SDSB 79-04
Technical Report
January, 1979
Light-Duty Diesel Gaseous Emissions Measurement
Comparison of Dilution Tunnel Test Results to
Certification Cell Test Results
by
Jeff Alson
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 devel-
opments 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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Ab s t r ac t
This report summarizes gaseous emissions data for eleven
light-duty diesel vehicles using both the standard certification
test procedure and the dilution tunnel test procedure which incor-
porates particulate measurement. The' greatest variability was
found in the HC measurements. This is partially attributed to the
variability inherent in measuring HC and, in the extreme cases,
also to equipment inconsistencies between the test cells. CO, NOx,
and CC>2 data from the dilution tunnel test procedure were gen-
erally in good agreement with .the certification data with the. only
trend being slightly lower NOx and C02 values from the dilution
tunnel. This is hypothesized as a possible dynamometer effect. It
is concluded that there are no significant differences in the two
test procedures with regards to the measurement of gaseous emis-
sions.
Introduct ion
During the past six months eleven light-duty diesel vehicles
have been tested for gaseous emissions using the light-duty diesel
test procedure which has been developed to facilitate particulate
measurement. This testing was conducted as the final phase of the
light-duty diesel particulate baseline study. Emissions test
results have also been obtained for these vehicles using the
current light-duty diesel certification test procedure. A direct
comparison can be made between the proposed test procedure and the
present certification procedure regarding the measurement of
gaseous pollutants. Obviously the viability of the new test
procedure will rest heavily on its ability to closely duplicate the
results of the present certification system. This report will
assess the ability of the new test procedure to do this.
Test Procedure
The certification emissions test results were obtained accord-
ing to the procedure outlined in the Federal Register and the tests
were performed in light-duty diesel certification test cells 5 and
6. The new test procedure was described in the "Draft Test Proce-
dure for Measurement of Gaseous and Particulate Emissions from
Light-Duty Diesel Vehicles," September, 1978, and was implemented
in test cell 508. With regards to gaseous pollutants the only
major difference between the procedures is that the new one incor-
porates a dilution tunnel rather than a large baffle box as the
mixing medium. Henceforth, the new test procedure will be referred
to as the dilution tunnel system.
Results
The results of the dilution tunnel-certification comparison
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are given in Tables I and II and in Graphs I through IV. Table I
gives the actual HC, CO, NOx, CC^, and fuel economy data for
the eleven vehicles tested by both the dilution tunnel and certifi-
cation test procedures. Both Federal Test Procedure (FTP) and
Highway Fuel Economy (HWFE) tests we.re conducted. Table II pre-
sents the same data with the difference between the dilution tunnel
and certification values expressed as a percentage of the latter.
It also gives recent Repca (correlation vehicle) values which are
indications of the variability present among the various test cells
at EPA at. this time. It should be noted, however, that Repca is a
gasoline-fueled vehic.le which limits its applicability with regards
to diesel test cells.
Graphs I, II, III, and IV give a Cartesian presentation of the
same data for each pollutant. The X's represent data from the HWFE
tests and the solid points represent FTP data. Each graph shows
the "ideal" fit which would result from perfect duplicity of the
data from the two test procedures, as well as the "best" fit
(least-squares regression) lines for both the FTP and HWFE data.
In addition, Graph I includes the "best" fit lines for HC excluding
the one pair of data from the Peugeot 504D which greatly deviates
from the rest of the HC data.
Analysis of Results
As is often the case with diesel- vehicles, and which is
indicated in Table II, HC was the pollutant most sensitive to the
change in test cells. The trend was most pronounced in the HWFE
data with nine of the eleven vehicles registering relative dif-
ferences of 8.6 percent or more but was also evident in the FTP
data where seven vehicles experienced differences of 7.3 percent or
more.
There are several factors which help to explain or ameliorate
this apparent problem, however. The first is the fairly large
Repca value of 14 percent which indicates the inherent variability
problems with HC measurements. Admittedly, Repca is a gasoline-
fueled vehicle but the same variability problems with regards to
diesel HC and the heated flame ionization detector (HFID) are well
known. Assuming the Repca number to be some measure of statistical
acceptability, we find that just three of the relative FTP values
and four of the relative HWFE values exceed this figure.
A second factor to be considered is the general scatter of the
FTP data about the. ideal fit line as shown in Graph I. Except for
the Peugeot, Mercedes, and International Scout vehicles (the
highest and two lowest FTP values), the FTP data all lies very
close to the ideal fit line with no trend indicated. This latter
fact indicates that the effect, if any, of the dilution tunnel upon
the majority of HC measurements is.a random one.
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-3-
As mentioned above and indicated in Table II, the Peugeot,
Mercedes, and International Scout vehicles experienced the greatest
relative HC differences. The latter two were the lowest HC emit-
ters with concentrations in the 0.3 gram per nile (gpm) range over
the FTP. The high relative values for these two vehicles are
clearly due in part to their small absolute magnitudes. The
Mercedes, for instance, experienced a 0.05 gpm difference between
the two test procedures. This doesn't appear to be a problem until
it is realized that it represents a 16.7 percent relative change.
Thus the small magnitudes of the values contribute to the apparent
correlation problem.
Still, the absolute differences of 0.05 and 0.09 gpm for the
Mercedes and Scout vehicles have another possible explanation. The
HFID HC analyzers in the certification test cells utilize only one
range (0 to 100 ppm HC) for all HC measurements. The HFID analyzer
in the dilution tunnel test cell utilizes three different ranges (0
to 100, 0 to 50, 0 to 25 ppm HC), the lowest of which allows much
greater sensitivity as compared to the certification range. Thus
when testing cars with fairly high HC emissions the same ranges
were used for both the dilution tunnel and certification tests.
But when testing low emitters like the Mercedes and Scout vehicles
the lowest, most sensitive range was used in the dilution tunnel
test cell while the higher range was still used in the certifica-
tion test cells. To further compound the problem all background HC
readings in the certification test cells were taken at the higher
range while all such readings in the dilution tunnel test cell were
taken from the most sensitive scale. Thus this factor may explain
why the Mercedes and Scout vehicles had greater absolute HC dif-
ferences than most vehicles which emitted far more HC. This could
also account for the wider differences in the HWFE data base since
most of it is clustered around the 0.2 to 0.3 gpm range, where the
dilution tunnel analyzer was set as its most sensitive scale.
The most baffling HC data are those of the Peugeot vehicle.
The dilution tunnel measurements were 0.22 and 0.47 gpm less than
the certification measurements for the FTP and HWFE tests and 20
and 69 percent less on a relative basis. These data have such an
effect on the least-squares regression technique (since they are
the highest values) that Graph I includes regression lines exclud-
ing the Peugeot data.
One possible explanation has been suggested. Peugeot vehicles
are certified using a special high volume cooling fan which has a
much larger capacity than the standard certification cooling fan.
Thus the Peugeot certification results were taken using the high
volume fan. When tested in the dilution tunnel test cell, however,
the standard cooling fan was used. The effects, if any, of the
special cooling fan have not been quantified. One possibility is
that the higher volume fan results in a decrease of the coolant
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temperature which accordingly decreases the combustion chamber
surface temperatures. Lower combustion chamber surface tempera-
tures are known to increase HC and CO emissions due to a larger
quenching zone and the resultant increase in incomplete combustion.
NOx, on the other hand, would be expected to be lower due to the
greater heat losses to the cylinder walls resulting in lower peak
temperatures in the cylinders. The data in Tables I and II support
this theory completely as the certification cell using the high
volume fan recorded higher HC and CO values and lower NOx emis-
sions. As further support of this theory it should be noted that
the Peugeot was the only vehicle to have lower FTP NOx emissions in
the certification test cell. Thus it is likely that much of the HC
differences for the Peugeot can be attributed to the difference in
cooling fans.
As Tables I and II and Graphs II, III, and IV indicate, there
do not seem to be any significant problems in sampling CO, NOx, or
C02 with the dilution tunnel test procedure. The CO values were
in very good agreement, especially in view of the 11% Repca number
indicating the variability among EPA test cells in measuring CO.
As Graph II indicates, the FTP data was well scattered about the
ideal fit line showing no trend whatsoever. The HWFE data from the
dilution tunnel did prove to be somewhat lower, but this doesn't
seem to be a serious concern at this time.
The NOx relative values were generally within the Repca value
of nine percent as well. The dilution tunnel FTP values were
consistently lower than the certification values (except for the
Peugeot discussed earlier) while the HWFE values were more scatter-
ed. The C02 relative values were rarely much greater than five
percent although they were often greater than the Repca value of
three percent. As with NOx, there was a clear indication that the
dilution tunnel test cell measured slightly lower C02 emissions.
This combination of lower NOx and COj emissions points to a pos-
sible dynamometer effect since these two pollutants are most
affected by dynamometer-road load considerations. As noted earlier
there were no clear trends with regards to higher or lower HC or
CO measurements from the dilution tunnel. This latter fact, along
with the lack of constant differences in the NOx and C02 data,
makes it unlikely that a CVS problem was a factor.
Conclusion
Based on the above results and discussion and the realization
of the variability inherent in emissions testing, it is concluded
that there are no significant differences between gaseous emissions
measurements made with the dilution tunnel test procedure and those
made using the current light-duty diesel certification test proce-
dure.
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TABLE I
LIGHT-DUTY DIESEL COMPARISON OF DILUTION TUNNEL TEST RKSULTS TO CERTIFICATION CELL TEST RESULTS
Vehicle & ID
Oldsmobile 350
93JF127
'79 Cert Vehicle
Oldsmobile 260
93HFI.49
'79 Cert Vehicle
Oldsmobilc 260
93HF-84482F
'79 F E Vehicle
Ohlsmobile 260
93HFI81
'79 Cert Vehicle
(5 Epd)
Chcv. Pickup 350
8TJ9-168K
' 79 C;:rt Vehicle
(3-hole injection)
Dutige Truck
B356
'79 Cert Vehicle
(4 spd)
Mercedes 300D
123.130-12017745
Special Uuild/Turbo-
Ch.irged with ECR
Volksv.igt'n Dasher
406 2 :4t>6
'79 Ccrl Vehi.-le
(4 spd)
Volkswagen Rabbit
iOb Z 2465
'79 Cert Vehicle
(5 spd)
Peugeot 504D***
622
' 79 Cert Vehicle
(4 spd)
Int'l Harvest Scout
300
' 79 Cert Vehicle
(4 spd)
Total HC -v
Dilution
Tunnel*
0.59
0.32
0.58
0.20
0.60
0.22
0.69
0.19
0.78
0.64
0.54
0.35
0.25
0.08
0.52
0.30
0.51
0.20
0.87
0.21
0.27
0.16
,pm/mi
Cert
Cell**
0.55
0.35
0.53
0.24
0.61
0.27
0.66
0.21
0.76
0.57
0.51
0.36
0.30
0.14
0.55
0.37
0.55
0.22
1.09
0.68
0.36
0.16
CO igi
Dilution
Tunnel*
1.51
0.92
1.35
0.75
1.49
0.89
1.91
0.72
1.58
1.16
2.61
1.37
1.35
0.73
1.19
0.64
1.01
0.41
1.69
0.69
1.40
0.64
m/mi
Cert
Cell**
1.60
1.00
1.32
0.78
1.52
0.92
1.90
0.73
1.63
1.28
2.50
1.47
1.41
0.79
1.21
0.72
1.00
0.43
2.01
0.76
1.42
0.58
NOx .vj
Dilution
Tunnel*
1.49
1.20
1.67
i.48
1.56
1.24
1.62
1.22
1.52
1.41
1.82
1.57
1.36
1.25
0.98
0.78
0.87
0.58
1.16
1.12
1.40
1.55
^m/mi
Cert
Cell**
1.63
1.28
1.84
1.54
1.58
1.28
1.73
1.26
1.52
1.34
1.86
1.71
1.40
1.01
1.05
0.83
0.95
0'.65
1.05
1.03
1.43
1.34
CO.,
Dilution
Tunnel*
458
334
409
312
412
304
391
270
501
398
469
403
463
363
262
198
238
172
362
307
407
383
^gm/mi
Cert
Cell**
486
362
459
329
422
315
396
283
538
427
489
443 '
480
394
277
220
246
185
361
307
441
367
Fuel Economy
Dilution
Tunnel*
22.1
30.3
24.6
32.9
24.4
33.2
25.7
37.5
20.2
25.3
21.4
25.1
21.8
27.9
38.3
50.9
42.4
58.9
27.3
32.6
24.8
26.5
mpg
Cert
Cell**
20.8
27.9
22.0
30.7
23.9
32.1
25.4
35.7
18.7
23.7
20.6
22.8
21.1
25.8
36.3
45. S
40.8
54.6
27.7
•32.8
22.9
27.7
Cycle
FTP
HWFE
FTP
HWFE
FTP
HWFE
FTP
HWFE
FTP
KWFE
FTP
HWFE
FTP .
HWFE
FTP
HWFE
FTP
HWFE
FTP
HWFE
FTP
HWFE
Dilution tunnel measurements were made in cell 508.
Cc r11f teat Ion measurements were made in cells 5 and 6.
Died special high-flow cooling fan for certification testing.
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TABLE II
LIGHT DUTY DIESEL COMPARISON OF DILUTION TUNNEL TEST RESULTS TO CERTIFICATION CELL TEST RESULTS
Relative Values*
Vehicle & VID
Oldsmobile 350
93J7127
'79 Cert Vehicle
Oldsmobile 260
93HF149
'79 Cert Vehicle
Oldsmobile 260
93HF-84482F
'79 FE Vehicle
Oldsmobile 260
931IF18J.
'79 Cert Vehicle (5 spd)
Chevrolet Pickup
8TJ9-168F
'79 Cert Vehicle
(2-hole injection)
Dodge Truck
B356
'79 Curt Vehicle (4 spd)
Mercedes 300D
123.130-12017745
Special Build/Turbo-
Charged with EGR
Volkswagen Dasher
406 Z 2466
"79 Cert Vehicle (4 spd)
Volkswagen Rabbit
406 Z 2465
'79 Cert Vehicle (5 spd)
Pc-Jgcot 5041)**
6*1-
'73 Cert Vehicle (4 spd)
Int'l. Harvester Scovit 300
'79 Cert Vehicle (4 spd)
Repca - one std. dev.
as 2 of mean
Total HC
7,
-7.3
8.6
-9.4
16.7
1.6
18.5
-4.6
9.5
-2.6
-12.3
-5.9
2.8
16.7
42.9
7.3
9.1
7.3
9.1
20.2
f9.1
25.0
0
14%
Total CO
%
5.6
8.0
-2.3
3.8
2.0
3.3
-0.5
1.4
3.1
9.4
-4.4
6.8
4.3
7.6
1.6
11.1
-1.0
4.6
15.9
9.2
1.4
-10.3
112
* Rcl;
Total
8.6
6.2
9.2
3.9
1.3
3.1
6.4
3.2
0.0
-5.2
2.2
3.2
2.9
-23.8
6.7
6.0
8.4
10.8
-10.5
-8.7
2.1
-15.7
9%
itive Value =
NOx Total CO
; %
5.8
7.7
10.9
5.2
2.4
3.5
1.3
4.6
6.9
6.8
4.1
9.0
3.5
7.9
5.4
10.0
3.2
7.0
-".3
0.0
7.7
-4.4
3%
Cert Cell — Dilution Tunnel
Fuel Economy
%
-6.2
-8.6
-11.8
-7.2
-2.1
-3.4
-1.2
-5.0
-8.Q
-6.7
-3.9
-10.1
-3.3
-8.1
-5.5
-11.1
-3.9
-7.9
1.4
0.6 '
-8.3
4.3
3X
Cycle
FTP
HWFE
FTP
HWFE
FTP
HWFE
FTP
HWFE
FTP
HWFE
FTP
HWFE
FTP
HKFE
FTP
HWFE
FTP
HWFE
FTP
i.i i ~
FTP
HWFE
FTP
Cert Cell
** Used special high-flow cooling fan for cert cell testing
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GR.APH I- DILUTION TUNNEL.
. CERTIFICATION CELL HC
• FTP DATA
X HW FED ATA
U
.1.0
J
U.1
•z
\
o
0.8
0.1
o
CD
5
o
Oi
k
o
h
Qfe
0,5
0.3
o.\
HVOFE
FTP
0.3 o.M o.s o.b 0.1 0,6
TOTAL UMPROCARBOM- ceftT^FicA.TioM CELL
i. a
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TUUUEL CO vs. CERT I F 1CA.TIO t\ CELL CO
9-6
• FTP
X HNWFE DATA,
a.o
0.3. O.M
0.8 »-O (.a |,^ l.b
tAcmoxtPE-CERTIFICATION
a.o
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GRAPH'S!- "DILUTION TUWE.L UOX «. CERTIFICATION! CELL NOX
• Rf> "DATA
X HWE DATA
a.o
FTP
0.4
0,b 0.6 1.0 LSI l.M »,t
OF >4|TRO&EK> CERTlFIC^T^O^i CELL
1,8
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