EXPERIMENTAL SUPERSONIC HYDROGEN COMBUSTION EMPLOYING STAGED INJECTION BEHIND A REARWARD-FACING STEP

An experimental investigation of a Mach 2 combustor has been conducted in order to characterize flow properties in a supersonic reacting flo wfield. Hydrogen was injected transversely as staged, underexpanded je ts behind a rearward-facing step into a ducted Mach 2 air freestream. The effects of the chemical reaction on the supersonic flowfield was i nvestigated using shadowgraphs, broadband flame emission photography, and planar laser-induced fluorescence of OH. The shadowgraphs indicate d that the wave pattern in the combustor along with flowfield unsteadi ness was strongly affected by the heat release. The broadband flame em ission photographs revealed large regions of no combustion in the vici nity of the fuel injectors where fuel/air mixing was insufficient to s upport combustion. These regions decreased in size as the freestream s tagnation temperature was decreased for fixed hydrogen mass flow rate, consistent with an increase in the effective Q-ratio with combustion. The size of the zones containing OH in the planar fluorescence images also increased as the main flow stagnation temperature was decreased. Reaction zones were found in the planar fluorescence images away from regions containing injectant in a nonreacting study of the same geome try, indicating that the pressure rise associated with the reaction fo rced a large redistribution of the fuel.