Experimental Study On The Effect Of Inlet Water Injection On The Combustion And Emissions Of Heavy-duty Diesel Engine

The upgrading emission regulations put forward higher requirements on internal combustion engine technology,improving fuel economy while reducing NOx and PM emissions is the main problem faced by diesel engine.Exhaust gas recirculation(EGR)is one of the effective technologies in diesel engine combustion and emission control,while inlet water injection has similar effect with EGR on combustion without the problems of EGR theoretically,which has the potential to replace(or partially replace)EGR.Therefore,this work conducted experimental research on the effect of inlet water injection on the combustion and emissions of heavy-duty diesel engine,and explored the efficient and clean combustion technology of diesel engine.The experimental study was conducted on a high pressure common rail heavy-duty diesel engine.First,working conditions of WHSC test cycle were selected,and the effect of inlet water injection on diesel engine combustion and emissions was studied,and compared with high and low pressure EGR strategy respectively.The results show that increasing the water injection quantity increases the inlet pressure and excess air coefficient slightly,prolongs the ignition delay to different degrees,reduces the peak heat release rate,and significantly decreases the combustion temperature in the cylinder.With the increase of water injection quantity,NOx emission presents a linear decline.In current research,the NOx emission can be reduced by about 60% at different working conditions.At light load,the increase of water injection quantity will lead to more soot emission,but overall below the sixth stage limit.Fuel consumption trend along with the change of water injection quantity is greatly influenced by the load,inlet water injection improves fuel consumption better as load increases,at B100 working condition,fuel consumption can be reduced by 4 g/(kW·h).Then,the control strategy of combining inlet water injection with EGR was further studied,and when to utilize high pressure EGR,water injection or both was determined according to the characteristics of different working conditions.At light load,the overall temperature and activity in the cylinder are low,and water inejction is not conducive to combustion,while high pressure EGR can reduce fuel consumption and NOx emission,thus high pressure EGR should be used alone at light load.At medium load,both water injection and EGR can improve fuel consumption to some extent.Combining them at such working conditions,better fuel consumption and emission characteristics can be obtained than using high pressure EGR or water injection alone.High pressure EGR is difficult to be introduced at heavy load conditions,while the inlet water injection is not limited,it improves fuel consumption obviously,so the inlet water injection strategy should be used alone at such conditions.WHSC cycle weighted results show that the optimized control strategies present lower emissions and fuel consumption than that of high pressure EGR or water injection alone.Compared to original strategy,the NOx emission is reduced from 17.06 g/(kW·h)to 9.35 g/(kW·h)(by 45%),the weighted fuel consumption is reduced by 1.2 g/(kW·h).The soot emission is far lower than the sixth stage limit,and HC and CO change slightly.It can be seen that inlet water injection is a feasible way to achieve efficient and clean combustion for diesel engine.