A piston type internal combustion engine operating on the stratified charge principle with the object of nonpolluting combustion wherein the engine has a standard valve-charging with a rich mixture. After admission of the rich mixture a quantity of air is introduced into the combustion region opposite the spark plug, before ignition, through the exhaust valve opening or by an independent valve opening into the combustion chamber or a precombustion chamber. The introduction of air can be effected either by the exhaust valve with a precombustion chamber being associated with the inlet valve or exhaust valve.