An engine requiring two complete revolutions of the crankshaft to fire
each piston once. The first stroke down ( intake stroke ) pulls fuel and air into the combustion chamber . The second stroke up ( compression stroke ) compresses the mixture. The third stroke down ( power stroke ) comes about through the rapid burning of the compressed fuel mixture. The
fourth stroke up ( exhaust stroke ) expels the exhaust gases from the cylinder . It is also called the " Otto cycle ."