A new type of engine concept is proposed, namely a rotating disk cylinder engine. Unique secondary rotors with grooves act as guide vanes for a working fluid to power a main rotor with multiple cylindrical pistons. Currently, no literature exists on the proposed device and the modelling thereof. The aim of this paper is to determine the dynamic and thermodynamic behaviour of the machine so that recommendations can be made for further research work. A transient as well as a steady-state thermodynamic model is developed for an adiabatic expansion process using first and second law analysis with air as ideal gas. The model is compared with experimental results of a piston engine driven by compressed air. Results show that the secondary rotor's angle of rotation is not a linear function of the main rotor's angle of rotation, which suggests a limitation in terms of operating speed. Furthermore, for constant power, the efficiency increases as the inlet pressure and speed decrease, while for constant efficiency, the power increases as the inlet pressure and speed increase. Results show the advantage of using three secondary rotors as it drastically decreases the pressure requirement for a constant torque output. The speed and inlet pressure of the device is, however, limited by the mass and material properties of the rotors as well as the effects of leakage. These limitations have not been considered in this initial analysis of the device and are recommended for future work.