ABOUT ENGINE
@chsan M
Although
the engine is major system by itself (figure 1-3), its output should be
considered a component of the drive train. The engine provides the
power to drive the wheels of the vehicle. An engine develops a rotary
motion or torque that, when multiplied by the transmission gears, will
move the car under a variety of conditions. The engine produces power by
burning a mixture of fuel and air in its combustion chambers.
Combustion cases a high pressure in the cylinders, which forces the
pistons downward. Connecting rods transfer the downward movement of the
pistons to the crankshaft, which rotates by the force on the pistons.
All
automobile engines, both gasoline and diesel, are classified as
internal combustion engines because the combustion or burning that
creates energy takes place inside the engine. Combustion is the burning
of an air and fuel mixture. As a result of combustion, large amounts of
pressure are generated in the engine. This pressure or energy is used to
power the car. The engine must be built strong enough to hold the
pressure and temperatures formed by combustion.
Diesel
engines have been around a long time and are mostly found in big
heavy-duty trucks. However, they are also used in some pick-up trucks
and will become more common in automobiles in the future ( figure 1-4).
Although the construction of a gasoline and diesel engine are similar,
their operation is quite different.
A
gasoline engine relies on a mixture of fuel and air that is ignited by a
spark to produce power. A diesel engine also uses fuel and air, but
does not need a spark to cause ignition. Diesel engines are often called
compression ignition engines. This is because its incoming air is
tightly compresses air. The heat of the compressed air ignites the fuel
and combustion takes place. The following sections cover the basic parts
and the major systems of a gasoline engine.
Most
automotive engines are four-stroke cycle engines. The opening and
closing of the intake and exhaust valves are timed to the movement of
the piston. As a result, the engine passes through four different events
or strokes during one combustion cycle. These four the intake,
compression, power, and exhaust strokes.
One
the intake stroke, the piston moves downward, and charge of air/fuel
mixture is introduced into cylinder. As the piston travels upward, the
air/fuel mixture is compressed in preparation for burning. Just before
the piston reaches the top of the cylinder, ignition occurs and
combustion starts. The pressure of expanding gases forces the piston
downward on its power stroke. When it reciprocates, or moves upward
again, the piston is on the exhaust stroke. During the exhaust stroke,
the piston pushes the burned gases out of the cylinder. As long as the
engine is running, the cycle of event repeats itself, resulting in the
production of engine torque.
