Research On The Technology Of Jetting Fuel Into The Scramjet Isolator

As a core component of hypersonic vehicle, Scramjet received more and more attention in recent years. However, Scramjet performance also faces many technical problems and challenges.This paper focus on research and analysis of the thermal protection, combustion, the influence of shock wave boundary layer separation and frictional resistance on the performance of isolator.Based on the ideal Brayton cycle, the paper established the equations of jet fuel in advanced、combustion process and expansion process in the isolator, writed a program in Matlab that can describe the engine performance with Pre-jet fuel. It is assumed that the fuel jetted in the isolator didn’t burn, due to the reduction of inlet temperature in chamber inlet, at a given maximum temperature of the combustor exit,it increased jet fuel potential of the combustion and the flux of working fluid, the engine thrust ratio increased, but led to a decline in fuel economy. Because of the pre-jet flux was little, and there was some similarity between methane and water vapor(relative molecular mass and specific heat capacity), the influence of methane and water vapor on the engine performance is similar.Considering the influence of Pre-jet fuel on the blow of isolation segment separation zone, the thermal insulation of the wall, drag reduction and anti-pressure capability, the paper conducted the numerical simulation without chemical reaction in Fluent, focused on aerodynamic performance. The paper analyzed the effects of different injection scheme and its effect on the engine. Defined the blending efficiency of the engine, the total pressure recovery coefficient and the outlet flow unevenness of the isolator.The results show that, on the one hand, a small angle jet and equivalence ratio could blow the separation zone, the effect of injection for improving the thermal protection is remarkable. Even when the jet equivalence ratio is large, the blending effect of isolator could reach a high level.in addition, injection increased the exit flow non-uniformity of the isolator and temperature non-uniformity were less affected, improved Mach number inhomogeneity, so that it is helpful for organizing the combustion. large equivalence ratio with medium angel jet improved the ability to resist backpressure. On the other hand, the front jet increased the total pressure loss of the isolator, when the injection location was in the first half of the isolator, the vertical injection with medium equivalence ratio led to the inlet unable to start. In short, in view of aerodynamic performance, he advantages outweigh the disadvantages of the Pre-jet fuel on in the isolator.The combustion performance of the Pre-jet fuel was analyzed.Fixed the gross engine equivalence ratio, explored the performance of different supporting plate/ the rear wall fuel injection without Pre-jet fuel. The paper analyzed the influence of front wall injection with small equivalence ratio、different positions of injection and Tower-Bridge structure on the combustion efficiency、frictional resistance and backpressure pass- forward. The results show that the Pre-jet fuel with small equivalence ratio could improve combustion efficiency,reduce the frictional resistance and When Shared plate parts injection, it would control the backpressure pass-forward effectively. When increasing the equivalence ratio, the wall Pre-jet fuel would replace the supporting plate and become the dominant factor for backpressure pass-forward. Reasonable tower –bridge structure and riding position could inhibit the backpressure pass-forward, but lower the combustion efficiency, meanwhile, the front wall injection with large equivalence ratio would be invalid.