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Pneumatic motors of various types are widely used as a drive for various mechanisms and machines in many industries: shipbuilding, transport, construction, and in production of hand tools. Design and operational features of pneumatic motors make them indispensable in explosive-related industries and in conditions in which the use of electric motors can lead to electric shock to workers. For example, pneumatic motors are used in hazardous areas such as chemical, petrochemical, and mining industries. In addition, pneumatic motors have a fairly low relative mass, are not afraid of overloads, feature a fairly simple design which ensures their reliability in operation and low cost in manufacturing. One of the problems when using pneumatic motors is a significant decrease in the temperature of the spent working medium in comparison with the initial storage temperature. For example, a decrease in temperature of the working medium is observed: ‒ when throttling the working medium from storage pressure in cylinders to the required operating pressure in the engine receiver (Joule–Thomson effect); ‒ when expanding in the working cylinder of the engine (Siemens–Claude effect). Compressed air storage pressure can reach 30...40 MPa while the working pressure of most pneumatic motors is about 0.4...1.0 MPa. Accordingly, to provide the required operating pressure before the pneumatic motor, the compressed air is subjected to throttling in a special reducer. In the process of throttling, not only the air pressure decreases to the operating value but its temperature as well. Depending on its initial value after throttling in a reducer, the compressed air temperature can already be negative before expansion in the pneumatic motor. Accordingly, after expansion in the pneumatic motor, the temperature of the exhaust air can fall below the permissible values that ensure the operability of this pneumatic motor. At the same time, with a decrease in the initial temperature and an increase in the initial pressure (temperature and pressure of compressed air storage), the cooling effect increases during throttling. First of all, the relevance of scientific studies in this area is associated with the fact that a significant decrease in the exhaust air temperature negatively affects the efficiency of the pneumatic motor [1‒3]. For example, a drop in temperature below permissible values can lead to a violation of lubrication regimes of rubbing parts and the growth of mechanical losses up to the pneumatic motor jamming. In addition, a decrease in temperature causes the icing of the exhaust channels and Copyright © 2020, O. Mytrofanov, A. Proskurin

Determining a change in the compressed air temperature during the operation of a rotary piston engine