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ENCYCLOPEDIA ARTICLE

Automotive engine


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.  See also: Engine
Automotive engine, which has six cylinders, double-overhead camshafts, 24-valve electronic coil-on-plug spark ignition, and
multiport fuel injection. (Oldsmobile Division, General Motors Corp.)
Page 1 of 4 McGraw-Hill's AccessScience
9/22/2008 http://www.accessscience.com/popup.aspx?id=064300&name=printOtto-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.
Engine design trends

Page 2 of 4 McGraw-Hill's AccessScience
9/22/2008 http://www.accessscience.com/popup.aspx?id=064300&name=printIn many automotive engines, the camshaft, which operates the intake and exhaust valves, has been moved from the
cylinder block to the cylinder head (see illus.). This overhead-camshaft arrangement allows the use of more than two
valves per cylinder, with various multivalve engines having three to five. Some overhead-camshaft engines have only
one camshaft, while others have two camshafts, one for the intake valves and one for the exhaust valves. A V-type
engine may have four camshafts, two for each bank of cylinders. Some multivalve overhead-camshaft engines have
the power and performance of a turbocharged engine of similar size.
Most engines have fixed valve timing, regardless of number of camshafts or their location. Variable valve timing can
improve fuel economy and minimize exhaust emissions, especially on multivalve engines. At higher speeds, volumetric
efficiency can be increased by opening the intake valves earlier. One method drives the camshaft through an
electrohydraulic mechanism that, on signal from the engine computer, rotates the intake camshaft ahead about 10°.
Another system varies both valve timing and valve lift by having two cam lobes, each with a different profile, that the
computer can selectively engage to operate each valve. Computer-controlled solenoids for opening and closing the
valves will allow elimination of the complete valve train, including the camshaft, from the automotive piston engine
while providing variable valve timing and lift.
Materials trends

Historically, major engine components have been made from ferrous metals, either by casting or by forging. However,
emphasis on weight reduction for improved fuel economy has greatly increased the usage of aluminum for cylinder
blocks, cylinder heads, and other engine components. Some engine covers and intake manifolds are made of
magnesium. Internal engine parts, such as connecting rods, sprockets, oil-pump rotors, and valve guides, are cast or
forged to nearly net shape using powder metallurgy. High-speed engines may use titanium connecting rods to reduce
reciprocating mass.  See also: Powder metallurgy
Parts such as engine covers, intake manifolds, and oil pans also can be fabricated of plastic or composite materials.
These materials provide weight savings while reducing engine noise and vibration. Ceramic engine parts and coatings
will allow engine operation at higher temperatures, raising engine efficiency. Ceramic-lined exhaust ports in the
cylinder head can lower its temperature while increasing the effectiveness of the catalytic converter.
Fuel-metering trends

With the introduction of electronic controls, a device was added to the carburetor to automatically adjust the air-fuel
ratio in response to feedback from an exhaust-gas oxygen sensor. Demand for more accurate fuel metering resulted in
the feedback carburetor being replaced by a similarly located throttle-body fuel-injection unit. It meters fuel through
the computer-controlled pulsing of one or two solenoid-operated fuel injectors. Further improvements in engine power,
fuel economy, and exhaust emissions are provided by multiport fuel injection, which places a fuel injector in each
intake port. Solenoid-operated fuel injectors can be pulsed or energized in simultaneous, group, or sequential
fashion—the last energizes each injector individually in firing-order sequence.
Ignition trends

On many automotive engines, the ignition distributor has been replaced with computer-controlled distributorless
ignition; this in turn is being replaced with coil-on-plug or direct ignition, in which an ignition coil sits directly above,
and is connected to, each spark plug. Some engines have two spark plugs per cylinder to provide higher power output
with cleaner combustion and less tendency for spark knock, or detonation. Spark knock can be monitored by a knock
sensor, which signals the computer for less spark advance to prevent engine damage. The knock sensor also is used,
especially with a supercharger or turbocharger, to allow engine operation on a more economical, lower-octane-rated
fuel than otherwise would be required.
Onboard diagnostic developments

An onboard computer with self-diagnostic capability has become standard equipment for automotive engine control.
Page 3 of 4 McGraw-Hill's AccessScience
9/22/2008 http://www.accessscience.com/popup.aspx?id=064300&name=printThe first generation of onboard diagnostics (OBD I) identified the failure of certain emission-control components. The
second generation (OBD II), required for 1996 and later model vehicles, has additional capability, including detection
of deterioration in performance of emission-control components throughout the life of the vehicle.
Alternative engines

Alternative engine designs have been investigated as replacements for the four-stroke Otto-cycle piston engine,
including the two-stroke, diesel, Stirling, Wankel rotary, gas turbine, and steam engines, as well as electric motors and
hybrid power plants. However, only two engines are in mass production as automotive power plants: the four-stroke
gasoline engine described above, and the diesel engine. Continuing improvements to the Otto-cycle piston engine,
such as electronic controls and value actuation and other changes in design and materials, appear to assure its
predominance in the short term.  See also: Battery; Diesel engine; Electric vehicle; Fuel cell; Gas turbine; Motor;
Power plant; Rotary engine; Solar cell; Steam engine; Stirling engine
Donald L. Anglin
Bibliography

l H. Heisler, Advanced Engine Technology, Society of Automotive Engineers and Edward Arnold, 1995
How to cite this article

Donald L. Anglin, "Automotive engine", in AccessScience@McGraw-Hill, http://www.accessscience.com, DOI
10.1036/1097-8542.064300
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