Summary: The use of fuel cell power plants is a promising area in the generation of electricity. The path to their widespread use is hindered by their high cost and the availability of the fuel used. To solve this problem, effective energy conversion systems operating on diesel fuel are being developed. The main goal is to create a device (a fuel processor), which would convert diesel fuel into a hydrogen-containing gas. The device consists of several components: a nozzle for injecting liquid fuel having the form of drops into superheated steam, a mixing and vaporization zone for diesel fuel, an air supply area, and a reaction zone including a catalyst. The selection of temperature for the vaporization process should be made in such a way that, on the one hand, liquid droplets do not come into contact with the catalyst surface, and, on the other hand, gas-phase reactions are not initiated in the mixing zone. Developing such a device requires not only conducting laboratory experiments and studying the process catalyst, but also optimizing the basic physical parameters of the device. These parameters are its linear dimensions, operational temperature, reactant flow rates, and many others. Carrying out such a study is impossible without using methods of mathematical modeling. This significantly reduces the time and cost of work. This paper presents a digital model of an air-hydrocarbon mixture generator in an axisymmetric formulation. The dynamics of subsonic multiphase flow of water vapor carrying drops of liquid diesel fuel, the process of diesel fuel evaporation and mixing with water vapor and air are studied. The mathematical model is implemented in the ANSYS Fluent package (academic license of SSCC SBRAS). A series of calculations for various mixture feed temperatures are performed to optimize the main parameters. For the established optimal temperature, modeling of the mixture mixing process with air is carried out.