The Mechanism And Modeling Of Flame Stabilization By Horizontal Jet In The Upper Reaches Of The Cavity In Supersonic Flow

This paper applied a detailed analysis on the flame structure of flow injection upstream of the cavity flame-holder in supersonic flow.The Mach number of the flow was set to 5.5.This paper mainly focus on the conditions of lean flame blowout limits.The injection pressure as well as the number of holes was changed to compare the mechanism of flame stability.Besides the model of blowout limits upstream of the cavity is also studied.Numerous flameholding modes are presented in the combustion chamber,which is equipped with a single-side expansion cavity,with C2H4 been set as the working medium.Those modes include the shear-layer stabilized flame mode,the cavity recirculation zone and shear-layer combined stabilized flame mode,cavity-assisted jet wake-stabilized flame mode.Among these,the robustness of shear-layer flameholding mode is believed to be the best.The flameholding mode under the condition of lean-fuel flame blowout limits is shear-layer flameholding mode.The analysis tells that cavity will reach the lower boundary of flame stability when the condition is lean-fuel flame blowout limits.Under this condition,the recirculation zone in the cavity will be compressed.The reaction zones mainly concentrate in the rear area inside the cavity.The fields of OH and CH,which exist mainly in the shear-layer and the rear portion of the cavity,are thin and short thus being not able to cover the cavity.The recirculation zone cannot afford enough energy and free radical to the shear layer.As a result,the position of the flame base move to downstream apparently.The oscillation character of flame base is the key factor of flameholding as well as flame blowout.When the equivalence ratio is high,the flame base will be stable while the oscillation phenomenon is weak.Also,the flame base can be holden near the leading edge of the cavity and the flame can exist stably.When the equivalence ratio is decreased the flame base move to the downstream with the oscillation phenomenon being intensified.When the dynamic condition inside the shear-layer cannot hold the flame base,which is oscillating fiercely,the flame will be blown out.The trailing edge of the cavity is the place with fierce burning.The static pressure can reflect the burning process of this place.The static pressure is high when the equivalence ratio is in a high level.With the decreasing of the equivalence ratio,the static pressure will show a tendency of decreasing at a moment.After that,this moment will move forward with the continuous decreasing of the equivalence ratio.This leads to the reduction of duration time of flame burn intensity summit.When the equivalence ratio is too low,this moment will be too early that the flame cannot be stabled and the burn condition changes to oscillating burn condition.This paper mainly analyzed the physical mechanism of flameholding in the shear layer and the recirculation zone.Auto ignition is thought to be the leading mechanism in supersonic injection flame.Moreover,the physical explanation of lean flame blowout phenomenon is presented.Finally,the lean flame blowout model is improved.