Oblique detonation stabilized on a hypervelocity projectile

Abstract

We present new experimental results demonstrating the initiation and stabilization of an oblique detonation by a hypervelocity projectile. Projectiles 25 mm in diameter were launched at nominal velocities of 2700 m/s into stoichiometric H 2 -O 2 -N 2 mixtures at pressures between 0.1 and 2.5 bar. A critical threshold in initial pressure was found to be required for the establishment of detonations. Initiation events similar to DDT in propagating waves were observed after 300 mm of travel in H 2 -O 2 mixtures diluted with 25% N 2 . A more direct initiation process was observed in H 2 -air mixtures. A stabilized but overdriven oblique detonation was observed in a stoichiometric H 2 -air mixture at an initial pressure of 2.5 bar. The pressure threshold can be explained in terms of competing reaction and flow-quenching effects along a curving streamline in supersonic flow behind a curved shock wave. This competition can be characterized by a critical Damkohler number Da 0 , which is inversely proportional to the product of wave curvature κ and reaction zone thickness Δ. Only if the reaction zone is sufficiently thin in comparison with the projectile, Da>Da 0 , is it possible to obtain stabilized detonations. Otherwise, the reactions quench and the wave splits into a nonreactive shock wave followed by flamelike contact surface. The inverse pressure dependence Δ∼ P 0 −1 of the reaction zone length and the scaling of the wave curvature κ∼1/ a with the body radius a implies the standard binary scaling relationship P 0 a =constant for the critical conditions of stabilization for a given mixture composition characterized by a bimolecular rate-limiting step.