Traditionally mass (kg or moles) or volume fractions of substances and products of combustion or other chemical reactions are used in the processes of thermodynamical and thermal calculations. The process of calculation reveals significant differences in properties of the substances in question according to their calorific value and the amount of air required for complete combustion of the fuel. It is difficult to make a generalized analysis of the properties of products of combustion of various substances as working media of the cycle and heat transfer agents in heat exchangers. At the same time the calculation of combustion and design of gas generators using the idea of fuel reduced characteristics are widely used in steam turbine manufacturing. The feasibility of using these possibilities to calculate the cycles of heat engines is analyzed.