This chapter presents the possibility of use of the pneumatic piston engine with twostroke cycle or four stroke-cycle of the work as an alternative driving source or additional power for the battery regeneration in the electric vehicles. Additionally, such engine can work together with combustion engine as a drive unit in a road vehicle. During city driving, such engine is driven by compressed air. The energy for the engine work is taken from the energy of the air stored at high pressure (about 30 MPa) in bottles or tanks. The chapter presents the thermodynamic theory included in the mathematical model of the engine based on thermodynamic processes (mass and energy balance). On such considerations, the chapter shows the results obtained from specially written computer program for the determination of the most important factors. The results of the calculations are included in the graphs showing the influence of the control parameters (air pressure, injection timing and rotational speed) on the engine working parameters. Certain chapters concern to a hybrid combustion system with an air injection only for a compression ignition engine in order to achieve higher indicated mean pressure and lower fuel consumption.