is the heart of your car. It is a complex machine built to convert heat from burning
that turns the road wheels.
The chain of reactions which achieve that objective is set in motion by a
, which ignites a mixture of petrol vapour and compressed air inside a momentarily sealed
and causes it to burn rapidly. That is why the machine is called an
internal combustion engine
. As the mixture burns it expands, providing power to drive the car.
To withstand its heavy workload, the
must be a robust structure. It consists of two basic parts: the lower, heavier section is the cylinder block, a casing for the engine's main moving parts; the detachable upper cover is the
The cylinder head contains valve-controlled passages through which the air and
mixture enters the cylinders, and others through which the gases produced by their
The block houses the
, which converts the
at the crankshaft. Often the block also houses the
, which operates mechanisms that open and close the
in the cylinder head. Sometimes the camshaft is in the head or mounted above it.
Different engine layouts
The simplest and most common type of engine comprises four vertical cylinders close together in a row. This is known as an
. Cars with capacities exceeding 2,000cc often have six cylinders in line.
The more compact
is fitted in some cars, especially vehicles with eight or 12 cylinders, and also some with six cylinders. Here the cylinders are arranged opposite each other at an angle of up to 90 degrees.
Some engines have
horizontally opposed cylinders
. They are an extension of the V-engine, the angle having been widened to 180 degrees. The advantages lie in saving height and also in certain aspects of balance.
The cylinders in which the pistons operate are cast into the block, as are mountings for ancillary equipment such as a
for the oil which lubricates the engine, and a
for the fuel. An oil
, called the
, is bolted underneath the
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The valve which allows mixture into the cylinder is the inlet valve; the one through which the spent gases escape is the exhaust valve. They are designed to open and close at precise moments, to allow the engine to run efficiently at all speeds.