The advanced approach to the dual-fuel engine combustion process simulation using detailed chemistry coupled with CFD

Abstract

According to the depletion of the oil resources and increase in petroleum fuel prices, as well as toughening of legislation in the area of environmental safety of road transport, automotive engineers and researchers have faced with the problem of searching and investigating technologies, which will make it possible to increase engine fuel efficiency and environmental safety, and to maintain engine efficiency at high level. One of the promising solutions to this problem is to use dual-fuel engines. Nowadays, investigating a dual-fuel engine combustion process is very relevant, and special attention is paid to dual-fuel engines since the use of them provides lower exhaust emissions, as well as extended transportation range, because such an engine can be operated in both a dual-fuel and a conventional diesel operating mode. In a dual-fuel engine, the ignition of the premixed gaseous fuel-air mixture is provided by diesel pilot fuel dose. In such an engine, gaseous fuel is supplied through MPI system, while diesel fuel is injected directly into the cylinder. This paper aims to develop a detailed chemistry mechanism for 3D CFD simulation of the combustion process of a dual-fuel engine with the use of detailed chemistry equations, which provides sufficient convergence with the experimental data. In the course of the research, the calculation results of methane and diesel fuel combustion within the constant volume bomb with the use of different detailed chemistry mechanisms as well as their combinations were compared. The obtained results were also compared to the published results of the experiments. It should be noted that the combustion process proceeds very fast, and the parameters like pressure and temperature change within the wide range and with high speeds. For this reason, the results of the calculations with the different detailed chemistry mechanisms, obtained in the conditions of the constant volume bomb, can only be used approximately regarding the evaluation of whether the chemical mechanism provides the required convergence under the conditions of the combustion process of an engine. To develop a detailed chemistry mechanism providing sufficient convergence between the calculation and experimental results, the mechanism must meet the evaluation criteria like diesel fuel self-ignition delay period and methane flame-front propagation speed. For this reason, it was performed the search and definition of the reaction equations that have the most impact on the parameter value for each criterion. Following the results of the research, the detailed chemistry mechanism providing a sufficient degree of convergence with the experimental data was developed for simulation of the dual-fuel engine combustion process. This mechanism can be used at the stage of development and calibration of the dual-fuel engines. The application of the developed mechanism allows obtaining correct data when investigating the engine at the operating modes that may not be safe during the experiments on the test bench. For example, at the high-load operating modes, the knock can occur that can result in the engine break down.