Experimental Study On Combustion And Emission Of Hydrogen Mixing Engine With Combined Injection

With the energy and environmental issues becoming increasingly prominent,energy saving,emissions reduction has become an inevitable trend in the course of the development of internal combustion engine.A combined injection engine experimental platform was built to study the effects of injection mode,injection strategy and ignition timing on combustion and emission characteristics.The study was performed in three modes,including gasoline port injection(PFI)mode,gasoline port injection plus gasoline direct injection(PFI+GDI)mode and gasoline port injection plus hydrogen direct injection(PFI+HDI)mode.By means of contrast,the effects of combined injection technology and hydrogen addition are highlighted.The conclusions based on experimental results were shown as follows:(1)The combustion and emission performance can be obviously improved through adopting combined injection due to the formation of stratified mixture.By using combined injection,the stratified mixture will burn more completely,which is propitious to increase brake torque,brake thermal efficiency and decrease HC and CO emissions.However,higher temperature in cylinder leads to more NOx emission.(2)Adding hydrogen leads to lower BSFC,higher heat release rate,higher combustion temperature and pressure.Hydrogen's short quenching distance can reduce HC emissions.However,higher temperature brings about the formation of NOx,therefore,NOx emissions will increase with hydrogen addition.(3)The influence rules of ignition timing on combustion and emission performance are basically consistent under three modes.With the increase of ignition advance angle,the brake torque and brake thermal efficiency first rises then falls.And the best ignition advance angle for lowest BSFC is the same in three modes.As for emissions,the nitrogen oxides and hydrocarbon emissions decrease with the decrease of ignition advance angle.Furthermore,changing ignition timing has little effect on reduction of the CO emissions.(4)For liquid fuel gasoline,there is a cylinder injection pressure that makes the engine performance the best,the gasoline atomization effect will become worse when the pressure less than the best pressure and the long penetration distance leads to the spray wall collision,both of them will make the engine performance decline.For the gaseous fuel hydrogen,there is also a cylinder injection pressure which makes the engine performance the best.The change of the jet pressure in the cylinder affects the velocity of the air flow,which affects the air flow in the cylinder.There is a best injection pressure makes the mixture the best.It is found that the optimum injection pressure is different at different ignition timings,indicating that there is a relationship between the injection pressure and ignition timing.(5)For liquid fuel gasoline,there is an injection timing makes the engine performance the best,and the best injection timing is not affected by the ignition timing.For gaseous fuel hydrogen,there is also an injection timing makes the engine performance the best,but the best injection timing will be affected by the ignition timing.(6)Under the conditions of best injection pressure and best injection timing,the combusiton state in the cylinder is the best,the fuel burns more faster,more concentrate and more complete,therefore,the power performance improve,HC emission and CO emission decrease.However,higher temperature in cylinder leads to more NOx emission.