A linear alternator assembly is provided that includes a block defining a cylinder. The cylinder block has inlet ports at which fluid enters the cylinder, exhaust ports at which fluid is exhausted from the cylinder, and a fuel port. Energizable coils surround the cylinder. A first and a second magnetic or magnetizable piston are contained within the cylinder and are positionable within the cylinder in response to energization of selective ones of the coils and combustion of fuel within the cylinder to selectively establish a four-stroke working cycle having an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke, producing at least one of compressed gas and electrical energy. The four-stroke working cycle may be varied to adapt to changes in power demanded, thereby balancing required output power with efficiency considerations.