13-08-2012, 02:08 PM
Automotive engine
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The component of the motor vehicle that converts the chemical energy in fuel into mechanical energy for power. The
automotive engine also drives the generator and various accessories, such as the air-conditioning compressor and
power-steering pump. See also: Automotive climate control; Automotive electrical system; Automotive steering
Early motor vehicles were powered by a variety of engines, including steam and gasoline, as well as by electric
motors. The flexibility of the gasoline engine operating on the four-stroke Otto cycle soon made this engine
predominant, and it remains the dominant automotive power plant. The basic modern automotive engine (see illus.)
is a gasoline-burning, liquid-cooled, spark-ignition, four-stroke-cycle, multicylinder engine. It has the intake and
exhaust valves in the cylinder head, and electronically controlled ignition and fuel injection.
tto-cycle engine
An Otto-cycle engine is an internal combustion piston engine that may be designed to operate on either two strokes or
four strokes of a piston that moves up and down in a cylinder. Generally, the automotive engine uses four strokes to
convert chemical energy to mechanical energy through combustion of gasoline or similar hydrocarbon fuel. The heat
produced is converted into mechanical work by pushing the piston down in the cylinder. A connecting rod attached to
the piston transfers this energy to a rotating crankshaft. See also: Gasoline; Internal combustion engine; Otto cycle
Cylinder arrangement
Engines having from 1 to 16 cylinders in in-line, flat, horizontally opposed, or V-type cylinder arrangements have
appeared in production vehicles, progressing from simple single-cylinder engines at the beginning of the twentieth
century to complex V-12 and V-16 engines by the early 1930s. Increased vehicle size and weight played a major role
in this transition, requiring engines with additional displacement and cylinders to provide acceptable performance.
High-volume usage of the V-8 engine began in the mid-1930s and accelerated dramatically after World War II, until it
was the predominant engine used in American-built vehicles by the late 1950s. Manufacturers in other countries
continued large-volume production of smaller engines with four and six cylinders, primarily because of significantly
higher fuel costs. As vehicle size and weight increased, average engine displacement also increased until the early
1970s, when V-8 engines approaching 500 in.3 (8 liters) displacement were in production. However, oil shortages in
1973–1974 and 1979–1980 reversed this trend, and V-8 engine usage dropped in favor of engines with four and six
cylinders.
Turbocharger and supercharger
To provide acceptable vehicle performance with a smaller engine, forced induction may be used. A turbocharger or
supercharger forces more air into the intake manifold, allowing the engine to burn more fuel and produce more power.
The turbocharger is a centrifugal air compressor driven by an exhaust-gas-powered turbine mounted on a common
shaft. The energy in the exhaust gas spins the turbine, which spins the compressor, forcing more air or air-fuel
mixture into the combustion chambers. In a typical passenger car, this may increase engine power output by up to
40%.
A supercharger, which is belt-driven from the engine crankshaft, may be used instead of a turbocharger. The
supercharger does not have the brief acceleration lag, or so-called turbo lag, that is found objectionable by many
drivers of vehicles with turbocharged engines. See also: Automobile; Combustion chamber; Compressor; Muffler;
Supercharger; Turbine; Turbocharger
Emissions
In the United States, passenger-car emission standards became effective in California in 1966 and in the other 49
states in 1968. These regulations began placing limits on crankcase, exhaust, and evaporative emissions into the
atmosphere. The limits became increasingly stringent over the years, requiring the use of catalytic converters and
unleaded gasoline beginning with 1975-model cars. Because more accurate fuel metering and ignition timing were
required on engines to meet the tightening standards, electronic controls became necessary. As a result, fuel injection
replaced the carburetor on automotive engines.
Electronic controls
Ignition, fuel, and emissions systems are integrated under an electronic engine control system. The system utilizes an
onboard computer to provide management of various engine-operating parameters and emissions devices. The
computer, known as the powertrain control module, may also control shifting of the automatic transmission or
transaxle.