| Under the background of the current carbon peak dioxide emissions and carbon neutrality era,low carbon emissions and even zero carbon emissions is the development trend of Marine engines in the future.So far,natural gas is the best choice to reduce carbon emissions in the short term for the shipping industry,and it is the key fuel for the shipping industry to move towards the zero-carbon era.However,natural gas engines will still produce a significant amount of carbon emissions due to natural gas fuel characteristics and methane emissions.In order to further reduce the carbon emissions of natural gas engines,starting from the engine fuel and methane emissions,this paper adopts the numerical simulation method to establish a simulation model of low-pressure natural gas dual-fuel engines,studies the influence law of mixing hydrogen into natural gas on engine combustion and emissions,focuses on analyzing the influence on engine carbon emissions,and explores the control strategy to inhibit methane emissions.It provides design ideas for low carbon emission and performance optimization of Marine low pressure dual fuel engine.Based on this,the main work and conclusions of this paper are as follows:1)Taking a certain marine two-stroke low-pressure natural gas dual-fuel engine as the research model,and the one-dimensional simulation model and three-dimensional simulation model of the low-pressure dual-fuel engine are constructed.The initial conditions and boundary conditions of the three-dimensional simulation model are based on the one-dimensional simulation model.2)The influence law of hydrogen blending of natural gas on combustion and emissions of Marine low-pressure dual-fuel engine is studied,and the influence on engine carbon emissions is analyzed.The results show that hydrogen mixing of natural gas increases the content of active free radicals such as OH in the cylinder,accelerates the combustion process,and increases the indicated thermal efficiency of the engine.Hydrogen mixing of natural gas reduces the content of CH4 into the cylinder,increases the flame propagation speed,makes the combustion process more complete,reduces the content of unburned CH4,and realizes the purpose of low carbon emissions of the engine.3)The application of EGR technology can effectively control the methane emissions of Marine low-pressure dual-fuel engines.At the same time,the use of hydrogen mixing technology of natural gas and the selection of appropriate fuel injection timing can make up for the defects of EGR technology.By coupling the three technologies,the engine carbon emissions can be further reduced.The results shows that the use of EGR technology reduces the indicated thermal efficiency of the engine,decreases the maximum combustion pressure and the rate of pressure rise in the cylinder,the combustion duration is prolonged,the CH4 emissions is reduced,and the methane emissions of the engine is inhibited.The advance of fuel injection timing indicates that the thermal efficiency increases first and then decreases,the combustion pressure in the cylinder and the combustion heat release rate increase,the combustion duration is shortened,and the CH4 emissions decreases first and then increases.The optimized scheme of-9.8°CA-10%H2+90%CH4-20%EGR（-9.8°CA fuel injection timing,10%hydrogen mixing of natural gas ratio and 20%EGR rate）is adopted.The indicated thermal efficiency is basically the same as that of the original engine,the methane emissions decreases by about 52%,the GHG emissions decreases by about 16%,and the other performance indexes of the engine are higher than that of the original engine. |
