Experimental study on ejector-to-ramjet mode transition in a divergent kerosene-fueled RBCC combustor with low total temperature inflow

RBCC engine commonly fulfills the ejector-to-ramjet mode transition at a Mach number far below 4, and thus the divergent kerosene-fueled RBCC combustor will encounter tough technical challenges of completing the mode transition and maintaining sustained subsonic combustion at low total temperature inflow conditions. These important issues were studied by direct-connect tests in a divergent JP-10-fueled RBCC combustor at M_∞=3 and T₀=630 K, and two different rocket control methods, in terms of “stepped (switching off)” and “progressive (maintaining a significant reduction in the mass flow rate)” rocket control method, were validated. As a result: (1) Credible ignition could be obtained when the fuel was directly injected into the high temperature zone comprehensively affected by the rocket plume and its secondary combustion zone. (2) Self-sustained ramjet combustion in the stepped rocket control case required an excellent collaboration among the different combustion enhancement facilities (fuel struts and cavities) in the combustor. (3) Rocket-aided mode transition and ramjet combustion in the progressive rocket control case required less limitation on the combustor configuration, and permitted an improved reliability for the engine operation, although it sacrificed a small part of engine specific impulse.