U.S. Environmental Protection Agency

   Regulatory Development  and Support Division
                  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
    Fundamentals of Gasoline Engines Which Impact	2-1
                    NMHC + NOx emissions
           Air-to-Fuel Ratio	2-1
           Ignition Timing	2-2
           Combustion Chamber Design  	2-3
    Current Gasoline Emissions Control Technology  	2-3
           Exhaust Gas Recirculation  	2-4
           Aftertreatment Systems  	2-4
                 Catalytic Converters  	2-4
                 Electronic Controls 	2-5
    Future Gasoline Emissions Control Technology  	2-5
           Electrically-Heated Catalytic Converters	2-6
           Closed-Coupled Catalytic Converters	2-6
           Lean-Bum Calibration	2-6
    Expected Approaches for Clean-Fuel Gasoline	2-7
       2.3 Diesel Engines  	2-7
    Technical Background/Fundamentals of Diesel	2-7
                    Engines Which Impact NMHC + NOx emissions
           Fuel System  	2-8
           Air System	2-8
    Current Diesel Emissions Control Technology	2-9
           Retarded Injection Timing	2-9
           Injection Pressure	2-9
           Injector Nozzle Holes  and Diameters	2-10
           Intake Air Turbocharging  	2-10
           Aftercooling 	2-10
           Cylinder Design	2-10
    Future Diesel Emissions Control Technology	2-11
           Exhaust Gas Recirculation  	2-11
           Improved Turbocharging	2-12
           Injection Rate Shaping	2-12
           Electronic Controls	2-13
           Aftertreatment Devices	2-13
                  Particulate Trap-Oxidizers  	2-14
                  Catalytic Oxidizing Converters	2-14

                Catalytic NOx reduction  	2-14
          Variable Compression Ratio  	2-15
    Expected Approaches for Clean-Fuel Diesel Engines	2-15
      2.0.4 Alternative Fuel Technologies	2-15
    Methanol	2-16
    Natural Gas  	2-16
    Liquefied Petroleum Gas	2-17
    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
    Light and Medium-Heavy Duty Fleet Vehicle  	3-2
    Emission Factor Calculations	3-7
          1998 and Later Baseline Emission Factors  	3-7
          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
    Operating Costs  	4-1
    Engine Costs 	4-2
          Otto-Cycle Heavy-Duty Engines 	4-2
                Hardware Costs	4-2
                Development Costs	4-3
                Certification Costs	4-3
          Diesel-Cycle Heavy-Duty Engines	4-3
                Hardware Costs  	4-3
                Development Costs	4-4
                Certification Costs	4-4
    Aggregate Costs	4-4
          Manufacturer Costs 	4-5
          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
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  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.

 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.


     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
  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


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.

  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.  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


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-
  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

     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.
  Aftertreatment Systems

       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


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

     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

        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. 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:


electrically-heated catalytic converters,  close-coupled catalytic
converters, and lean-burn calibration.
  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.
  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.
  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


technology is uncertain at this time for heavy duty engines.  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^  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


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.
  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

     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.
  Air System

     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.  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.

  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

  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


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

  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

  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


     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.

  Cylinder Design

     The  combustion  chamber  shape  may be optimized  in order to


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.  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.
  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


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
  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.
  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


-------  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

     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.
  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


     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.

     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

      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.

     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
  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  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


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  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. 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


gasoline  engines)  and  lean-burn  (e.g.,   the  Cummins  L-10  bus

     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.  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.


-------  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.


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.


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

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

                           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"

    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

-------  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.


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
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
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
*i —
fc*^*-t— * 	

Vehicle Miles Travelled (million
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


Total Vehicle
Miles Travelled
(million miles)

Billions of Miles Travelled
>-*- i\j cj >f»- en CTI -j co

' 	 o 	 °

\j; \,y \\} \y \j \_j. \\y \y
•— •••£} 	
' « ••• A- •• • •
AvA Total
'"^v^~- 	 ~A~,, 	

1 1 1 1 1

95 2000 2005 2010 2015 2020 2025
Figure 3-1 - Clean-fuel fleet vehicle VMT

     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


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.  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.
  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.

    Table 3-3 Sales-Weighted 1991 Light and Medium Heavy-Duty
                      Certification Values
Sales-Weighted Heavy-Duty Certification Values
Vehicle class
Light Heavy-Duty Diesel
Medium Heavy-Duty Diesel
Light Heavy-Duty Gasoline
Medium Heavy-Duty Gasoline
     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

     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

L-H diesel
M-H diesel
L-H gasoline
M-H gasoline
Zero Mile EF
Deterioration Rate
(g/Bhp-hr/10, OOOmi)

-------  Projections for 1998 Clean-Fuel Fleet Emission
     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

L-H diesel
M-H diesel
L-H gasoline
M-H gasoline
Zero Mile EF
Deterioration Rate
(g/Bhp-hr/10, OOOmi)
                              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.

 Table 3-6 Nationwide Emissions Inventories  of Fleets  Covered by
                  the Clean-Fuel Fleet Program

NMHC Emissions Benefit
(tons per year)
NOx Emissions Benefit
(tons per year)
13,537 1 30,462
1, 971
     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  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


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

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  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


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.  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
  Otto-Cycle Heavy-Duty Engines

   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


g/Bhp-hr NOx standard in 1998.

  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

   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
  Diesel-Cycle Heavy-Duty Engines

   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


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.

  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

   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.  Aggregate Costs

     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.
  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).


Table 4-1   Manufacturer  Fixed Costs  for Heavy-Duty  Clean-Fuel




Costs ($)



Costs ($)






& Fees
Costs ($)


     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

Table 4-2  Costs to Manufacturers

1998 NPV


31,826, 900

-------  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,

     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


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
1998 NPV
$2f 300f 600

    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.

   Table 4-4  Cost Effectiveness in $/ton (1998 Present Value)

Costs ($)
NMHC (tons)
NOx (tons)
NOx Cost
E f f e ct i vene s s
15 - 21 million
1,900 - 10,200
11,000 - 11,300
800 - 5,500
700 - 900
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


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