Wave dynamic mechanisms in coaxial hydrogen/liquid-oxygen jet flames

Abstract

Coaxial gaseous hydrogen/liquid-oxygen jet flames were studied experimentally as a function of the outer-to-inner momentum flux ratio J using high-speed shadowgraphy and hydroxyl radical (OH) chemiluminescence imaging at 25 kHz. Particular attention was paid to wave dynamic mechanisms that could be observed. It was found that large structures generated at the exit of the annular flow created a chain of events that had a strong effect on the flame. These structures were found to impinge on the liquid-oxygen core and created local increases in OH emission (interpreted as combustion waves), local troughs in the liquid-oxygen core caused by increased vaporization, and waves composed of expansion gases: all of which convected downstream at different velocities, with the combustion wave propagating the fastest. The combustion waves were found to sometimes merge, sometimes spontaneously disappear, or sometimes continue to propagate as pairs. Earlier results had shown the importance of large-scale structure dynamics in the outer flow to simpler nonreacting coaxial flow. These results also confirmed their importance in combusting flows.