Flame Acceleration And Its Effect On Auto-ignition Of End-gas In Constant Volume Combustion Chamber

As the shortage of energy sources and environmental pollution caused by the increasing of car parc get more and more serious,energy conservation and emission reduction have become the most important demand of the development of automobile industry.Gasoline engine downsizing technology has gained the position of hot research topic for its outstanding performance in reducing carbon dioxide emission and fuel consumption.However,the development of this technology is now severely restricted by knock.Based on a generally accepted opinion that knock is caused by the auto-ignition of end-gas before the flame propagation comes,this thesis researched on the effect of accelerated flame on the occurrence of the auto-ignition of the end-gas in a constant volume combustion chamber,using experimental measures and simulation means.Accelerated flame can be produced by an adaptor with bores.This thesis firstly researched on the effect of initial pressure,equivalence ratio and bore diameter on the acceleration characteristic of jet flame.It is found that initial pressure has little effect on the acceleration characteristic of jet flame.Equivalence ratio affects the variation of flame propagation speed,while having little effect on the position where the flame propagating speed maximizes.Bore diameter affects not only the variation of flame propagating speed but also the position where the flame propagating speed maximizes.Then this thesis researched on the effect of accelerated flame on the occurrence of the auto-ignition of the end-gas.Next,this thesis researched on the effect of initial pressure,equivalence ratio and bore diameter on the flame propagating speed,pressure wave and occurrence of auto-ignition.It is found that these three parameters enhanced the occurrence tendency of auto-ignition by making flame propagate speedily.High-speed flame is the direct factor that lead to auto-ignition.One of the disadvantage of experimental measures is that details of the end-gas cannot be gained when auto-ignition occurs.In order to cover this shortage this thesis also did some simulation research on AVL-FIRE.It is found that some spots near end-gas will rise its pressure and form pressure waves when auto-ignition occurs.The superposition of those pressure waves causes the shock of pressure in chamber.This thesis found that the two key factors in the process that accelerated flame causes auto-ignition of end-gas are acceleration characteristic of jet flame and thermodynamic states of end-gas.High propagating speed of flame,the existence of pressure wave in the forward of flame front,high pressure state of end-gas and proximity-1 equivalence ratio are all enhancing factors of auto-ignition.The research done by this thesis provides support to the exploration of knock research.