EPA-BMW Correlation Program
Abstract
Exhaust emission and gas cylinder analysis data were gathered.at
the EPA laboratory and at the new !>MU tent facility in Farmingtcm. The
two laboratories agreed closely in the measurement of CO. Although
there were, significant differences in the measured levels of HC, KO
and CO it is believed that these discrepancies were caused by differ-
ences in dynamometer type and ambient conditions. Because of .the limited
amount of testing done, it was not possible to generate ambient correla-
tion factors for the exhaust emissions.
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EPA-BMW Correlation Program
1. Introduction
«
BMW has recently completed construction and instrumentation of a
light--duty vehicle exhaust emission test cell in the Detroit area. The
facility is located at Erhart Motors at 32715 Grand River in Fannington.
The facility becan;e operational o'n approximately Hay 1, 1975. JiHW
rajueyted a correlation test: program with tlie KPA automotive laboratory
in order to assess the .operation, of their new test facility.
2. Technic_al Digcussion
2.1 Pro fir am Ob j cc t J.y e
The purpose of this study is to determine any differences.in exhaust
emission tests, fuel economy tests and gas cylinder analysis tests at
EPA facilities and the Ul-iW laboratory. In addition to comparing these.
test results, this study also compares the test equipment used at each
facility. ' . ,
2.2 Facilities and Equipment .
2.2.1 Test Sites
The BMW facility consists of one test, cell v;hich has temperature
but not humidity control. EPA used their designated "master cell" which
is cell number 5. This facility has both temperature and humidity control
The equipment and instrumentation used within each test cell is
listed in Table I. Perhaps the most significant difference in test
equipment is the dynamometers. The EPA used a direct-drive inertia
wheel unit, while BMW has the belt-driven type.
2.2.2. Test Vehic3.es
One test vehicle was used in this program. This was a 1975 3.0 Si
BMW equipped with a 4-speed manual transmission. The engine was an.
electronic fuel-injected 6-cylinder,- equipped with a thermal reactor.
The inertia and actual h.p. setting for this vehicle were 3500 Ibs, and
11.2 IT. p., respectively. The same fuel (commercial leaded) was used
for all tests. . ^
2^ Program Design
The test was designed so that, after several .vehicle tests had .be-?.n
done at EMW, three tests would be conducted at the EPA. The day prior
to testing at the KPA, five tests were conducted nt BMV'. For purposes
of the st.-Jtiotiool analysis, the. last three of t:lu:se. te?;t:s were used.
In aridition to vehicle tests, a set of gas cylinders was also analysed
at each lab.
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Table.I Test". Site Equipment and Instrumentation
Analyzers
JIG
CO
NO -
x
C0n
Analyzer Bench
CO Cond itionin
CVS
Dynamometer-
Driver 's Aid
Computer
EPA
BecbiKm AGO, 0-30 ppm,
I12/1*2 fuel
Bendix 8501, 0-500 ppra
TECO 10A, 0-100 ppm,
0- Osone Sourer.
BccUman 3ISA, 0-3.3%
Houie.built according to
Federal Register
Ascaritn, Silica Gel
in Common Tube.
Ford .Pliilco, CFV
Clayton CT-50, Direct-
Drive Inertia, Au'-.o
Loading not usexl
Varian, 5" - 60 mph,
6"/.n. Preprinted Trace
IBM 370, Off-line
I I'M Model R55, 0-100 ppm
100% H2 fuel
Il&B Type 2T, 0-500 ppm
TECO 10, 0--100
Air Ozone Source
ll&B Type 2T, 0-2%
according to
Federal- Register
Ascarite, Silica Gel
in Separate Tubes
Scott 302, 6-bag, AP = 22r
1120
Clayton C.150, Belt-Drive
Inertia, Manual Loading
Servogor, 7.6" = 60 mph
12 cm/tain, Hand-made trace
Hand-calculated
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2.4 Test Procedure
2.4.1 Vehicle Preparation
All vehicle tests were "hot-start" so vehicle preconditioning con-
sisted of stabilizing the vehicle at some constant; condition prior to
the start of each test. Oil temperature was used as the control con-
dition. Prior to testing, the vehicle was operated at a steady speed
of 25 .nph until the oil temperature rose to 72°C. Then the vehicle was
brought to an idle. When the oil temperature readied 75°C (.1.67 °F) the
test was begun. .
2.4.2 Em i ssion Test s
The driving cycle used was the urban dynamometer driving schedule
(LA-4). The vehicle began the cycle at idle with an oil temperature of
75°C. Emissions were measured.according to the .1974 FTP. Between each
test the vehicle was shut-off and allowed to cool for approximately .15
minutes so that the following test could be started at an oil temperature
of 75°C. . -
2.4.3 Fuel Consumption Tests
Fuel Economy was calculated for each LA-4 cycle based on .the carbon
balance technique as described in the Federal Register.
2.4.4 Cylinder Gas Check
Five gas cylinders were analyzed at both test sites. These cylinders
were analyzed on the same, analyzer trains that were used for the vehicle
emission tests; Three concentrations of CO (nominally 0.8%, 1.7%, and
3.2%) and two concentrations of'CO (nominally 170 ppm and 1300 ppm) were
used. '
3. Data Analysis
In addition to the calculation of means and standard deviations
for HC, CO, CO-, NOX and fuel economy at each test site, a Student's
"t" test was used to detect any significant differences between, the
test sites.
4. Test Resuits
4.1 Eiiiis s ion nnd F u el Economy Da t a
Data and statistical analysis results from the emission and fuel
economy tests arc contained in Table 11. -As shown, the two labs agreed
in CO measurei'ient; however, the 10-. <-'« difference .in C0.; :;iuy..!ed high
..' tafifatJCiil significance. The BMW Ir.b r.i-jar.ured ?.'.'. 3'/.: Tcv/ri: SiC ,-^nd 13.27..
higher NO. and these differences vere. at the. 97% and 98/j confidence.
level, rel:jiC:cLlvely. Repeatability of the IIC ni-asuremout \/as much
poorer than repeatability of tlie other emissions.;.
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Tablc II Vehicle Emission and Fuel Economy Data
and Statistical Analysis Results (Data uncorircctecl
for any ambient or instrumentation difference)
Test
BMW
1
2
3
X
0
A..LUU/0
XEPA
t-value
Confidence
Level -
HC, sa
' mi
0.54
0.64.
0.51
0.563
.068
12.1 %
0.71
0.90
0.78
0.796
0.096
12.0 %
-0.233
-29.3 %
3.43
97 %
CO, £? '
' nu.
7.20
7.49
7.58
7.42
0.20
2.7 %
7.58
7.37
7.62
7.52
0.13
1.7 %
-0.10
-1.3%;
.72
<60 %
rn gm
LO , r
2 ' mi
656
647
654
65?.
4.7
0.7 %
595
585
585
588
5.77 '
0.9 %
64
10.9%
-14.86
>99..9 %
NO , £S
X Till
2.26
2,06
2.09
2.14
0.11
5.0 %
1.91
1.89
1.87
1.890
.020
1.0 %
.25
13.2 %
-3.89
98 %
Fuel Economy, :~-
gal
13.3
13.4
13.3
13.33
.06
0.4 %
14.6
14.8
14.8
14,73
0.12
0.8 %
-1.40
-9.5 %
-18.78
>99.9 %
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Due to the fact that each facility tested on only one day, the
ambient conditions changed very little within each test site. Therefore,
it is not reasonable to attempt to' obtain ambient correction factors for
this vehicle;. Also, there were only very small differences in temperature
and humidity conditions between the test sites. However, Lire barometric
pressure at EPA was about 0.4 in. Hg lower than at BMW. In an attempt to
adjust the data for this difference in barometric pressure, the correc-
tion factor obtained from, the 1975 MVMA correlation study (-"-'was applied
to the dai'a. In doing this, it was assumed that barometric pressure had
the sauic percentage effect on the emissions from .vehicles used in both
studies. So, obviou.sly, correctness of the result depends on validity
of this assumption. In the MW1A study, a -0.4 in. Hg difference in barometric
pressure v/ould have accounted for nearly 30% of the observed difference
in NO and about 20% of the observed difference in HC in the KMW-EJ.'A data.
And these adjusted differences are at the 94% confidence, level, which is
a significant reduction of the 97% and 98% confidence level of the un-
ccrrected data.
Also in the 1975 MVMA study, a difference in dynamometer load was
observed ."between direct-drive and belt-driven inertia .wheels; -and this
resulted in a significant effect on NO . The MVMA program yielded a
dynamometer type vs 1-:0X relationship which would account for about 35%
of the observed NO difference in the BMW-EPA data.
J»
The statistically significant difference of 10.9% in C02 values
cannot be explained by dynamometer and/or ambient effects. Results of
the 1975 EPA-MVMA correlation study indicate that about a 4% difference
could be a dynamometer difference and about 1% could be attributed to
the difference in barometric pressure. But the remaining 6% difference
would stiJl be significant at greater than a 99% confidence level.
4.2 Gas Cross-check Tests
Results of the five, gas cylinder analyses are shown in Table III.
As listed, the only analysis that was not in good agreement was the
nominal 1.7%. COo. BMW measured this concentration as being 4.2% higher
than did the EPA. Since this analysis was conducted on the same analyzers
that were used for the vehicle test, this discrepancy accounts for part
of-the. 10.9% observed difference in C02 emissions. Taking into account
the 4.2% analyzer difference, a 4%' dynamometer effect and a 1% barometric
pressure effect, the 10.9% observed difference in C02 is reduced to only
about a.'2% difference. .. .
-> Con c.1.11 ^ j ons
1. CO data showed good agreement between the two laboratories.
.2. Differences in dynamometers (direct-drive vs belt-driven inertia)
and barometric pressure are believed to be responsibile for the observed
difference in NOX values.
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Table 111
Results of Gas Cylinder Cross-Checks
Gas .
CO
CO
co2
co2
co2
--" ' '"" - '
BMW
169 ppm
1321 ppm
0.80 %
1.74 %
3.24 %
EPA
167.5 ppm
1323.8 ppm
0,80 %
1.67 %
3.21 %
A'(BMW-KPA)
1.5 ppm
2.8 ppm
0.00 .
0.07 %
'0.03 %
A,%
0.9
-0;,2
0.00
4.2
0.9
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3. The only difference in gas .cylinder analysis greater than 1% was
a 4. 2%. -difference (lli'W higher than EPA) on a C02 concentration of about 1.72.
4. The above mentioned 4.2% difference in CC^ analysis is responsible.
for part, of the observed CC^ emission difference of 10.9%. The remaining
difference is believed to be caused mostly by differences in. dynamometer
type and barometric pressure.
1. In future correlation work, it would be desirable to have testing
performed at one location on more than one day. This. would most likely
result in greater ambient condition variations within each laboratory
and would make possible the calculation of ambient correction factors.
2. During vehicle tests at BMW the te.st cell temperature rose from
about 73°!' at the beginning of a test to approximately 83°F a-t the. end
of the test. Decreasing this temperature; rise would most likely .improve
testing repeatability. (The temperature, range encountered during the EPA
tests was from 72°1< to 78°F.)
3. Dynamometer type should.be standardized or . quantitatively charac-
terized in order to improve laboratory correlation.
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