The article determines the critical parameters of the oil fraction-temperature, pressure and density. The experimental results are compared with the calculated results, the calculation method closest to the experimental results is chosen, the calculation error is estimated. The main results and conclusions are presented. The use of the theory of thermodynamic similarity in the method of density calculation and DNP required first of all knowledge of the parameters of the state at the critical point. The accuracy of the calculation of critical parameters affects the reliability of the results.

The results of experimental studies of gasoline and petroleum fractions are discussed in the article, as well as their main physical and chemical properties, density and pressure of saturated vapors, liquid phase, two-phase region, critical region, and boundary curves. The article is recommended for agricultural specialists, researchers, teachers, graduate students, undergraduates, and students of agricultural universities in the field of “Agricultural Engineering”.

Important physical properties, that characterize a substance, are the density and pressure of saturated vapors (PSV). These parameters need to be known when developing new technological processes in oil refining and chemical industries, designing pipelines, pumping equipment, fuel equipment, hydraulic cleaning processes, calculations related to the amount of petroleum products in mass volume, when operating technical systems running on liquid fuel. For gasoline fractions, the density is a normalized quality parameter, it is an integral part of various combined constants and calculation formulas.