Study On Intake And Combustion Process Of High-speed Gasoline Engine

The air motions in cylinder have a significant impact on the formation of air-fuelmixture and its working process. The distribution of flow field before ignition time willdetermine flame propagation velocity and combustion efficiency. The strengthen ofturbulence in cylinder should improve flame propagation, combustion efficiency as well asreducing combustion cyclic variations and should also result in a better performance intractive, economical, combustion noise and exhaust gas.In this paper, AVL-Fire software was used to the intake and combustion process of ahigh-speed port-injection gasoline engine. Through the analysis of the original engine, theunreasonable design of its intake port was found. To improve its tumble ratio and dischargeefficiency, the dip angle and cross section of intake port were modified. The differences offlow field and combustion process between the original and the modified were also studied.To the beginning, through a steady flow test of the original intake port, the dischargeefficiencies in different valve lift were measured, which then was set to the criterion toestimate the accuracy of numerical simulation. Then the simulations of its intake processwere proceed to analysis the flow field in different valve lift, especially in max valve lift.The simulation results showed an acceptable circulation and tumble-forming ability as wellas some negative factors which should lead to intake resistance. Based on the results, theintake port structure was modified, and its results showed an improvement in dischargeefficiency and tumble ratio in a certain extent.Bench test datum was used to calibrate the transient working process simulation of theoriginal engine. Based on calibrating, the modified model was simulated. The resultsindicated the modified intake port model formed higher turbulence, higher cylinder pressuresince compression process. After ignition, it turned to be more flame front fold, higherflame propagation velocity, higher combustion efficiency. The modified model outputsmore power with no rude working conditions.