United States Air and Radiation EPA420-F-97-015
Environmental Protection May 1997
Agency
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
production.
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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.
Aftertreatment
Technologies
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
technologies.
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
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