Environmental pollution should be understood as a permanent process caused mostly by anthropogenic factors, that is man. The products of combustion from internal combustion engines are toxic and harmful effects on humans and the environment. This is one reason for research of biogas as an alternative fuel and its benefits for smaller amounts of harmful products in its combustion. For this purpose is reconstructed diesel engine that runs with a mixed fuel diesel- biogas where diesel fuel used for combustion and biogas propulsion engine combustion. Thus it is given the overall internal construction of this type of engine. There is calculated speed characteristics of the diesel engine and the reconstructed motor biogas. Thus these diagrammatic comparisons will indicate the nature of the changes in both engines.