72-7
EXHAUST EMISSIONS
FROM A 25 - PASSENGER
INTERNAL COMBUSTION ENGINE POWERED
GASOLINE FUELED BUS
October 1971
H. Anthony Ashby, Engineer
Test and Evaluation Branch
Division of Emission Control Technology
Mobile Source Pollution Control Program
Environmental Protection Agency
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Background
Under a grant from the U.S. Department of Transportation,
LTV Aerospace of Dallas will install a Rankine cycle power
system, built by Sundstrand Aviation, in a 25-passenger city
bus for use in the Dallas public transit system. The bus
chosen for this project is a Twin Coach built by Highway
Products, Inc. of Kent, Ohio. The engine usually installed
in the bus is a gasoline fueled V8 internal combustion
engine.
The Test and Evaluation Branch will test the bus when the
Rankine system installation is completed and it was
necessary to test the conventionally powered bus in order
to establish "baseline" emissions, with which the Rankine
system emissions could be compared.
Vehicle Tested
The vehicle was a Twin Coach 25-passenger city bus powered
by a 413 C.I.D. Chrysler V8 engine burning gasoline. The
engine was mounted in the rear and drove the rear wheels
through an automatic transmission. The engine had positive
crankcase ventilation, but no other emission control tech-
nique was in evidence.
The normal curb weight of the bus is about 10,500 pounds. .
The bus we tested was somewhat lighter, since none of the
passenger seats had been installed.
Test Program
The bus was delivered to the Willow Run laboratory on
Monday, September 13, 1971. Engine trouble delayed testing
until Friday, September 17.
For these tests a simulated inertia weight of 5500 pounds,
the maximum available on the Clayton two-roll dynamometer,
was used. All emissions tests employed the Constant Volume
Sampling method. Operating conditions used were the
Ann Arbor-l (AA-I) Urban Bus Cycle, steady state modes, and
an approximation of the CARB-E~~ Diesel Emissions Test
Procedure.
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Normal analysis methods were employed: FID for unburned
hydrocarbons, NDIR for CO and C02' and chemiluminescence
(C.L.) for NOx.
The AA-1 Bus Route was developed by EPA for this project
and is an actual speed versus time trace generated using
a fifth wheel on one of the busses of the Ann Arbor Trans-
portation Authority. It can be and was used with either
a hot or cold start. The modes used for the steady state
tests were idle, 15, 25, and 35 mph cruises, each maintained
for two to five minutes to allow time for an adequate sample
to be collected.
The CARB-E~~ Diesel procedure used is described in SAE paper
number 700671. It is a steady state procedure for testing
a Diesel engine on an engine dynamometer with engine load
as the operating variable at each of two engine speeds,
"Rated" and "Intermediate." The load is varied from zero
to maximum torque available at the particular engine speed,
in steps of 25% of maximum torque. Three idle periods are
interspersed among these load poin;ts, for a total of 13
operating modes. :
From data supplied by Mr. J.M. Nunez of Chrysler (who was
contacted for us by Mr. David Randolph of LTV) it was
determined that Rated speed for the 413 engine was 3200 rpm.
The Intermediate speed is defined in the Diesel procedure
as "Peak torque speed or 60% of rated speed, whichever is'
higher." On the Chrysler 413, peak torque occurs at 2000-
2100 rpm, so 2000 rpm was used as the Intermediate speed.
The engine loads at each speed were based on the estimated
output of the Rankine system, which information was acquired
from Sundstrand. The Rankine system will deliver to the
wheels a maximum of 70 hp at its Rated speed and 50 hp at
60% of its Rated speed. .. .
The procedure for our l3-mode tests was to establish the
desired engine speed with the transmission engaged and the
chassis dynamometer water brake fully unloaded. In this
condition the dynamometer still absorbed 7 hp because of
internal friction. After sufficient time in this mode for
collection of an adequate sample of the diluted exhaust gas,
the water brake load was then increased to 25%, 50%, 75%,
and 100% of the maximum power at the chosen engine speed,
with bag samples collected at each condition. The idle
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modes were run with the transmission engaged and the bus
brakes on to prevent creeping. Power absorption limitations
prevented us from running in the 70 hp @ 3200 rpm mode.
In addition to the emissions test a simple exterior noise
test was conducted using the SAE Recommended Practice J366,
for full throttle acceleration only. Two runs were made in
each direction. The closed throttle deceleration test was
not run.
Results
Mass emissions are reported here in grams per minute for
the 13-mode tests. Specific mass emissions in grams per
rear wheel horsepower-hour have also been calculated. Data
from the AA-1 bus route tests is presented in grams per
mile. The length of the bus route was estimated to be
eight miles. From the steady state tests the data is pre-
sented in both grams per minute and grams per mile.
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Data from the bus route tests are presented in Table 1.
Emissions of C02 are included to indicate fuel consumption.
The variability of CC>2 emissions was greater than normally
experienced, and the variability of HC and NOx emissions
was less than expected, considering the apparent condition
of the engine.
Quite early in our testing a random knocking noise was
heard in the engine. Informal diagnosis by our experienced
technicians was that the noise was due to problems in the
valve train of one of the cylinders. The bus was taken,
at the suggestion of Chrysler, to the Continental-Kromis
engine repair center, which specialize in Chrysler engines.
It was returned two days later with a report that the engine
Was okay. The tests and the knocking continued, with an
intermittent miss developing soon after. The knock and the
miss disappeared when the engine was heavily loaded.
Data from the steady state tests are presented in Table 2.
On the basis of grams per mile there was little change in
emissions when speed was increased, except for the HC
emissions. The increase in road load power from 15 mph
to 35 mph was apparently not enough to affect NOx emissions
greatly. The C02 emissions, in grams per mile, decreased
about 10% when cruise speed was increased from 15 mph to
25 or 35 mph.
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Listed in Tables 3 and 4 are the results from the 13-mode
tests. Table 3 presents emissions in terms of grams per
minute. The Intermediate speed data are fairly repeatable.
Repeatability of the Rated speed data is poor, except for
NOx emissions. The mass emissions in Table 4 are in terms
of grams per rear-wheei horsepower-hour. The efficiency of the
drive train was not knmffl so it was not possible to calculate
brake horsepower.
The arithmetic average of four noise tests, two in each
direction, was 83 dBA. See Table 5. Runs 1 and 3 were
in one direction, with the bus radiator on the opposite
side of the bus from the microphone, and were 2 dBA lower
the runs in the opposite direction with the radiator on
the same side as the microphone.
than
Conclusions
These tests of a gasoline-powered bus were of value to the
T&E Branch mainly for the experience of testing a large
vehicle at high engine loads. The value of the emissions
data is suspect because significant test conditions were
not as they should have been. Because the data are probably
not suitable even as a rough approximation of baseline for
this bus, additional baseline tests are pla-ned when these
limitations are overcome.
Among the conditions that gave rise to questionable data
were the following:
o
The simulated inertia weight was only 5500 pounds,
while the actual bus weight is about 10,500 pounds.
Thus, C02 and NOx emissions were certainly lower
than they should be.
o
Because of power absorption limitations we were not
able to test the maximum load at Rated speed.
The bus was new, with only about 500 to 600 miles
on the odometer. Thus the engine was probably still
in a break-in period and the emissions were probably
not typical of the same engine when broken in.
o
o
The intermittent knocking and misfiring condition of
the engine should not be considered typical or baseline,
and probably had a ~etrimental effect on emissions.
It was not known whether the engine timing and carb-
uretion conformed to the manufacturer's specifications.
o
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It would be valuable to conduct a similar series of tests
in the future, using an adequate chassis dynamometer, on a
Diesel-powered bus as well as a properly operating gasoline
powered bus.
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Table 1
2S-Passenger Gasoline Powered Bus
Mass Emissions
Ann Arbor -1 Bus Route
Grams per mile
Date HC CO C02 NOx Comments
9-17 22.09 100.10 1035.6 10.23 Cold Start
9-20 25.77 130.29 1145.5 11.52 Cold Start
9-23 25.31 97.80 962.8 10.73 Cold Start
9-24 23.75 91. 82 1068.91 11.57 Cold Start
9-20 22.63 115.77 1049.83 11.66 Hot Start
9-21 23.85 101.55 1003.09 11.58 Hot Start
9-23 25.09 109.87 1064.98 11.54 Hot Start'
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Table 2
25-Passenger Gasoline Powered Bus
Mass Emissions
..
Steady State Modes
Grams minute Grams per mile.
per
Mode Date HC CO C02. NOx HC CO CO?, NOx
Idle 9-20 3.70 9.09 93.15 .12 Not applicable
Idle 9-21 3.65 4.35 103.26 .11 Not applicable
I 15 mph 9-20 9.36 17.52 257.5 .65 37.44 70.08 1030.0 2.60
"
ij 15 mph 9-21 9.00 15.89 220.1 2.42 36.00 63.56 880.4 9.68
I 15 mph 9-23 off 15.5 243.3 2.61 off 62.0 973.2 10.44
i scale scale
,
25 mph 9-20 12.83 -"32.26 373.3 5.06 30.79 77.42 895.9 12.14
25 mph 9-21 13.07 25.05 365.7 4.87 31.37 60.12 877.7 11.69
25 mph 9-23 off 23.71 335.7 4.54 off 56.90 805.7 10.90
scale scale
off off
35 mph 9-20 . ".\.,,;....-. 7.42 9.39 899.5 12.72
; 5.48 scale 524.7 scale
i~ . 35 mph 9-21 6.46 46.62 510.2 6.44 11.07 79.92 874.6 11.04
, - 35 mph 9-23 7.41 43.99 472.7 5.79 12.70 75.41 810.3 9.93
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Table 3
25-Passenger Gasoline Powered Bus.
Mass Emissions
CARB-EMA 13-Mode
Diesel Engine Test Procedure
Grams per minute
Mode Date HC CO C02 NOx
Idle 9-23 2.91 10.61 109.95 .15
Idle 9-23 3.58 4.36 91.97 no data
Idle 9-24 3.40 4.10 92.85 .16
7 hp@2000 rpm 9-23 8.91 35.20 457.94 6.24
7 hp@2000 rpm 9-23 9.16 34.41 428.20 5.28
7 hp@2000 rpm 9-24 3.36 31.90 446.63 6.89
13 hp@2000 rpm 9-23 6.38 39.76 . 464.30 7.06
13 hp@2000 rpm 9-23 6.15 38.41 4 36 . 4 i'" 5.99
25 hp@2000 rpm 9-23 2.73 off scale 562.05 9.66
25 hp@2000 rpm 9-23 3.04 off scale 550.49 9.02
25 hp@2000 rpm 9-24 2.47 47.12 530.16 10.47
tp@2000 rpm 9-23 6.59 48.15 off scale off scale
3"'l'J"""hp@2000 rpm 9-23 2.42 off scale 588.21 11.20
SO hp@2000 rpm 9-23 2.34 45.49 686.40 off scale
50 hpG2000 rpm 9-24 2.56 off scale 674.93 12.78
Idle 9-23 3.13 5.70 92.63 .07
Idle 9-23 2.76 9.27 130.0 .23
Idle 9-24 2.18 5.95 107.16 .39
7 hp@3200 rpm 9-23 3.65 off scale 714.69 12.45
7 hp@3200 rpm 9-24 2.79 49.53 619.55 12.18
18 hpG3200 rpm 9-23 3.11 off scale 752.74 14.48
18 hp03200 rpm 9-24 2.18 47.09 591.72 12.76
35 hpG3200 rpm 9-23 3.33 off scale 867.07 off scale
35 hpG3200 rprn 9-24 1. 78 35.88 574.07 13.94
53 hp@3200'rpm 9-23 3.70 off scale off scale off scale
I d 1 c 9-23 2.22 10.93 110.33 .23
Idle 9-24 1. 84 4.48 ~0.48 .28
"
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Table 4
25 - Passenger Gasoline Powered Bus
Mass Emissions
CARB - EMA 13 - ~Iode
Diesel Engine Test Procedure
Grams per rear wheel horsepower-hour
Mode Date HC CO C02 NOx
7 hp @ 2000 rpm 9-23 76.4 301.7 3925.2 53.49
7 hp @ 2000 rpm 9-23 78.5 294.9 3670.3 45.26
7 hp @ 2000 rpm 9-24 28.80 273.4 3828.3 59.06
13 hp @ 2000 rpm 9-23 29.45 183.5 2142.9 32.58
13 hp @ 2000 rpm 9-23 28.38 177.3 2014.2 27.65
off
25 hp @ 2000 rpm 9-23 6.55 scale 1348.9 23.18
off
25 hp @ 2000 rpm 9-23 7.30 scale 1321.2 21.65
25 hp @ 2000 rpm 9-24 5.93 113.1 1272.4 25.13
off off
38 hp @ 2000 rpm 9-23 10.41 76.03 scale scale
off
38 hp @ 2000 rpm 9-23 3.82 scale 928.7 17.68
off
50 hp @ 2000 rpm 9-23 2.81 54.59 823.7 scale
off
50 hp @ 2000 rpm 9-24 3.07 scale 809.9 15.34
off
7 hp @ 3200 rpm 9-23 31.29 scale 6125.9 106.7
7 hp @ 3200 rpm 9-24 23.91 424.5 5310.4 104.4
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Table 4 conti,nue"d
Mode Date HC CO C02 NOx
-
off
18 hp @ 3200 rpm 9-23 10.37 scale 2509.1 48.27
18 hp @ 3200 rpm 9-24 7.27 157.0 1972.4 42.53
off off
35 hp @ 3200 rpm 9-23 5.71 scale 1486.4 scale
35 hp @ 3200 rpm 9-24 3.05 61.51 984.1 23.90
off off off
S3 hp @ 3200 rpm 9-23 4.19 scale scale scale
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Table 5
25 - Passenger Gasoline Powered Bus
Noise Tests
per
SAE RP J366
Full Throttle Acceleration,
Run 'No. Noise Level
!
1 ~ 8 2 d BA
2 84 dBA
3 82 dBA
4 84 dBA
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