EPA-AA-TEB-EF-86-03
Emission Factor Testing
Needs in the Latter 1980s
by
Thomas L. Darlington
June 1986
Test and Evaluation Branch
Emission Control Technology Division
Office of Mobile Sources
U.S. Environmental Protection Agency
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Emission Factor Testing Needs
in the Latter 1980s
1.0 Summary
2.0 Background
3.0 General Testing Needs by Vehicle Type
3.1 Light-Duty Gasoline Vehicles
3.2 Light-Duty Gasoline Trucks
3.3 Heavy-Duty Trucks, and Buses
3.4 Light-Duty Diesel Vehicles and Trucks
3.5 Off-Highway Vehicles
4.0 Specialized Needs
4.1 Evaporative Emissions
4.2 Exhaust Emissions at Different Temperatures
4.3 CO Emissions at Low Speeds
4.4 Effects of Repairs
4.5 Disablement Testing
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Emission Factor Testing Needs in
the Latter 1980s
1.0 Summary
Emission Factor testing is important because of its use
in MOBILES, which is in turn used to prepare State
Implementation Plans (SIPs), Environmental Impact Statements
(EISs), and develop real world benefits for EPA regulatory
proposals. Many others (auto manufacturers, GARB) use the
emission factor data directly for many different purposes.
There are a variety of current and future emission
factor testing needs which are enumerated below. EPA should
consider increasing its commitment to emission factor testing
so that these needs are adequately addressed.
Summary of EF Testing Needs
0 Carbureted Cars - at higher mileages (70+K)
0 Fuel injected cars - at higher mileages (50+K)
0 Continued or increased testing at alternate sites
0 Older cars (10-15 years old)
0 Future cars/trucks with onboard systems or systems
certified with higher volatility fuels
More emphasis on LDGTs
Chassis testing of heavy duty trucks
Continued testing of transit bus engines
Continued testing of heavy duty gasoline engines, if
feasible
0 Some testing of LDDTs
Continued testing of temperature effects on
evaporative emissions
Characterization of evaporative HC running losses
High altitude evaporative HC testing
Low temperature testing of carbureted and fuel
injected cars with wintertime fuels
0 Modal testing of new technology cars to aid in CO
modeling at intersections
* Effectiveness of certain repairs
4 FTP effects of pattern case fixes
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2.0 Background
EPA's emission factor data base, which contains emission
tests on over 12,000 in-use light-duty vehicles and trucks
tested since 1971, is EPA's best source of information on how
cars and trucks actually perform on the road. As a data set on
in-use car performance with respect to emissions and fuel
economy, it is second to none in size and completeness of
information on each car tested- It is used primarily by the
Emission Control Technology Division of EPA's Office of Mobile
Sources (QMS) to update its in-use emissions' models such as
MOBILES, and to estimate the benefits of certain regulatory
proposals, for example, volatility controls. States and local
areas are relying on the data through the use of MOBILE3 to
estimate emission inventories, determine the effects of I/M and
antitampering programs, and determine the effects of
transportation control measures and construction projects.
Others are given free access to the data, and use it on a
periodic or as-needed basis. For example, most of the major
auto manufacturers have requested access to the data, and some
review the new data on a weekly or monthly basis to determine
the in-use performance of their cars. The potential benefits
of their concern with in-use performance should not be
underestimated. Another example user is the California Air
Resources Board (GARB), which has an ongoing in-use testing
program of its own. CARB is currently using the EPA data to
compare their estimates of light-duty vehicle emission factors
to EPA's. Other QMS divisions have also used the emission
factor data base on numerous occasions.
With all of its current merits, in order for the data
base to remain useful, EPA must have a high commitment to
continued emission factor testing, and should consider
increasing that commitment. There is, and will be, a great
need to test new technology vehicles at a wide range of
mileages and ages (to assess durability); vehicles with new
fuel delivery systems (fuel injection), new emission standards,
and perhaps new evaporative control hardware (onboard
systems). Additionally, there are many special emission factor
testing needs which have not yet been addressed. All of these
needs, both present and future, will be discussed in this paper.
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3.0 General Testing Needs by Vehicle Type
3.1 Light-Duty Gasoline Vehicles (LDGVs)
Carbureted Cars - Although fuel injected cars are
rapidly becoming more common, carbureted closed loop cars will
continue to dominate the in-use fleet in the late 1980s. The
emission factors for these cars are based on quite a few cars
tested at low mileages and some cars tested at the higher
mileages (see Figure 1). The emission data indicated that cars
could be divided into three groups by emission levels - normal
emitters, high emitters, and super emitters. The high emitting
cars usually have one or two problems which make them emit
above the normal cars. The super emitters have extraordinary
problems, either in numbers or type, that make them emit far
above the high emitters. As the fleet of new technology cars
grows older, more are expected to migrate from the normal
category into the high and super emitter categories. The
emission rates of the fleet of carbureted closed-loop cars are
very dependent on how quickly this migration occurs. In turn,
the emission rates of all LDGVs are quite dependent on the high
mileage cars, since 50% of the LDGV VMT is from cars with
odometer values above 50,000 miles. Therefore, it is important
to be able to predict the rate of growth of the high and super
emitter categories with confidence, and also their average
emission levels. To do this effectively, EPA needs more data
on carbureted cars tested at mileages above 7OK miles.
Another point with respect to the high mileage data we
do have is that it is from cars that accumulated the mileage
quickly, since most of the tests were performed two or three
years ago on 1981 cars when they were only about two to three
years old. Most cars accumulate mileage slower than that, for
example, a 1981 car sold in January of 1981 would be expected
to have about 55,000 miles on it at this time. Emissions from
normally accumulated mileage cars could be somewhat higher than
advanced accumulated mileage cars since they may experience
more cold starts and more severe stop-and-go driving than the
advanced mileage cars.
Fuel Injected Cars - Manufacturers are introducing fuel
injection on new and existing engines at a rapid pace. EPA's
emission factor program has been focusing on these cars in the
last two years for evaporative as well as exhuast emission
reasons, but we clearly have little high mileage data on fuel
injected cars (see Figure 2). Generally, our experience to
date has been that fuel injected cars are cleaner than
carbureted cars. We have not found a fuel injected car in the
super emitter category yet, and those in the high" and normal
categories have lower average emissions than their carbureted
counterparts. However, a somewhat new development with fuel
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injected cars may change this outlook. Many fuel injected cars
are experiencing injector plugging from deposits that are
building up in the nozzles of the injectors. These deposits
come from in-use gasolines with little or no detergent
additives. (Higher detergent gasolines supposedly can clear
away these deposits.) In a multipoint fuel injected car, the
deposits can disturb the distribution of gasoline into the
cylinders, causing driveability problems potentially resulting
in incomplete combustion and higher HC emissions. We plan to
monitor this situation by inspecting and testing injectors on
EF cars that have HC emissions in excess of about 0.6 g/mi, and
have few or no other apparent problems (such as a three-way
system failure or faulty ignition system). In the last few
months we have seen very few fuel injected cars above 0.6 g/mi
(most are 0.2-0.3 g/mi HC); however, these have been mostly
lower mileage (20K-30K) cars.
All Cars - For the last few years our primary emission
factor testing has been conducted in Ann Arbor (other smaller
and specialized programs have taken place in Denver and East
Liberty, Ohio). Resource considerations have been the
motivating factor in consolidating the testing at the Ann Arbor
site. We do not fault the testing here in any way, but we are
concerned about the risks of basing nationwide vehicle emission
factor estimates on testing primarily at one site. We have
seen differences in evaporative emissions between samples
tested in Ohio and Ann Arbor. Most of the difference we have
been able to attribute to minor test procedure differences, but
the potential exists for different evaporative emissions
between different sites because of the wide differences in
in-use fuels used. It is possible that some fuels cause more
rapid deterioration in evaporative systems than other fuels.
Another consideration is the severity of weather in the
Detroit area. Detroit cars undoubtedly experience more low
temperature cold starts than the national average, and these
conditions are well known for producing engine wear. There is
also more possibility of choke malfunctions. These factors
would make the Detroit sample a higher emitting sample than the
national average.
An ideal solution would involve a return to the
multicity EF programs of the past. As an alternative, it is
imperative that we maintain and perhaps increase our commitment
to the off-site testing we are doing in Ohio and possibly at
other contractor facilities. In addition to studying
specialized concerns at these sites, we can continue to make
comparisons between the as-received tests on cars at the
different sites.
Future Cars - Due to the need for ozone control and
control of air toxics, it is almost a certainty that EPA will
require auto manufacturers to control excess evaporative
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emissions, refueling emissions, or both. This could occur with
the 1989 or 1990 model year. The manufacturers will have to
develop new hardware and alter purge system management to
accomplish this. Naturally, there will be a need to test how
these systems perform in use. A continued and consistent
commitment to EF testing will allow us to perform this critical
testing when the time comes.
Older Cars - The data in Figure 3 illustrate that age
0-5 cars accumulate 50% of the fleet VMT, but only contribute
16-22 percent of the fleet emissions because of their
relatively low emission levels. The most emissions come from
the age 11-15 group, which contributes 35-37 percent of the
fleet emissions. These values take into account the fact that
many of these 11-15 year old cars have been scrapped. The
dominance of the fleet emission factor by these cars can be
traced to the deterioration rate, or increase in emissions with
age/mileage.
This concept is illustrated further in Figure 4 which
shows the yearly emissions of a 1985 car which lasts for 20
years. Each year's emissions are estimated as the product of
the annual VMT and the average emission factor (at year
midpoint) for that year. For 1985 cars that last 20 years,
they produce the most emissions in their twelfth year, the
reason being that their emission rates have increased much
faster than their yearly VMT has dropped.
The implications of these concepts are that if EPA has
missed the mark at all in estimating emission rates of the
1970-75 cars by extrapolating low mileage data to higher
mileages, the current fleet emission rates could be
significantly affected. We suggest that at least 50 twelve
year old cars be tested each year to check the older emission
rates. If the average emissions of these cars are
significantly higher than the equations predict, then some
adjustment could be made. ... ... .
It should be noted that it will be more expensive to
test 50 older cars than 50 newer cars. With newer cars, our
current rejection rate is about 12 percent. These cars are
rejected for being too expensive to repair prior to testing on
the dynamometer. Where a car needs minor nonemission control
repairs such as new brake linings or a new exhaust pipe, we do
make those repairs so the cars can be tested. To conserve
resources we do not, however, replace expensive items such as
faulty transmissions unless they fail during testing.
On older cars there is a greater likelihood that we will
have to reject more cars as too expensive to repair, and that
cars will fail while we are testing them. This will increase
the recruitment and repair costs over what we now pay for newer
cars.
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3.2 Light Duty Gasoline Trucks (LDGTs)
Light duty gasoline trucks, which are all gasoline
trucks under 8500 Ibs gross weight, make up roughly 20% of the
total VMT of all vehicles combined. However, because their
emission rates are higher than light-duty vehicles, they
account for about 32% of the HC and CO emissions of the fleet
(see Table 1), and therefore it is important that their
emission factors are accurately characterized.
Light duty truck manufacturers use very similar emission
control equipment on their cars and light trucks. Many light
trucks are currently equipped with closed loop fuel controls
and 3-way catalysts, even though the current NOx standard is
2.3 gpm, which in many cases probably does not require closed
loop fuel control to attain. Because of the similarities
between light trucks and cars, the emission factors of trucks
are in part developed from the emission factors of cars, for
which there are much more data. However, there are indications
that the resulting emission factors for trucks are too low.
Recently we tested 50 1981 LDTs in Ohio, and found that the CO
emissions of the untampered trucks were 20% higher than what
NOBILE3 would predict for untampered 1981 trucks. Therefore,
we have started testing trucks again in the current EF program,
and since the emission standards of trucks are still changing,
this effort should continue. (The 1985 trucks have a full
useful life definition, 1987 trucks will have a particulate
standard of 0.26 g/mile, and 1988 and later trucks will have a
NOx standard of 1.2 and 1.7 g/mile for 0-6000 pounds and
6000-8500 pound trucks, respectively). Although we do not
think it is necessary or feasible to devote equal resources to
light trucks and cars, there will be a continuing need to
support EF testing of trucks.
3.3 Heavy Duty Trucks (Gasoline and Diesel), and Buses
EPA's data base on in-use emissions for gasoline and
heavy duty trucks has been greatly augmented through
cooperative testing with NVMA and EMA of in-use truck engines.
The cooperative testing program is complete, and the emissions
of these 1979-82 engines will be used in a future update of
model year 1979-1986 emission rates for heavy duty trucks.
The emission rates of trucks tested in this program are
quite similar to MOBILE3 emissions with the exception of HC
emissions from heavy-duty gasoline vehicles, which from the
test data are around 8.7 g/bhp-hr, where MOBILES predicts
around 3.7 g/bhp-hr. The HC emissions for the test engines are
driven by one truck with HC emissions of 43.8 g/bhp-hr, while
the rest of the engines ranged from 3-8 g/bhp-hr. Many of the
gasoline engines were poorly maintained and had evidence of
being tampered.
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The heavy-duty gasoline engine market is dominated by GM
and Ford. Only Ford and Chrysler, however, contributed engines
to the in-use emissions project. If they could be encouraged
to continue sending a few engines each year, we may be able to
refine our emission estimates, particularly for HC.
For both diesel and gasoline engines, it would make
sense to encourage ENA and MVMA to continue the cooperative
in-use testing program on a more limited basis, for example,
each member agreeing to send one or two engines per year. This
way we could have a continuing program, as with light-duty
vehicles and light-duty trucks.
The emission factors for trucks have also been improved
with further attention to the development of the heavy duty
conversion factors which translate engine emissions in g/bhp-hr
to on-road emissions in g/mile. While the emissions in g/mile
have been improved through this analysis, there is still a need
to do further chassis testing of heavy duty trucks as a check
to see that the converted engine emissions are realistic.
Several trucks from each truck class from light-heavy to
heavy-heavy (both gas and diesel) would be needed in this
analysis.
Looking ahead, heavy duty truck HC and CO standards are
made more stringent in 1987, and the NOx and particulate
standards are more stringent in 1988. The NOx and particulate
standards are further tightened in 1991 and 1993. The next
major cooperative in-use program on heavy duty engines should
occur when the 1988 and 1989 model year engines have
accumulated some mileage.
EPA has recently begun to test some transit bus engines
on bus duty cycles, which are significantly different than the
truck transient test, and yield higher levels of some
emissions. Only one bus engine has been tested so far, and to
adequately characterize emissions a. few more are probably
.needed. Although bus emissions are probably not a large part
of any urban inventory, they are important from an exposure
standpoint. ; : •• - --
3.4 Light Duty Diesel Vehicles and Trucks (LDDVs and LDDTs)
Although the manufacturers have significantly pulled
back in their effort to develop diesel cars, there has been
continued development and demand for diesel engines in light
duty trucks. In 1980 the percent of light truck VMT that was
attributed to diesel trucks was less than 1%. It is expected
to grow to about 10% in 1990 and 28% by the year 2000.
The zero mile levels of light diesel trucks are based on
certification levels and the deterioration rates are borrowed
from light diesel vehicles. This, coupled with the fact that
the particulate standard for diesel trucks was lowered in 1985
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to 260 mg/mile, underscores the need to test a few (perhaps
2Q-aQ) 1985 and 1986 light diesel trucks in the next two years.
3.5 Off-Highway Vehicles
There are four main types of off-highway vehicles:
locomotives, construction equipment, aircraft and ships
(vessels). New data are being compiled for locomotives and
aircraft, and the current AP-42 emissions factors for
construction equipment are based on a recent California study.
The off-highway source that needs additional attention is
ships. Although there are some new data, the applicability is
limited. For example, the new data available are for large
diesels used in commercial ships. However, most of the
emissions in a harbor area come from the smaller and newer
diesel powerplants found in tugs and construction barges.
There are very little data for this size engine (around 1500
hp). Testing of a few of these engines on representative duty
cycles is needed for cities like San Diego, Houston and New
York.
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4.0 Specialized Needs
4.1 Evaporative Emissions
As it has become more apparent that many areas of the
nation will not attain the ozone standard by the end of 1987,
EPA has searched for additional HC control measures.
Evaporative emissions from mobile sources have come under close
scrutiny because the volatility of in-use fuels has increased
dramatically over the last decade, thereby leading to higher
vehicle evaporative HC emissions.
EPA has concentrated its testing efforts in quantifying
the "first order" effects on evaporative emissions, namely,
fuel volatility and ambient temperature. EPA now has a
substantial volatility data base with which to estimate
volatility effects and the benefits of volatility controls.
Characterizing the effects of temperature, however, has thus
far proved to be more elusive. The temperature testing is
resource intensive on a per car basis, therefore, only 20 fuel
injected and 20 carbureted cars have received temperature
testing. Furthermore, evaporative emissions are very sensitive
to temperature, leading to high variability in the data. This
underscores the need for continued temperature testing so that
the temperature effects can be reasonably estimated.
Quantifying the temperature effects is also a very
important issue from the standpoint of controls. Ozone
exceedences are known to be associated with hotter summer
weather. The maximum diurnal temperature in EPA's Federal Test
Procedure is 84°F. EPA needs to be sure that whatever
evaporative controls are put in place, that they are effective
for most situations. Accurately characterizing the effects of
temperature on evaporative emissions, and also the ambient
temperatures associated with most ozone exceedences, will
enable us to do that. --..
High ambient temperatures and extended vehicle driving
can also produce an evaporative emission from cars known as
"running losses." When cars are driven, fuel in the tank is
heated by the exhaust system, and in fuel injected cars is also
heated by unused fuel recirculated from the injection system.
The increase in tank fuel temperature produces additional vapor
which is normally purged into the engine while the car is
operating. Under some conditions, however, the rate of vapor
generation can overwhelm the purge system, leading to a rapid
buildup of pressure in the fuel tank. All fuel tanks are
designed to release that pressure through the fuel cap at about
1.5 psi for safety reasons, and that release is a "running
loss." Running losses can also occur during periods of engine
operation where purge is not taking place, such as extended
idle operation. Here the losses may not vent through the cap,
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but instead build-up and overwhelm the canister, since the
canister is not being purged.
At this time there are very little data on the
conditions under which running losses occur. EPA has initiated
a small scale test program on one fuel injected and one
carbureted car to characterize the extent of driving which
would trigger running losses. However, the occurrence of
running losses is probably also very system dependent, and so a
larger scale effort on more cars is needed in the very near
future.
A third area where EPA needs more evaporative data is at
high altitude. Starting with the 1985 model year the high and
low altitude evaporative standard is the same (2g). Since
atmospheric pressure is lower at high altitude, more HC is
produced during a given diurnal at high altitude than at low
altitude. For the same reason, vapor lock is more of a problem
at high altitude than at low altitude, so the oil companies
typically market lower volatility fuels at high altitude during
the summer than are marketed at low altitudes with similar
temperatures.
In EPA's High Altitude Report to Congress, it was stated
that the manufacturers might need to increase canister capacity
to meet the 2g standard at high altitudes. It is known,
however, that some companies are using exactly the same systems
at high as well as low altitude, either because they feel that
their low altitude systems have enough capacity for high
altitude, or that there is a lack of EPA enforcement effort at
high altitude, or both.
The current MOBILE3 high altitude evaporative emission
factors for 1985+ LDGVs are set equal to the low altitude
levels because the standards are the same. But if the systems
are not different, the in-use high altitude evaporative rates
may be higher than at lower altitudes. Therefore, there is a
clear need for in-use evaporative testing of 1985 and later
cars at high altitude. This testing should utilize a
representative in-use high altitude fuel.
4.2 Exhaust Emissions at Different Temperatures
Exhaust HC and CO emissions are very sensitive to
temperature. During a cold start at cold temperatures choke
operation in carbureted cars produces very rich mixtures at a
time when the catalyst is not operating, thereby producing high
HC and CO emissions. Fuel injected cars need rich mixtures
during cold starts also, but these systems achieve tighter
control of fuel/air ratios, thereby producing less HC and CO at
cold temperatures than carbureted cars.
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The primary needs in the area of cold temperature data
are for additional testing of carbureted cars at cold
temperatures on typical wintertime fuels of 13+ psi (most tests
have been done on Indolene, at 9 psi), and for fuel injected
cars tested at low temperatures. The fuel injected testing
should also utilize typical wintertime fuels. We currently
have about 30 fuel injected cars which have been tested at 20°
and 50°, and we need a minimum of 30-40 more cars to accurately
characterize the behavior of these cars separately from
carbureted cars. Also, there may be substantial differences
between throttle-body and multiport fuel injection that need to
be identified. The cold temperature testing is currently being
done by TEB, drawing on the pool of fuel injected emission
factor cars that we are recruiting.
As previously discussed, HC and CO emissions are high at
very low temperatures. As the temperature is increased, these
emissions decrease because less choke operation is needed.
Emissions find a low point around 70° to 80°. This is not
surprising because it is the test temperature range in which
cars are certified, therefore, manufacturers have designed cars
for low emissions in this range. At temperatures above 85°,
however, HC and CO emissions start to increase again. This
increase is due to a change in the density of air as the
temperature rises. As it rises, the air becomes less dense,
causing an increase in the fuel/air ratio since there are less
oxygen molecules per unit volume of air than at a lower
temperature.
The temperature correction factors for the different
model year groups for HC and CO are shown in Figures 5-10.
There is a separate figure for each bag of the FTP. Figure 6-
shows the HC correction factors for the stabilized bag. The
1975-80 cars display significantly more emission sensitivity to
higher temperatures than the other cars. (CO correction
factors for these cars display a similar sensitivity in Figure
9.) These correction factors are based on four 1977-78 cars
tested in the 1979 Gulf Study of emissions versus temperature.
Of the four cars, three were very sensitive to temperature,
i.e., the stabilized HC emissions of a 1978 Buick (V6> were
1.93 g/mi at 80F°, and 26.01 g/mi at 110°F with the air
conditioning on.
The high temperature correction factors for 1981 and
later cars are based on a few prototype and California cars
tested in the same (Gulf Research) test program. Therefore,
there appears to be a need for more high temperature testing of
newer fuel injected and carbureted cars. Some of this testing
has already been done as a part of our evaporative emissions
versus temperature and RVP program (exhaust emissions were
collected at 75, 85, and 95°F). This most recent testing also
includes heat builds (diurnal evap emissions), which the
previous Gulf Research testing did not. These data will be
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analyzed, and additional new technology- emission factoc cars-
may be tested at high temperatures.
The effects of higher temperature on fleet HC and CO
emissions of LDGVs are shown in Table 2. NOBILE3 predicts for
calendar year 1985 that LDGV CO emissions are 82% higher at
100° than 75°, and that HC emissions are 20% higher. The
magnitude of these differences decrease significantly in the
year 2000, when all cars are assumed to have closed loop fuel
control, and can better compensate for the change in fuel/air
ratio brought about by the less dense air.
4.3 CO Emissions at Low Speeds
One of the most persistent problems facing air'quality
modelers today is how to estimate low speed CO emissions. The
applications are numerous since most states require that an
Environmental Impact Statement (EIS) be prepared for any new
construction in a downtown area. The EIS must assess the
impacts of changes in traffic behavior on local or "hot spot"
CO emissions.
EPA provided states with a low speed version of MOBILE3
which is capable of predicting CO emissions in g/mi down to
about 2.5 mph. These are transient emissions, which involve
stops, idle periods, acceleration and deceleration modes.
While this seems to have met the needs of some, there are
problems with this approach. The emissions in g/mi are very
sensitive to low speeds, as evidenced by the emissions at 3, 4,
and 5 mph presented in Table 3. In an effort to study CO
emission sensitivity at low speeds, EPA developed three low
speed cycles under 5 mph from the GM chase car data, and will
soon be testing all emission factor cars on these and other
speed cycles. ;;; ;;•
An alternative to transient modeling at low speeds is
modal modeling, where a given cycle is. broken down into its
various modes (idle, accel, decel, cruise) and emissions are
estimated for each mode. These estimates are then placed in an
indirect source model such as HIGHWAY oc CALINE, which predict
CO concentrations around the area of interest. EPA has
published modal factors which can be used to convert transient
emissions into modal emissions. The limitation with these
factors is that they were developed eight years ago on
1972-1976 cars, and therefore do not account for the behavior
of new technology closed loop fuel control cars. Updating
these factors to include newer technology cars is vital to
indirect source modeling, and therefore vital in order to
accurately prepare EISs. EPA should give high priority to
developing an intersection-type modal testing program for newer
technology cars.
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Another concern with low speed CO emissions is the
interaction with temperature. The speed correction factors for
HOBILE3 were developed from cycles which were run in the hot
stabilized (as opposed to cold start) mode at about 75°F.
Alternately, the temperature correction factors were developed
with tests at different temperatures using the FTP cycle with
an average speed of 19.6 mph. No other cycles were used.
When a MOBILES user specifies that they want emissions
at 7 mph and 25°, the speed and temperature correction factors
are estimated separately and applied independently. If the
speed correction factor is 3.0 and the temperature correction
factor is 3.5, the resulting combined factor is 10.5, which can
result in very high emissions.
There are a great many factors which can affect the
amount of CO emissions produced under these low speed and low
temperature conditions, such as choke action, extent of choke
pull-off, idle speed, rate of engine warm-up, catalyst
light-off time, etc. Since CO emissions are sensitive to both
speed and temperature, EPA should test some cars at low speeds
and temperatures to determine the interactions.
4.4 Effects of Repairs
Cars with the highest as-received emission levels
generally receive maintenance (called restorative maintenance,
or "RM") and an after maintenance FTP test. The historical
objective for RM is to confirm our diagnosis of the
malfunctioning systems: once repaired, the car's emission
levels should significantly drop. If they do not, we know we
have not yet made the complete diagnosis and further RM is
generally performed, depending on the continued availability of
the car and/or other resource considerations.
Recently, however, two other objectives for RM have
emerged. One has been the need to characterize the emission
reductions associated with specific three-way system repairs.
This is in support of a preliminary effort to estimate the
benefits of requiring on-board diagnostics on all cars. These
systems are probably most readily integrated with the three-way
system and computer.
Emission benefits on cars receiving 3-way system repairs
are clearly higher than on those receiving only non-3-way
system repairs as the data in Table 4 demonstrate. The
limitations of these data are that many of the cars receiving
3-way repairs also received some non-3-way repairs
simultaneously, so it is difficult to determine 'the emission
benefits of specific 3-way repairs. For this reason we are
implementing a step-wise RM procedure with cars which qualify
for RM. Preference will be given to repair 3-way items first.
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A retest will be performed, and then additional non-3-way
repairs if necessary. We are also using a short test (the
restart idle test) as a "flash" estimate for evaluating whether
repairs have been effective.
The second new objective in KM is to determine effects
of field fixes on "pattern case" failures. Pattern case cars
are those that experience an abnormally high I/M failure rate,
usually because of a common problem. These cars may or may not
have high FTP emissions. In some cases, the manufacturers have
suggested field fixes for these cars so they won't continue to
fail I/M tests. Currently, we do not know what the FTP effects
of these field fixes are. EPA should do some testing on cars
which have received field fix repairs.
4.5 Disablement/Misfueling Testing
EPA does disablement and misfueling testing to determine
the effects of tampering on in-use emissions. The analysis of
the effects of tampering that was performed prior to the
release of MOBILES identified areas where additional testing
was needed. This testing included disablement testing
(primarily catalyst removal) at high altitude, and additional
misfueling studies. That testing is nearly complete and the
results should be summarized in the next few months. This may
identify additional disablement or misfueling testing that is
needed for cars.
The effects of tampering on truck emissions were
borrowed from cars with some modifications. However,
disablement testing should be extended at least on a limited
basis to light-duty trucks, particularly in light of the fact
that tampering rates are higher for trucks than for cars.
-------
17
Table. L
MOBILES Fleet VMT and Emission Fractions:
1990 Calendar Year
Vehicle
Type
LDGVs
LDGTs
HDGVs
LDDVs
LDDTs
HDDVs
MCS
Fleet VMT
Fractions
0.635
0.201
0.041
0.046
0.021
0.049
0.007
1.000
Emission Factors
(g/mi)
HC CO
2.28
4.67
6.95
0.40
0.62
3.51
6.01
18.44
35.93
66.48
1.32
1.53
11.11
19.73
Emission Fractions
HC CO
0.50
0.32
0.09
0.01
0.0
0.06
0.02
1.00
0.52
0.32
0.12
0.0
0.0
0.03
0.01
1.00
Note: Emission fractions are estimated by multiplying emission
factors by fleet VMT fractions, adding these products
together to get the fleet emission factor, and dividing
the weighted emission factor of each vehicle type by the
fleet emission factor.
-------
18
Table 2
LDGV Fleet HC and CO Emissions
at Varying Temperatures
Calendar
Year
1985
2000
Pollutant
HC
CO
HC
CO
(g/mi)
(g/mi)
(g/mi)
(g/mi)
50°
4
40
2
26
.32
.39
.31
.40
75°
3
27
1
13
.48
.52
.60
.66
4
50
1
15
100°
.21
.09
.79
.51
Source: MOBILES, default operating mode percentages,
speed =19.6 mph
-------
19
Table 3
CO Emissions in g/mi of LDGVs
at Low Speeds
CO, g/mi
Speed 75°F 30°F
3 mph 159 305
4 mph 121 231
5 mph 96 181
Source:Low-speed MOBILES. Default operating
mode percentages used.
-------
20
Table 4
HC and CO Emission Benefits of
3-Way System and Non-3-Way
System Repairs
Category
Carbureted Cars
No 3-way System Repair
3-way System Repair
Fuel Injected Cars
No 3-way System Repair
3-Nay System Repair
NOTE: No 3-way system repairs: could have received multiple repairs, but none to
3-way system.
3-way system repairs: could include some non-3-way system repairs also.
N
144
48
26
21
Bef
Rep
1.
2.
0.
2.
ore
air
36
43
95
68
After
Repair
0.81
1.28
0.76
0.91
Reduc .
0.55
1.15
0.19
1.78
Be
Re;
18
47
11
51
fore
pair
.32
.78
.50
.86
After
Repair
10.49
23.76
8.80
10.16
Red
7
34
2
41
uct
.83
.02
.70
.70
-------
20
i.
10
Figure 1
Distribution of 1981+ Carbureted
Cars by Odometer Values
4.78
1
18.08
^
>>
y>
>>
>>
>>
>>
2x
13.04
1
9.27
!
14.2
i
13.04
I
13.91
i
9.42
!
|Corto.N»690|
3.78
W t19 U
0-10 -20 -30 -40 -50 -60 -70 -80 -90 -100 100+
Mileage in Thousands of Miles
35
30-
29
10
Figure 2
Distribution of 1981+ Fuel Injected
Cars by Odometer Values
3t41
9.13
24.77
I
|nnj.N =
14.8
I
9.08
4.93 4M
0-10 -20 -30 -40 -50-60-70-60 -90 -100 100+
MilMfe in Thousand* of Mile.
-------
Figure 3
Distribution of Travel fractions and HC and CO Emissions
by Age Group, CY 1988 — LDGVs
w-
•8
CZHCCminiefM
• COCmMm
20
10
0-
0-5 5-10 10-15
Age Group
15+
180000-
X. 140000 H
01
a
1
01 100000-
60000-
80000
FIGURE 4
CO YEARLY EMISSIONS vs. AGE
t 2 3 4 » • 1 » 9 W U U U 14 15 IS 17 18 19 20
-------
FIGURES
TEMPERATURE CORRECTION FACTORS
LIGHT DUTY GASOLINE POWERED
BAG 1 - HYDROCARBONS
Low Altitude
14
12-
e 10-
§
OS
§
w
05.
os
w
Du
8-
2-
198H
1980
1968-69
1975-79
1970-74
Pr«-1968
1981+
1970-74
Pr«-1970
1975-80
10 30 50 70 90 110
AMBIENT TEMPERATURE (F)
•log
i
•8
14
12
o
8 QS
1
OS
•4
•2
-------
FIGURE 6
TEMPERATURE CORRECTION FACTORS
LIGHT DUTY GASOLINE POWERED
BAG 2 - HYDROCARBONS
Low Altitude
2.6
2.4 A
2.2 H
HM
OS
§
Ed
B
§
05
Ed
Ed
1980-f
1975-79
1.4 A
1968-69
Pr«-1968
1970-71
1972-74
197S-80
1968-69
1972-74
Pr«-1968
198H
1970-71
0.8-
10 30 SO 70 90 110
AMBIENT TEMPERATURE (F)
2.6
2.4
2.2
2 K
I
6
1.8 Ed
o:
hl.6 Ed
hl.4
CU
S
Ed
0.8
-------
FIGURE?
BAG 3 - HYDROCARBONS
Low Altitude
UJk.
0.8
10 30 50 70 90 110
AMBIENT TEMPERATURE (F)
-------
FI6UBE8
8
7-
-------
FIGURE 9
TEMPERATURE CORRECTION FACTORS
LIGHT DUTY GASOLINE POWERED
BAG 2 - CARBON MONOXIDE
Low Altitude
5.5
5-
4.5-
-------
FIGURE 10
TEMPERATURE CORRECTION FACTORS
LIGHT DUTY GASOLINE POWERED VEHICLES
BAG 3 - CARBON MONOXIDE
Low Altitude
3.5-
3-
2.5-
CIS
§
OS
W l'8
£
I
1-
0.5
1972-74
1975-80
1970-71
1972-74
1968-69
Pr«-1968
198H
10 30 50 70 90 110
AMBIENT TEMPERATURE (F)
•2.5
3.5
•• §
o
sa
g
O,
2
w
-1
0.5
------- |