Experimental Research On Pumping Losses And Fuel Economy Performance In The Unthrottled SI Engine

The main problems in the process of the traditional gasoline engine are the large pumping losses and low thermal efficiency.The fundamental reason is that the traditional gasoline engine regulates the loads by controlling the throttle opening,resulting in large pumping losses during the ventilation process,which leads to lower thermal efficiency and poor fuel economy performance in the traditional gasoline engine.However,fully variable valve technology can achieve variable valve lift,valve timing and valve opening duration continuous variations to reduce pumping losses and improve the thermal efficiency of the engine.The unthrottled SI gasoline engine studied in this paper is refitted with the fully variable hydraulic valve train(FHVVS)on the basis of BJ486EQ gasoline engine.FHVVS was independently developed by the team in Shandong University.It can achieve continuous variations in maximum valve lift,valve opening duration and the timing of valve closing.In this paper,the pumping losses and fuel economy performance were studied in the unthrottled SI engine,the main contents are as follows:Firstly,the effects of time value and cam profile on pumping losses are explored.In this paper,the influences of the original cam profile and FHVVS cam profile on the valve lift and acceleration are analysed.The results show that with the valve opening timing and maximum lift unchanged,the larger time value,the smaller the resistance,the greater the circulation capacity.Secondly,we study the effects on pumping losses under different operating conditions in the unthrottled SI gasoline engine.The experimental researches in the throttled and the unthrottled SI gasoline engines have been conducted.The pumping losses which are measured on the same speeds with different loads and the same loads with different speeds between two kinds of engines were analyzed.Experimental studies have found that pumping losses in the unthrottled SI gasoline engine are significantly reduced compared to the throttled SI gasoline engine.The pumping losses have reduced about 80%on the speed of 2000 rpm and 3000 rpm.Thirdly,the combustion performances of the throttled SI gasoline engine and unthrottled SI gasoline engine are analysed.The in-cylinder pressures,the heat release rates and the combustion characteristics parameters of CA50 and COV are compared and analysed between two kinds of SI gasoline engines.Experimental studies have found that CA50 is away from the top dead center,combustion cycle increases,the combustion rate decreases and so on in the unthrottled SI engine at medium to low load.In addition,measures are put forward to improve the problems combustion deterioration.Fourthly,the economic performances of the throttled and unthrottled SI gasoline engines are compared and analysed.BSFC at different speeds and different loads are measured to form the load characteristic curves.Tests have shown that BSFC can reduce 4.1%to 11.2%at 2000 rpm and 3000 rpm.