Effects Of Injection Strategies On Stratified Lean Burn Characteristics Of A Gasoline Engine

Direct-injection gasoline engine（GDI）has become a mainstream gasoline engine technology due to its higher thermal efficiency and better power output.However,with the increasingly strict emission regulations,especially the recently issued China VI emission regulations,emission of particulate matter in gasoline engines is limited to 6×10¹¹#/km.The characteristics of high particulate emissions in direct-injection gasoline engines have become a huge challenge for its further development.Compared with GDI engines,the traditional intake port injection has a much lower particulate emissions than a GDI engine because of its more sufficient fuel-air mixing and less fuel impingement effects.Therefore,in this study,a dual-injection engine is formed by combining these two injection strategies into a direct-injection gasoline engine with an intake port injection device,which fully combines the respective advantages of the two to ensure a high-efficiency power output while generating lower emissions.In addition to the strict restrictions of emission regulations,energy efficiency is also an eternal development direction in the research of internal combustion engines.Lean combustion technology is an effective combustion strategy to reduce the fuel consumption of the engine.By properly increasing the air-fuel ratio,the in-cylinder mixture can be more fully combusted to improve thermal efficiency and reduce fuel consumption.The stratified lean burn is a further lean burn scheme.By achieving a higher air-fuel ratio,a more obvious effect of reducing fuel consumption is achieved.The research in this article implied the dual-injection system to develop a new in-cylinder oil and gas stratification strategy,that is,the injection of the intake port forms a thin mixture atmosphere inside the cylinder.Direct injected fuel then forms a rich mixture near the spark plug when the piston comes near the top dead center.This solution can stabilize the combustion with an excess air ratio of 1.8 under the conditions of2000rpm and 2Bar BMEP,and the fuel consumption is significantly reduced compared to the original engine.This research adjusted the control strategy of the dual injection engine to investigate its influence on the combustion and emission characteristics of the engine.The study of the combustion characteristics includes fuel consumption,cylinder pressure and heat release rate,combustion phase and duration,and combustion stability.The emission characteristics include the number and mass concentration of particles,particle size distribution,modal ratio of particles,and GMD characteristics,as well as gas emission characteristics including CO,THC,and NOx.Experimental research showed that by adjusting the control strategy,the fuel consumption of the engine was reduced by 15.85%compared to the original engine.Through the adjustment of the direct injection ratio,direct injection fuel pressure,and direct injection timing,the combustion cycle-by-cycle variation can be kept within an ideal range.In terms of particulate matter emissions,increasing the excess air ratio,advancing direct fuel injection,increasing fuel injection pressure,and delaying ignition timing will all reduce particulate matter emissions.Reducing the direct injection ratio will also bring significant particulate matter emissions down.The optimized control strategy can reduce the particle concentration by orders of magnitude from 10⁶ to 10⁵compared with the original engine,the effect is significant.The characteristics of gas emissions are mainly to provide guidance for the selection of control strategies to avoid excessive deterioration of gas emissions while optimizing particulate matter emissions and fuel consumption.