187
Engines 187-
WHEN PREHISTORIC PEOPLE discovered fire, they found
a way of obtaining energy, because burning releases heat and
light. About one million years later, the steam engine was
invented, and for the first time people could harness that
energy and turn it into movement. Today, there are
many different kinds of engines that drive the
world’s transportation and industry. All
engines serve one function—to use
the energy stored in a fuel such as oil
or coal, and change it into motion to
drive machines. Before engines were
invented, tasks such as building and
lifting depended on the strength of
people and their animals. Today,
engines can produce enough power
to lift the heaviest weights and drive
the largest machines. The most
powerful engine is the rocket
engine; it can blast a spacecraft
away from the pull of Earth’s
gravity and out into space.Most engines have between
four and eight cylinders. These
work in sequence to produce
continuous movement.
The piston
moves up
and down
inside the
cylinder.
Piston 1 moves
down and sucks
fuel-air mixture
in through
inlet valve.
Piston 3 is pushed down
by expanding gases when
the mixture explodes.Piston 4 rises and
pushes waste gases out
Piston 2 rises and through exhaust valve.
compresses (squeezes)
fuel-air mixture.FOUR-STROKE ENGINE
Most car engines are four-stroke engines,
which means that each piston makes
a set of four movements.
Valves open and
close to admit
and expel the
fuel-air mixture.
Spark plug
produces electrical
spark that ignites
fuel-air mixture.
DIESEL ENGINE
Many trains and trucks have powerful diesel engines, which
are internal-combustion engines that burn diesel fuel
instead of gasoline. The engine works in the same way as a
gas-fueled engine, but does not have spark plugs. Instead,
each cylinder has an injector that squirts diesel fuel into the
cylinder. The piston compresses the air, making it very hot.
The hot air is all it needs to make the diesel fuel explode.Crankshaft
changes the
up-and-down
movement of the pistons
into a circular movement
that drives the wheels.INTERNAL-COMBUSTION ENGINE
The engine that powers almost all of the
world’s cars is the internal-combustion
engine. It uses the power of gases created
by exploding fuel to produce movement.
A mixture of air and tiny droplets of gasoline
enters the engine’s cylinders, each of which
contains a piston. An electrical spark
ignites (sets alight) the fuel mixture,
producing gases that thrust each
piston down.ELECTRIC MOTORS
Gas and diesel engines produce waste gases that
pollute the air and contribute to the greenhouse
effect (which causes Earth’s temperature to rise).
Electric motors are clean, quiet, and produce no
pollution. Several car manufacturers are developing
cars powered by electric motors. Hybrid cars such
as the Toyota Prius (below) use a combination of
electric and gas power to provide good
performance with low pollution.