The article deals with the analysis of theoretical cycles of internal combustion engines. Presents Otto cycle, Diesel and Sabate-Trinkler. The theoretical cycle is a closed cycle occurring in the cylinders of the piston engine with its inherent features and assumptions. Each cycle is characterized by two main indicators, such as heat use and efficiency. In this case, the thermal utilization is determined by the thermal efficiency. The estimation of influence of thermodynamic factors on change of thermal efficiency for reception of the best efficiency and the maximum specific work of cycles is resulted. The thermal efficiency of the mixed cycle is obtained. The conclusions of the influence of the compression ratio on the thermal efficiency are presented. A comparison' of different theoretical cycles from the point of view of their cost-effectiveness and efficiency under the same conditions.

Keywords: internal combustion engine, ideal cycle, thermal efficiency, thermal processes