>>11548231The mass doesn’t change but the volume does. When the spark plug ignites the fuel-air mixture, the combustion process occurs. As the fuel burns, the chemical reaction changes the atomized fuel into a gas (exhaust). The process is exothermic, generating lots of heat, which causes the gas to expand further and significantly increase pressure inside the cylinder. The mechanism is designed to take advantage of this expansion, as it forces the piston away from the cylinder head and turns the crankshaft via the connecting rod. Once the piston has reached the limit of its travel and reverses direction, the exhaust valve opens and allows the exhaust to escape. The next turn of the crankshaft (and as a result, the next “push and pull” of the piston) draws fuel and air in before closing the intake valve, then compressing the mixture, before the spark plug fires again. The process repeats from there.
