Study Of Incylinder Direct Injection Process And Combustion Process In Diesel Pilot Natural Gas Engine

Due to the lack of oil resources and the great environment pollution caused by diesel engine combustion,both at home and abroad are focusing on the research and development of natural gas engine recently,especially the researches for a pilot diesel ignited high pressure direct injection natural gas engine,which has good power performance.The mass production and application of this kind of engine are restricted by some unsolved technical difficulties.This paper explored the injection characteristic and mixing processes of high pressure direct injection diesel/ natural gas dual fuel engine based on AVL-Fire software and schlieren method.In this paper,a modular injector was designed to realize the injection of diesel and natural gas,and based on the combined injector,a dual fuel jetting test bench was built.Based on the Fire software,the simulation model of dual fuel injection was established.The injection development and mixing process of diesel and natural gas under different ambient pressure were studied.The results show that with the increase of the ambient pressure,the penetration of natural gas and diesel decrease gradually,the spray cone angles of natural gas and diesel increase gradually.Diesel spray has a significant effect on the natural gas development process,while natural gas has little effect on the shape of diesel spray.In the diesel-natural gas engine,position of natural gas nozzle and diesel nozzle will affect the injection and mixture of the fuels,which have much effect on the combustion and emission performance.The combustion process and emissions of a dual fuel engine fueled with directly injected natural gas and pilot diesel was researched by using the AVL-Fire software.This simulation investigated the effects of three important geometric position parameters: relative crossing angles,distances and included angles of the diesel hole and natural gas hole.The results show that different crossing angles of two holes can affect the NO and Soot emissions,the minimum NO emission is 36 percent lower than the maximum NO emission.By changing the crossing angle,NO emissions and Soot emissions can be reduced at the same time,while the crossing angle has little effects on the average cylinder pressure.The relative distances of the two holes have effect on the pollution formation,and the smaller nozzle hole distance will result in more uniform temperature distribution and higher average cylinder pressure.With the decreasing of the relative included angle,both the average pressure and NO increase.This paper also studied the effects of natural gas substitution rate for diesel on the engine combustion process.It was found that the natural gas substitution rate has a great influence on the cylinder temperature and pressure during the combustion process.When the natural gas substitution rate is 75%,the peaks of the average temperature and pressure in the cylinder are the highest.The natural gas substitution rate will directly affects the temperature of the exhaust gas.The research of this paper provides a good guide for researchers to pursue their future research on the position of the diesel and nozzle holes,and have a certain important meaning to guide the development of diesel ignition dual fuel engine.