This paper presents calculated analysis of the equilibrium emission of nitrogen oxides at the exhaust of carburetor and diesel internal combustion engines. The temperature of the fuel oxidation process is assumed to be 1,400 °C, the pressure for carburetor and diesel engines to be 60 and 80 at, respectively. We have conducted studies for natural and artificial fuels: hydrogen, ethanol, methanol, gasoline, diesel fuel and methane with an excess air ratio corresponding to the oxidation temperature of fuels 1,400 °C. The method of calculating the equilibrium composition based on the equilibrium constant and the equations of mass conservation is applied. It is shown that with an increase in pressure from 1 to 60 bar for the carburetor engines and up to 80 bar for the diesel engines the reaction of nitrogen dioxide formation shifts towards an increase in NO2. Increasing the pressure has no effect on the formation of NO, since the reaction proceeds without changes in the volume. It is established that the main polluting atmospheric component is NO. However, it is advisable to make greater use of fuel with the lowest yield nitrogen dioxide (methane and methanol) because nitrogen dioxide (NO2) pertaining to the chemicals 2nd class of danger is the most dangerous to humans. It is established that the reducing temperature of oxidation using hydrogen as fuel for electrochemical power generators allows us to reduce the emission of nitrogen oxides over an order of magnitude in comparison with the best results for internal combustion engines.