Air bag inflator

The air bag inflator is particularly useful for mounting in a steering wheel of a vehicle for inflating an air bag. A magnetic control unit (14) is disposed concentrically of an injection piston (13) through which liquid propellant is injected from a liquid propellant chamber (28) into a combustion chamber (11). In one embodiment, the injection piston (13) and a pump piston (27) are contoured to define a contoured liquid propellant chamber (28). In a second embodiment, an annular injection piston (17) is slidably mounted on an annular pump piston (16) to define an annular liquid propellant chamber (18).