carbon monoxide (CO)
and nitrogen oxides (NOx). Most of these emissions are associated with light-duty cars and trucks. Heavy-duty trucks
motorcycles
and off-road vehicles are also significant sources. In urban areas
motor vehicles are estimated to be responsible for 40 to 50% of HC
50% of NOx
and 80 to 90% of CO emissions. Similar patterns have been reported in Europe and Japan. Motor vehicle pollutants such as nonmethane hydrocarbons (NMHCs) and NOx serve as precursor molecules for the production of elevated tropospheric ozone (O3) levels. Within the context of primary pollutants and subsequent formation of secondary pollutants such as O3 and other smog and haze constituents
it is not surprising that motor vehicle emission control has been a major regulatory priority in the U.S. for more than three decades and an increasing priority in other developed and developing countries. Regulatory efforts to control motor vehicle emissions (Chapter 8) have a history dating back to the early 1960s. Emission reduction requirements over that time have become more stringent
requiring motor vehicle manufacturers to continuously develop and employ new emission control techniques. As a consequence of regulatory and technological efforts
aggregate CO and HC emissions from motor vehicles were reduced by ~40%
and NOx by 25%
in the period from 1982 to 1997. This reduction occurred despite a substantial increase in vehicle miles driven. 9.1 MOTOR VEHICLE ENGINES Two types of engine systems are used in motor vehicles: (1) Otto cycle spark ignition (SI) reciprocating internal combustion engines (ICEs)
and (2) diesel cycle compression ignition (CI) ICEs. The former are widely used in cars and light-duty trucks
motorcycles
boats
and other small-horsepower consumer products. The latter are used in utility vehicles
e.g.
trucks
earth-moving and mining equipment
farm tractors
and ships
where high-torque
low-speed performance is required. Because of their higher fuel economy
CI engines are widely used in light-duty vehicles in Europe.
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