Research of the Gas Fuel Supply Process on the Compression Stroke in Ship’s Low-Speed Gas-Diesel Engines 2020-01-2107

In connection with the tightening of environmental standards, the leading manufacturers of marine low-speed engines are carrying out intensive work on their conversion to gas fuels. Due to the design features in this class of engines, only internal mixture formation is possible. For the organization of which two different approaches are possible. To date, only two are currently implemented. MAN started production of engines with gas fuel supply to the working cylinder under high pressure at the end of the compression stroke, and WinGD under low pressure at the beginning of the compression stroke. The analysis, performed by the authors, showed, that increasing the pressure before the gas supplying mechanisms to 3.5...6.0 MPa can reduce the residence time of the gas-air mixture in the working cylinder and reduce the likelihood of detonation combustion. The supply of gas fuel to the working cylinder with a changing back pressure significantly affects on the flow characteristics of the gas supply devices and the nature of the outflow from them. The authors developed a mathematical model, that allows to determine the nature of the outflow and consumption of gas fuel in the conditions of changing back pressure. As a result of the simulation, a family of flow characteristics was obtained for pressures up to 6.0 MPa before the gas supply device. It was found, that the most rational techniс is the gas supply at the site of its supercritical outflow, and the moment of end of the supply should coincide with the moment of character transition of the outflow from the supercritical to the subcritical. In this case, the goal of ensuring a given injection rate is to determining the start of the supply. Based on the calculation results, the optimal opening and closing angles of gas valves were determined