United States              Air and Radiation          EPA420-F-97-015
                    Environmental Protection                           May 1997

                    Office of Mobile Sources
SEPA        Environmental
                    Fact Sheet
                    Emission Control  Potential for
                    Heavy-Duty Diesel Engines
                    Diesel engines are typically used to power trucks, buses and nonroad
                    equipment (for farming, construction, mining, etc.) because of their
                    exceptional fuel economy and durability advantages. To reduce oxides
                    of nitrogen (NOx) and particulate matter (PM) emissions from these
                    engines, the Environmental Protection Agency (EPA) is collaborating
                    with engine manufacturers to research the potential control options.
                    Diesel engines use compression instead of spark plugs to ignite the fuel.
                    The high temperatures typical of diesel compression ignition cause
                    oxygen and nitrogen from the intake air to combine as NOx. NOx reacts
                    with hydrocarbons (HC) and sunlight to form ground-level ozone
                    (smog); NOx also combines with other atmospheric constituents to form
                    fine particulate matter. Ozone and particulate matter are associated with
                    many adverse health and welfare effects, including respiratory illness,
                    acid rain, eutrophication,  and visibility problems (haze).

                    Despite previous design improvements, diesel engines contribute a
                    substantial portion of the NOx, PM, and, to a lesser extent, the HC
                    emissions from mobile sources. Manufacturers have begun a comprehen-
                    sive review of diesel engine design to move toward more effective con-
                    trols for NOx, PM and HC. One strategy may be to better manage the
                    process of air and fuel delivery to the cylinder, reducing emissions
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                  Another strategy may be to use "after treatment" (post-combustion)
                  technologies to break down or capture emissions. Diesel engines of the
                  future may use a combination of strategies, possibly incorporating fuel
                  changes as well. The following is a brief description of several potential
                  diesel emission control options:

    Fuel          Designing electronic controls and improving fuel injectors to deliver fuel
    Delivery      at tne best combination of injection pressure, injection timing and spray
                  location to burn its fuel more efficiently without causing the temperature
                  spikes that increase NOx emissions.

   Air Intake     Redesigning turbochargers, aftercoolers and intake valving to provide
                  optimum pressure, temperature and routing of the intake air is important
                  for managing the physical and chemical processes needed to achieve
                  good air-fuel combustion. Exhaust gas recirculation (mixing some
                  exhaust gas with the intake air) is an established diesel engine technology
                  that could be used more extensively in future diesel engines.
Catalysts and paniculate traps can be used to convert or capture emis-
sions prior to exhaust. Traps are used to remove and eventually burn
particulate emissions. Catalysts for diesel engines are more complex than
similar technologies used in cars, but hold promise for reducing NOx and
particulate emissions by converting them to less-harmful compounds.
   Diesel Fuel   Employing fuel additives and improving fuel properties such as raising
   Parameters   the cetane number, lowering the aromatics content and decreasing sulfur
                  may contribute to reduced NOx and PM emissions and may also provide
                  engine manufacturers with greater flexibility to use new emission control

                  As part of its current rulemakings, EPA, in conjunction with industry and
                  other concerned groups, is researching and comparing the costs and
                  benefits of these and other potential engine and fuel changes to deter-
                  mine the most feasible, cost-effective, durable and safe emission-reduc-
                  tion program for heavy-duty diesel engines.

                  For further information, please call the NOx/PM Initiative voice mailbox
                  at (313) 741-7887, or write to:

                        U.S. Environmental Protection Agency
                        Office of Mobile Sources
                        Engine Programs and Compliance Division
                        2565 Plymouth Road
                        Ann Arbor, Michigan 48105