Results
CO
CO 2 BHP-hr
2.06+46
2.00+2.4 654+0.7 16.5+0.9
2.25+3.6 641+3.0 17.5+0.8
—
Results
1.98+46.4 — 17.50
1.86+2.4 648.9+0.7 16.48+0.9
2.132+3.7 636.5+3.1 17.50+0.9
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Results
2.54
2.89 684 16.56
^ 2.98+3.1 670+2.5 17.44+0.4
— , — —
1
Steady-State Testing
Cummins
SwRI
EPA
DDA
*x
0.81
0.95
1.23
0.84
0.87+8.
6.07
6.39
6.52
6.36
5 6.27+2.8
13 -Mode
0.44
0.38
0.45
0.33
0.38+14.4
Results
1.52
2.00
1.57
—
Particulate
Mode 6
0.25
0.29
0.32
0.23
Mode 11
0.72
0.72
0.813
0.71
0.25+13.3
* Excludes EPA's results because tests were conducted with a suspected turbocharger oil leak.
** x.xx + xx.x = x + s/x x 100
0.73+4.4
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Table IB
Cummins VTB-903 Emission Results, g/BHP-hr
Transient Testing
Testing
Laboratory
Cummins
SwRI
EPA**
DDA
*x
Cummins
SwRI
EPA**
DDA
Cummins
SwRI
EPA**
DDA
HC
1.69+3.3
2.24+5.0
2.01+0.94
1.91+6.8
1.96+11.6
1.50+3.3
1.87+5.0
1.61+5.8
1.61+6.8
2.79
4.42
3.65
3.41
WOx
5.63+2.7
5.57+3.9
4.92+2.9
4.87+2.6
5.24+7.8
5.63+2.7
5.7+3.92
5.14+4.7
5.01+2.6
5.68
4.95
4.74
4.74
Composite
Particulate
0.67+8.1
0.67+2.9
0.63+3.0
0.65+8.6
0.66+2.9
Hot Start
0.63+8.12
0.61+2.9
0.54+5.2
0.58+8.6
Cold Start
1.02
1.02
0.91
0.96
Results
CO
CO 2 BHP-hr
2.06+46
2.00+2.4 654+0.7 16.5+0.9
1.92+5.4 645+1.8 17.4+0.3
—
1.99+3.5 650+0.98 17.0+.03
Results
1.98+46.4 — 17.50
1.86+2.4 648.9+0.7 16.48+0.9
1.69+6.3 647.5+. 04 17.49
— — —
Results
2.54
2.89 684 16.56
2.50 667
— — —
Steady-State Testing
Cummins
SwRI
EPA**
DDA
*x
0.81
0.95
0.94
0.84
0.89+7.9
6.07
6.3^9
5.73
6.36
6.14+5.0
13-Mode
0.44
0.38
0.44
0.33
0.40+13.3
Results
1.52
2.00
1.36
—
Particulate
Mode 6
0.25
0.29
0.25
0.23
0.26+9.9
Mode 11
0.72
0.77
0.72
0.71
0.73+3.;
* X.XX + XX.X = X + S/X X 100
** Results from second set of tests after turbocharger replacement.
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Table 1C
Cummins VTB-903
Transient Test Emissions
(g/BHP-hr)
6.00T
5.00'
4.00
Cummins
SwRI
EPA-1
DDA
EPA-2
NOx Combined x
4.00"
3.00.
2.001
1.00
HC Combined x
1.00 —
.90-.
.80..
.70"
.60
Particulate Combined x
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Table 2
Comparison of Inter-Lab HC Emissions
Cummins
Bag
1
2
3
4
Grams
5.7
9.0
6.3
6.7
27.7
% Total
Grams
20.6
32.5
22.7
24.2
100.0
SwRI
Grams
5.9
10.2
8.2
7.4
31.7
% Total
Grams
18.6
32.2
25.9
23.3
100.0
EPA*
Grams
12.1
18.2
13.9
11.2
55.4
% Total
Grams
21.8
32.8
25.1
20.2
100.0
EPA**
% Total
Grams Grams
5.8 20.6
9.2 32.6
7.0 24.8
6.2 22.0
28.2 100.0
EPA first test run.
** EPA second test run after turbocharger replacement.
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Table 3
Steady-State Particulate Results - Mode 6 and Mode 11
Mode 6
Mode 11
Date of Test g/BHP-hr Date of Test g/BHP-hr
First Testing
Phase
Second Testing
Phase
Third Testing
Phase
8/7/81
8/11
8/11
9/10
9/11
9/11
9/14
9/14
9/15
9/25
9/25
9/28
2/5/82
2/5
2/10
2/12
0.272
0.44
0.472
0.513
0.435
0.370
0.282
0.378
0.363
0.304
0.420
0.340
0.463
0.260
0.473
0.235
8/7
8/11
8/11
9/10
9/11
9/14
9/15
9/15
9/25
9/25
2/5
2/12
0.749
0.785
0.754
0.911
0.874
0.756
0.994
0.986
0.830
0.795
0.784
0.693
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