REGULATORY SUPPORT DOCUMENT
EMISSIONS STANDARDS FOR HEAVY-DUTY
CLEAN-FUEL FLEETS
U.S. Environmental Protection Agency
Regulatory Development and Support Division
Draft
May, 1993
-------
Table of Contents
1. Introduction i -1
2. Technology Assessment Chapter 2-1
2.0.1 Introduction 2-1
2.0.2 Gasoline Engines 2-1
2.0.2.1 Fundamentals of Gasoline Engines Which Impact 2-1
NMHC + NOx emissions
2.0.2.1.1 Air-to-Fuel Ratio 2-1
2.0.2.1.2 Ignition Timing 2-2
2.0.2.1.3 Combustion Chamber Design 2-3
2.0.2.2 Current Gasoline Emissions Control Technology 2-3
2.0.2.2.1 Exhaust Gas Recirculation 2-4
2.0.2.2.2 Aftertreatment Systems 2-4
2.0.2.2.2.1 Catalytic Converters 2-4
2.0.2.2.2.2 Electronic Controls 2-5
2.0.2.3 Future Gasoline Emissions Control Technology 2-5
2.0.2.3.1 Electrically-Heated Catalytic Converters 2-6
2.0.2.3.2 Closed-Coupled Catalytic Converters 2-6
2.0.2.3.3 Lean-Bum Calibration 2-6
2.0.2.4 Expected Approaches for Clean-Fuel Gasoline 2-7
Engines
2.3 Diesel Engines 2-7
2.0.3.1 Technical Background/Fundamentals of Diesel 2-7
Engines Which Impact NMHC + NOx emissions
2.0.3.1.1 Fuel System 2-8
2.0.3.1.2 Air System 2-8
2.0.3.2 Current Diesel Emissions Control Technology 2-9
2.0.3.2.1 Retarded Injection Timing 2-9
2.0.3.2.2 Injection Pressure 2-9
2.0.3.2.3 Injector Nozzle Holes and Diameters 2-10
2.0.3.2.4 Intake Air Turbocharging 2-10
2.0.3.2.5 Aftercooling 2-10
2.0.3.2.6 Cylinder Design 2-10
2.0.3.3 Future Diesel Emissions Control Technology 2-11
2.0.3.3.1 Exhaust Gas Recirculation 2-11
2.0.3.3.2 Improved Turbocharging 2-12
2.0.3.3.3 Injection Rate Shaping 2-12
2.0.3.3.4 Electronic Controls 2-13
2.0.3.3.5 Aftertreatment Devices 2-13
2.0.3.3.5.1 Particulate Trap-Oxidizers 2-14
2.0.3.3.5.2 Catalytic Oxidizing Converters 2-14
-------
2.0.3.3.5.3 Catalytic NOx reduction 2-14
2.0.3.3.6 Variable Compression Ratio 2-15
2.0.3.4 Expected Approaches for Clean-Fuel Diesel Engines 2-15
2.0.4 Alternative Fuel Technologies 2-15
2.0.4.1 Methanol 2-16
2.0.4.2 Natural Gas 2-16
2.0.4.3 Liquefied Petroleum Gas 2-17
2.0.4.4 Electric Vehicles 2-18
2.5 Summary 2-18
3. Environmental Benefits Chapter 3-1
3.0.1 Introduction 3-1
3.0.2 Calculation Method 3-1
3.0.3 Discussion of Data 3-1
3.0.3.1 Light and Medium-Heavy Duty Fleet Vehicle 3-2
Demographics
3.0.3.2 Emission Factor Calculations 3-7
3.0.3.2.1 1998 and Later Baseline Emission Factors 3-7
3.0.3.2.2 Projections for 1998 Clean-Fuel Fleet 3-10
Emission Factors
3.0.4 Environmental Impacts 3-11
4. Costs and Cost Effectiveness 4-1
4.0.1 Introduction 4-1
4.0.2 Costs 4-1
4.0.2.1 Operating Costs 4-1
4.0.2.2 Engine Costs 4-2
4.0.2.2.1 Otto-Cycle Heavy-Duty Engines 4-2
4.0.2.2.1.1 Hardware Costs 4-2
4.0.2.2.1.2 Development Costs 4-3
4.0.2.2.1.3 Certification Costs 4-3
4.0.2.2.2 Diesel-Cycle Heavy-Duty Engines 4-3
4.0.2.2.2.1 Hardware Costs 4-3
4.0.2.2.2.2 Development Costs 4-4
4.0.2.2.2.3 Certification Costs 4-4
4.0.2.3 Aggregate Costs 4-4
4.0.2.3.1 Manufacturer Costs 4-5
4.0.2.3.2 Costs to Users 4-8
4.0.3 Cost Effectiveness 4 - 10
4.0.4 Summary 4-11
-------
List of Tables
Table 3-1 Heavy-Duty Clean-Fuel Fleet Vehicle Population 3-3
Table 3-2 Vehicle Miles Travelled by Clean-Fuel Fleet LHDVs/MHDVs 3-4
Table 3-3 Sales-Weighted 1991 Light and Medium Heavy-Duty Certification 3-8
Values
Table 3-4 1998 Model Year Baseline Emission Factors 3-9
Table 3-5 1998 Heavy-Duty Clean-Fuel Fleet Vehicle Emission Factors 3-10
Table 3-6 Nationwide Emissions Inventories of Fleets Covered by the 3-12
Clean-Fuel Fleet Program
Table 4-1 Manufacturer Fixed Costs for Heavy-Duty Clean-Fuel Engines 4-6
Table 4-2 Costs to Manufacturers 4-7
Table 4-3 Costs to Consumers 4-9
Table 4-4 Cost Effectiveness in $/ton (1998 Present Value) 4-11
-------
List of Figures
Figure 3-1 - Clean-Fuel Fleet Vehicle VMT 3-5
-------
1.0 Introduction
This document is intended to provide technical, environmental
and economic analyses of the heavy-duty portion of the Clean-Fuel
Fleet program. The heavy-duty portion of the fleet program applies
to only light heavy- and medium heavy-duty vehicles and the engines
designated for use in these vehicles. EPA is proposing to set a
heavy-duty clean-fuel fleet vehicle standard of 3.5 g/Bhp-hr non-
methane hydrocarbon (NMHC) + oxides of nitrogen (NOx). Credit
generating standards for the fleet program are also being proposed.
Technological discussions of NMHC and NOx formation and control,
calculations of environmental benefits and an assessment of costs
and cost effectiveness are contained in separate chapters.
Chapter 2 contains an assessment of technologies available for
reducing NMHC and NOx emissions in conventionally-fueled heavy-duty
vehicles as well as technologies capable of meeting the credit
generating standards. First the formations of NMHC and NOx in
gasoline engines and the impacts of gasoline engine design are
discussed. Next, emissions formation and control in diesel engines
are covered. Finally, alternative fuel technologies and their
emissions capabilities are presented.
Chapter 3 contains a discussion of the environmental benefits
expected from this program. The chapter begins with a presentation
of the vehicle demographics used in the calculations. This is
followed with a discussion of how new emissions factors applicable
to the vehicles covered by these standards were derived. Finally,
the emissions benefits are presented and discussed.
Chapter 4 begins with an estimate of the costs associated with
meeting these standards. Expected costs for research, development
and testing are combined with certification costs and the
anticipated incremental hardware and operating costs to derive both
manufacturer and consumer costs associated with this program.
These costs are then combined with the emissions estimates from
chapter 3 in a calculation of the 22-year cost effectiveness of the
heavy-duty portion of the Clean-Fuel Fleet program.
-------
Chapter 2
Technology Assessment:
2.0.1 Introduction
Internal combustion engines produce hydrocarbon1 and oxides
of nitrogen (NOx) emissions through a series of complex related
processes which also control the production of other pollutants
such as CO and particulates as well as the power output and
efficiency of the engines. Hydrocarbon (HC) emissions generally
result from the incomplete combustion of the fuel, while NOx
results from the reaction of oxygen and nitrogen present in the
combustion air. The reactions which produce NOx occur much more
rapidly under conditions of high temperature and pressure.
Engine design and operations which affect emissions of HC and
NOx will be discussed for both heavy-duty diesel and gasoline
engines as well as for alternative fuel technologies. Other
emission control technologies such as catalytic aftertreatment will
also be discussed. The purposes of these discussions are to: 1)
provide background information regarding the fundamentals of the
technologies, 2) describe the technologies which are being commonly
used today, 3) describe innovative technologies which may be used
by clean-fuel fleet vehicles, and 4) identify the approaches that
are most likely to be used by manufacturers to comply with the
clean-fuel fleet vehicle standards. The discussions in this
chapter will be qualitative in nature and generally do not include
predictions of emissions reductions likely to result from use of a
particular technology.
2.0.2 Gasoline Engines
2.0.2.1 Fundamentals of Gasoline Engines Which Impact NMHC
+ NOx emissions
NMHC and NOx emissions from gasoline engines (i.e., spark-
ignited, otto cycle) are impacted by the following characteristics
of the engine and its operation: air-to-fuel ratio, ignition
timing, and combustion chamber design. Adjustments or variations
to these parameters can substantially affect the performance as
well as the emissions of gasoline engines.
2.0.2.1.1 Air-to-Fuel Ratio
1 For simplicity, the term hydrocarbon (HC) is used
throughout this chapter to describe general effects in emissions
control. The term non-methane hydrocarbon (NMHC) is used for
clarity when discussing the emissions standards or specific
emission levels. The discussions using the term HC, therefore,
should be considered to be equally applicable to NMHC emissions.
2-1
-------
Emissions from gasoline engines are extremely sensitive to the
ratio of fuel and air in the combustion system. A critical
parameter then in the performance and emissions characteristics of
gasoline engines is the excess air factor designated as A.. An
excess air factor of 1.0 indicates the engine is operating at
stoichiometric conditions while A, values of more than 1.0 indicate
there is excess air in the combustion chamber. The current
strategy, especially with the presence of three-way catalytic
converters, is to attempt to keep A. at 1.0.
The air-to-fuel ratio, since it affects nearly all the
operational parameters of the engine, is a primary design element
in the operation of a gasoline-fueled engine. Proper air-to-fuel
ratio control is critical in controlling both the engine out
emissions of hydrocarbons (HC) and NOx and, as will be discussed in
a later section, in the performance of catalytic converter
aftertreatment devices. In principle, as A. is increased (i.e.,
leaner air-to-fuel ratio), HC emissions decrease due to the
increasing availability of oxygen for more complete combustion.
NOx emissions, on the other hand, show slight increases in engine-
out emissions levels at A. values slightly above 1.0 and decreasing
levels at higher values of A.
NOx values increase at A. values slightly greater than 1.0 due
to the increased availability of oxygen and nitrogen to react to
form NOx. As A. increases, the additional air has a competing
effect on NOx; by adding mass to absorb the heat of combustion, it
lowers the peak temperatures and pressures, which leads to a
decrease in the rate of formation of NOx. Also as A increases, HC
emissions begin to increase slowly at first and then rapidly as the
lean misfire point is approached. Within reasonable limits,
however, the effects of air-to-fuel ratio on engine-out emissions
of HC are much less than the effects on engine-out NOx emissions.
Engines using lean air-to-fuel ratios also tend to show
greater thermal efficiencies due to factors such as lower heat
losses and the ability to use higher compression ratios (lean fuel
mixtures are less susceptible to autoignition). At higher values
of A., however, the power output per volume can drop off despite the
increase in thermal efficiency due to the lower fuel content. This
effect can be offset by either using lean burn only at partial load
conditions or by turbocharging the intake mixture to pack more air
and the same quantity of fuel into the cylinder at a higher initial
pressure.
2.0.2.1.2 Ignition Timing
Control of the timing of the ignition spark is important in
controlling both NOx and HC emissions as well as in maximizing the
work output of the engine. Delaying the ignition as much as
possible reduces the amount of NOx produced by reducing both the
peak temperatures and pressures of the combustion cycle and the
2-2
-------
length of time that the gases are exposed to high temperatures and
pressures. Retarding the ignition timing can also increase the
work output of the engine by reducing the amount of extra work the
piston must do during the final stages of compression after the
combustion has already begun. If the ignition timing is retarded
too much, however, the combustion process begins late, resulting in
somewhat incomplete combustion. Under these conditions, the power
output drops and under conditions of greater timing retard the HC
emissions can go up. Ideally, to minimize the NOx and HC emissions
and to maximize the fuel economy of the engine, the combustion
process needs to be optimized so that the ignition timing can be
delayed to as close to the point in time when the piston reaches
top dead center and to have as much of the combustion as possible
take place just after the piston reaches top dead center.
2.0.2.1.3 Combustion Chamber Design
Combustion chamber parameters can affect the peak temperatures
and duration of the combustion process, which in turn impact on the
level of NOx emissions and the amount of work produced. The
primary goals in the design and operation of the combustion chamber
are to maximize the amount of work and power output by the
combustion process (which also implies maximum combustion of the
HC) while minimizing the production of NOx, the amount of wear on
the engine and the likelihood of autoignition (knocking).
Reducing the combustion time is an important goal in chamber
design. Shorter combustion time allows the timing to be retarded,
which thereby reduces the formation of NOx and HC, while still
allowing the combustion to proceed to completion earlier in the
expansion stroke (thereby capturing more of the energy of
combustion). Decreasing the combustion time can be accomplished by
making design changes to the combustion chamber which minimize the
distance the flame front needs to travel and/or increases the flame
speed. Flame speed can be increased by increasing the turbulence
in the chamber. In addition to decreasing emissions and increasing
the percentage of the fuel burned near the optimal point in the
process, "fast-burn" techniques also reduce the tendency of the
engine to knock by reducing the amount of time available for the
unburned fuel to auto-ignite. Therefore, compression ratios can be
increased which in turn further increases the efficiency of the
engine.
2.0.2.2 Current Gasoline Emissions Control Technology
All heavy-duty gasoline engines certified for model year 1992
were equipped with exhaust gas recirculation (EGR), and almost all
were equipped with some form of catalytic converter and electronic
engine controls. Most were equipped with three-way catalytic
converters (converters which are capable of both reducing NOx
emissions and oxidizing HC and CO emissions). These technologies
are described below. It is also worth noting that some current
2-3
-------
engines are already very close to complying with the proposed
NMHC+NOx emission standard of 3.5 g/Bhp-hr for heavy-duty clean-
fuel fleet vehicles. Three of the gasoline-fueled engines families
certified for the 1992 model year had HC+NOx emissions of 4.0
g/Bhp-hr or less, including one with HC+NOx emissions of 3.6 g/Bhp-
hr.
2.0.2.2.1 Exhaust Gas Recirculation
From a NOx control standpoint, it is desirable to have some
inert gases in the cylinder to take up some of the heat of
combustion. The recirculation of exhaust gases can provide these
inert gases. Recirculating exhaust gases is a more effective means
of NOx emissions control than using additional air to absorb the
heat of combustion (leaning out the air-to-fuel ratio) since the
water and C02 in the exhaust gases have high heat capacities which
make the exhaust gases more effective at absorbing the excess heat
of combustion. Thus by using EGR, the peak temperatures can be
reduced further before the volume of inert gases reach the point of
interfering with the combustion process. Furthermore, recirculated
exhaust gases do not add the excess oxygen. Modest levels of
excess air can lead to increases in the engine-out levels of NOx
emissions.
In some instances, exhaust gas recirculation can lead to a
reduction in engine-out HC emissions. However, EGR normally has
very little effect on HC emissions. At high levels of EGR (i.e.
>25%), the combustion process can become unstable, just as in the
case of too much excess air. Under these conditions, the HC
emissions begin to rise sharply.
2.0.2.2.2 Aftertreatment Systems
2.0.2.2.2.1 Catalytic Converters
Catalytic converters are an important means of further
reducing the emissions of gasoline engines. As already noted,
heavy-duty gasoline engine systems are usually equipped with
catalytic converters which remove HC, CO and NOx from the exhaust
stream. Others use catalysts that are designed only to oxidize the
HC and CO.
In three-way or oxidation/reduction catalysts, the HC and CO
are oxidized to either less complex intermediate products or COa
and water vapor, while NOx is reduced to N2 and oxygen. The
reduction of NOx is accomplished by simultaneously utilizing the
oxygen from the NOx molecules to oxidize the remaining HC and CO in
the exhaust. This results in partial oxidation of the HC and CO.
Further oxidation may be achieved using an oxidation catalyst.
However, if there is excess oxygen in the exhaust stream, the HC
will preferentially react with the free oxygen rather than the
oxygen contained in the NOx molecules thereby leaving the NOx
2-4
-------
molecules relatively unaffected. On the other hand, if there is
not sufficient oxygen available in the exhaust stream, the HC will
not be oxidized or will be only partially oxidized due to the lack
of oxygen. Therefore, the performance of three-way catalytic
converters is very sensitive to the air-to-fuel ratio in the
engine.
This problem can be partially overcome by using a catalytic
converter that consists of two separate beds (a reduction catalyst
followed by an oxidation catalyst) and injecting extra air between
the two beds. This allows the air-to-fuel ratio to be run slightly
on the rich side to ensure that good conversion of the NOx will be
achieved in the first bed. However, this technique results in a
decrease in fuel economy because of the slightly rich calibration.
Furthermore, the injection of too much air into the second bed has
the potential for cooling the gases down to the point that the
catalytic converter can lose some of its effectiveness.
Each catalytic converter design has its advantages and
disadvantages. The best approach for a given engine design is
determined based upon the composition and level of the engine-out
emissions.
2.0.2.2.2.2 Electronic Controls
Recent advances in electronic controls have made it possible
to achieve very tight control over engine parameters such as the
air-to-fuel ratio and ignition (spark) timing. This improvement in
the controllability of the combustion process minimizes the
excursions of these engines in non-optimized operating ranges which
result in both increased emissions and decreased performance.
The most significant advantage to using electronic controls is
that it provides a means by which the air-to-fuel ratio can be
adjusted to ensure that the concentration of oxygen in the exhaust
is at a level which leads to the optimum efficiency of a three-way
catalyst under a broad range of operating conditions. By
installing oxygen sensors in the exhaust stream near the catalytic
converter, the system can diagnose whether or not the proper air-
to-fuel ratio is being maintained. Using these feedback signals,
the engine, computer can then adjust the air-to-fuel ratio rapidly
to compensate if the exhaust stream does not contain the optimal
level of oxygen.
2.0.2.3 Future Gasoline Emissions Control Technology
Due to the 1998 4.0 g/Bhp-hr NOx standard, general
improvements can be expected to current gasoline emissions control
technology such as exhaust gas recirculation, catalytic converters
(likely catalyst improvements), and especially electronic controls.
Additional emission control of gasoline engines may occur with
other emission control technologies that are under development:
2-5
-------
electrically-heated catalytic converters, close-coupled catalytic
converters, and lean-burn calibration.
2.0.2.3.1 Electrically-Heated Catalytic Converters
Catalytic converters require fairly high temperatures to be
effective. Heat is provided by the exhaust and from the reactions
of the HC in the catalyst bed. Following a cold start, there is a
delay before the catalytic converter becomes effective, while it
heats up to its operating temperature; once the converter reaches
the desired operating temperature, it performs well with very high
efficiency. Electrically heating catalytic converters at vehicle
start-up can reduce the delay before the converters become
effective. This approach may also be of value to the emissions
control strategy for light and medium duty vehicles. Electrically-
heated catalytic converters are made of metals rather than
ceramics, thus, these converters experience less cracking and are
more durable than other catalytic converters. However, some
electrically-heated catalytic converters are susceptible to
aluminum washcoat degradation. This technology is currently
available. Other catalyst bed improvements are also available
which could improve emission reductions efficiency.
2.0.2.3.2 Close-Coupled Catalytic Converters
Another approach that can be used to minimize the delay is to
install the converter very close to the engine, so that the exhaust
gases contacting the catalyst are hotter. However, these close-
coupled catalytic converters are more susceptible to thermal
degradation because they are continually exposed to significantly
higher temperatures than converters located further away from the
engine. By installing converters only slightly closer to the
engine than current converters so that the exhaust gases contacting
the catalyst are only at a slightly higher temperature, smaller
emission benefits may occur. Closed-coupled catalytic converters
will be available for the 1994 model year due to the California LEV
standards. Insulating exhaust pipes may provide similar benefits
at lower costs.
2.0.2.3.3 Lean-Burn Calibration
While the air-to-fuel ratios of current engines are generally
calibrated at stoichiometry, there would be potentially significant
benefits with leaner calibrations. Leaner air-to-fuel ratios could
lead to lower engine-out HC, CO, and perhaps NOx emissions, as well
as a decrease in fuel consumption. On the other hand, there can be
a loss of power and problems with ignition and flame propagation.
Also, leaner combustion would lead to leaner exhaust which would
present the additional challenges of developing catalysts and
oxygen sensors that work well under such conditions. It is likely
that lean-burn calibration would only be used on engines with
advanced electronic feedback controls. The availability of this
2-6
-------
technology is uncertain at this time for heavy duty engines.
2.0.2.4 Expected Approaches for Clean-Fuel Gasoline Engines
Overall, given that emissions from some current gasoline-
fueled engines are already very close to those required by the
proposed standard, it is expected that optimization of existing
technologies will be adequate to allow a significant number of
gasoline-fueled engines to comply with the clean-fuel fleet
standard, and that dramatic changes will not be necessary. Engine
changes, such as but not limited to changes in the EGR system,
combustion chamber design improvements, and tighter control over
the air-to-fuel ratio, are expected to provide much of the
necessary reductions in NMHC+NOx emissions for many engines.
Slightly leaner calibrations may be used under some conditions;
however, very lean calibrations should not be necessary.
Additional reductions will also likely come from upgraded
exhaust aftertreatment systems. It is expected that all gasoline
engines in the Clean Fuel Fleet program will be equipped with
three-way catalysts; and that these catalysts will be slightly more
effective than those currently being used, through either
optimization of the catalytic materials, increases in the catalyst
loading and/or bed size or exhaust pipe insulation. The Agency
does not currently expect that electrically-heated or close-coupled
catalysts will be necessary in order for most gasoline-fueled
engines to comply with the proposed standards.
The docket contains further supporting material on the
feasibility of the proposed NMHC + NOx emission standard for heavy-
duty engines.1
2.0.3 Dlaatt^
2.0.3.1 Technical Background/Fundamentals of Diesel Engines
Which Impact NMHC + NOx Emissions
In diesel engines, NOx is formed in the early phases of
combustion where temperatures and pressures reach a peak. In
diesel engines, as fuel is injected into the combustion chamber it
mixes with hot compressed air already present, and after a brief
period known as ignition delay, this fuel-air mixture ignites. In
this premixed burning phase, the fuel-air mixture burns in an
uncontrolled manner, which causes a rapid rise in cylinder pressure
and heat release, until the mixing controlled combustion phase
(diffusion-controlled burning) takes control of the combustion
process. Once diffusion-controlled burning begins, fuel
essentially burns as it is injected, allowing partially burned
droplets and particulates to be consumed as oxygen becomes
available at local combustion sites. It is believed that most of
the NOx is formed during the period before diffusion takes control
of combustion.2 Therefore, anything which can be done to reduce
2-7
-------
the temperatures during this uncontrolled burning phase will tend
to reduce the formation of NOx.
Hydrocarbons are the result of incomplete combustion of the
fuel. Because of the lean combustion technology used in diesels,
out hydrocarbon emissions tend to be inherently low. However,
controls that reduce NOx often have an adverse effect on HC
emissions since they are inversely related to oxygen availability
and peak conbustion temperature.
2.0.3.1.1 Fuel System
The fuel system in a diesel engine is responsible for
controlling both the amount of fuel delivered to the cylinder and
the timing of the fuel delivery. Since the fuel is injected into
an air mass that is already compressed and has consequently been
heated to a temperature above the auto-ignition point for the fuel,
the injection timing determines when combustion will begin and
serves some of the same functions in diesel engines as ignition
(spark) timing does in gasoline engines. There are two types of
injection systems available for diesel engines: direct and indirect
injection.
Diesel engines can use either direct injection (DI) or
indirect injection (IDI) combustion systems. Direct injection
engines inject the fuel into a hollow in the piston and have the
air/fuel mixing controlled by swirling motions in the intake air
and the momentum and spray characteristics , of the fuel jet.
Indirect injection engines, on the other hand, inject the fuel into
a pre-chamber and accomplish most of the air/fuel mixture through
turbulence created by the expansion out of the chamber. Since
indirect injection engines do not expose the bulk of the initial
uncontrolled burning to as much oxygen, they have somewhat lower
NOx emissions rates.3
The primary disadvantage of engines using IDI technology is
that they are less fuel efficient than DI engines due to heat and
frictional losses in the pre-chamber. However, indirect injection
technology has low initial costs which make it well suited for
small high-speed diesel engines where the fuel consumption is least
significant. In addition, IDI is a useful option for small
diesels because it helps address problems with air utilization due
to their small cylinder volume.3 Concerns about the fuel economy
penalties, however, are leading some manufacturers to use
alternative methods of controlling NOx emissions.
2.0.3.1.2 Air System
2-8
-------
Air system improvements also show promise for NOx and HC
control. By increasing the mass of gases contained in the
cylinder, the temperature rise can be decreased which results in
reduced NOx formation. If some of the extra gas is oxygen, the
increased oxygen availability will result in more complete
combustion reducing HC and particulate emissions. Cooling of the
intake air will further reduce the in-cylinder temperatures
resulting in reductions in NOx formation.
2.0.3.2 Current Diesel Emissions Control Technology
Current emissions control for diesel engines is generally
based upon optimization of engine parameters such as ignition
timing, injector nozzle and cylinder design, and air intake.
Nearly all of the light and medium heavy-duty engine families
certified in 1992 used turbochargers with aftercooling. A very
small number of current light and medium heavy-duty engine families
use electronic controls, but most use mechanical controls. The use
of mechanical controls is probably the most significant limitation
of current diesel emission control. While some mechanical
improvements are still being made, it is generally true that
emissions from mechanically controlled engines have been optimized
nearly as much as is possible without the development of
dramatically new technologies, or reductions in fuel economy. For
example, NOx emissions could be reduced from current levels by
retarding the injection timing, but this would lead to reduced fuel
economy and increased HC and PM emissions (which would increase the
need for exhaust aftertreatment). The following sections discuss
some of the currently technologies which affect diesel emissions.
2.0.3.2.1 Retarded Injection Timing
Retarding the injection timing is a well-known and proven
technique for significantly reducing NOx emissions. The primary
mechanism for reducing NOx emissions by this technique is the
reduction in the duration of uncontrolled burning. However,
retarded timing has undesirable effects, particularly when used
alone. Retarding the timing significantly will increase
particulate and hydrocarbon emissions and decrease fuel economy due
to reduced time for the fuel and initial combustion products to mix
with the excess air in order to burn.5 The regulatory pressures
on particulate emissions and the market pressures on fuel economy
combine to limit the use of retarded timing in controlling NOx
emissions.
2.0.3.2.2 Injection Pressure
Injection pressure increases in DI engines can be used to
limit particulate emissions and speed up the completion of
injection. Increased injection pressure increases the air/fuel
mixing in direct injection engines because of increased air
entrainment into the fuel spray and higher turbulence therein (less
2-9
-------
condensation is likely to occur). This has little direct effect on
NOx formation; however, it does lead to a decrease in particulate
formation. Furthermore, an injection pressure increase will
shorten the duration of the injection.6 The combination of reduced
particulate formation and shortened injection duration should allow
the timing to be retarded without incurring other impacts.
Hydrocarbon emissions are insensitive to injection pressure at
full-load, and only increase slightly under half-load high speed
conditions.7
2.0.3.2.3 Injector Nozzle Holes and Diameters
Nozzle characteristics are important to optimize for emissions
and performance reasons, particularly for direct injection engines.
Decreasing the nozzle hole diameters increases the injection
duration without increasing the ignition delay; therefore, the
maximum heat release in the pre-mixed burning phase decreases. In
addition, reducing the hole,size better atomizes the fuel allowing
more complete burning. For these reasons, smoke can be decreased
without an increase in NOx by decreasing the nozzle diameter.2
Changing the number of holes in the injection nozzle may be used to
affect the spray characteristics of the fuel. Hydrocarbon
emissions are only slightly affected by the number of holes;
however, CO and smoke have been found to be least sensitive to
injection pressure for a 6-hole injector.8
2.0.3.2.4 Intake Air Turbocharging
Turbochargers are used to force additional air (mass) into the
combustion chamber allowing a shorter ignition delay and more
complete burning of a given amount of injected fuel. Therefore,
turbocharging may be used to reduce HC emissions at partial loads
which increases the capability of retarding timing (lower NOx).8
As with other lean burn systems the addition of additional air to
make the mixture even leaner results in reduced cylinder
temperatures. This change has a direct positive impact on NOx
emissions.
2.0.3.2.5 Aftercooling
If the intake air is turbocharged, the temperature will rise
during compression. Cooling the intake air after it has been
turbocharged. will help lower the in cylinder temperature, and
therefore reduce NOx formation.5. There are several approaches to
aftercooling, including air-air and air-liquid aftercoolers. By
using air-to-air aftercoolers, some manufacturers have been able to
reduce the temperature of the turbocharged intake air to about ten
or fifteen degrees Fahrenheit above the ambient air temperature.
2.0.3.2.6 Cylinder Design
The combustion chamber shape may be optimized in order to
2-10
-------
promote mixing with enhanced turbulence. Enhanced turbulence can
reduce particulate and hydrocarbon emissions through better mixing
but has a tendency to increase NOx emissions through the increased
heat release. A reentrant chamber has a small lip around the top
of the bowl cut into the piston. This combustion geometry has been
found to reduce particulate emissions and the sensitivity of
particulate emissions to timing retardation.6 Since the
sensitivity of particulate emissions to timing retardation is
reduced, the timing can be retarded to reduce NOx emissions in many
cases to the point that there is a reduction of NOx emissions at
either the same level of particulate emissions or even with a
reduction of particulate emissions.
Valve timings and, particularly for direct injection engines,
degree of swirl can also be critical. Control of these events to
optimize air/fuel mixing minimizes the formation of pollutants.
Swirl increases the mixing of the air and fuel in the combustion
chamber, and the degree of swirl depends on both air patterns and
cylinder geometry. It is difficult to ^incorporate a degree of
swirl which will achieve good mixing at all operating conditions.
Although increasing the swirl in the combustion chamber may be used
to reduce particulate emissions,12 the NOx, smoke, and fuel
consumption may increase.8 Experiments on engines equipped with a
two position variable swirl device have shown simultaneous
reductions in both particulate emissions and NOx emissions by
allowing the engine to be optimized for NOx or particulate
emissions reductions at operating conditions under which formation
of either of these pollutants is of particular concern.
2.0.3.3 Future Diesel Emissions Control Technology
Future emission control for diesel engines will be based upon
further optimization of engine parameters such as injection timing,
injection pressure, injector nozzle and cylinder design, air
intake, and aftercooling. Additional diesel emission control may
occur with the following new emission control technologies among
others: exhaust gas recirculation, electronic controls,
particulate trap-oxidizers, catalytic oxidizing converters,
catalytic NOx reduction, and variable compression ratio.
2.0.3.3.1 Exhaust Gas Recirculation
Exhaust gas recireulation (EGR) is a proven NOx control
strategy for gasoline engines (see above discussion). Previously,
EGR has not been necessary in diesel-cycle engines due to the
availability of other approaches, such as increased air mass
charging, to accomplish similar objectives. However, with the
practical limits of these approaches now being faced, the increased
heat capacity of recirculated exhaust may now provide a valuable
advantage. The higher levels of particulate emissions
traditionally found in diesel engines also led to concerns that
recirculation of exhaust gases would lead to decreased engine
2-11
-------
durability. With the advent of diesel engines with low engine-out
particulate emissions and diesel fuel sulfur control, however, EGR
is becoming more feasible for diesel engines.
Exhaust gas recirculation reduces the temperature of the
cylinder by adding inert gases to expand to do work. This can
increase PM emissions, especially at full load, due to the lack of
oxygen present in the combustion chamber which results in
incomplete combustion. Moderate EGR rates (5-15%) have been shown
to bring NOx down into the 1.9 - 3.4 g/Bhp-hr range. This may be
done without increasing particulates significantly or de-rating the
engine by using electronically-controlled EGR (see discussion
below). In addition with a NOx reduction engines using EGR have
shown significantly better fuel economy than engines using timing
retard. More research must still be done to demonstrate the full
potential of EGR.9
2.0.3.3.2 Improved Turbocharging
Two improvements to intake air turbocharging which are being
developed may result in significant emissions reductions. The
first is the variable geometry turbocharger (VGT), which allows a
more optimized flow of air into the engine, such as more air at
high loads. VGT would not directly impact NOx emissions, but would
decrease particulate emissions and fuel consumption, thereby
allowing further retard of the injection timing. It also provides
a means of controlling cylinder pressures for engines using EGR.
The second approach called turbo expanding involves over-
compressing the intake air, then expanding it to a lower pressure
after the charge is cooled by the aftercooler. The result is a
reduced intake temperature, and thus lower NOx emissions.
2.0.3.3.3 Injection Rate Shaping
Injection rate shaping is a very promising technology for
reducing NOx emissions without adversely affecting other
performance parameters. The basic approach is to reduce the amount
of fuel injected in the early phases of injection so that the
amount of fuel which undergoes premix burning reactions is reduced.
Preliminary testing and even production system development has
begun in earnest over the last few years.
Results from the Ricardo HDD engine research program
demonstrate that rate shaping may be used to achieve very low NOx
levels without a penalty in fuel economy or particulate
emissions.10 By injecting the fuel with a "gradual rise and a
sharp cut" as opposed to a constant injection, the NOx is reduced
because of a lower heat release during the pre-mixed burning phase
where NOx is formed.2 In addition, a clean injection cut-off will
reduce smoke and HC emissions by avoiding the poorly atomized end
of injection.8
2-12
-------
2.0.3.3.4 Electronic Controls
One historical problem with managing the engine operation
parameters is the inherent problem that mechanical controls have
only a limited ability to adjust the operating parameters to match
the optimal conditions for any given speed and load condition. An
engine set up to produce low emissions at one set of conditions may
have relatively high emissions at some other sets of operating
conditions. These problems are especially pronounced in the
smaller diesel engines affected by new clean-fuel fleet vehicle
regulations.
The advent of electronic engine control devices will allow
more flexible control of engine operation. Electronic controls are
expected to be installed on essentially all heavy-duty diesel
engines by 1994 in order to both achieve improved engine
performance and to assist in achieving compliance with the 1994
emission standards. Through the use of electronic controls and the
advent of advanced fuel delivery systems, it will become possible
to store a map of the optimum operation parameters and then to
control the engine operation at these conditions over a wide range
of operating modes thereby reducing some of the needs to make
design trade-offs in cases where engine operation parameters
optimized for one operating condition may not be appropriate for
other operating conditions.8 Among the parameters that could be
controlled electronically are injection timing, injection rate, and
EGR rate.
One example of the use of electronic control would be to use
it to significantly retard injection timing under most operating
conditions except high loads, where the need for both particulate
control and high power is significant. Similarly, EGR rates could
be reduced at high loads to decrease the impact on particulate
emissions. It may also be possible to use exhaust gas sensors for
oxygen and/or NOx in a closed-loop control system to correct for
in-use deterioration. EPA believes that, of the technological
advances expected in the next several years, electronic controls
have the greatest potential for improving the emissions and fuel
economy of diesel engines.
2.0.3.3.5 Aftertreatment Devices
Aftertreatment devices have not yet come into widespread use
on diesel engines. Up to the present time, emissions control
strategies for most diesel engines have relied on technologies
which control engine out emissions. However, both particulate trap
oxidizer systems and flow through catalytic oxidizers are under
development and expected to be available for wide-scale commercial
production if necessary to comply with the 0.10 g/Bhp-hr PM
standard for the 1994 model year. In addition, there is active
research ongoing in the area of catalytic converters capable of
reducing NOx emissions in lean exhausts. These are discussed
2 - 13
-------
below.
2.0.3.3.5.1 Particulate Trap-Oxidizers
A trap-oxidizer system primarily affects PM and HC emissions.
This method of aftertreatment consists of a durable particulate
filter (trap) which collects particulate emissions in the exhaust
stream. Developers of these systems claim that collection
efficiencies of 80 percent or greater can be achieved. Since
collection of the particulates without a system for eventual
removal would quickly plug the traps and shut down the engine, some
method of regenerating the filter by burning off (oxidizing) the
particulates is required. The traps must be regenerated before the
systems become plugged to the extent that back pressures in the
exhaust system rise too much, but too frequent regenerations
increase the amount of energy which must be put into the systems to
effect the regeneration.
Trap-equipped urban bus engines have been certified recently,
but manufacturers remain reluctant to rely on these systems because
of their relatively high costs and remaining concerns over the
durability of the systems. However, these systems should be
available for use prior to 1998, if needed.
2.0.3.3.5.2 Catalytic Oxidizing Converters
Catalytic oxidizing converters greatly reduce HC emissions.
Reductions of as much as 40 or 50 percent of the engine out HC
emissions may be seen from the designs likely to be available prior
to 1998. Since catalytic converters may see widespread use in the
control of particulate emissions, large reductions in HC emissions
will result as a corollary benefit. The catalytic converter avoids
the problem of regeneration due to its flow-through design and some
believe this is a simpler, more cost efficient and more durable
method of aftertreatment than particulate traps. However, its
major drawback is sulfate production. This problem is expected to
be managed with the low sulfur fuels being mandated for sale
beginning in October of 1993.9
2.0.3.3.5.3 Catalytic NOx Reduction
Aftertreatment devices to control NOx emissions in lean
exhausts are not available at this time, although research on
promising technologies is progressing in Japan and Germany.11 The
only aftertreatment device to be demonstrated to date involves the
injection of ammonia or urea into the exhaust stream to consume
NOx. However, there are no acceptable methods to ensure that there
will always be a supply of ammonia or urea to keep these devices
operating. Therefore, actual in-use emissions reductions cannot be
relied on and use of these devices could be problematic. There is
also concern about harmful effects from the emissions of ammonia.
2-14
-------
Passive flow-through catalytic converters to reduce NOx
emissions in lean-burn exhausts are under investigation. These
devices appear to operate by simultaneously reducing NOx and
oxidizing HC or particulates with the oxygen produced from the NOx.
However, the development of useful devices is still some years away
and availability of these devices for the 1998 model year can not
be assumed.8
2.0.3.3.6 Variable Compression Ratio
Increasing the compression ratio in the engine reduces white
smoke and hydrocarbon emissions. There is, however, an optimum
point at which a further increase in the compression ratio causes
an increase in particulate emissions.12 A prototype diesel engine
has been developed that had a variable compression ratio. NOx and
NMHC emissions from this engine were very low. This technology
thus may become available to reduce particulates without increasing
NOx.13
2.0.3.4 Expected Approaches for Clean-Fuel Diesel Engines
Diesel engines will need to make changes to comply with the
proposed clean-fuel fleet emission standard for NOx and NMHC,. but
this should be feasible for a significant number of engines. It is
expected that electronically controlled EGR will be necessary, and
that highly optimized electronic control of injection timing and
rate shaping will also be incorporated. Some catalytic
aftertreatment may be used to control NMHC and PM emissions, since
engine-out emissions of NMHC and PM could increase as a result of
timing retard. EPA does not expect that catalytic aftertreatment
will be used to reduce NOx emissions. It is not clear, at this
time, how fuel economy will be affected, since electronic controls,
EGR, and improved turbocharging can improve fuel economy, while
timing retard will have a negative impact. Manufacturers will be
faced with a decision of how to best trade off improvements to the
engines with increases in fuel consumption, in order to control
emissions in the most cost effective manner.
The docket contains further supporting material on the
feasibility of the proposed NMHC + NOx emission standard for heavy-
duty engines.1
2.0.4 Altarrtatlv* Fual Tachnologlaa
While alternative fuel technologies are certainly viable
candidates for use in clean-fuel fleet vehicles, the proposed
emission standards are not set at a level which will require their
use. It will be difficult, however, for most diesel engines, and
possibly some types of gasoline engines, to reach the proposed
credit-generating standards. Alternative fuel technologies such as
methanol- and gaseous-fueled engines are expected to meet these
standards while electric vehicles are viewed as being the only
2-15
-------
technology capable of meeting the proposed zero emission vehicle
standards. The docket contains further supporting material on the
feasibility of the proposed credit level NMHC + NOx emission
standards for heavy-duty engines.1
2.0.4.1 Methanol
Methanol is an attractive fuel from an emissions standpoint.
Its lower flame temperature leads to an inherent reduction in the
formation of NOx emissions. Exhaust emissions of NMHC (more
appropriately called organics for methanol-fueled engines) are
generally comparable to those of similar petroleum-fueled engines.
Nevertheless, methanol-fueled engines can still provide some
benefit with respect to organic emissions for two reasons. First,
organic emissions from methanol-fueled engines, while not
necessarily less than those from engines using conventional
petroleum fuels, tend to be less reactive in the processes which
form ozone, and thus can have a less significant impact on ambient
air quality. It should be noted, however, that this benefit is
difficult to quantify. Second, non-exhaust (e.g., evaporative)
emissions of organics are much lower than those from gasoline-
fueled vehicles due to the lower vapor pressure of methanol.
Both otto-cycle and diesel-cycle methanol-fueled engines and
vehicles are under development currently. While it is expected
that otto-cycle technology will be capable of meeting the proposed
credit standards by 1998, these vehicles are being developed
primarily for light-duty uses. Diesel-cycle engines, however,
because of their inherent fuel economy advantages, are more likely
to see applications in heavy-duty vehicles. Recently, Detroit
Diesel certified the first heavy-duty diesel cycle methanol engine
for commercial sale. This engine was recertified for the 1993
model year as having NMHC+NOx equivalent emissions of 1.8 g/Bhp-hr,
CO emissions of 2.1 g/Bhp-hr and particulate emissions of 0.03
g/Bhp-hr. As can be seen, this engine is already in compliance
with the proposed credit standard. This particular engine is a
heavy heavy-duty engine intended for use in urban buses, but the
technology should be transferrable to other engines more likely to
be used in the Clean Fuel Fleet program.
2.0.4.2 Natural Gas
Natural gas, in either the form of compressed natural gas
(CNG) or liquified natural gas (LNG), is likely to be used as an
alternative fuel in some light and medium heavy-duty vehicles for
use in the Clean Fuel Fleet program. Indeed, experimental delivery
vans converted from gasoline to CNG are being used by several
delivery fleets due to its potential for fuel cost savings.
Moreover, Cummins has recently certified a CNG-fueled L-10 bus
engine with the State of California. Two types of CNG-fueled
engines are being developed: stoichiometric (i.e., converted
2-16
-------
gasoline engines) and lean-burn (e.g., the Cummins L-10 bus
engine).
EPA analyzed the emissions characteristics of CNG-fueled
vehicles and engines in an April 1990 special report.14
Stoichiometric engines, which are the type of engines being used by
delivery vans, were projected in that report to have emissions of
0.88 g/Bhp-hr NMHC+NOx, 7.4 g/Bhp-hr of CO, 0.01 g/Bhp-hr of
particulate and 0.0006 g/Bhp-hr of formaldehyde for optimized
engines. Projections for optimized lean-burn engines, which are
favored for use in heavy heavy-duty applications (greater than
26,000 Ibs GVWR) for fuel economy reasons, indicated that NMHC+NOx
emissions of 4.06 g/Bhp-hr, CO emissions of 1.5 g/Bhp-hr,
particulate emissions of 0.05 g/Bhp-hr and formaldehyde emissions
of 0.03 g/Bhp-hr can be achieved using traditional technology.
However, the Cummins L-10 engine that was recently certified had
emissions that were much lower than those projected for such a
lean-burn engine: NMHC+NOx emissions of 2.6 g/Bhp-hr, CO emissions
of 0.4 g/Bhp-hr, and particulate emissions of 0.02 g/Bhp-hr. While
neither the projected emissions, nor the emissions from the Cummins
L-10 engine, would comply with all the credit standards, it is
expected that the standards could be met by engines using more
advanced technology. Although the L-10 engine is for heavy heavy-
duty applications, the L-10 engine demonstrates that it ought to be
feasible to meet the clean-fuel fleet vehicle standards with light
and medium heavy-duty vehicles. Lean-burn CNG engines will need to
improve the control of NOx and/or NMHC emissions in order to meet
the credit standards, but it is likely that this would be
accomplished by incorporating the advances in NOx control which are
being developed to comply with the 4.0 g/Bhp-hr standard for all
heavy-duty engines. Stoichiometric technology will also require
minor advances, such as slightly higher catalyst loadings, in order
to comply with these standards by 1998.
2.0.4.3 Liquefied Petroleum Gas
Liquefied Petroleum Gas (LPG) is another gaseous fuel which
expected to be used to some extent in the Clean Fuel Fleet program.
It is a very clean-burning and economical fuel, and has been the
most widely used alternative fuel for many years. Most of the
incentive for its use has come from its economic advantages, and
there is only a limited amount of emissions data available,
especially for heavy-duty vehicles. In general, emissions from
LPG-fueled engines should be similar to the emissions from CNG-
fueled engines, except for NMHC which could be slightly higher from
LPG-fueled engines. This is because NMHC emissions are generally
due to unburned fuel, and LPG is largely a non-methane fuel (unlike
CNG which is comprised mostly of methane). As with CNG-fueled
vehicles, it is expected that LPG-fueled heavy-duty engines will
also be able to comply with the credit standards with similar
control approaches. EPA plans to release a report on LPG fuels and
vehicles in the next few months.
2-17
-------
2.0.4.4 Electric Vehicles
EPA anticipates that electric vehicle technology will be
required for a vehicle to comply with the zero standards. While
light and medium heavy-duty vehicles may be better equipped to
handle the bulk and mass of the necessary batteries, the additional
batteries, limited driving range, and operating expenses will
probably still make electric vehicle technology an unpopular
choice. Advances in technology and market incentives for credits,
however, may combine to make such technology viable at some point
in time.
2.0.5 Summary
The proposed clean-fuel fleet vehicle standards should be
achievable using a wide range of technologies. Gasoline-fueled
engines should be able to reach compliance with the standards
through the further optimization of technologies already in use.
Diesel engines will significant developmental work, including the
introduction of new technologies such as EGR for diesels. EPA also
believes that optimized electronic 'controls for fuel will be
required for all diesel engines in this program but much of this
will be incorporated meet the 4.0 g/Bhp-hr NOx standard. Optimized
(or in some cases non-optimized) alternative fuel technologies
capable of meeting the clean-fuel fleet vehicle standards are
already available.
Credit-generating standards may be achievable in some cases
using conventional fuel technologies and will certainly be
achievable using alternative fuels. These standards might be
achievable with highly advanced gasoline engines using electrically
heated catalytic converters and possibly even by diesel engines
using optimized EGR and electronic fuel control should they become
available. A methanol engine which meets all of the proposed
credit standards has already been certified, and natural gas-fueled
engines appear to be promising candidates also. Zero-emitting
vehicles will probably require electric vehicle technology.
2-18
-------
REFERENCES
1. Presentation to EPA Office of Mobile Sources on developments
in automotive emission control technology, Manufacturers of
Emission Controls. Association (MECA), May 11, 1993 (found in the
docket for this rulemaking).
"Regulatory Impact Analysis, Oxides of Nitrogen Pollutant
Specific Study and Summary and Analysis of Comments," EPA Office of
Mobile Sources, March 1985.
"Final Regulatory Support Document and Summary and Analysis of
Comments on the NPRM — 1993 Model Year Bus Particulate Standard,
1994 and Later Model Year Urban Bus Particulate Standard, Urban Bus
Test Procedures, and 1998 and Later Model Year Heavy-Duty Engine
NOx Standard," EPA Office of Mobile Sources, February 1993.
Acurex Environmental Project Under Contract with California
Air Resources Board, "Technical Feasibility of Reducing NOx and
Particulate Emissions Form Heavy-Duty Engines," Acurex
Environmental Project 8450, Contract No. A132-085, July 27, 1992.
"Draft Regulatory Support Document— 1994 and Later Model
Year Urban Bus Particulate Standard, Urban Bus Retrofit/Rebuild
Program, 1998 and Later Model Year Heavy-Duty Engine NOx Standard,"
EPA Office of Mobile Sources, May 1991.
2. Research work done by Wade et. al., 1987; Cartellieri and
Wachter, 1987.
3. "Feasibility of Controlling Emissions form Off-Road, Heavy-
Duty Construction Equipment," Energy and Environmental Analysis,
Inc., December 1988.
4. "Feasibility and cost-Effectiveness of Controlling Emissions
from Diesel Engines in Rail, Marine, Construction, Farm, and other
Mobile Off-Highway Equipment," Radian Corporation, February 1988,
5. "Mobile-Source NOx Emissions Sources and Control Options," US
EPA, November 1990.
6. "Combustion Chamber Shape and Pressurized Injection in High-
Speed Direct Injection Diesel Engines," M. Ikegami, M. Fukuda, Y.
Yoshihara, J. Kaneko, SAE Paper 900440.
7. "Application of a High Flexible Electronic Injection System to
Heavy Duty Diesel Engine," R. Racine, M. Miettaux, Y. Drutel, J.
Heidt, SAE Paper 910184.
8. "The Effect of Injection Parameters and Swirl on Diesel
Combustion with High Pressure Fuel Injection," S. Shundoh, T.
Kakegawa, K. Tsujimura, SAE Paper 910489.
2-19
-------
9. ""The Low NOx Engine," J. Needham, D. Doyle, A. Nicol, SAE
Paper 910731.
10. "Injection Timing and Rate Control—A Solution for Low
Emissions," J. Needham, M. May, D. Doyle, S. Faulkner, SAE Paper
900854.
11. Ward's Engine and Vehicle Technology Update, "Lean-Burn
Catalysts Under Development" April 15, 1991.
12. "Technology for Meeting the 1991 U.S.A. Exhaust Emission
Regulations^on Heavy Duty Diesel Engine," K. Mori, H. Kamikubo, T.
Kawatani, T. Obara, I. Fukano, K. Sugawara, SAE Paper 902233.
13. "The Development of a Novel Variable Compression Ratio, Direct
Injection Diesel Engine," R. Sobotowski, B. Porter, A. Pilley, SAE
Paper 910484.
14. Analysis of the Economic and Environmental Effects of
Compressed Natural Gas as a Vehicle Fuel, Volume II Heavy-Duty
Vehicles, Special Report Office of Mobile Sources, Environmental
Protection Agency, April 1990
2-20
-------
Chapter 3
Environmental Benefits
3.0.1 Introduction
The environmental benefits of the use of heavy-duty clean-fuel
fleet vehicles which meet the proposed combined 3.5 g/Bhp-hr
NMHC+NOx standard have been estimated by comparing the total
emissions from clean-fuel fleets which are covered by this program
to what the emissions from these same heavy-duty fleets would be in
the absence of a fleet program. Projections have been made of the
number of vehicles which will be affected by these requirements,
the number of miles each of these vehicles travel during a year,
and the emission factors for clean-fuel and 1998 "baseline"
vehicles.
3.0.2 Calculation Method
Efforts were made to estimate emissions in a manner consistent
with the methodology used in the MOBILE4 computer model. These
estimates will be updated using MOBILES for the final version of
this document accompanying the final rule on heavy-duty standards.
The same basic approach of multiplying deteriorated emission
factors by the total number of vehicle miles traveled to estimate
the total emissions was used. Some departures from the MOBILE4
methodology were necessary, however. MOBILE4 lumps all heavy-duty
vehicles together for emissions calculations purposes. In these
calculations, the affected vehicles were broken up into light
heavy-duty (8,501-19,500 Ibs gross vehicle weight (GVW)) and medium
heavy-duty (19,501-26,000 Ibs GVW) vehicle subclasses since these
subclasses are the ones affected by the Clean-Fuel Fleet program
and they vary distinctly from the heavy heavy-duty (greater than
26,000 Ibs GVW) subclass and each other in terms of population
growth, usage, and engine type. Separate emissions factors thus
had to be generated for both light heavy- and medium heavy-duty
gasoline and diesel engines. Furthermore, the fleet vehicle miles
traveled (VMT) and age distribution of vehicles were modified to
reflect information about the operations of fleet vehicles. In the
methodology employed for these calculations, the fleet specific VMT
is converted to a per-vehicle VMT and is then broken down into
light heavy- and medium heavy-duty vehicle subclasses.
3.0.3 Discussion of Data
3-1
-------
3.0.3.1 Light and medium heavy-duty fleet vehicle
demo gr aph i c s
Several factors about fleet vehicle demographics control the
results of the emissions inventory modeling. Because of the
specialized nature of the analysis of fleet emissions, heavy-duty
fleet vehicles have been distinguished by heavy-duty subclass
(i.e., light heavy or medium heavy-duty) and engine type (i.e.,
otto-cycle or diesel-cycle). The characteristics of these four
subclasses will be discussed in order to provide the background
data necessary to make the emissions inventory calculations and to
interpret the results of the emissions inventory modeling.
EPA has estimated that, in 1989, there were 305,000 light
heavy-duty and 668,000 medium heavy-duty vehicles operating in
fleets of ten or more heavy-duty vehicles in areas affected by the
fleet provisions.1 Based on information available from EPA's
MOBILE4 emissions model, the light heavy-duty fleet population is
projected to grow at a rate of 2.75 percent per year while the
population of medium heavy-duty fleet vehicles is projected to
decline at a rate of 1.11 percent per year.2 It is also estimated
that heavy-duty fleet vehicles are replaced every six years and
that 80 percent of the vehicles operating in fleets of ten or more
heavy-duty vehicles in affected areas will actually be covered by
the program. (Twenty percent of such vehicles are assumed not to
be covered because they are not centrally fueled or capable of
being centrally fueled or are exempt under the CAA fleet program.)
Combining these data and assumptions with the fact that 50 percent
of the purchases of affected heavy-duty fleets will be required to
be clean-fuel fleet vehicles starting in 1998, it is projected that
8,516 light heavy-duty and 11,124 medium heavy-duty clean-fuel
fleet vehicles will be required to be purchased in 1998.3 The
results of this projection of the number of light heavy-, medium
heavy- and total heavy-duty vehicles affected by the Clean-Fuel
Fleet Program from 1998 through 2020 are shown in Table 3-1.
3-2
-------
TABLE 3-1: HEAVY-DUTY CLEAN-FUEL FLEET VEHICLE POPULATION
Yssr
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
AW
LHDV Acquisitions '
OM-Cnto 1 M.ilOJ. 1 Vf||
5,961 2.555 8,516
6.126 2,625 8.751
6.294 2,698 8,902
6.467 2,772 9,239
6.645 2.848 9,493
6.628 2.926 9,754
7.015 3,006 10,021
7.209 3.069 10,298
7.407 3,174 10,561
7.610 3.262 10,672
7.620 3,351 11,171
6.035 3.443 11,478
8.256 3.538 11,794
8.483 3.499 11,982
8,716 3.460 12.176
8.956 3,422 12.378
9.202 3.384 12.566
9.455 4.052 13,507
9.715 4.007 13.722
9.982 3.963 13.945
10,257 3.919 14.176
10.539 3.875 14.414
10.829 4.641 15.470
ggom 1 IN-USE Vshldss
MHOV Acquisitions
nairidi ! rmi "ntr 1 T«*I
3.337 7.787 11.124
3.300 7.700 11,000
3.264 7.615 10,879
3,227 7.530 10,757
3.192 7.447 10,639
3.156 7.364 10,520
3.121 7.282 10,403
3,086 7.202 10.288
3.052 7,121 10.173
3.018 7.043 10,061
2,984 6.964 9,948
2,952 6,687 9,839
2,919 6,810 9.729
2,999 6,736 9.735
3.082 6.661 9.743
3,167 6,587 9,754
3,254 6,514 9,768
2,761 6,441 9.202
2,837 6,370 9.207
2,915 6,299 9.214
2,995 6,229 9,224
3,077 6,160 9,237
2.611 6.092 8.703
LHDV IN-USE
ou-Crdi ' Plml r>j.
5.961 2.555
12,087 5,180
18,381 7.878
24,849 10,649
31,494 13.497
38,322 16,424
39,375 16,875
40,458 17,339
41,570 17,816
42,713 18.306
43,888 18,809
45.095 19,326
46,336 19,858
47.610 20,268
48,920 20,554
50.265 20,714
51.647 20.747
53,068 21,355
54.527 21.824
56,026 22,288
57,567 22.747
59,150 23,200
60.777 24.457
T.UI
8.516
17,267
26,259
35,498
44,991
54,745
56,250
57,797
59,386
61,019
62,697
64,421
66,194
67.878
69,473
70,979
72,394
74,423
76.351
78,314
80,314
82,350
85,234
MHOV IN-USE
Ottt-Crdt 1 DtaJ-Cld. 1 Total
3,337 7,787 11.124
6,637 15,487 22.124
9,901 23,102 33,003
13,128 30,632 43,760
16.320 38,079 54,399
19,476 45,443 64,919
19.259 44.939 64.198
19,046 44,440 63,466
18.834 43,946 62,780
18,625 43,459 62.084
18,418 42,975 61,393
18,214 42,498 60,712
18,011 42,027 60.038
17,924 41,561 59,485
17,954 41.101 59.055
18,103 40,645 58,748
18,372 40,196 58,568
18,182 39,749 57,931
18,100 39,309 57,409
18,016 38,872 56,888
17,929 38,440 56,369
17,839 38,013 55,852
17.196 37.591 54,787
Total
*i —
now
Acquisitions
19.640
19,751
19,871
19,996
20,132
20,274
20.424
20.586
20,754
20,933
21,119
21,317
21,523
21,717
21,919
22,132
22,354
22,709
22,929
23,159
23,400
23,651
24,173
Total
IN-USE
fc*^*-t— *
WfNVMOT
19,640
39,391
59,262
79,258
99,390
119,664
120.448
121,283
122,166
123,103
124,090
125.133
126.232
127,363
128,528
129,727
130,962
132,354
133,760
135,202
136.683
138.202
140.021
-------
TABLE 3-2: VEHICLE MILES TRAVELLED BY CLEAN-FUEL FLEET LHDVs/MHDVs
Year
1998
1999
2000
2001
2002
2003
2004
2005
2010
2015
2020
Vehicle Miles Travelled (million
LHDV
Otto-Cycle Mead-Cycle Total
107 46 152
216 93 309
328 141 469
444 190 634
563 241 804
685 293 978
704 302 1005
723 310 1033
828 355 1183
948 382 1330
1086 437 1523
Otto-Cyde
121
240
358
475
591
705
697
689
652
658
622
miles)
MHDV
Diesd-C?de
282
560
836
1108
1378
1644
1626
1609
1521
1438
1360
Total
403
801
1194
1584
1969
2349
2323
2298
2173
2096
1983
Total Vehicle
Miles Travelled
(million miles)
555
1109
1664
2218
2773
3328
3328
3331
3356
3426
3506
-------
Billions of Miles Travelled
>-*- i\j cj >f»- en CTI -j co
v£>
' o °
\j; \,y \\} \y \j \_j. \\y \y
Light-Heavy
•— •••£}
MeQiuni-neavy
' « ••• A- •• • •
AvA Total
'"^v^~- ~A~,,
...v"-'-""""
1 1 1 1 1
95 2000 2005 2010 2015 2020 2025
Year
Figure 3-1 - Clean-fuel fleet vehicle VMT
3-5
-------
Information about fleet operating practices and data available
from MOBILE4 were combined to calculate annual vehicle miles
traveled (VMT) by the clean-fuel fleet vehicle population. For
simplicity, it was assumed that all fleet vehicles within a given
class travel the same number of miles per year regardless of age.
Since light heavy- and medium heavy-duty fleet vehicles are both
projected to accumulate their average fleet life miles within six
years, the annual VMT per vehicle for each class was calculated by
averaging the VMT per vehicle projections for the first six years
of each class as published in the User's Guide to MOBILE4. It was
further assumed that the VMT/vehicle data will remain constant from
year to year. Using this methodology, it is projected that light
heavy-duty fleet vehicles will travel 17,870 miles per year and
medium heavy-duty fleet vehicles will travel 36,190 miles per year.
The projections of the total number of vehicle miles traveled
by heavy-duty vehicles affected by the Clean-Fuel Fleet program are
shown in Table 3-2 and Figure 3-1. It can be seen that, due to the
simultaneous growth in light heavy-duty fleet vehicles and the
decline in the population of medium heavy-duty fleet vehicles, the
number of light heavy-duty vehicles is projected to surpass the
number of medium heavy-duty vehicles by approximately the year
2008. The total number of vehicles increases throughout the time
period evaluated. However, due to the fact that medium heavy-duty
fleet vehicles accumulate approximately twice as many miles per
vehicle each year as light heavy-duty fleet vehicles (see previous
paragraph), medium heavy-duty fleet vehicles together accumulate
more miles each year than the light heavy-duty fleet vehicles even
out to the year 2020.
In order to understand some of the complexities of the results
which will be shown later, it is important to understand some of
the contrasts between light heavy- and medium heavy-duty vehicles
and between otto-cycle (gasoline) and diesel-cycle engines. As has
already been pointed out, the population of light heavy-duty
vehicles is growing while the population of medium heavy-duty
vehicles is declining. Furthermore, it has also been stated that
medium heavy-duty vehicles travel about twice as many miles in a
year as do light heavy-duty vehicles. Another important contrast
between light heavy and medium heavy-duty vehicles is the mix of
engine types these vehicles use. It is estimated that 70 percent
of the light heavy-duty vehicles use gasoline powered otto-cycle
engines with the remainder being primarily diesel-cycle engines.
For medium heavy-duty vehicles, the engine mix is nearly the
opposite of the engine mix for light heavy-duty vehicles (30
percent otto-cycle and 70 percent diesel-cycle).2
The distinction between engine type mixes becomes particularly
critical when the contrasts in emission factors between gasoline
and diesel powered vehicles are taken into account. Diesel engines
typically emit higher levels of NOx than do gasoline engines while
simultaneously emitting lower levels of HC due to the fact that
3-6
-------
diesel engines use lean-burn modes of operation and consequently
have relatively low engine-out HC emissions levels. Today's diesel
engines are not equipped with catalytic converters to reduce the
engine-out HC and NOx emissions as are gasoline engines.
3.0.3.2 Emission Factor Calculations
In order to calculate the emissions inventories for the
desired scenarios, emission factors and deterioration rates for
light heavy-duty and medium heavy-duty vehicles are needed. In
this analysis, ail the vehicles are either gasoline- or diesel-
powered so emission factors for only these two fuel types will be
needed. It is expected that some alternative-fueled vehicles will
be produced, but that the numbers will be sufficiently small, and
certification emission levels and deterioration characteristics
sufficiently similar, so as to not substantially impact the results
of this analysis.
3.0.3.2.1 1998 and Later Baseline Emission Factors
Determination of the environmental impacts of fleet vehicles
requires estimates of emission factors for in-use vehicles. For
this analysis, data is used that projects that in-use 1998 and
later heavy-duty vehicles will behave similarly to certification
vehicles, and that they will meet their respective standards
(intermediate useful life and full useful life standards) in use.
In order for this approach to be valid, it would be necessary for
there to be an extensive inspection and maintenance program, as
well as an active field enforcement program, for heavy-duty
vehicles. Both of these seem reasonably likely, especially in the
areas that will be affected by the fleet program. As will be
discussed later, a similar approach is also being used for heavy-
duty clean-fuel fleet vehicles. Since the same approach is being
used for both baseline and clean-fuel fleet emission factors, these
assumptions should not significantly impact the calculation of
incremental benefits even if the assumptions were to be somewhat in
error. The 1998 baseline vehicle emission factors are derived from
1991 sales-weighted certification emissions, taking into account
the effects of new emission standards. The 1991 certification
emissions rates are shown in Table 3-3.
NMHC estimates for pre-1998 vehicles were derived from MOBILE4
projections. Non-methane hydrocarbon (NMHC) emission factors were
estimated at 95 percent of the total hydrocarbon emission factor
for diesel engines and at 75 percent of the total HC emission
factor for gasoline engines.4 For gasoline engines the same
deterioration rates for HC emission factors are applied to the NMHC
emission factors since present catalytic converters have little
effect on methane emissions.
3-7
-------
Table 3-3 Sales-Weighted 1991 Light and Medium Heavy-Duty
Certification Values
Sales-Weighted Heavy-Duty Certification Values
(g/Bhp-hr)
Vehicle class
Light Heavy-Duty Diesel
Medium Heavy-Duty Diesel
Light Heavy-Duty Gasoline
Medium Heavy-Duty Gasoline
THC
0.56
0.41
0.45
0.79
NMHC
(estimate)
0.54
0.39
0.34
0.59
NOx
4.44
5.01
3.87
3.84
The most significant standard affecting 1998 baseline heavy-
duty vehicles is a reduction in the NOx emission standard from 5.0
to 4.0 g/Bhp-hr beginning in that model year. Light and medium
heavy-duty diesel engines currently exceed this level and will
therefore require new compliance effort. Although the sales-
weighted certification values for NOx emissions from 1991 heavy-
duty gasoline engines are numerically low enough on average to just
meet the 1998 4.0 g/Bhp-hr NOx standard, the relatively small
compliance margins and the fact that some engine families do not
meet the standard indicates that further reductions are needed.
Manufacturers will likely incorporate compliance margins of 10 to
15 percent for certification vehicles to allow for production
variability and in-use operation. Thus, in-use emissions may be
under the standard on average. For this analysis, however, average
NOx emissions will be modeled as being at the level of the 4.0
g/Bhp-hr standard at the end of the vehicle's useful life.
Hydrocarbon standards for 1998 heavy-duty engines will be the
same as for current engines. Heavy-duty diesel NMHC emissions may
drop if catalytic converters achieve a significant penetration into
the light heavy- and medium heavy-duty diesel engine market for
particulate control. This is because, in addition to providing
particulate-control, these catalytic converters are expected to
reduce HC emissions. However, it is also possible that engine-out
HC emissions will be allowed to rise somewhat in the presence of
the catalyst in order to provide more control flexibility for NOx.
This would result in little or no net reduction of NMHC for 1998
baseline vehicles. For this analysis, 1998 baseline diesel NMHC
will be modeled as being at a level equivalent to the 1991 NMHC
levels.
3-8
-------
Hydrocarbon emissions from heavy-duty gasoline vehicles are
also projected to comply with the applicable HC standards in use.
Light heavy-duty gasoline vehicles are assumed to comply with the
1.1 g/Bhp-hr HC standard for vehicles 14,000 Ibs GVW and under, and
medium heavy-duty gasoline vehicles are assumed to comply with, the
1.9 g/Bhp-hr HC standard for vehicles over 14,000 Ibs GVW. Given
the Mobile model vehicle grouping scheme laid out in the beginning
of this chapter for light and medium heavy-duty vehicles, these
assumptions could introduce some analytical error into the
analysis, since some light heavy-duty gasoline vehicles (those
between 14,000 and 19,000 Ibs GVW) could emit up to the 1.9 g/Bhp-
hr standard. However, this should not introduce significant error
into the analysis since there are few gasoline vehicles in this
weight range. For this analysis, as with diesels, 1998 baseline
gasoline NMHC will modeled as equivalent to 1991 NMHC levels since
some reductions in NOx emissions will be needed in 1998.
The deterioration rates for heavy-duty diesel engines are
based on the assigned deterioration factors for heavy-duty diesel
engines with aftertreatment, and the deterioration rates for
gasoline engines are based on the assigned deterioration factors
for light-duty gasoline trucks with three-way catalysts.5 For this
analysis, the estimated zero-mile emission factors are
back-calculated by using the emission projections estimated above
and the respective deterioration factors. These estimated zero-
mile emission factors and deterioration rates for 1998 baseline
vehicle engines are presented in Table 3-4. The deterioration
factors presented in Table 3-4 are the additive equivalents of the
multiplicative deterioration factors, divided over the useful life.
Table 3-4 1998 Model Year Baseline Emission Factors
Vehicle
L-H diesel
M-H diesel
L-H gasoline
M-H gasoline
Zero Mile EF
(g/Bhp-hr)
NMHC
0.42
0.30
0.20
0.35
NOx
3.33
3.33
3.33
3.33
Deterioration Rate
(g/Bhp-hr/10, OOOmi)
NMHC
0.011
0.005
0.013
0.022
NOx
0.061
0.036
0.061
0.061
3-9
-------
3.0.3.2.2 Projections for 1998 Clean-Fuel Fleet Emission
Factors
Emission factors and deterioration rates for clean-fuel fleet
heavy-duty vehicles were estimated using the following methodology.
The clean-fuel engine emission factors are based on the projection
that average NMHC + NOx emissions will comply with a combined 3.5
g/Bhp-hr NMHC+NOx standard at the end of the vehicle's useful life.
The vehicles' emissions are also assumed to deteriorate in a manner
consistent with baseline vehicles, and thus the same assigned
deterioration factors were used for the clean-fuel fleet vehicles
as for the baseline vehicles. However, since the end-of-useful-
life projections are different between these two types of vehicles,
the multiplicative deterioration factors will result in different
additive deterioration rates.
with a combined NMHC + NOx standard manufacturers can get the
required reductions from NMHC and NOx. Each engine family is
likely to use a different mix, but in most cases reductions in both
pollutants are expected. This analysis assumes that the end of
life NMHC level for clean-fuel engines will be 30 percent lower in
1998 than in 1991. This is based on the NMHC reduction expected
from improved catalysts in gasoline and diesel applications. To
estimate NOx levels for 1998 clean-fuel engines, the just-
calculated 1998 NMHC level is subtracted from the proposed NMHC+NOx
standard of 3.5 g/Bhp-hr. Zero-mile emissions are estimated by
back-calculating using the emissions projections estimated above
and the respective deterioration factors. Table 3-5 contains the
projected zero-mile in-use emission factors and deterioration rates
for heavy-duty clean-fuel fleet vehicles.
Table 3-5 1998 Heavy-Duty Clean-Fuel Fleet Vehicle Emission
Factors
Vehicle
L-H diesel
M-H diesel
L-H gasoline
M-H gasoline
Zero Mile EF
(g/Bhp-hr)
NMHC
0.29
0.21
0.14
0.24
NOx
2.60
2.69
2.72
2.57
Deterioration Rate
(g/Bhp-hr/10, OOOmi)
NMHC
0.008
0.003
0.009
0.016
NOx
0.047
0.029
0.049
0.047
3 - 10
-------
3.0.4 Environmental Impacts
Based on the baseline and clean-fuel fleet vehicle emission
factors developed above, emission inventory estimates have been
calculated for NMHC and NOx emissions from heavy-duty fleet
vehicles. Historically, carbon monoxide emissions and particulate
emissions from diesel engines have been directly proportional to HC
emissions and inversely proportional to NOx emissions. However,
the introduction of new technologies such as catalytic converters,
rate-shaped electronically-controlled unit injectors and exhaust
gas recirculation will change the relationships between pollutant
emissions rates in ways which can not be accurately predicted.
Therefore, projections of emission inventories will be made only
for NMHC and NOx, the primary pollutants targeted by the clean-fuel
fleet requirements.
The inventories of NMHC and NOx emissions from heavy-duty
clean-fuel fleet vehicles 1998 baseline vehicles have been
calculated for the years during which these standards are being
phased in and for every five years beyond that until the year 2020.
In general, for each vehicle subclass these per-vehicle emission
benefits were calculated by subtracting the clean-fuel fleet
vehicle emission factors from the baseline emission factors for the
respective pollutants and then multiplying the result by the
estimated vehicle miles traveled by all clean-fuel fleet vehicles
in that vehicle subclass during each year. The overall emission
benefits results from light heavy-duty and medium heavy-duty
vehicles were then combined for each year and are presented in
Table 3-6 according to engine type.
As demonstrated in Table 3-6, the emission inventories and
benefits climb rapidly during the first six years as the fleet is
turned over; after 2003, however, the emissions inventories and
benefits become relatively constant. After 2003 diesel-cycle NOx
benefits begin to decline as otto-cycle benefits increase due to
the gradual replacement of medium heavy-duty vehicles by light
heavy-duty vehicles which are mostly otto-cycle vehicles.
11
-------
Table 3-6 Nationwide Emissions Inventories of Fleets Covered by
the Clean-Fuel Fleet Program
calendar
year
1998
1999
2000
2001
2002
2003
2004
2005
2010
2015
2020
Total
NMHC Emissions Benefit
(tons per year)
Otto-
Cycle
26
60
101
149
204
266
265
264
261
260
261
5,251
Diesel-
Cycle
60
124
193
266
345
428
425
422
408
397
387
8,286
Total
86
184
294
415
548
693
689
686
669
657
648
NOx Emissions Benefit
(tons per year)
Otto-
Cycle
206
429
667
922
1,192
1,479
1,479
1,480
1,490
1,513
1,550
13,537 1 30,462
Diesel-
Cycle
415
850
1,304
1,779
2,273
2,787
2,766
2,745
2,648
2,563
2,492
53,923
Total
621
1,278
1, 971
2,701
3,465
4,266
4,245
4,224
4,138
4,076
4,042
84,385
This analysis generates emission reductions based on the
assumption that the end of life NMHC level for clean-fuel engines
will be 30 percent lower than the end of life NMHC level for 1998
baseline engines and the remainder of the required reduction comes
from NOx. There are any number of potential approaches which could
be used to meet the NMHC + NOx levels of the proposed standard.
For example, another possibility is that otto-cycle engine NMHC
levels increase over 1991 levels under pressure from the 4.0 g/Bhp-
hr NOx standard and diesel-cycle NMHC emissions decrease as a
result of the particulate matter control technology discussed in
Chapter 2. Thus, a different set of NMHC benefits would be
expected for clean-fuel heavy-duty engines. Assuming the NMHC +
NOx split for 1991 engines the NMHC benefit for otto-cycle would be
about 28,000 tons (an increase) but for diesel-cycle engines the
3 .- 12
-------
benefits would drop to about 1,200 tons. NOX benefits would
essentially be the same.
Either the scenario laid out in section 3.0.3.2 or that
discussed above is conceivable and depending on what strategies are
used a range of values is the best estimate at this time. Based on
the scenarios above, the 22-year total of emission benefits for
otto-cycle engines range from 5,300 to 28,000 tons of NMHC benefits
and from 30,500 to 31,000 tons of NOx benefits. The 22-year total
of emission benefits for diesel-cycle engines range from 1,200 to
8,300 tons of NMHC benefits, and from 52,700 to 53,900 tons of NOx
benefits. Combined benefits range from 14 to 29 tons of NMHC and
83 to 84 tons of NOx.
3 - 13
-------
References
1. "Highway Statistics, 1989," U.S. Department of Transportation,
Federal Highway Administration, 1989.
2. "User's Guide Mobile 4.0," Terry Newell, Test and Evaluation
Branch, Environmental Protection Agency, PB 89 164271. The
document is available from EPA's Emission Planning and Strategies
Division.
3. U.S. Environmental Protection Agency, Office of Mobile
sources, "Estimated Number of Fleet Vehicles Affected by the Clean
Fuel Fleet Program," Memorandum from Sheri Dunatchik to Docket A-
91-25, June 11, 1991.
4. "Analysis of the Economic and Environmental Effects of
Compressed Natural Gas as a Vehicle Fuel; Volume II: Heavy-Duty
Vehicles," Office of Mobile Sources, EPA, April 1990.
5. EPA Office of Mobile Sources Advisory Circular 51C, as revised
February 26, 1987. The document is available from EPA's
Certification Division.
3 - 14
-------
Chapter 4
Costs and Cost Effectiveness
4.0.1 Introduction
This chapter describes EPA's analysis of the economic impact
of the Clean-Fuel Fleet program on heavy-duty vehicles. The
purpose of this analysis is to estimate of the per-vehicle costs,
the total cost, and the cost effectiveness of the proposed program.
To do this, it is necessary to make several assumptions about how
manufacturers will choose to comply with the program. The Agency
recognizes that manufacturers may deviate from the control
techniques assumed here, and that such deviations could lead to
different costs. Nevertheless, in the absence of better
information, EPA believes that these approaches are technically
reasonable and that they result in reasonably accurate estimates of
the costs associated with this program.
It should also be noted that this analysis does not assume
that all current light-heavy and medium-heavy duty vehicle engine
families will comply with the standards of this program, but rather
that only those engine families which could comply with relatively
minor changes would be produced for the clean-fuel fleet vehicle
program. This is important because costs would be significantly
higher if it were necessary that all light-heavy and medium-heavy
duty vehicle engine families comply with the standards. However,
this is not the case, and given the small size of the affected
market, there should be a significant incentive to modify only
those engine families for which costs were relatively small or
demand was larger from a nationwide perspective.
4.0.2 Costs
4.0.2.1 Operating Costs
Increased operating costs can arise from three sources;
increases in fuel consumption, increases in maintenance costs and
decreases in engine life. Increased fuel consumption has
traditionally been a potential problem in engines designed to
reduce NOx.emissions. This reduction in fuel economy is usually a
side effect of retarding the timing of the combustion (i.e., spark
timing in otto-cycle engines or fuel injection timing in
diesel-cycle engines). It is not clear at this time, however,
whether engine manufacturers will need or choose to sacrifice fuel
economy to reduce NOx emissions. Historically, manufacturers have
been reluctant to do so and have sought other technologies which
reduce NOx emissions without increased fuel consumption. Up to a
one percent increase in fuel consumption is possible if
manufacturers choose emission control approaches which have an
adverse effect on fuel consumption. However, based on the
4-1
-------
technology being developed to meet the 4.0 g/Bhp-hr NOx standard
(see Chapter 2 of this document), it is more likely that NMHC+NOx
emissions will be reduced through the addition of emission control
hardware without a fuel economy penalty.
Since engines for heavy-duty clean-fuel fleet vehicles are not
expected to have significantly different designs than the engines
designed to meet the 1998 heavy-duty NOx standard, they are not
expected to be less durable or more expensive to maintain than
their general-use counterparts. Therefore, EPA does not anticipate
that heavy-duty clean-fuel engines or vehicles will be any more
expensive to operate than their contemporary general use
counterparts and therefore that all costs will be associated with
engine and emission control modifications.
4.0.2.2 Engine Costs
Engine costs consist of four elements: research and
development (R&D) costs, additional hardware requirements, added
manufacturing costs and engine certification costs. Additional
hardware and added manufacturing are variable costs included in the
price of each engine purchased. Engine certification and R&D costs
are fixed costs paid up-front by the engine manufacturer and
recovered through additional costs added to each engine over a
period of time. For purposes of this analysis, the certification
costs will be recovered on a yearly basis, while the R&D costs will
be amortized over a period of five years using a rate of return of
10 percent. (Since this analysis was performed, EPA's Office of
Policy, Planning, and Evaluation has recommended that a rate of
return of 7 percent be used for this type of analysis. The
analysis performed for the final RIA will use this value.)1
4.0.2.2.1 Otto-Cycle Heavy-Duty Engines
4.0.2.2.1.1 Hardware Costs
Gasoline (otto-cycle) heavy-duty engines are not expected to
require the development of new hardware to meet the heavy-duty
clean-fuel fleet vehicle emission standard. However, as discussed
in Chapter 2, some will require improvements in the existing
hardware. Nearly all otto-cycle heavy-duty engines currently have
electronically controlled fuel injection and three-way catalytic
converters capable of both reducing NOx emissions and oxidizing HC
emissions, with oxygen sensors and feedback controls. Compliance
with the clean-fuel fleet vehicle standards, however, may require
higher catalyst loadings, which would increase catalyst costs.
Other improvements or minor modifications may or may not increase
the manufacturing costs. In order to take these potential costs
into account, engine production cost increases will be estimated at
$50 per engine. This is conservative given that current NMHC+NOx
certification levels are already close to the standard (see Table
3-3) and the need for all heavy-duty engines to meet the 4.0
4-2
-------
g/Bhp-hr NOx standard in 1998.
4.0.2.2.1.2 Development Costs
In order to comply with the heavy-duty clean-fuel fleet
vehicle standard,, some otto-cycle heavy-duty engines will require
minor improvements to existing systems beyond those needed to
achieve compliance with the 1998 4.0 g/Bhp-hr NOx standard. It is
expected that some combination of better air/fuel handling,
improved catalytic converter technology, exhaust pipe insulation
and enhanced exhaust gas recirculation will be the main compliance
strategies. In order to make the design changes necessary, EPA
estimates that the calibrations and other development efforts will
cost approximately $30,000 per engine family.2
4.0.2.2.1.3 Certification Costs
To certify an engine family, manufacturers must perform
emission tests on a representative engine from that family and
submit the results to EPA; this only need occur once for each
engine family at the beginning of its production, with
certification being carried over in each subsequent year for about
80 percent of families. Recordkeeping and reporting requirements
accompany new certification and annual recertification. EPA has
estimated that the cost of certification testing for heavy-duty
gasoline engine families is about $200,'000 per family3 and the cost
for reporting and recordkeeping is about $100,000 per family
certified or recertified.4 In addition to these costs,
manufacturers must pay a certification fee of $12,500 for each
heavy-duty engine family. Thus the total certification costs for
each heavy-duty gasoline engine family are projected to be about
$312,500.
4.0.2.2.2 Diesel-Cycle Heavy-Duty Engines
4.0.2.2.2.1 Hardware Costs
Manufacturers will apply refined or improved control
technologies that will allow compliance without an increase in fuel
consumption. As was discussed in Chapter 2, it appears likely that
further optimization of the technology that will be available as a
result of the 1998 4.0 g/Bhp-hr NOx and 1994 0.10 g/Bhp-hr PM
standards will allow manufacturers to meet the clean-fuel fleet
vehicle standards for many engine families. Technologies which are
expected to be used in some conventional diesel engines to comply
with the 1998 4.0 g/Bhp-hr NOx standard include improved electronic
engine controls and exhaust gas recirculation, and some of the
other technologies discussed in Chapter 2. Particulate trap
oxidizers and catalytic oxidizing converters (to reduce PM and HC
emissions) should make a broad penetration into the heavy-duty
diesel engine market in order to facilitate compliance with the
0.10 g/Bhp-hr PM standard. Clean-fuel diesel engines are expected
4-3
-------
to be optimized versions of the cleanest of these conventional
engines, and may also include advanced turbocharging and catalytic
converters (for NMHC control).
By basing the clean-fuel diesel engines on only the cleanest
conventional diesel engine families, manufacturers will be able to
minimize costs. EPA estimates that the additional manufacturing
cost of the improved control system hardware for heavy-duty clean-
fuel vehicle engines, which will improve emissions while
maintaining the same fuel consumption, will be about $100 dollars
per engine more than the costs associated with the cleanest 1998
baseline engines. This $100 is roughly equivalent to the lifetime
cost of a one percent increase in fuel consumption (i.e., $ 100
fuel economy penalty) for light- and medium-heavy duty diesel
vehicles. Thus, in order . to avoid the fuel economy penalty,
manufacturers would likely make the necessary hardware changes at
a cost ($100) equivalent to the amount the consumer would spend in
lifetime operating costs.
4.0.2.2.2.2 Development Costs
As with otto-cycle engines, diesel-cycle engines are expected
to require additional development beyond that required for engines
meeting the 1998 4.0 g/Bhp-hr NOx standard. It is expected that
several additional calibrations will be required. These
calibrations will require design changes and engine modifications.
The cost of these calibrations and other development is estimated
to be about $100,000 (in 1992 dollars) for each engine family.2
4.0.2.2.2.3 Certification Costs
As with otto-cycle engines, HDD engine manufacturers will
incur costs for certification of engines for clean-fuel vehicles as
well as the associated reporting and recordkeeping requirements.
EPA estimates that these costs are $260,000s per family for
certification testing and $78,000 per family certified for
reporting and recordkeeping. (The estimated reporting and
recordkeeping costs for diesels are less than those for otto-cycle
engines because information collection for evaporative testing does
not exist for diesels.)4 As was the case with gasoline engines,
EPA projects that about 80 percent of the families will be
recertified each year using carryover provisions and that 20
percent will engage in new certification and the accompanying
testing. The recordkeeping and reporting costs cited above apply
to each family each year as does the certification fee of $12,500.
Thus the total certification costs for each heavy-duty diesel
engine family is projected to be about $350,500.
4.0.2.3 Aggregate Costs
4-4
-------
As was discussed above, heavy-duty clean-fuel fleet vehicles
are not expected to have any increases in operating costs over
general heavy-duty vehicles; thus, essentially all the costs of
this program should come from increased engine/vehicle costs.
Since the number of clean-fuel heavy-duty engines required to be
purchased will be relatively small, the per engine and total costs
of this portion of the Clean-Fuel Fleet program will be a strong
function of how many engine families are developed and certified
for this program. For this analysis, it is estimated that a total
of six light and medium heavy-duty otto-cycle and twelve light and
medium heavy-duty diesel-cycle engine families will be certified
for participation in the Clean-Fuel Fleet program. For comparison,
in 1991 a total of nine otto-cycle and fourteen diesel-cycle light
or medium heavy-duty engines were certified. If significantly
fewer engine families are certified, costs will be less than those
estimated here.
In addition, to be conservative this analysis has assumed that
full certification costs will be incurred for each engine family
certified, even though most families will probably be able to be
certified based on California test data. In such cases, separate
federal testing would probably not be necessary and the
certification testing costs correspondingly lower.
4.0.2.3.1 Manufacturer Costs
Based on the development costs projected above, the total cost
of developing six otto-cycle engine families will be approximately
$180,000; the total cost of developing twelve heavy-duty diesel-
cycle engine families will be approximately $1,200,000. Similarly,
the first-year certification costs for six otto-cycle and twelve
diesel-cycle engine families will be $1,200,000 and $3,120,000,
respectively. For subsequent years, this analysis assumes that one
otto-cycle engine family and two diesel-cycle engine families will
be recertified with emission testing required each year
(approximately 20 percent); certification costs would then total
$200,000 per year and $520,000 per year, respectively. Annual
reporting, recordkeeping, and certification fees for all families
amount to $675,000 for otto-cycle engines and $1,086,000 for
diesel-cycle engines. The fixed costs to manufacturers for
developing each engine family are presented in Table 4-1.
The total costs to manufacturers will consist of these fixed
costs of developing and certifying each engine family combined with
the variable costs of manufacturing the engines. Using the
projections of the number of clean-fuel fleet vehicles required to
be purchased from Table 3-1 in chapter 3, the yearly variable costs
to manufacturers from hardware and production costs can be
calculated (per vehicle production + hardware cost * number of
vehicles). These costs have been analyzed through the year 2020
(the first 22 years that the standard is in effect).
4-5
-------
Table 4-1 Manufacturer Fixed Costs for Heavy-Duty Clean-Fuel
Engines
Otto-
cycle
Diesel
-cycle
Number
of
Families
6
12
Total
Develop.
Costs ($)
180,000
1,200,000
Total
First-Year
Cert.
Costs ($)
1,200,000
3,120,000
Total
Annual
Cert.
Costs
($)
200,000
520,000
Total
Annual
Recording
Reporting
& Fees
Costs ($)
675,000
1,086,000
In order to calculate the total aggregate costs to
manufacturers, all costs are discounted to the first year of the
standard, 1998. Research and development costs will be assumed to
occur in the second year before the standard goes into effect
(1996). Initial costs for certifying (and fulfilling
reporting/recordkeeping requirements) for all engine families
certified as clean-fuel vehicles is assumed to occur in 1997, with
full recertification occurring annually thereafter for only one
otto-cycle family and two diesel-cycle families, as described
above. The assumed chronology for the incurring of costs for
research, development, and testing (RD&T), certification and
reporting, and for the hardware costs is presented in Table 4-2.
The present value costs to manufacturers accrued during the first
22 years of the standard discounted to 1998 (in 1992 dollars) are
also presented in Table 4-2. The total present value costs to
manufacturers of the first 22 years of the program discounted to
1998 (in 1992 dollars) is approximately $15.9 million for otto-
cycle engines and approximately $31.8 million for diesel-cycle
engines.
4-6
-------
Table 4-2 Costs to Manufacturers
Year
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2010
2015
2020
1998 NPV
Otto-Cycle
RD&T/
Cert.
$180,000
$1,875,000
$875,000
$875,000
$875,000
$875,000
$875,000
$875,000
$875,000
$875,000
$875,000
$875,000
$875,000
Hardware
$464,900
$471,300
$477,900
$484,700
$491,800
$499,200
$506,800
$514,800
$558,700
$610,800
$672,000
15,941,600
Diesel-Cycle
RD&T/
Cert.
$1,200,000
$4,206,000
$1,606,000
$1,606,000
$1,606,000
$1,606,000
$1,606,000
$1,606,000
$1,606,000
$1,606,000
$1,606,000
$1,606,000
$1,606,000
Hardware
$1,034,200
$1,032,500
$1,031,300
$1,030,200
$1,029,500
$1,029,100
$1,029,000
$1,029,100
$1,034,900
$1,049,400
$1,073,300
31,826, 900
4-7
-------
4.0.2.3.2 Costs to Users
Since clean-fuel heavy-duty vehicles are not expected to have
different fuel consumption or maintenance costs than general use
light and medium heavy-duty vehicles, the only cost to the consumer
will be the first cost of purchasing the vehicles. In addition to
the cost for hardware changes, consumers will also have to pay for
the amortized cost of the research, development, and testing as
well as for the retail price mark-up.
Manufacturers are expected to recover the development costs
and first-year certification costs over the first five years of
engine sales. By amortizing these costs over the predicted sales
during the first five years of the program, EPA has calculated that
the development costs and first-year certification costs of these
engine families will add an average of $62 to the manufacturer's
cost of a clean-fuel heavy-duty otto-cycle engine and $152 to the
manufacturer's cost of a clean-fuel heavy-duty diesel engine,
respectively.
Adding on the estimated additional certification, hardware and
manufacturing costs for both otto- and diesel-cycle heavy-duty
clean-fuel engines and factoring in an estimated 29 percent retail
price mark-up it is estimated that these engines will cost about
$250 more per otto-cycle engine and $482 more per diesel-cycle
engine than for engines that would be used in general heavy-duty
vehicles during the first five years of the program. During the
remaining years of the program (from year 2003 to 2020), clean-fuel
otto-cycle engines are estimated to cost an additional $147 to
$178, and clean-fuel diesel-cycle engines are estimated to cost an
additional $322 to $338 in 1992 dollars. (These additional costs
for clean-fuel engines are different from year to year due to
variations in the projected number of clean-fuel fleet vehicles
required to be purchased (see Table 3-1).)
This analysis generates additional costs for clean-fuel fleet
vehicles that may be overly conservative since as described above
it assumes that the manufacturers will have to incur costs for
certification testing on all engine families. Without the
certification testing, these engines would cost about $165 more per
otto-cycle engine and $306 more per diesel-cycle engine than for
engines that would be used in general heavy-duty vehicles during
the first five years of the program. During the remaining years of
the program (from year 2003 to 2020), clean-fuel otto-cycle engines
are estimated to cost an additional $129 to $152, and clean-fuel
diesel-cycle engines are estimated to cost an additional $265 in
1992 dollars.
Table 4-3 presents total consumer cost projections through the
year 2020, along with the aggregate cost, expressed in 1992 dollars
discounted to the year 1998. As the table shows, costs in the
first five years of the program are marginally higher than in
4-8
-------
successive years because development costs are being recovered
during this period. The.22-year present value costs of the fleet
program range from $15.4 to $20.6 million for otto-cycle engines
and from $28.4 to $41.1 million for diesel-cycle engines.
Table 4-3 Costs to Consumers
Year
1998
1999
2000
2001
2002
2003
2004
2005
2010
2015
2020
1998 NPV
Otto-Cycle
$2f 300f 600
$2,316,600
$2,333,300
$2,350,500
$2,368,400
$1,772,700
$1,782,500
$1,792,800
$1,849,500
$1,916,700
$1,995,600
$20,564,700
Diesel-Cycle
$4,978,100
$4,973,500
$4,970,000
$4,966,800
$4,965,000
$3,399,200
$3,398,900
$3,399,300
$3,406,700
$3,425,300
$3,456,300
$41,056,700
4-9
-------
4.0.3 Cost Effectiveness
The cost effectiveness of the heavy-duty portion of the Clean-
Fuel Fleet program was calculated using a 22-year cost
effectiveness method. The 22-year cost effectiveness analysis is
performed by discounting both the total consumer costs and the
total benefits of the first 22 years of the program to 1998 and
dividing the costs by the benefits. Since the costs have been
estimated separately for otto-cycle and diesel-cycle engines, their
cost effectiveness will be analyzed separately also. It should be
noted that for otto-cycle engines which have both NMHC and NOx
emissions reductions, the costs have been divided evenly between
NMHC and NOx.
The 1998 present value for the 22 years of emission reductions
are calculated from the data in Table 3-6 of chapter 3. As
discussed in Chapter 3, this analysis generates emission benefits
for clean-fuel fleet vehicles that may be overly conservative. The
22-year present value emission benefit for diesel-cycle engines
ranges from 500 to 3,100 tons of NMHC emission reductions and
19,600 to 20,100 tons of NOx emission reductions. For otto-cycle
engines, the 22-year present value benefit ranges from 1,900 to
10,200 tons of NMHC emission reductions and 11,000 to 11,300 tons
of NOx emission reductions. For diesel-cycle engines the minimal
NMHC reduction is not used in the cost effectiveness analysis, and
thus, the cost effectiveness for diesel-cycle engines will be
calculated by assigning all costs to NOx reduction.
The 22-year cost effectiveness, in dollars per ton, can now be
calculated by dividing the present value costs by the present value
emission benefits. The costs of the otto-cycle and diesel-cycle
engines are divided evenly between the NMHC and NOx benefits. The
22-year cost effectiveness for otto-cycle and diesel-cycle engines
is presented in Table 4-4. This analysis generates 22-year cost
effectiveness projections for clean-fuel fleet vehicles that may be
overly conservative. The 22-year cost effectiveness for otto-cycle
engines ranges from $800 to $5,500 per ton of NMHC emission
reductions and $700 to $900 per ton of NOx emissions reductions.
For diesel-cycle engines, the resulting 22-year cost effectiveness
is $6,700 per ton of NMHC emission reductions and ranges from
$1,000 to $1,400 per ton of NOx emission reductions. The
relatively high cost effectiveness of NMHC control and low cost
effectiveness of NOx control is a result of the cost allocation
method used. Given the nature of the standard (NMHC + NOx) and the
large number of possible ways to split controls and control costs
undue importance should not be placed on the numerical values
derived. A simple reallocation of costs or assumed change in
NMHC/NOx control fraction would change the cost effectiveness
value. Given, the depth of analyses possible at this time any
change probably would not be meaningful until further information
becomes available.
4-10
-------
Table 4-4 Cost Effectiveness in $/ton (1998 Present Value)
Costs ($)
NMHC (tons)
NOx (tons)
NMHC Cost
Effectiveness
($/ton)
NOx Cost
E f f e ct i vene s s
($/ton)
Otto-Cycle
15 - 21 million
1,900 - 10,200
11,000 - 11,300
800 - 5,500
700 - 900
Diesel-Cycle
28- 41 million
500 - 3,100
19,600 - 20,100
n/a - 6,700
1,000 - 1,400
4.0.4 Summary
The total cost of the heavy-duty Clean-Fuel Fleet program to
consumers is estimated to be approximately $4.7 to $7.3 million per
year during the first five years of the program (1992 dollars), and
approximately $4.3 to $5.5 million per year after that. Estimates
of the cost effectiveness of this program range from $800 to $5,500
per ton for NMHC control and range from $700 to $1,400 per ton for
NOx control.
As was presented above there are a number of different ways
costs and benefits could be developed and attributed and each
scenario would yield a different value for each entry in Table 4-4.
EPA recognizes that each of the values in Table 4-4 has validity
based on the analysis presented above; further information and
reanalysis is needed in the final rule to refine the estimates.
For purposes of this report the figures presented in bold type will
be carried forward in further analysis. However, the other values
also have validity and merit equal consideration.
4 - 11
-------
References
1. "OMB Presentation and Discussion on OMB Circular A-94
Regarding Discount Rates and Benefit-Cost Analysis," Memorandum
from Brett Snyder to Addressees, EPA Office of Policy, Planning and
Evaluation, March 23, 1993.
2. Based on calibration estimates from the "Gaseous Emission and
Particulate Emission Regulations," 50 FR 10606, EPA Office of
Mobile Sources, March 15, 1985
3. "Regulatory Impact Analysis, Oxides of Nitrogen Pollutant
Specific Study and Summary and Analysis of Comments," EPA Office of
Mobile Sources, March 1985.
4. "Information Collection Request Supporting Statement; Clean
Fuel Fleet Emission Standards, Conversions, and General
Provisions," EPA Office of Mobile Sources, August 1992 Draft.
5. "Final Regulatory Support Document and Summary and Analysis of
Comments on the NPRM — 1993 Model Year Bus Particulate Standard,
1994 and Later Model Year Urban Bus Particulate Standard, Urban Bus
Test Procedures, and 1998 and Later Model Year Heavy-Duty Engine
NOx Standard," EPA Office of Mobile Sources, February 1993.
"Draft Regulatory Support Document — 1994 and Later Model
Year Urban Bus Particulate Standard, Urban Bus Retrofit/Rebuild
Program, 1998 and Later Model Year Heavy-Duty Engine NOx Standard,"
EPA Office of Mobile Sources, May 1991.
4 - 12
------- |