Optimization of the working cycle of a transport diesel engine by simulating the combustion process with a double Wiebe function

Abstract

For modeling the working cycle of transport diesels, models with two laws of combustion according to the Wiebe, mathematically related to each other and corresponding to the initial and main periods of the process, are increasingly being used. However, known mathematical models give different results in estimating the distribution of fuel shares between these periods. These models also do not allow to simulate a smooth start of the combustion process. Therefore, a new mathematical model was developed for calculating the working cycle of a diesel engine with two independent laws of combustion of fuel, described by the functions of Wiebe. Communication between them is carried out through a new parameter, which is the proportion of fuel, burning in the initial period, from the total cyclic feed. The novelty of the model is also the ability to set, within a wide range, independently of each other, the angles of the start and duration of the first and second combustion laws for the initial and base periods, respectively. A program for calculating the operating cycle with simulation of the combustion process using a new mathematical model is developed. Calculations have been made for a transport diesel engine equipped with a fuel-supply system of a battery type. The results of the calculation showed that an increase in the fraction of the fuel burned according to the first law from 0.1 to ~ 0.3 with other parameters being constant leads to a significant increase in the maximum pressure in the diesel cylinder and some improvement in the indicator indexes. With a further increase in the fuel fraction to 0.5, the maximum gas pressure continues to increase, and the indicator indexes slightly deteriorate. At the same time, in the initial period, the value of the index of the combustion character has practically no effect on the indicator index of the diesel engine and the maximum pressure in the cylinder. In the main period, the value of the indicator of the nature of combustion, on the contrary, significantly affects the indicator indexes of the diesel engine and the maximum pressure in the cylinder. The calculation determines the optimal heat release law in the diesel cylinder of ChN15/16 type, which provides the best indicator values when the maximum pressure in the cylinder is limited.