An experimental study of oblique detonation waves

Recently, the interest of hypersonic propulsion was revived and Oblique Detonation Waves (ODW\u27s) were suggested as an alternative for supersonic combustion. A new method has been used to study ODW\u27s at a laboratory scale. A normal detonation traveling down a shock tube induces an ODW in a secondary detonative mixture by deflecting into it a thin film because of the high post-detonation pressure. The film separating the two mixtures initially acts like a wedge moving at hypersonic speed in the driven mixture. It is thick enough to allow setting different original pressures for the two mixtures. The driven mixtures used are $\rm C\sb2H\sb2 + 2.5O\sb2 + 10.5Ar,\ 2H\sb2 + O\sb2 + xI$ and $\rm CH\sb4 + 2O\sb2 + xAr$ original pressures of 10-70 kPa, where the inert I is N$\sb2$ or Ar. The phenomenon is observed by schlieren photography, pressure measurements and direct radiation of some combustion intermediates. As expected, the onset of the detonation is delayed by the film inertia. An oblique shock is usually first induced and at some point behind it, a high pressure combustion wave occurs. This is the point of transition where a strong, overdriven ODW is initiated. However, when the thinnest films are used, the ODW is formed close to the apex of the wedge and its characteristics (wave angle and pressure jump) are found to be in good agreement with theory. The cellular structure of the ODW is determined from imaging the natural fluorescence of the OH radical and is found to be similar to that of normal detonations under the same conditions.