75-29 AEB
Idle Fuel Consumption in Passenger Cars
July 1975
Technology Assessment and Evaluation Branch
Emission Control Technology Division
Office of Mobile Source Air Pollution Control
Environmental Protection Agency
-------
Background
The Environmental Protection Agency has received numerous requests
for idle fuel consumption data. The purpose of this report is to provide
data which can be used to calculate the energy impact of various actions
taken to reduce vehicle.time spent at idle.
The conclusions drawn from the test data are necessarily of limited
applicability. The data base includes only late model vehicles. A com-
plete evaluation of the energy impact of actions taken to reduce vehicle
idle time requires more vehicle models and a larger sample of these
test vehicles than is included in the data base.
Vehicles Tested
EPA conducts surveys of the sources and causes of air pollution,
including light duty vehicle emissions, the results of which are used
to calculate and predict emissions on a national and local basis.
Idle fuel economy for 1972-74 vehicles was a by-product of a recently
conducted survey of passenger car exhaust emissions.
The vehicles tested, passenger cars using the conventional gasoline
engine, were selected on the basis of mileage, make, and age to be
representative of in-use vehicles. Vehicle weights ranged from 2000 to
5500 pounds. The vehicles were checked for exhaust leaks and safety,
and were tested in the as received condition.
Several passenger cars using other engines have been tested at the
EPA emissions laboratory, some of which used a diesel or stratified charge
engine. These types of engines are presently available in a limited
number of production passenger cars (Honda CVCC stratified charge, Mercedes-
Benz Diesel, Peugeot Diesel). A few experimental steam and turbine
engined cars were also tested. Thewehicles tested at EPA were properly
tuned prior to testing. ^
Test Procedure
Vehicle exhaust emission tests were conducted using methods similar
to the 1975 Federal Test Procedure (1975 FTP). After the vehicle had
stabilized at idle,, a diluted exhaust sample was drawn off and analyzed.
Idle mass emissions were calculated from the mass flow rate and pollutant
concentrations of the diluted vehicle exhaust. Fuel consumption was
calculated by a carbon balance method, which equates the carbon in the
fuel to the carbon in the emission products.
Test Results
The results of tests for vehicles in the Denver, Detroit, and Houston
areas were:
-------
—2—
Average Idle Mass Emissions
grams per minute
HC C0_ NOx Fuel Consumption
1972 Vehicles .94 18.6 .38 .82 gallons/hr.
1973 Vehicles .88 15.4 .15 .80 gallons/hr. .
1974 Vehicles . .86 .13.2 .20 .85 gallons/hr.
All Vehicles .90 16.4 . " .25 .82 gallons/hr.
The sales-weighted idle fuel consumption was .82 gallons per hour.
The average idle fuel consumption ranged from .4 gallons per hour for light
vehicles with small engines to 1.2 gallons per hour for heavy vehicles with
large engines. The results are tabulated in Table 1 and 2 and plotted
in Figures 1 and 2.
Vehicle inertia weight categories were selected according to the 1975
FTP. Vehicle engine displacement categories were selected to place the
most popular engine sizes (i.e., 250, 307, 350, 400 and 455 CID) in
separate categories.
For each engine displacement or vehicle weight category the idle
fuel consumption mean (x) and standard deviation(s) were calculated (Table
1 and 2). The considerable variability in vehicle-to-vehicle idle fuel
consumption is evident from the magnitude of the standard deviation (15
to 65% of the mean). The cause of this large variability is most likely
caused by differences in idle speed, idle air/fuel ratio and idle spark
timing.
A linear regression analysis of the graphs of Figures 1 and 2 shows
a correlation between idle fuel consumption, vehicle weight, and CID.
Idle fuel consumption increased .16 gallons per hour for each 100 cubic
inch increase in engine displacement. Because heavier vehicles tend to
use larger engines idle fuel consumption increased .21 gallons per hour
for each 1000 pound increase in vehicle weight.
The results for vehicles using the non-standard engines are tabulated
in Table 1 and plotted in Figures 1 and 2. The diesel and stratified
charge vehicles had significantly lower idle fuel consumption than the
conventional vehicles.
-------
-3-
The TCCS is known to be capable of much lower fuel consumption
levels, but at a very high level of HC. The technique used to obtain
low HC levels is to increase the exhaust temperature during idle and
light load conditions by throttling the intake air. This can cause
substantial increases in fuel consumption.
Conclusions
The sales-weighted idle fuel-consumption for 1972 to 1974 vehicles
is .82 gallons per hour. Because heavier vehicles tend to use larger
engines, idle fuel consumption ranges from .4 gallons per hour for light
vehicles with small engines to 1.2 gallons per hour for heavy vehicles
with large engines. The idle fuel consumption penalty is .08 gallons
per hour for each 50 cubic inch increase in engine size.
-------
Figure 1
Idle Fuel Consumption vs. Engine Displacement
For Production and Experimental Cars
Texaco
© Diesel
X Stratified Charge
A Lean Burn
Chrysler
A
* CVCC
Dresser
CVCC
204D
O220D, Nissan, TCCS
504D Q9 Opel
® Turbocharged 220D
71/100 101/125 126/175 176/225 226/275 276/325 326/399
Displacement (Cubic in)
406/450 451 +
* See text on TCCS
-------
Table I
Idle Fuel Consumption vs. Engine Displacement
Idle Fuel Consumption - Gallons/Hour
Displacement
cubic inches
71-100
101-125
126-175
176-225
226-275
276-325
326-399
400-450
451 & above
Number of
Vehicles
21
16
10
8
8
36
64
35
24
Mean
.39
.48
.48
.56
.69
.80
1.01
.98
.96
Standard
Deviation
.17
.31
.21
.17
.34
.25
.44
.34
.23
Low
.20
.20
.26
.32
.28
.44
.39
.46
.57
Range
High
.80
1.34
1.01
.78
1.43
1.34
3.43
1.92
1.67
-------
Table II
Idle Fuel Consumption vs. Inertia Weight
Idle Fuel Consumption - Gallons/Hour
Inertia 'Weight
Pounds
2000
2250
2500
2750
3000
3500
4000
4500
5000
5500
Number of
Vehicles
5
13
21
7
23
31
48
51
19
4
Mean
.44
.40
.41
.48
.72
.93
.92
.98
.94
1.16
Standard
Deviation
.22
.16
.19
.23
.38
.55
.23
.32
.23
.36
Low
.21
.20
.20
.28
.28
.45
.39
.52
.50
.88
Range
High
.80
.71
1.01
.95
1.48
1.91
1.91
1.95
1.36
1.67
Note: The above trend is obviously one of engine size not vehicle weight
because heavier vehicles tend to use larger engines.
-------
Table III
Idle Fuel Consumption
Vehicle
*
Aerojet Steam (Vega)
Carter Steam (VW)
Chrysler Turbine (Satelite)
Dresser (Capri)
Honda CVCC (Civic-stratified)
Honda CVCC (Impala-stratified)
Mercedes Benz (Turbocharged
220 Diesel)
Mercedes Benz (220 Diesel)
**
Nissan Diesel
Opel Rekord (2100 Diesel)
Peugeot 204D (Diesel)
Peugeot 504D (diesel)
Steam Power Systems*
Texaco TCCS (M-151, Jeep)
(Stratified)
Yamaha Lean Combustion System
(Corolla)
Ethyl Lean Burn
Chrysler Lean Burn
TCCS Cricket (Diesel)
Displacement
cubic inches
Inertia Weight
pounds
Idle Fuel Consumption
gallons/hour
**
(Gasoline)
**
N/A
N/A
N/A
159
119
350
134
134
131
126
83
129
N/A
141
97
360
440
141
3000
2750
4500
'2750
2000
5000
3500
3500
3500
3000
2500
3500
3000
2750
2250
4500
5500
2500
1.90
.64
1.44
.42
.26
.58
.18
.26
.13
.21
.24
.21
1.26
1.73
.67
.79
1.22
.24
.24
**
Not EPA test data
EPA sponsored test
-------
Idle Fuel Consumption vs. Weight
For Production and Experimental Cars
Aerojet
Texaco
Diesel
Stratified Charge
Steam
Gas Turbine
Lean Burn
Chrysler
Steam Power Systems
Chrysler
.Yamaha
CVCC
Dresser
CVCC®)
204D, TCCS
Opel
220D , Nissan
504D
220D (Turbocharged)
2000
2500 3000
3500 4000
4500 5000
* See text on TCCS
Vehicle Inertia Weight (pounds)
5500
------- |