The increasing attention to the use of dual-fuel engines with compression ignition leads to the need to study the thermal engineering processes occurring in them. A model for calculating the thermal engineering stages in a cylinder of a dual-fuel engine with a refined composition of the working fluid is presented, including the determination of fuel supply characteristics, fuel injection and evaporation functions and allowing theoretically to determine with high accuracy the pressure function, cycle operation, power, efficient and thermal criteria for the operation of a dual-fuel engine. The paper attempts to show the mutual relationship between the individual processes of heat generation, their influence on the design parameters under the operating conditions characteristic of a dual-fuel engine, as well as on the operating conditions of components and parts.