Effects of Hydrogen Fuel Injection in a Mach 12 Scramjet Inlet

Abstract

To investigate the potential benefits of hydrogen fuel injection in a three-dimensional scramjet inlet, flow through a Mach 12 rectangular-to-elliptical shape transitioning scramjet inlet was simulated with and without hydrogen fuel injection along its body-side compression surface. The observed flowfields showed that, at an equivalence ratio of 0.33, the fuel cannot escape the body-side boundary layer, having little effect on macroscopic inlet flow structures. Interaction with the surrounding boundary-layer turbulence causes robust mixing of the fuel in the inlet. Fuel radicals are produced immediately following injection, particularly where the fuel plumes interact with thin, hot hypersonic boundary layers sweeping inward from the inlet side walls. Combustion does not proceed until the inlet compression process is nearly complete due to low static pressures in the inlet. Once the well-mixed fuel is processed by the final inlet compression shock, ignition and combustion occurs rapidly in the nearly constant cross-section region just upstream of the throat. The net drag increase observed was less than 5%. This modest increase was primarily due to the fuel-injection process, with almost no additional drag due to fuel combustion. Similar flow structures in other inlets suggest they would benefit from inlet fuel injection.