Optimization Of Thermal Efficiency Of Marine Medium-Speed Diesel Engine Based On Multiple Injectors

Marine medium-speed engines are widely used in various ships.Improving the effective thermal efficiency of Marine medium-speed engines is of great significance of reducing energy consumption and greenhouse gas emissions.In recent years put forward a new fuel system: more fuel injector system,namely each cylinder to install two or more than two fuel injectors,this new type of fuel system is expected to improve the combustion provides three advantages: reducing fuel injection time,through the spray upstream promote the formation of the mixture of the continuous flow of air and reduce the impact of the fire near the cylinder wall to wall heat loss.However,most of the research on this new fuel system is based on vehicle engine,and the research on Marine engine has not been found yet.In this paper,the effective thermal efficiency of Marine diesel engine based on multi-injector system is optimized by CFD simulation.In this paper,it firstly adopts CFD software Converge to conduct 3D modeling on Marine medium-speed diesel engine.Based on the experimental data,initial and boundary conditions are set,appropriate sub-models are selected,and the cylinder pressure curve of spray penetration distance and diesel engine under different working conditions is calibrated.Then,on the model of single-injector diesel engine,the parameter optimization is carried out,and the influence of variable such as changing fuel injection law and fuel injection pressure on combustion characteristics is studied.Then,two side injectors are installed on the cylinder head.According to the actual situation and calculation results,the installation position of side injectors and the fuel injection Angle of the injection hole is determined first.On this basis,the fuel injection ratio is optimized.Finally,based on the existing optimization results,the effects of fuel injection strategy and side injector parameters on combustion characteristics are studied.The results show that by increasing the injection pressure and using multiple injection times,the air efficiency between the oil bundles and the central region of the combustion chamber can be increased while the mixture of oil and gas is improved.When the two were combined,the improvement on combustion was superimposed,and the effective thermal efficiency was increased by 2.8%.In the application of multi-injector system,the combustion tends to be concentrated near the center of the combustion chamber.Compared with single-injector diesel engines,the temperature field distribution of the combustion chamber is more uniform and the combustion near the wall is reduced,which can effectively to improve the air utilization rate and reduce the heat loss.The effective thermal efficiency can be significantly improved by adjusting the ratio of fuel injection of three injectors and shortening the injection time.When the total injection time of the three injectors is the shortest(at this time,the ratio is 4: 1: 1),the thermal efficiency can be improved by 1.26%,while NOx can be reduced by 18.4%.On this basis,the research of increasing the aperture of the side injector and increasing the injection pressure shows that under the current injection strategy,increasing the aperture of the side injector and accelerating the injection cannot continue to improve the thermal efficiency.However,when the injection pressure increases in180 MPa,the effective thermal efficiency is 2.85% higher than that of the original machine,but NOx emission increases greatly.