Characteristics of Cascaded Fuel Injectors Within an Accelerating Scramjet Combustor

Performances of cascaded hydrogen injectors within an accelerating scramjet combustor were characterized via a three-dimensional numerical study. Two streamwise-aligned jets are employed, with the upstream injector half the diameter of the rear jet. Each are inclined at 45 deg to the freestream and achieve a jet-to-freestream momentum ratio of unity. Performance was evaluated over a range of freestream Mach numbers, modeling combustor entrance conditions on an accelerating access-to-space scramjet trajectory. Distance between injectors was varied to estimate the optimum jet-to-jet spacing to achieve robust performance across the Mach number range. It is shown that the downstream injector benefits jointly from shielding effects induced by the smaller upstream injector, as well as its increased diameter. Injector spacings greater than two total jet diameters displayed improved absolute jet penetration, spanwise spread, and entrainment rates over an equivalent single injector across all Mach numbers. Jet bow shock pressure recovery was improved at spacings above . Unique optimal injector spacings existed for each performance metric, at each freestream Mach number examined. Although no universal optimum spacing was determined, spacings between 4 and provided substantial performance enhancements over single injectors, throughout the accelerating scramjet flight conditions.