The Impact On Combustion And Emissions Of Fuel Injection Strategy In Lean Combustion Mode Of GDI Engine

In recent years,with the vehicle industry of China has been growing up,air pollution becomes a more and more serious problem,and the treatment of vehicle exhaust has become an important subject of the people's livelihood for governments.There are two kinds of injection modes,port fuel injection and gasoline direct injection.By means of optimizing the mechanical structure,controlling parameters,and using three-way catalyst,power performance and emission characteristic of engine are improved.In order to further improve the engine performance,gasoline direct injection becomes more and more popular.At the same time,the electronic control system and mechanical structure have to meet higher requirements.Lean combustion mode is an important method to reduce fuel consumption and particulate emissions for gasoline direct injection engine.In this article,by changing the excess air coefficient,adjusting engine fuel injection strategy and ignition parameters,the influence on combustion and emissions of the fuel injection strategy of lean combustion engine has been researched.In the end,the conclusion how to optimize the power performance and emissions of engine have been reached.Followings are the research conclusions of this article:1.In lean combustion mode,in the case of other parameters constant,with the gradual increase of excess air coefficient,the mixture in the cylinder is become leaner,the maximum cylinder pressure decreases.The change tendency of the heat release rate is the same with the cylinder pressure.When the excess air coefficient is 1.2,the maximum cylinder pressure and the maximum heat release rate are slightly lower than them when the excess air coefficient is 1.1,but the mixture combustion rate is the highest,and the torque reaches a higher level,combustion performance is the best.In lean combustion mode,with the increase of excess air coefficient,the CO concentration appears decreasing firstly and then increasing,and THC emissions increase.With the increase of excess air coefficient,the temperature in cylinder gradually reduces.NOx decreases with the excess air coefficient decreases apparently.The sizes of particulate emissions concentrate on a only one peak region which is the nuclear state.With the increase of excess air coefficient peak particle size decreases,and the total number of particles increases after decreasing trend.2.In lean combustion mode,in the case of other parameters constant,when fixed the first injection time 310°CA BTDC,and change the second injection time from 60°CA BTDC to 120°CA BTDC,the cylinder pressure increases after the decreasing trend.And 75°CA BTDC is the best injection time,on which the phase of the maximum heat release rate advances,while the total combustion time decreases,and the torque is the largest.When the second injection time changes from 75°CA BTDC to 120°CA BTDC,THC emissions increases.As the second injection time advances,the quantity of NOx emissions decreases after first increasing.As the increasing of secondary injection time,particle number distribution decreases after the first increasing,and most of the particles are nuclear states particles.Particles concentrate in 14 nm-19 nm,and there is only one peak in this region.3.In lean combustion mode,in the case of other parameters constant,the injection ratio between two injections is changed.With the decreasing of the fuel injection quantity for the first time,meanwhile,the second injection quantity increasing,the maximum cylinder pressure gradually decreases,and the phase of the maximum heat release rate puts off.At the same time,the combustion period becomes longer,torque smaller.When two injection ratio is 6:2,the combustion performance is best,and the engine torque is the highest.With the increasing of the quantity of the second fuel injection,HC and CO emissions all increase.And the combustion speed in cylinder gradually slows down,as a result,temperature in cylinder is reducing,and NOx emissions decreases gradually.Particle number concentration distribution is unimodal.The peak appears increasing.The peak ranges between 10-20 nm.4.In lean combustion mode,in the case of other parameters constant,as the ignition time advances,the heat release delays.As a result,the maximum cylinder pressure increases gradually.Considering both of the cylinder pressure and the heat release,when ignition time is 15 ° CA BTDC,the combustion efficiency is the best,and the corresponding torque is the highest.It is the best ignition time.As the ignition time advances,THC emissions increases after decreasing first,and there is no difference for CO emissions.Meanwhile,NOx emissions increases gradually.The peak particle size ranges between 10-20 nm.As the ignition time increases from 10°CA BTDC to 30°CA BTDC,particles quantity density increases after the first reducing.