Optimization Study On The Fuel Injection And Mixing Process In A Scramjet

The process of the fuel injection and mixing is the initial stage of all physical processes in a scramjet.The ability to achieve efficient fuel mixing is one of the key issues that need to be addressed to achieve stable combustion.The injection and mixing process of fuel is affected by many factors,and the analysis of the influence of different factors is benefical to optimize the injection scheme.In this paper,we mainly studied the effects of the injection Mach number,the injection angle and the boundary layer thickness of the nozzle on the fuel injection and mixing process.Due to the limitation of the pressure outside the orifice,the penetration does not increase monotonically with the increase of the injection Mach number.The pressure outside the orifice is approximately equal to the pressure after the supersonic inflow passing through a normal shock.Under the condition that the pressure outside the orifice is regarded as the backpressure,if the injection Mach number can make the Laval nozzle meet the design condition,the penetration reach its maximum.Through the simulation research,it is found that the variation of the flow field structure characteristics with the injection Mach number is not monotonous,but there is a turning point.Through the quantitative analysis,the injection Mach number when the penetration reach its maximum was obtained,and the results of the theoretical analysis were verified.With the increase of the injection angle,the component of the jet momentum in the direction perpendicular to the wall increases first and then decreases,which determines that the maximum penetration can be produced by transverse injection.However,the change of the momentum component in the direction of streamwise makes the interaction between the jet and the supersonic inflow stronger,which improves the mixing efficiency,but increases the total pressure loss at the same time.In addition,with the increase of the injection angle,the spanwise extened is increasing at the same streamwise direction.When the injection angle is larger than 90°,the position of the mixing process will be move forward,which is beneficial to reduce the size of the engine.The influence of the boundaey layer thickness of the jet orifice on the structure of the flow field is very small,but the larger boundary layer thickness will bring the loss of mixing efficiency.