Engine
Automotive production down the ages has required a wide range of
 energy-conversion
systems. These include electric, steam, solar, turbine, rotary, and
different types of piston-type internal combustion engines. The
reciprocating-piston internal -combustion system, operating on a
four-stroke cycle, has been the most successful for automobiles, while
diesel engines are widely used for trucks and buses.
The gasoline engine was originally selected for the automobile due to
its flexibility over a wide range of speeds. Also, the power developed
for a given weight engine was reasonable; it could be produced by
economical mass-production methods; and it used a readily available,
moderately priced fuel--gasoline. Reliability, compact size, and range
of operation later became important factors.
In today’s world, there has been a growing emphasis on the
pollution producing features of automotive power systems. This has
created new interest in alternate power sources and internal-combustion
engine refinements that were not economically feasible in prior years.
Although a few limited-production battery-powered electric vehicles have
appeared from time to time, they have not proved to be competitive owing
to costs and operating characteristics. However, the gasoline engine,
with its new emission-control devices to improve emission performance,
has not yet been challenged significantly.
The first half of the twentieth century saw a trend to increase engine
horsepower, particularly in the American models. Design changes
incorporated all known methods of raising engine capacity, including
increasing the pressure in the cylinders to improve efficiency,
increasing the size of the engine, and increasing the speed at which
power is generated. The higher forces and pressures created by these
changes created engine vibration and size problems that led to stiffer,
more compact engines with V and opposed cylinder layouts replacing
longer straight-line arrangements. In passenger cars, V-8 layouts were
adopted for all piston displacements greater than 250 cubic inches (4
litres).
Smaller cars brought about a return a to smaller engines, the four- and
six-cylinder designs rated as low as 80 horsepower, compared with the
standard-size V-8 of large cylinder bore and relatively short piston
stroke with horsepower ratings in the range from 250 to 350.
The automobile engines from Europe had a bigger range, varying from
1to12 cylinders with corresponding differences in overall size, weight,
piston displacement, and cylinder bores. Four cylinders and horsepower
ratings from 19 to 120 was followed in a majority of the models. Several
three-cylinder, two-stroke-cycle models were built while most engines
had straight or in-line cylinders. There were several V-type models and
horizontally opposed two- and four-cylinder makes too. Overhead
camshafts were frequently employed. The smaller engines were commonly
air-cooled and located at the rear of the vehicle; compression ratios
were relatively low. The 1970s and '80s saw an increased interest in
improved fuel economy which brought in a return to smaller V-6 and
four-cylinder layouts, with as many as five valves per cylinder to
improve efficiency.
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