An Experimental Investigation On The Effects Of Injection Strategy On Combustion And Emission Characteristics Of Partially Premixed Combustion Of Neat N-butanol And Gasoline

Partially Premixed Combustion(PPC)has been regarded as one of the potential novel combustion concepts to achieve a clean combustion with high efficiency in a broad range of load,it has become a research hotspot in recent years.However,fast combustion rate causes problems,such as the high pressure rise rate,high maximum cylinder pressure and high soot emission.N-butanol is a second generation fuel containing oxygen,which has high volatility,high octane number and high oxygen content,blended fuel of gasoline and n-butanol has the potential to reduce the emission of soot in the high load.Besides,the injection strategy can control the concentration distribution of the mixture,which can achieve the control of ignition process and heat release regulation,reduce pressure increase rate and maximum cylinder pressure.In this study,an experimental investigation on the effects of injection strategies on the combustion and emission with PPC combustion has been carried out in a modified single-cylinder test engine fueled with gasoline and n-butanol blend fuel.Firstly,the effect of n-butanol ratio on in-cylinder pressure and heat release rate(HRR)under different exhaust gas recirculation(EGR)was explored.The results showed that increasing the ratio of n-butanol in gasoline,the ignition delay becomes longer,premixed combustion rate increases,NOx and soot emissions decrease.However,the maximum pressure rise rate is too high because of the fast burning rate.With the increase of the EGR ratio,the maximum pressure rise rate and NOx emission are reduced,the indicated thermal efficiency is decreased also after rising first,but the soot and CO emissions are increased.After that,the effect of injection strategy on combustion and emission characteristics of PPC was studied,which the ratio of n-butanol was 30%,and the EGR rate was 25%.The result showed that the ignition delay of dual injection became shorter compared to the single injection.The combustion rate decreased,it resulted in decreasing soot emissions while maintaining the low maximum rate of pressure rise and NOx emissions.Increasing the interval between pilot and main injection could reduce the maximum pressure rise rate.Increase the pilot ratio,soot emissions were decreased obviously,but emissions of CO and THC were increased.Finally,the potential for improving the engine preformance and emission of PPC were studied using compound injection strategy.It could be founded that the increase of the ratio of the port fuel injection could shorten the ignition delay,reduce the maximum pressure rise rate and NOx and soot emissions,but it indicated a decrease in thermal efficiency.When the ratio of the port fuel injection maintained the same,with the increase of the pilot ratio,the proportion of premixed combustion increases,the engine performance and emission could be improved.When the port injection ratio and pilot ratio are both 30%,the interval between pilot and main injection is 100°CA,soot emission is only 0.0045 g/kW·h,while NOx emission is 1.1 g/kW·h,the maximum pressure rise rate is 11.7 bar/°CA.