72-18
INTERIM REPORT ON TESTING OF A MERCEDES
BENZ DIESEL SEDAN
March 1972
H. Anthony Ashby
Test and Evaluation Branch
Division of Emission Control Technology
Mobile Source Pollution Control Program
Environmental Protection Agency
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Background
The Test and Evaluation Branch has the responsibility for
testing the prototype vehicles being delivered under the Federal
Clean Car Incentive Program. Since one of the cars in the
program will be powered by a diesel engine, it became necessary
for the T§E Branch to develop testing techniques for accurately
determining emissions from this kind of engine. The Mercedes
Benz 220 diesel sedan is the most readily available diesel car
in the United States, so the Branch asked to borrow one from
the U.S. distributor, Mercedes Benz of North America. Our test
vehicle was furnished through the courtesy of Mr. Hans Prykop
of Mercedes Benz of North America. A Branch representative
received the car at the distributor's headquarters in New Jersey
and drove the car back to the Motor Vehicle Emission Laboratory
in early December.
Vehicle Description
The car is a 1972 Mercedes Benz 220 Diesel four-door sedan,
equipped with automatic transmission. On its arrival in
Ann Arbor the car had about 2000 miles on the odometer. Curb
weight of the vehicle is approximately 3200 pounds, and the
vehicle wa<; tp?f?d using a simulated inertia weight ol 3500
The car is powered by a water cooled in-line four cylinder diesel
engine of 134 cubic inches displacement, having a maximum
outp'ut of 65 SAE horsepower.
Test Program
Testing to date has been by the 1975 Federal Emission (3-bag)
Test Procedure, with the inertia set at 3500 pounds. There have
also been some emissions tests under cruise conditions for
sampling investigations.
Instrumentation was as specified in the Federal Register, with
additions necessitated by testing this car. Normal CVS bag
samples were analyzed for unburned hydrocarbons (HC) with a
FID, for CO and C02 with NDIR, and for nitrogen oxides (NOx)
with chemiluminescence (CL) . Three different CO analyzers were
used, though not all on the same tests: a standard length NDIR
with a range of about 0-2500 ppm, a similar analyzer with EPA
modifications having a range of 0-250 ppm, and a long path NDIR
having a range of 0-200 ppm. ---------
The widely recognized problem of having hydrocarbon condensation
on CVS ducting, .sample lines, and sample bags was approached
with the following technique. A small sample of the diluted
exhaust mixture was pulled from the CVS system through the
heated sample line and analyzed continuously with the heated FID.
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Integrating the output signal gave average HC concentrations over
the appropriate test interval.
For expediency the sample was taken at the same point as the
CVS bag on the first series of three tests. There are two
reasons why this was not the best sample point to use. First,
the pressure depression at that point, just upstream of the CVS
Roots blower, is large enough to reduce sample flow to the FID,
thereby reducing response. Secondly, there are several feet of
ducting and heat exchanger upstream of this point where the
unburned heavy hydrocarbons could condense and not be analyzed.
The last three tests employed a modified CVS in which the exhaust/
dilution air mixing chamber was only about four feet downstream
of the vehicle exhaust pipe. Thus, the diesel exhaust was
diluted much sooner than in the previous, more conventional, CVS
system. A pitot-type sample probe was placed in the mixing
chamber outlet duct and the sample transported to the FID through
the heated sample line.
This setup had the effect of reducing response time of the FID
to a change in engine operation from twenty seconds to four
seconds. Traversing the duct with the probe revealed no
appreciable stratification of the mixture.
Results
Emissions data are presented in Table 1. The CO data are those
that were determined by the more sensitive analyzer used in
each test. Two sets of HC data are shown: from the standard
CVS bag procedure and from continuous hot FID analysis. Oxides
of nitrogen are presented as N02, corrected to 75 grains humidity.
Ambient temperatures ranged between 74 and 79 degrees Fahrenheit
from test to test. Emissions of CO were obviously well within
the required level for 1975.
Mass emissions of HC from the continuous hot FID method were
about twice as high as from the bag samples, but still quite
low, being very close to the 1975 levels.
Emissions of NOx were about four times the level required
for 1976.
Conclusions
Comparison of our emissions data with data from Mercedes diesels
from other sources shows good agreement in CO and NOx, when it
is considered that different cars were tested in different lab-
oratories. For instance, five tests on a Mercedes diesel sedan
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at Southwest Research Institute-gave these average results:
.22 grams per mile HC (CVS bag), .87 gpm HC (hot continuous),
1.62 gpm CO, and 1.27 gpm NOx (by a Saltzman method). This
indicates that the present CVS bag procedure is valid and
reliable for determining CO and NOx emissions.
The sampling method for HC needs to be refined, chiefly for
two reasons: we do not know how much HC is lost through
condensation in the mixing chambers and we do not know the
best sample points of the various CVS units in use at the
Ann Arbor facility.
Investigations underway at this time are aimed at answering
those questions.
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Table 1
Mercedes Benz 220 Diesel
Mass Emissions, Grams Per Mile
1975 Federal Test Procedure
Test No. HC HC • CO NOx C02
Cold Bag Hot Continuous
1.61 508.73
1.49 495.30
1.50 498.21
1.47 404.26
1.62 398.78
1.62 420.16
1
2
3
4
5
6
.22
.20
.24
.17
.14
.16
.31
.37
.42.
.39
.31
.30
1.11
1.47
1.56
1.44
1.34
1.37
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