MECHANISMS OF DETONATION TRANSMISSION IN LAYERED H-2-O-2 MIXTURES

When a plane detonation propagating through an explosive comes into co ntact with a bounding explosive, different types of diffraction patter ns, which may result in the transmission of a detonation into the boun ding mixture, are observed. The nature of these diffraction patterns a nd the mode of detonation transmission depend on the properties of the primary and bounding explosives. An experimental and analytical study of such diffractions, which are fundamental to many explosive applica tions, has been conducted in a two channel shock tube, using H-2-O-2 m ixtures of different equivalence ratios as the primary and bounding or secondary explosive. The combination of mixtures was varied from rich primary / lean secondary to lean primary / rich secondary since the n ature of the diffraction was found to depend on whether the Chapman-Jo uguet velocity of the primary mixture, D-p, was greater than or less t han that of the secondary mixture, D-s. Schlieren framing photographs of the different diffraction patterns were obtained and used to measur e shock and oblique detonation wave angles and velocities for the diff erent diffraction patterns, and these were compared with the results o f a steady-state shock-polar solution of the diffraction problem. Two basic types of diffraction and modes of detonation reinitiation were o bserved. When D-p > D-s, an oblique shock connecting the primary deton ation to an oblique detonation in the secondary mixture was observed. With D-p < D-s, two modes of reinitiation were observed. In some cases , ignition occurs behind the Mach reflection of the shock wave, which is transmitted into the secondary mixture when the primary detonation first comes into contact with it, from the walls of the shock tube. In other cases, a detonation is initiated in the secondary mixture when the reflected shock crosses the contact surface behind the incident de tonation. These observed modes of Mach stem and contact surface igniti on have also been observed in numerical simulations of layered detonat ion interactions, as has the combined oblique-shock oblique-detonation configuration when D-p > D-s. When D-p > D-s, the primary wave acts l ike a wedge moving into the secondary mixture with velocity D-p after steady state has been reached, a configuration which also arises in ob lique-detonation ramjets and hypervelocity drivers.