Soot is the main component of the solid particles contained in exhaust gases of diesel engines, which is formed from the products of thermal decomposition of hydrocarbon fuel. A mathematical model for predicting the fluidity of exhaust gases of diesel engines at different load and speed modes of operation is proposed. The current content of the gas mixture components in the reaction zone, depending on the angle of rotation of the crankshaft, was obtained by numerical simulation. Such indicators of soot content in the cylinder volume as the minimum average diameter of the particles, the maximum soot mass, the angle of the maximum soot content, the total mass of soot particles in the cylinder and the total soot release were determined. Laboratory and bench studies of diesel 2F 10.5/12.0 have been carried out, determining indicator pressure, indicator temperature of the gases in the cylinder, heat release rate and indicators of toxicity and smoke exhaust gases. The results of simulation of smokiness of the diesel exhaust gases are confirmed by experimental measurements in different operating modes.