Internal combustion engine

An internal combustion engine in cutawayA car is usually powered by a piston engine, a kind of internal combustion engine. It is so-called because fuel, usually petrol or diesel oil but sometimes hydrogen or liquefied petroleum gas, is burned (combusted) inside it. In this way, the engine converts the chemical energy stored in its fuel into movement or kinetic energy. Inside the heavy engine block are cylinders: normally four in a car engine. Pistons fit snugly inside the cylinders. When the engine is running, the pistons turn the crankshaft via connecting rods, and the crankshaft turns the wheels.

How it works

Pistons turning the crankshaft

Liquid fuel is pumped from the tank to an electronic fuel-injection system. There it is turned into a fine spray and mixed with air. Inlet valves let the fuel/air mixture into the engine’s cylinders where it is ignited by electric spark plugs. The opening and closing of the valves is precisely controlled and timed by the rotation of the camshaft. Four or more cylinders sparking one after the other very quickly produce a continuous power to the wheels.

During what is called the four-stroke cycle, the explosions that result when the spark plugs ignite the fuel/air mixture drive the pistons inside the cylinders up and down. The crankshaft, to which the pistons are attached, turns this up-and-down motion into a turning motion. The crankshaft is, via the gears, connected to the wheels, and so the car is driven along. Exhaust gases, meanwhile escape the cylinders via the exhaust valve, and are piped out of the engine through the exhaust manifold. Lubricating oil allows the engine’s moving parts to slide alongside one another smoothly. Oil passing through the filter is cleaned of any grit and other impurities.

Four-stroke cycle

The four-stroke cycleMost internal combustion engines work on a four-stroke cycle which is repeated again and again as the pistons move up and down. On the first stroke, as the piston moves down, the inlet valve opens to allow a mixture of fuel and air to be sucked into the cylinder. This is called the inlet stroke (1). On the second stroke, as the piston moves up, the air and fuel is squeezed into the top of the cylinder: the compression stroke (2). Now a spark is created electrically by the spark plug, igniting the fuel, which forces the cylinder down. This is the ignition stroke (3). On the fourth stroke, the exhaust valve opens to let waste gases be forced out as the piston moves up again: the exhaust stroke (4).

High-powered engines

V-8 pistons and crankshaft

This piston engine has four cylinders, arranged “in-line”. Other, more powerful engines have two banks of four (or five or six) cylinders positioned on either side of the engine and tilted inwards to form a “V” layout. These are called V6, V8, V10 or V12 engines.

Battery and alternator

The car battery produces the strong current needed to turn the starter motor. It contains plates of lead immersed in acid. Taking power from the crankshaft, a drive belt turns the alternator. As it does so, it produces electricity to recharge the battery. The alternator powers the car’s electrical systems once the engine is running.