Today, power plants with internal combustion engines occupy one of the key positions in industry, energy, agriculture, military affairs, mining, transport and other areas of human activity. Such a wide distribution of internal combustion engines determines the extremely high relevance for humanity of the task of minimizing their negative impact on the environment, which, first of all, consists in the consumption of exhaustible fuel reserves and the emission of harmful substances with exhaust gases. Harmful substances from exhaust gases of internal combustion engines have a detrimental effect on the ecological situation both in Ukraine and in the world and cause such negative consequences as the greenhouse effect, acid rain, and ozone layer depletion. The introduction of alternative fuels for use in internal combustion engines contributes to a partial solution to the above problems. The paper considers the use of the following types of alternative fuels in internal combustion engines: low-calorie gas fuels, water-fuel emulsions, and biofuels. The impact of these types of alternative fuels on its performance and characteristics is shown. The paper analyzes the indicator diagrams of internal combustion engines on alternative fuels, reveals the mechanism of fuel influence on the working process of internal combustion engines. Conclusions are drawn on the feasibility of using these alternative fuels, and recommendations are given for their introduction into use in internal combustion engines.