Influence Of In-cylinder Water Injection On Combustion And Emission Performance Of Natural Gas Diesel Engines

The development of alternative energy and efficient clean combustion technology is an important way to alleviate the current shortage of traditional fossil energy supply and environmental pollution.Natural gas has the advantages of high octane number,high hydrocarbon ratio,no aromatic compounds,low emission,and so on.It is an ideal clean alternative fuel for automobiles.Diesel ignition is one of the main applications of natural gas in engines,which has been widely studied in recent years.However,due to its high thermal load and lean-burn mode,it limits its energy saving potential and leads to high NO_x emissions.Therefore,this paper proposes a method of in-cylinder water spraying,and discusses the influence of water spraying parameters on the combustion and emission performance of NG-DIESEL dual-fuel engine.In order to improve NG-diesel dual fuel engine combustion and emissions performance,this article adopts the method of combining experiment and numerical simulation,using the vertical water injection technology in cylinder,the diesel engine is converted into NG-diesel dual fuel engine bench test,according to the test data,using CONVERGE software to establish three-dimensional model,The validity of the model was verified by the experimental data,and the CFD simulation of water spraying in the cylinder was carried out on this basis.The effects of spray timing,spray temperature and water quality on the combustion process and the formation of pollutants in the NG-diesel dual-fuel engine were studied.The formation of pollutants and the three-dimensional distribution of free radicals in the cylinder were analyzed by simplified chemical kinetics mechanism and TECPLOT software.The following conclusions are drawn:（1）With water spray timing delay,the peak cylinder pressure,peak heat release rate,peak cylinder temperature drop,SOC,CA50,CA90 time delay,a small increase in IMEP,CO and CH₄emissions have risen,but NO_x emission appeared obvious drop.therefore,water injection under high load is more appropriate,in high load condition of 20°CAATDC moment about water spray to reduce emissions of pollutants.（2）With the water spraying temperature rising from 298.15K to 600K,the peak cylinder pressure and heat release rate increased,CA90 moment advanced,CO and unburned CH₄emissions increased,and NO_x emissions decreased.Therefore,in the water spraying temperature studied in this paper,the water spraying temperature of400K is the better water spraying temperature.（3）With the increase of steam injection amount,the peak cylinder pressure and HRR rise to a certain extent,CO and CH₄emission increases,NO_x emission decreases,and the area of OH free radical and O atom high concentration decreases significantly.Therefore,in order to improve the performance of the engine and control emissions,it is necessary to properly control the water quality.Through this study,the cylinder spray can effectively reduce NO_x emissions,spray parameters have an important impact on the combustion and emission process.This paper reveals the deep reasons for the influence of spray timing,spray temperature and spray volume on the combustion process and emission formation mechanism,and provides theoretical guidance for further improving the power performance and emission performance of NG-diesel engines.