77-16 AB
The Effects on Measured Emissions of a
Modified FTP Driving Cycle
November 1977
Technology Assessment and Evaluation Branch
Emission Control Technology Division
Office of Mobile Source Air Pollution Control
Environmental Protection Agency
Prepared by: Anthony E. Barth
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77-16 AB
The Effects on Measured Emissions of a Modified FTP Driving Cycle
November 1977
Technology Assessment and Evaluation Branch
Emission Control Technology Division
Office of Mobile Source Air Pollution Control
Environmental Protection Agency
Prepared by: Anthony E. Barth
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Background
EPA has been testing vehicles for many years using the Federal Test
Procedure (FTP). These procedures specify standard conditions for
vehicle emission testing. Certification tests and surveilance/testing
of in-use vehicles use these procedures to obtain data which can be used
as input for studies of atmospheric pollution.
However, localized control strategies or specific problems often require
data that is not normally generated using the standard FTP. To meet
these needs specific test programs are undertaken to answer the questions
raised. One recent program extensively investigated the effects of
vehicle soak temperatures on emissions. To complement this effort a
short test series was undertaken to quantify the probable emission
effects of a modified driving cycle and the results are the subject of
this report.
Specifically, this test program was designed to determine the effects of
delaying vehicle warm-up. This was accomplished by substituting slow
speed start-stop driving for the higher speeds normally used at the
start of the standard driving cycle.
The conclusions from this EPA evaluation test can be considered to be
quantitatively valid only for the specific car used; however, it is
reasonable to extrapblate the results from the EPA test to other types
of vehicles in a directional or qualitative manner, i.e., to suggest
that similar results are likely to be achieved on other types of vehicles
using similar emission control technology.
Abstract
For the test vehicle, a 1976 Chevrolet Impala, HC and CO emissions were
found to be sensitive to the sequence in which the speed versus time
profiles of the driving trace are arranged. In the case of the restructured
cycle which was investigated, cold start HC emissions increased by
approximately 18% because the activation of vehicle emission control
systems was delayed due to reduced vehicle speeds during the initial few
minutes of operation. Both cold and hot start CO emissions increased by
approximately 33%. A fuel economy penalty of 7% was also observed. No
change in NOx emissions was observed.
Vehicle Description
The test vehicle chosen for this project was a 1976 Chevrolet Impala
with an automatic transmission. The vehicle was equipped with a two
venturi, 350 CID V-8 engine. This vehicle uses a catalyst and EGR for
emission control. The vehicle was a production sedan calibrated to meet
the 1976 Federal Emission Standards of 1.5, 15, 3.0 grams per mile for
HC, CO, and NOx respectively. The vehicle, which had been used exten-
sively in other test programs at the MVEL, is described in detail at the
end of the report. This vehicle was equipped with temperature probes
for this program to monitor vehicle warm-up characteristics.
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Test Procedures
Gaseous exhaust emission tests were conducted as follows: one was run
using the standard urban driving cycle (UDDS) as specified in the 1977
Federal Test Procedure ('77 FTP) described in part 40 of the Combined
Federal Register of July 1, 1976 and two other tests were run using the
same procedure except with a modified driving cycle. No evaporative
emission tests were conducted.
The tests were conducted on a chassis dynamometer and use a constant
volume sampling (CVS) procedure, which gives exhaust emissions of HC,
CO, C0_, and NOx in grams per mile. Fuel economy was calculated by the
carbon balance method. The fuel used was indolene clear, a no-lead 91
RON gasoline. All tests were conducted using an inertia weight of 4500
pounds (2041 kg) with a road load setting of 14 horsepower (9.5 kw) at
50 miles per hour (80.5 km/hr).
The EPA Urban Dynamometer Driving Cycle is a speed versus time schedule
that is used for vehicle emission testing. This driving cycle is 7.45
miles long and takes 1371 seconds to drive. The cycle is divided into
two driving segments. The first segment is 3.59 miles long and takes
505 seconds to drive. The second segment is 3.91 miles long and takes
866 seconds to drive. The first segment of this cycle is repeated
following a 10 minute soak. The emissions results of each test segment
are weighted together to obtain emission and fuel economy results that
are representative of the vehicle's emission performance during hot and
cold driving. This cycle causes the vehicle to warm up quite quickly as
the freeway simulation part of the cycle occurs during the first few
minutes of driving.
The modified driving cycle was designed to deemphasize vehicle warm-up.
The first segment, less the initial 20 seconds of idle, was placed at
the end of the second segment. Thus, in terms of the standard cycle's
speed/time schedule, the modified cycle was 0 thru 20 seconds (idle),
511 thru 1366, 21 thru 505, and the last 5 seconds of idle. Thus by the
end of each cycle a vehicle has travelled the same distance and has been
driven similarly, although not in the same sequence. Since vehicles are
usually reasonably warmed up by the end of the first 505 second segment
of the test, the new cycle was split at a similar point. Thus, for both
cycles, bag 1 emissions should be representative of the vehicle cold
start and warm up emissions. The two cycles' characteristics are:
Bag 1 Bag 2
Time Miles Avg. Speed (MPH) Time Miles Avg. Speed(MPH)
Standard Cycle 505 3.59 25.6 867 3.91 16.2
Modified Cycle 538 2.69 18.0 834 4.76 20.6
Bag 3 is a repeat of bag 1 after a 10 minute soak of the vehicle. A
driving schedule detailing each cycle is given in Figure 12.
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To further quantify the emission effects of the altered driving cycle,
modal emissions were taken. The modal system is a continuous exhaust
measurement system which is used to calculate the pollutant emissions
throughout the driving cycle. The system gives total exhaust mass
emissions as well as mass emissions for each mode of the driving cycle
(a mode consists of an idle, acceleration, cruise, and deceleration to
zero mph). . Vehicle temperatures were also monitored during the modal
tests.
Test Results
Exhaust emissions data, summarized below, showed that the 1976 Chevrolet
was well within the standards of 1.5 gm/mi HC, 15.0 gm/mi CO, and 3
gin/mi NOx for both driving cycles. Detailed bag results are listed in
Tables I, II, and III at the end of this report.
'75 FTP Composite Mass Emissions
grams per mile (grams per kilometre)
Baseline Standard
Driving Cycle (1)
Modified Driving Cycle
Percentage Change (2)
From Baseline
.48
(.30)
7.31
(4.54)
662
(411).
2.29
(1.42)
HC CO C0_2. NOx Fuel Economy
13.2 miles/gal
(17.8 liters/100 km)
.56 9.85 699 2.41 12.3 miles/gal
(.35) (6.12) (434) (1.50) (19.1 liters/100 km)
17% 35% 6% 5% -77.
(1) Values in parenthesis denote metric units.
(2) A positive value indicates an increase in emissions or fuel .economy
In both cases the driving cycles were 7.45 miles long and the calcula-
tions use the standard weightings of 43% cold driving and 57% hot driving.
Thus this vehicle showed substantial increases in HC and CO emissions
with a low speed start/warm-up driving cycle. There was also a slight
decrease in fuel economy. The slight increase in NOx emissions is not
significant due to the data scatter.
The t'est data was also analyzed to determine if these effects were pri-
marily a function of cold start. The cold start driving cycle used in
Figure 1 is obtained by combining the emission results for bags 1 and 2.
The hot start driving cycle consists of bags 3 and 2. The results are
summarized in the following figure:
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a)
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HC
CO 2
Cold Start Cycle
(Bag 1 & Bag 2 Mod. Cycle)
(Bag 1 & Bag 2 Std. Cycle)
Hot Start Cycle
(Bag 2 & Bag 3 Mod. Cycle)
(Bag 2 & Bag 3 Std. Cycle)
NOx
MPG
Mass Emissions
Percentage Change from Baseline Cycle
Figure 1
These cold and hot start tests show that CO emissions increase sub-
stantially with driving cycles that do not cause rapid catalyst warm up.
HC emissions are increased substantially only during cold start. The
effects on NOx emissions and fuel economy are smaller. The tendency is
to raise NOx emissions slightly and lower fuel economy slightly,
To more thoroughly investigate the above effects, the tests were repeated
using a modal analyzer system. Figures 2, 3 and 4 show the total mass
emissions versus cycle miles traveled. These results reaffirm the above
findings and show the effects in detail. The vehicle HC emissions are
quite high on the modified cycle due to the delay in vehicle warm up.
Once the emission control system becomes effective, total HC emissions
increase at a very low rate. This rate of increase in total HC emission
appears to be the same for both cycles. Thus, HC emissions are apparently
relatively sensitive to driving patterns which delay vehicle warm up or
moderate catalyst cooling.
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Similarly, CO emissions are quite high due to the delay in vehicle warm
up. Once the emission control systems become effective, total CO emissions
increase at a very low rate. However, this rate of increase is higher
than for the standard cycle. Thus, CO emissions appear more sensitive
than HC emissions to cycle configuration and moderate cooling during
short vehicle shut down periods.
NOx emissions are very similar for both cycles. Figure 4 shows that,
although the standard cycle is initially higher in NOx, this is due to
the higher initial speeds. By 7.45 miles a vehicle using both cycles
has traversed the same distance and has experienced the same type of
driving. At this time, the NOx emissions are substantially equal.
The modal analysis system permits the determination of catalytic converter
efficiency by measuring pollutant concentrations before and after the
catalyst. Figures 5 through 8 detail the HC and CO converter efficiency
for both cycles. Figures 5 and 6 show that, at equal distances, the
modified cycle shows greater efficiency. However, this is due to the
greater time for warm-up, not efficiency in warming up. Figures 7 and 8
show that, for a given time, the standard cycle has warmed up the
catalyst more efficiently and thereby reduced total mass emissions.
Figures 9 through 12 provide engine temperature data to further illustrate
these trends. The most important difference between the two cycles is
the delay in engine coolant warm up on the modified cycle. . The summary
table following these figures further clarifies these trends.
The effect of this modified driving cycle on other vehicle technologies
is not known but can be surmised. Usually a vehicle with an air pump
and a catalyst will start out with high emissions and then drop to
extremely low levels for most of the FTP. Thus any delay in catalyst
light off could be expected to have more detrimental effects on a vehicle
with an air pump than this non-air pump equipped catalyst vehicle.
Vehicles operating with lean fuel/air ratios, such as stratified charge
engines, usually achieve their emission control by maintaining a relatively
low emission at constant levels. Thus the effect of this modified cycle
on a lean mixture vehicle would probably be minimal.
Conclusion
For a 1976 Chevrolet Impala, HC and CO emissions are sensitive to the
order in which a particular driving cycle is driven. Cold start HC and
CO emissions will increase about 18% and 30%, respectively if vehicle
emission control system functioning is delayed by reducing vehicle
speeds during the initial few minutes of operation.
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13
Vehicle Temperature Summary
Parameter Standard Cycle Modified Cycle
Carburetor air temperature
a) Peak temperature and time
into cycle 124°F @ 210 sec. 123°F @ 240 sec,
b) Stabilize temperature and
time into cycle 89°F @ 285 sec. 86°F @ 345 sec.
Engine water temperature 202°F @ 270 sec. 201°F @ 300 sec,
Engine oil temperature 216°F @ 21 min. 220°F @ 20 min.
Catalyst skin temperature 620°F @ 300 sec. 560°F @ 420 sec,
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14
TEST VEHICLE DESCRIPTION
Chassis model year/make - 1976 Chevrolet Impala
Emission control system - EGR, Catalyst
Engine
type 4 stroke, Otto cycle, OHV, V-8
bore x stroke 4.00 x 3.48 in (101.6 x 88.4 mm)
displacement 350 cu in. (5735 cc)
compression ratio . 8.5:1
maximum power @ rpm
fuel metering Single 2 barrel carburetor
fuel requirement . . ,~." .....' Regular unleaded (tested with 96 RON Indolent
unleaded, containing .03 percent sulfur)
Drive Train
transmission type . Automatic
final drive ratio 2.73
Chassis
type Front engine, rear drive
tire size 'HR 78 x 15
curb weight 4266 pounds
inertia weight 4500 pounds
passenger capacity , . 6
Emission Control System
basic type Exhaust Gas Recirculation (EGR)
Singel Pelletted Catalyst
Early Fuel Evaporative System (EFE)
Durability accumulated on system - 5100 miles
Vehicle Identification Number - 1L47V61234368
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Table 1
'75 FTP Mass Emissions
grams per mile
Test Bag 1 Cold Transient
Bag 2 Hot Transient
Number HC CO C02 NOx MPG HC CO CO 2 NOx MPG HC
78-0451* 1.58 27.32 688, 3.28 12
78-0559* 1.49 27.86 632 2.66 13
78-0484** 2.31 48.01 716 1.51 11
78-0485** 2.28 38.34 743 1.75 10
* Baseline standard cycle.
** Modified cycle.
.1 .14 1.53 733 1.92 12.1 .25
.0 .13 0.18(1) 665 1.70 13.3 .42
.1 .22 4.36 690 2.70 12.7 .22
.9 .23 4.53 727 3.03 12.1 .41
CO CO 2 NOx MPG
4.19 617 2.91 14.2
4.52 565 2.49 15.5
1.47 637 1.52 13.9
1.49 659 1.60 13.4
(1) Although this value is exceptionally low for CO for this vehicle,
for this test, identical results were achieved for bag 2 CO for
both the modal and CVS systems. These systems sample and analyze ^
the pollutants independently.
'75
Test Number
78-0451*
78-0559*
78-0484**
78-0485**
Table 2
FTP Composite Mass Emissions
grams per mile
HC- CO CO 7 NOx MPG
0.47 7.5.6 692 2.47 12.6
0.49 7.06 631 2.11 13.8
0.54 10.54 683 2.27 12.7
0.58 9.15 715 2.54 12.1
* Baseline standard cycle.
** Modified cycle.
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Table 3
174 FTP Composite Mass Emissions
grams per mile
Test Number
78-0451
78-0559
78-0484**
78-0485**
Cold Start
HC
.84
.79
.97
.97
CO
13.97
13.52
20.11
16.74
CO 7
716.41
654.9
700
732
NOx
2.59
2.17
2.27
2.57
MPG
12.1
13.8
12.1
11.6
HC
.20
.29
.22
.29
Hot Start
CO
2.82
2.27
3.32
3.43
CO?
682
622
671
702
NOx
2.41
2.09
2.28
2.52
MPG
12.9
14.2
13.1
12.5
** Modified cycle.
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17
Vehicle Temperature Summary
Parameter Standard Cycle Modified Cycle
Carburetor air temperature
a) Peak temperature and time
into cycle 124°F @ 210 sec. 123°F @ 240 sec,
b) Stabilize temperature and
time into cycle 89°F @ 285 sec. 86°F @ 345 sec,
Engine water temperature 202°F @ 270 sec. 20l°F @ 300 sec.
Engine oil temperature 216°F @ 21 min. 220°F @ 20 min.
Catalyst skin temperature 620°F @ 300 sec. 560°F @ 420 sec.
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. Bag 2
.Bag 1 . ••"•(. . .
» i _„._.;_.__
Standard Cycle
-(-Time
00
Modified Cycle
•frSpeed
Figure 12
Driving Cycles
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