There are four step to produce power in this kind engine, that’s why it called four stroke engine.
1st stroke (Intake): The piston moves down the cylinder and the pressure will drop (negative pressure). The intake valve is opened. Because of the low pressure the air/fuel mixtures is sucked into the cylinder
2nd stroke (Compression): At Bottom Dead Center (BDC) the cylinder is at its maximum volume and the intake valve is closed. Now the piston moves backward the Top Dead Center (TDC) and compresses the air/fuel mixtures. The pressure is increased and the volume is decreased. The necessary work for the compression increases the internal energy of the mixtures - the temperature is increased. Because of the fast compression only a small part of the energy is transfered to the environment.
3rd stroke (Combustion): The spark from the spark plug inflames the mixture. The following explosion presses the piston to the bottom, the gas is operating on the piston. The force drives the piston downward to crank shaft (the valves are closed). The volume is increased and the preasure is decreased. No more energy is added and because of this the internal energy of the gas is decreased as so as the temperature.
4th stroke (Exhaust): at BDC the exhaust valve is opend and the piston moves up the cylinder. The pressure drops near the preasure outside the cylinder because of the opened exhaust valve. Exhaust gas leaves the cylinder. The volume is decreased.
2nd stroke (Compression): At Bottom Dead Center (BDC) the cylinder is at its maximum volume and the intake valve is closed. Now the piston moves backward the Top Dead Center (TDC) and compresses the air/fuel mixtures. The pressure is increased and the volume is decreased. The necessary work for the compression increases the internal energy of the mixtures - the temperature is increased. Because of the fast compression only a small part of the energy is transfered to the environment.
3rd stroke (Combustion): The spark from the spark plug inflames the mixture. The following explosion presses the piston to the bottom, the gas is operating on the piston. The force drives the piston downward to crank shaft (the valves are closed). The volume is increased and the preasure is decreased. No more energy is added and because of this the internal energy of the gas is decreased as so as the temperature.
4th stroke (Exhaust): at BDC the exhaust valve is opend and the piston moves up the cylinder. The pressure drops near the preasure outside the cylinder because of the opened exhaust valve. Exhaust gas leaves the cylinder. The volume is decreased.
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