Experimental Research On The Effects Of Inlet Parameters And Injection Strategies On Gasoline Compression Ignition

Gasoline compression ignition(GCI)shows great potential to achieve high efficiency and clean combustion,which has been a hot research topic in recent years.Fuel injection strategies and inlet parameters have significant influence on the combustion process,which are the key technique approaches for combustion optimization.In this paper,the effects of inlet parameters and pilot-main injection strategy on combustion,performance and emission characteristics of gasoline compression ignition at different loads are comprehensively investigated.The experiment was carried out on a single-cylinder engine at three typical load conditions,including low,medium and high loads.Commercially available gasoline fuel with RON of 92 was adopted.The experiment results show that,,the indicated thermal efficiency(ITE)can be improved at low load by introducing appropriate EGR with single injection strategy,while adverse effects on ITE at medium and high loads are observed with such strategy.EGR has little impact on soot emission at low load,but increased with the increase of EGR at medium and high loads.The combustion efficiency and ITE at low load as well as the ITE and soot emission at high load can be simultaneously improved by increasing intake pressure.Injection timing shows significant influence on on GCI at low load,while soot emission and ITE at high load can be greatly improved by increasing injection pressure.Further investigations were conducted to explore the effects of pilot injection strategies on GCI combustion.Results show that small pilot-main injection dwell has strong impact on combustion.Compared with single injection mode,the MPRR(maximum pressure rise rate)can be reduced by pilot injection,better performance can be obtained with small dwell at low load while large dwell is beneficial for performance improvement at medium and high loads.Higher ITE can be achieved with small injection dwell,and longer dwell can effectively reduce MPRR at high load.The impact of injection timing on combustion is reduced with the increase of the load.Higher ITE,lower MPRR and NOx emission can be simultaneously obtained at medium and low loads by adopting smaller dwell and appropriately retarded injection timing.The maximum in-cylinder pressure and NOx emission can be reduced by retarding main injection timing at high load,while it has little impact on ITE and soot emission.The ITE,CO and THC can be simultaneously improved at low load by increasing the pilot mass ratio.At medium and high loads,higher pilot mass ratio is beneficial to reduce MPRR and maintain higher thermal efficiency,however,penalty in maximum in-cylinder pressure is also observed.Therefore,it is seen that the inlet parameters and injection parameters optimization can be effective approaches to obtain high efficiency and clean combustion over wide operation region according to the operation load.