Onset of Oblique H₂-Air Detonations Enhanced by a Turbulent Jet

Abstract

The influence of a turbulent injection of reactive mixture on oblique shock-induced combustions is experimentally studied for Mach number M of 6 in stoichiometric H₂-Air mixture initially at p₀ = 0.4 bar and T₀ = 293 K. For the same conditions (mixture, p₀, T₀), previous experiments in quiescent mixture have shown the establishing of different configurations of supersonic combustion stabilized by an oblique shock wave produced in the Lab oblique shock tube facility. In this facility, the lateral expansion of a normal CJ detonation in the driven section induced an oblique shock wave (OSW) into the H₂-Air driven mixture. Depending on strength of OSW (i.e. inclination angle θ) two essential configurations of the stabilization of supersonic combustion were displayed : i) the decoupled oblique flame attached to OSW only at the edge of the wedge, ii) the oblique detonation observed inside the range of possible theoretical solutions. This detonation, generally overdriven, occurs after a delay (the detonation is detached from the edge). During this delay, the above mentionned configuration is observed. Based essentially on schlieren pictures provided by high speed camera, it has been demonstrated than turbulent injection : (i) does not affect significantly the minimum conditions for onset of oblique decoupled shock-flame configuration and the configuration itself, (ii) lowers the minimum condition for observing the oblique detonation configuration and shortens considerably the delay.