Standard automobile engines are naturally aspirated four - stroke cycle, compression ignition with four or more cylinders. It has the following sequence of strokes.  Suction: Inlet valves open, piston moves down.  Compression: Both valves are closed. Piston moves upwards.  Power: Fuel is ignited which pushes the piston down.  Exhaust: Exhaust valve opens, piston moves upwards expelling the burnt gases out of engine. Stichometric charge is required for proper working of the engine. It increases the efficiency of the engine. This charge comprises of air and fuel. Air: It is sucked in through air cleaner, intake passages and valves from atmosphere. Fuel: It is supplied through the injectors.