Supersonic boundary-layer combustion: Effects of upstream entropy and shear-layer thickness

There is much interest in the way in which fuel is injected into scramjet combustors and the way this influences ignition and combustion. Experiments were conducted in the T4 Stalker Tube to assess the combustion of hydrogen when it is injected directly into the boundary layer of a circular constant-area supersonic combustion chamber (M > 4). The wall-layer conditions at the fuel-injection station were varied to study the effects on the ignition and combustion of the injected hydrogen. This was achieved by varying the leading-edge bluntness and the length of the constant-area inlet upstream of the annular fuel-injection slot that delivers fuel as a layer underneath the existing boundary layer. Flow properties at the injection location calculated using computational fluid dynamics are presented as well as experimental data and analytical predictions of the pressure distributions along the combustion chamber wall. It is shown that a thicker boundary layer promotes combustion and that leading-edge bluntness, which leads to more hot gas near the walls, is more effective for ignition