INTAKE STROKE:
INTAKE STROKE Piston moves downward , sucking in the fuel and air mixture. Pressure is constant . Volume is constantly increasing, until the piston reaches the BDC (bottom dead centre).
COMPRESSION STROKE:
COMPRESSION STROKE The volume decreases. Pressure increases due to the compression of the fuel and air mixture. Recall the formula: PV= nRT , where: P: pressure V: volume when pressure increases the volume decreases because pressure and volume are inversely proportional. Note: Only air gets compressed, as liquids are non-compressible.
POWER STROKE:
POWER STROKE A sudden jump in the pressure occurs, explained by ignition of the mixture, caused by the spark plug. The pressure then decreases, with the volume as well. NOTE: In this stroke the pressure decreases with the volume only because there has been a change in the chemical formation of the mixture (liquid to gas).
EXHAUST STROKE:
EXHAUST STROKE A sudden decrease in the pressure occurs when the exhaust valve first opens. The piston’s movement then blows out the burned fuel and air mixture.