Abstract
A shock-tunnel investigation of a scramjet with a rectangular-to-elliptical shape-transition inlet and an elliptical combustor has been conducted at conditions simulating flight at Mach 8.7. The inlet was designed using a quasistreamline-tracing method to have a design point of Mach 12.0 and operation down to Mach 6.0. The elliptical combustor began with a rearward-facing step around its perimeter and was followed by a constant-area and diverging section. The flowpath was completed by a short thrust nozzle. Gaseous hydrogen fuel was injected either through multiple portholes on the intake, a series of 48 portholes on the rearward-facing step at the combustor entrance, or a combination of the two. All fueling configurations resulted in a positive thrust coefficient at equivalence ratios above 0.3 without the use of ignition aids. Fuel injection in the intake produced robust combustion and good internal thrust levels, but led to inlet unstart at fuel equivalence ratios above 0.61. Stable mixing-limited combustion was observed for fuel injection at the step at all fuel equivalence ratios up to 1.23. Combined intake and step injection was observed to have the best performance. These experimental results demonstrate that rectangular-to-elliptical shape-transition scramjets designed for access-to-space applications can operate efficiently at conditions below the design Mach number.
Published Version
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