Influence Of In-cylinder Water Spray On Knock,Combustion And Emission Of Natural Gas Mixed Hydrogen Engine Based On CFD Simulation

The need to conserve fossil fuels and reduce greenhouse gas emissions is urgent.To achieve the goal of carbon emission peak by 2030 and carbon neutrality by 2060,increasing the energy use and supply of natural gas and hydrogen is an important means for the country.In recent years,as a promising technology to reduce cylinder temperature,reduce knock,improve combustion phase and reduce NO_x emissions,in-cylinder water spraying has attracted much attention.In order to reduce the knock tendency of natural gas hydrogen-doped engines,further improve fuel economy and meet stricter emission regulations,the numerical simulation method is used to study the water timing and water quality of the natural gas hydrogen mixed engine in this study.In order to induce the knock research conditions,the ignition timing of the test conditions was advanced to obtain a series of conditions with greater detonation intensity.Then,the influence of different ignition timings on the detonation intensity was explored.Subsequently,the knock characteristics of the selected detonation conditions were quantitatively analyzed by combining the maximum pressure oscillation amplitude of the monitoring point in the cylinder,the three-dimensional distribution of chemical free radical s,velocity and turbulent kinetic energy.The detonation intensity of the spontaneous combustion of the mixture near the No.3 and No.4 monitoring points and in this area is proved.Based on the spontaneous combustion position of the mixture and the inte rnal detonation characteristics of the cylinder,the effects of water injection timing on the detonation suppression and combustion emission performance of the natural gas mixed hydrogen engine were further studied.With the delay of spraying time,the detonation intensity in the cylinder decreases first and then increases.When spraying water at-150°CA,the atomization effect of droplets in the central flame area and the cooling effect on the piston are better,and the detonation intensity KI decreases most obviously,which is the best spraying time for detonation suppression.Finally,on the basis of spraying water at-150°CA,the effects of spraying water mass on the knock suppression and combustion,emission performance of the natural gas mixed hydrogen engine were investigated.With the increase of the amount of water spraying,the detonation intensity decreases rapidly and then has no significant change.Injecting 0.02g of water can basically suppress the detona tion.At the same time,the NO_x emission decreases obviously,while the CO and HC emission increases in the opposite trend.When the water spraying mass continues to increase,the detonation intensity does not change significantly,and HC and CO emissions will continue to rise within a certain range.Based on the simulation study of water injection in cylinder of natural gas hydrogen-doped engine,the influences of water injection timing and mass on knock suppression and combustion,emission performance are explored,which provides theoretical basis for further improving the economic,emission performance of natural gas hydrogen-doped engine.