How does a 'four-stroke' automobile engine work ?

In an automobile, the engine's task is to burn fuel so that fuel energy is converted into motion . A for-stroke engine gets its name because it does this conversion in four stages called strokes- the intake stroke, the compression stroke, the combustion stroke and the exhaust stroke .

    To understand the strokes, we must first know the structure of the engine. The engine consists of a hallow metal cylinder inside which fuel (petrol or diesel) is burned. The cylinder is fitted with a piston - a piece of metal that slides in and out of the cylinder like a plunger. The piston is attached to a rotating rod called the crankshaft which powers gears that turn the wheels of the automobile.
     The cylinder is sealed except for two openings (called valves) at the top. One is the 'inlet valve' and the other is called 'outlet/exhaust valve'. At the top of the cylinder, there is an electrical device called spark plug that sets fire to the fuel.

      The four strokes work in the following manner :-
1.Intake : The crankshaft rotates as the piston pushes downwards inside the cylinder. The inlet valve opens and lets in a mixture of air fuel.
2.Compression : The inlet valve closes and seals the cylinder, trapping the fuel and air mixture.As the piston is move upwards, the crankshaft and it squeezes(compresses) the mixture, making it more inflammable. As soon as the piston reaches the top of the cylinder, the spark plug fires.
3.Combustion : The spark ignites the fuel-air mixture causing it to burn rapidly. This creates hot gases that push the piston downwards with force & turn the crankshaft, causing the wheels(and the car, of course) to move.
4.Exhaust : The outlet valve opens. As the crankshaft continues its rotation, the piston moves upwards again, driving out the gases as exhaust.