Simulation Study On Combustion And Emission Characteristics Of Ammonia/Diesel Dual Fuel Engine

In the field of internal combustion engines,the use of low/zero carbon fuels to reduce carbon emissions is a major focus of current research.Ammonia is a carbon-free fuel,and using ammonia to replace part of diesel for combustion can significantly reduce carbon emissions from diesel engines.However,due to the problems of difficult ignition,slow combustion rate and high NOx and unburned ammonia emissions,excessive ammonia energy fraction can deteriorate the ammonia/diesel dual fuel combustion and emissions.Therefore,this paper establishes a numerical simulation model of ammonia/diesel dual fuel based on relevant parameters of a diesel engine,and investigates the influence of different ammonia energy fractions and boundary conditions on the combustion characteristics and pollutant emissions of ammonia/diesel dual fuel.The main work is as follows.(1)A numerical simulation model of ammonia/diesel dual fuel was established using CONVERGE.The original model was established based on the relevant parameters of a certain type of automotive diesel engine,and the accuracy of the original simulation model was verified based on the test data.The numerical simulation model of ammonia/diesel dual fuel was established by introducing the ammonia/diesel reaction mechanism on the basis of the original simulation model.(2)The variability of the effect of ammonia energy fraction on the combustion characteristics and pollutant emission patterns of the dual-fuel model under different compression ratios and load conditions was investigated.The result shows that the combustion efficiency and the indicated thermal efficiency of the ammonia/diesel dual fuel are mainly affected by the premixing equivalent ratio of ammonia and the combustion characteristics of ammonia itself,and when the ammonia energy fraction increases,the premixing equivalent ratio of ammonia increases so that ammonia can move away from the lean combustion boundary and accelerate the combustion rate of ammonia.Increasing the compression ratio can significantly increase the indicated thermal efficiency,while NOx emissions will increase with the increase of combustion efficiency and indicated thermal efficiency,and unburned ammonia emissions will decrease.At medium and low loads,as the ammonia energy fraction increases,the diesel ignition energy will be significantly reduced,and the combustion efficiency and indicated thermal efficiency of ammonia/diesel dual fuel will be significantly reduced,while NOx emissions will be reduced and unburned ammonia emissions will be increased.(3)The mechanisms of the effects of diesel injection strategy and inlet boundary conditions on the combustion and emission characteristics of the ammonia/diesel dual fuel under different ammonia energy fractions were investigated.Based on the study of the effect of ammonia energy fraction on combustion and emission characteristics,simulation tests were conducted for injection timing,intake air temperature and intake pressure.The results show that appropriately advancing the injection timing,increasing the intake air temperature and intake air pressure can increase the combustion efficiency and the indicated thermal efficiency of ammonia/diesel dual fuel,but at the same time it will increase the NOx emission.