Numerical investigation into the combustion behavior of an inlet-fueled thermal-compression-like scramjet

A numerical study on the combustion behavior of an inlet-fueled three-dimensional nonuniform-compression scramjet is presented. This paper is an extension to previous work on the combustion processes in a premixed three-dimensional nonuniform-compression scramjet, where thermal compression was shown to enhance combustion. This paper demonstrates how thermal compression can be used in a generic scramjet configuration with a realistic fuel-injection method to enhance performance at high flight Mach numbers. Such a scramjet offers an extra degree of freedom in the design process of fixed-geometry scramjets that must operate over a range of flight Mach numbers. In this study, how the combustion processes are affected is investigated, with the added realism of inlet porthole fuel injection. Ignition is established from within a shock-induced boundary-layer separation at the entrance to the combustor. Radicals that form upstream of the combustor within the inlet, from the injection method, enhance combustion. Coupling of the inlet-induced spanwise gradients and thermal compression improves combustion. The results highlight that, although the fuel-injection method imparts local changes to the flow structures, the global flow behavior does not change compared to previous premixed results. This combustion behavior will be reproduced when using other fueling methods that deliver partially premixed fuel and air to the combustor entrance

Analysis of a multi-porthole injector array in a supersonic crossflow

Computational fluid dynamic (CFD) simulations of hydrogen injection through a multi-porthole injector array into a Mach 10 enthalpy supersonic crossflow are presented and compared to experimental data. Reynolds-averaged Navier–Stokes simulations using a Menter shear-stress transport turbulence model are performed with the CFD code CFD++. The experimental results showed transient flow behavior in the boundary-layer separation upstream of the injector past the measurable test time. This complicated the validation process of the steady-state simulations to the experimental data. A hybrid simulation, which provides a laminar inflow boundary layer and turbulence production at the injector, matched the upstream separation length as measured from the experimental data. The simulation near-field shock structures and fuel penetration matched experimental schlieren photographs. The close jet-to-jet spacing leads to a blockage of injector-generated vortices. The simulations show that including three-dimensional spillage effects reduced the injection-induced separation length by 20%, and they resulted in a better match with the experimental data. The results also showed the injection-induced separation has a significant spanwise flow and alters the mixing process downstream of the multi-porthole injector array by enabling trailoff vortices to develop

Thermal and mixing efficiency enhancement in nonuniform-compression scramjets

Numerical simulations are presented to compare the heat addition, thermodynamic cycle, and mixing efficiency of generic uniform- and nonuniform-compression scramjets. The work builds on previous numerical studies that showed the coupling of nonuniform-inlet compression and thermal compression enhanced the performance of low-inlet compression scramjets. In line with previous work, both engines have the same inlet-fuelling method, inlet contraction ratio, and combustor geometry. The freestream corresponds to a Mach 10 flight condition with a dynamic pressure of 100 kPa. This study shows the mixing, heat addition, and thermodynamic cycle efficiency in the nonuniform-compression engine are higher than the uniform-compression engine. The mixing and heat release efficiency increase by 10 and 20% respectively. Enhancement of these performance parameters in the nonuniform-compression engine is caused by a staged-combustion process. This study offers new insight into how purposely induced nonuniform compression can be used to enhance scramjet engine performance

Scramjet Performance with Nonuniform Flow and Swept Nozzles

Numerical simulations are presented that compare the specific impulse of a generic inlet-fueled uniform-compression and nonuniform-compression scramjet over the flight Mach number range of 7-12 with a constant freestream dynamic pressure trajectoryof100 kPa. Both engine configurations have identical inlet contraction ratio, inlettonozzle area ratio, and combustor and nozzle geometries. The results show thatthespecific impulse in the nonuniform-compression scramjet is higher than the uniform-compression scramjet at each flight condition. The increase in specific impulse for Mach 8, 9, 10, 11, and 12 are 165, 178, 96, 74, and 15 s, respectively. Both the uniform- and nonuniform-compression engines unstarted at the Mach 7 condition. In addition, two three-dimensional swept-nozzle configurations (45 and 60 deg) are integrated into the nonuniform-compression engine to investigate an idea of coupling the nonuniform flow with a nonuniform expansion nozzle to improve performance. The 45 deg results show no change in specific impulse at Mach 8-11 and a 50 s improvementat Mach 12. The 60 deg configuration has less specific impulse at each flight condition, except Mach 12. The thermal loads are reduced by 15 and 30% for the 45 and 60 deg configurations at each flight condition. The findings provide new insight into how nonuniform compression with swept nozzles can provide an additional degree of freedom in the design of fixed-geometry scramjets that have robust performance over a range of flight conditions