Influence of Shock Structure on Stabilization of Hydrogen Jet Flames

Abstract

Non-premixed hydrogen jet flames spouted from a nozzle with a divergent channel were investigated experimentally to clarify the effect of shock structure created in the vicinity of a nozzle exit on flame stability. The experimental results show that the flame accompanied with ideal-expanded jet was the most difficult to stabilize, compared to both conditions of under- and over-expanded jet. To better understand how the shock structures affect to flame stabilization, a concept of characteristic length L_v based on the Damköhler number in turbulent flow was proposed, and CFD including LES turbulent model was performed under the conditions that either flame can stabilize or not. Consequently, L_v in blow-out condition was longer than that in stable condition. As L_v may indicate the quantity of delay of chemical characteristic time, the effect of shock structures can be discussed in various nozzles.