The direction of application of compressed air energy in various industries and transport is developing at a fairly intensive pace. The biggest drawback when using an air motor is the low energy efficiency of the working fluid, that is, the specific air consumption per kilowatt of generated energy. The design and basic parameters of the new rotary-piston engine 12RPE-4,4/1,75 with adjustable spool air distribution are presented. The engine has twelve cylinders evenly spaced, which ensures the balance of the engine and the ability to start at any position of the rotor. The proposed scheme of the mechanism of motion provides a fairly simple and compact design of a rotary-piston engine, with the value of the relative dead volume εo due to only technological gaps and slightly (εo = 0.015). The engine design provides for the presence of a central regulating cam shaft, the rotation of which allows adjusting the valve timing and engine operating modes due to the degree of filling of the cylinder ε1 over a fairly wide range. Thus, the values of the degree of filling of the cylinder are in the range of 0.135...0.175. With a decrease in the degree of filling ε1, a decrease in the specific consumption of compressed air is observed with a certain drop in the average indicator pressure due to a decrease in the area of the indicator diagram. The primary assessment and analysis of the influence of the main parameters of the air motor on the efficiency of energy conversion in a rotary-piston engine of a new design were carried out. Indicator diagrams for different values of working fluid pressure at the entrance to the rotary-piston engine are given. The pressure value of the working fluid at the inlet varied within 1.0...1.9 MPa, while the indicator engine power was 0.91...1.62 kW. The dependence of changes in the indicator indicators of the 12 RPE-4,4/1,75 engine, such as power, specific air consumption, average pressure and indicator efficiency, is given. It was established that, depending on the load of the rotor-piston engine, the specific indicator air flow rate is 29.9...18.4 kg/kW∙h, while the indicator efficiency varies within 0.47...0.83.