Introduction. The most promising direction toward increasing the economical efficiency and ecological safety of diesel engines is the improvement of the process of fuel combustion [1]. The character of this process is determined to a large extent by the quality of mixing and pre-burning treatment of the fuel-air mixture. Incomplete combustion manifested in the presence of soot and coke particles, underoxidized hydrocarbons, etc., is caused first of all by the formation of inhomogeneities in the jet [2], which contain different-scale time and space fluctuations of the fuel distribution density, and also by the violation of homogeneity of the mixture [3]. Therefore, many papers are devoted to the study of one of the key processes in the diesel combustor: the development of a high-speed pulse jet of a fuel-air mixture. Nevertheless, although the main results were obtained many years ago [4][5][6], numerical, theoretical, and experimental studies are continuing [3,[7][8][9], since the requirements on economical efficiency and ecological characteristics of existing and newly created engines are becoming more and more stringent, and the solution of these problems is intimately connected with more profound knowledge of the mechanisms of heat and mass transfer in the engine combustor.Based on the results of complex experimental investigations, a new physical model of the development of a high-speed pulse jet of a fuel-air mixture in a gaseous medium is proposed in the paper. The interaction of the head part of this jet with a gas is considered as cumulative [10]. The jet is represented as a comparatively dense high-speed axial flux of the mixture surrounded by the gas-liquid mass with a small content of the fuel component, which hangs in space. The specific feature of the flow in the head part of the jet is its similarity to the flow observed in a vortex ring [11].1. State-of-the-Art of the Problem. A jet formed by high-speed pulse injection of fuel into a gaseous medium is usually characterized by the dependence of the jet length L and root angle ~ on the time t (Fig. la). The third important quantity, the jet diameter D, is referred to much more seldom, since it is believed to be possible to express this parameter in terms of L and ~. But if we assume this parameter to be the jet diameter in the maximum cross section, it turns out that the position of the cross section Im relative to the nozzle has a different dependence on the time and test conditions than the total length of the jet L. Therefore, the shapes of jet structures at different stages of their evolution are not, strictly speaking,
