Quasi-closed mathematical model of transient modes of a combined diesel engine and its numerical implementation

The article is devoted to the urgent problem of increasing the efficiency of combined diesel engines in transient and unsteady modes. At present, the solution to this problem is aimed at improving the gas-turbine supercharging system and is carried out with the wide use of a numerical experiment, which is confirmed by the presented review of studies. The article considers the main provisions and principles of the numerical implementation of the mathematical model of transient modes of a combined diesel engine, which is distinguished by an extended mathematical description of thermo- and gas-dynamic processes in the flow parts of the radial-axial turbine and centrifugal compressor of the supercharging unit, and also takes into account the wave nature of the processes in the exhaust pipeline of the gas-turbine supercharging system. The central features of the proposed model are the calculation of heat release in the cylinder in the zero-dimensional approximation taking into account the incompleteness of fuel combustion at low values of the λ coefficient, the calculation of processes in an unbranched exhaust pipeline in a one-dimensional non-stationary approximation using the method of characteristics and boundary conditions at the turbine, taking into account the variability of its flow and energy characteristics, direct calculation of the turbine and compressor characteristics using the model of the average radius of the meridional section. The features of the numerical implementation of the mathematical model are the use of the «single cylinder» calculation scheme and quasi-closed modeling of the initial steady-state operating mode of the combined diesel engine. The article presents the main results of the verification and validation of the proposed mathematical model.