A motor car engine is an Internal Combustion Engine (ICE). Energy is created by burning either diesel or petrol in a combustion chamber. In such an engine, the energy is transferred from the pistons moving up and down at high speeds. This up-down motion is converted to a rotary motion through the crankshaft and axle. The axle turns the wheels and make the car move forward. The four strokes of the engine refer to intake, compression, combustion, and exhaust. One complete cycle occurs with every 2 crankshaft rotations.
The cycle begins when the piston is at the top of the cylinder and is moving downward. This causes a mixture of petrol and air (or just air in the case of a diesel engine) to be released into the cylinder.
The piston continues to move upward and compresses the mixture inside the cylinder.
The power stroke begins the second rotation of the crankshaft. A spark ignites the mixture of petrol and air inside the cylinder. In the case of a diesel engine it is during this phase that diesel is injected into the cylinder. The pressure created from combustion pushes the piston back down.