Numerical simulation is often used in the study of physical and chemical processes in order to increase the efficiency and reduce the level of harmful emissions in reciprocating engines. Changing the combustion chamber geometry is one of the ways to reduce the concentration of toxic components in exhaust gases. The combustion chamber shape determines the characteristics of the movement of air and fuel in the cylinder, the features of mixing and the quality of combustion. The article is related to the study of the influence of the combustion chamber shape on the environmental performance of a diesel engine. The article provides an analysis of scientific and technical results on this topic. Four forms of combustion chambers with different geometries were investigated for a diesel engine. The research was carried out in the program "Diesel-RK"through mathematical modeling. It is shown that the combustion chamber design leads to a significant change in the content of harmful substances in the exhaust gases of the engine. The range of NOx change in the exhaust gases was 15%, CO2-5%, particulate matter-70%, smoke-60%. The article also provides recommendations for improving the environmental friendliness of an engine. © 2022 IEEE.