| Firstly,we set up a one-dimensional simulation model in the GT-POWER,by adjusting the inlet valve close early or late and the lift of inlet valve to achieve the goal of changing effective compression ratio.The paper studies about the influence of engine pump,mechanical friction,heat transfer,fuel gas loses,exhaust loss,effective power and fuel economy performance under different inlet valve control strategy.At the same time,this paper builds the simulation model of the engine through the 3D software AVL-FIRE,then select the 2200r/min、25% load as the research condition,and analysis of the influence of the airflow in cylinder between A1(early intake valve closing)control mode and E1(late intake valve closing)control mode.The results show that:1.In the premise of constant fuel injection quantity by the early intake valve closing control,no throttle control makes the engine pump gas loss is greatly reduced;at the same time,due to the effective compression ratio decreases,pumping losses of the engine,mechanical friction and average heat transfer rate decreases with the increase of early intake valve closing angle;control of early intake valve closing for fuel loss had no obvious effect;the engine exhaust energy loss increases with the increase of early intake valve closing angle;A1(early intake valve closing)control mode while taking no throttle control makes the gas rapidly into the cylinder during the early of intake stroke,is conducive to enhancing the airflow.But the early intake valve closing causes that airflow can not provide energy in cylinder during the intake stroke later,and makes the airflow intensity in cylinder decline rapidly.The tumble motion,vortex motion and turbulence in cylinder of A1 control mode is stronger than that of E1(late intake valve closing)and the original control mode in the early intake stroke,but the tumble motion,vortex motion and turbulence are weaker than the other two kinds of control mode from the end of the intake stroke to the interim of compression stroke.In the end of the compression stroke,the airflow of A1 control mode is weaker than the original control mode but stronger than E1(late intake valve closing)control mode.At the same time,unlike the other two control methods,the turbulent kinetic energy center of A1 control mode is near the exhaust valve side;the engine effective power and economy with the early intake valve closing angle increases have been continuously improved;keeping air inflow same under the same load,fuel economy performance increases most obviously when it comes to the earliest intake valve closing control mode(minimum effective compression ratio).2.In the premise of constant fuel injection quantity by the late intake valve closing control,due to the change of the intake valve lift,and the effective compression ratio is constant,so the little change in performance.No throttle control makes the pumping losses of the engine is greatly reduced;pumping losses of the engine,mechanical friction and average heat transfer rate are reduced slightly with the increase of intake valve lift;due to the particularity of the intake process,resulting in a small part of the fuel loss in the small and medium load;the engine exhaust energy loss increases slightly with increase of intake valve lift;The intake valve lift of E1(late intake valve closing)control mode is consistent with the original engine,the tumble motion and vortex movement is weaker than A1(early intake valve closing)control mode but better than the original control mode during the early of intake stroke.Because of the particularity of E1 control mode,from the intake stroke to the early stage of the compression stroke,a large amount of gas has been poured into the cylinder to provide energy for the airflow movement,resulting in the cylinder tumble and swirl motion stronger than the other two kinds of control mode.However,in the late stage of the compression stroke,since the gas has been pushed out of the cylinder by the piston,the strength of the airflow in the cylinder is significantly reduced,resulting in that the tumble in the cylinder is weaker than the other two control methods,but the swirl is slightly stronger than the other two control methods.During the process,the intake valve lift has been in the maximum lift,which makes the turbulence intensity decreases continuously after the initial peak of the intake air,which is lower than that of the original and the A1(early intake valve closing)control mode;Under the condition of small and medium load,it is the most effective to improve the efficiency and economic efficiency by using the lower intake valve lift,while under the heavy load,it is the most effective to improve the efficiency and economic efficiency by using the higher intake valve lift.In this paper,the geometric compression ratio of the engine is increased from 10.5 to 12.5 by reducing the volume of the combustion chamber,and the performance of the engine is compared with that of the various control methods of the early and late closing of the intake valve.And draw the following conclusions:1.Increase the geometry compression ratio from 10.5 to 12.5,and find that simply increasing the geometric compression ratio makes the pumping loss,mechanical friction and average heat transfer rate increase,and the energy loss of the exhaust is decreased,so that the economy can be improved,but by the knocking limit makes the engine power reduction.2.The pump gas loss and exhaust energy loss of the early intake valve closing control is lower than that of the late intake valve closing control;mechanical friction and average heat transfer rate of the early intake valve closing control are higher than that of the late intake valve closing control;there is still fuel loss in the small load of late intake valve closing control mode;early intake valve closing and late intake valve closing control can reduce the knock tendency;the economic efficiency of the early intake valve closing control is better than that of the late intake valve closing control;with high-compression ratio,the earliest closing control mode(the minimum effective compression ratio)can improve the economy significantly,5.5%-11.5% in the low load,2%-5% in the high load,and fuel economy can be improved obviously at low speed,because of the knock limiting,power is probably reduced 18%-40% at speed of 1500-5000r/min. |
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