Optimization And Simulation Of Fuel Injection And Combustion System For A Medium-Speed Four-Stroke Marine Hydrogen Engine

As one of the most important power systems in the world,the internal combustion engine not only contributes 25%of the world’s power output every year,but also causes about 10%of the global greenhouse gas emissions.With the implementation of the International Maritime Organization(IMO)TierⅢemission regulation and the introduction of the preliminary reduction strategy of marine greenhouse gases(GHG),how to reduce harmful emissions and GHG emissions of marine engines has become an urgent task for many research institutions.At present,hydrogen produced from renewable energy is the fuel with the lowest carbon emissions in its whole life cycle.Meanwhile,with the adoption of premixed combustion mode,the hydrogen engines can directly meet the IMO TierⅢemission regulations without aftertreatment.However,the use of hydrogen in marine engines is quite difficult.Due to the extremely low ignition energy and high burning rate,abnormal combustion is prone to occur in hydrogen engines.Even worse,the characteristics of larger cylinder bore,higher mean effective pressure and lower rotate speed of marine engines further aggravate the abnormal combustion.Limited by the abnormal combustion,the research and development of marine hydrogen engines are just beginning.Based on a type of medium-speed diesel engine,a direct injection premixed combustion hydrogen engine was designed by optimizing the parameters of both fuel injection system and combustion system.The effects of each parameter on engine performance were investigated and a dimension reduction optimization method was proposed which provide reference experience for the design and optimization of similar engine models.Based on a medium-speed four-stroke marine diesel engine,1D simulation software GT-Power and 3D simulation software Converge were used to establish the 1D and 3D numerical simulation models of this diesel engine respectively.After the calibration according to the experimental data under 100%load carried out,the design and optimization of hydrogen engine were accomplished on the basis.The hydrogen injection duration,injection pressure,and fuel injection orifice were reduced into two factors:the average turbulence kinetic energy in cylinder and hydrogen jet penetration distance.The effects of various factors on the fuel-air mixing characteristic were explored.Besides,the multiple optimizations of the fuel injection system of the hydrogen engine were completed so that the homogeneity of fuel-air mixture in the cylinder and the efficient combustion of the lean pre-mixture could be guaranteed.Then,the combustion system parameters of the hydrogen engine were optimized from the aspects of the spark plug position,ignition energy,combustion space ratio and ignition time,and the influence of which on the engine performance was analyzed.The results shown that compared with the original diesel engine,the final optimized hydrogen engine can achieve more than 80%reduction of NO_X,which can meet the IMO TierⅢemission regulations without aftertreatment,except for slight decline of power performance.