Experimental Investigation on the Combustion Oscillation in a Model Scramjet Engine

摘要

A scramjet combustor with cavity-based flameholder was experimentally studied in a direct-connected testbed with the inflow conditions of M=2.64, Pt=1.84MPa, Tt=1300K. Ignition and self-sustained combustion with room temperature kerosene were achieved successfully by using pilot hydrogen, and kerosene was vertically injected into the combustor through 4xcpO.5mm holes mounted on the wall. The high speed camera and strain guage type pressure sensor were adopted to investigate the flowfield and pressure oscillation in the combustor. The combustion flame disturbulence and oscillation was observed by high speed camera. Furthermore, the fuel injection oscillation and flowfield shock train oscillation were observed by high speed Schlieren system with laser light. Results revealed that the flame seem to be periodically oscillation around the cavity flameholder, accompanied with the fuel injection oscillation, but not coupled with the pressure oscillation. The pressure oscillation in the combustion region and downstream flow appeared different range and frequency. Such phenomenon is probably determined by the local heat release intensity or the character of supersonic combustion. The two proposed acoustic reflection models, one for acoustic reflection between combustion zone and injection, the other for acoustic reflection between combustion and upstream shock trains, may both influence on the combustion oscillation in the combustor. More importantly, the periodically pressure fluctuation was not according to the gasenous ethylene and JP-7 frequency provide by the AFRL, which may be influenced by the fuel injection, change of precombustion shock or fuel combustion intensity.