diesel engine is an oil-burning internal combustion engine
patented by Rudolf Diesel (1838-1915), a German engineer,
in 1892 after several years of development work. Air enters
a cylinder and is compressed by a piston to a high enough
temperature and pressure for spontaneous combustion to occur
when fuel is sprayed in. This method of operation differs
from that of the gasoline engine in which air and fuel are
mixed before entering the cylinder, there is less compression,
and a spark is needed to initiate combustion.
In the first (intake) stroke of the cycle of a 4-stroke diesel
engine, the piston moves down, drawing in air through a valve. In the second (compression) stroke, the piston returns
up, compressing the air and heating it to over 300 degrees
C. (The exact value depends on the compression ratio, which
may be between 12:1 and 22:1.) Near the end of the stroke,
fuel is sprayed into the cylinder at high pressure through
a nozzle and ignites the hot air. In the third (power) stroke,
the burning fuel-air mixture increases the pressure in the
cylinder, pushing the piston down and driving the crankshaft.
Then, in the fourth (exhaust) stroke, the piston moves up
and again and drives the burnt gases out of the cylinder.
There are also 2-stroke diesel engines. These have only compression
and power strokes, the exhaust gases being scavenged and new
air introduced by a blower while the piston is at the bottom
of its stroke.
Diesel engines were initially less smooth-running, heavier,
and more expensive than gasoline engines, and were only widely
used in ships, heavy vehicles, and power installations. Increasingly,
modern diesels became used in cars, being smooth-running and
quiet and making efficient use of cheaper fuel.
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