| Summary: | The results of five experimental investigations on the initiation, propagation and transmission of detonation have shown that the wave behavior depends on the relative rates of gasdynamic expansion and chemical energy release occurring within the cellular detonation front. The former rate is controlled by the "boundary conditions" defined by the physical system, while the latter rate depends on the chemical and physical properties of the combustible mixture. The fractional increase (xi) in the area of the post-shock "stream tube", evaluated over a chemical kinetic distance equal to the cell length, has been identified as a parameter which satisfactorily characterizes the competition between these two rate processes. For (xi) less than about 20%, the chemical processes survive the gasdynamic expansion and self-sustained propagation is possible. However, under these "supercritical" conditions, the wave propagates with a velocity deficit which appears to be a universal and theoretically predictable function of (xi). === For (xi) greater than 20%, the shock/reaction zone coupling breaks down, resulting in failure of the wave. The "critical" conditions for the propagation of detonation waves subjects to a wide range of expansion inducing mechanisms, including viscous boundary layers, compressible boundary gases and yielding walls, are all found to be consistent with the 20% criterion. However, the criterion becomes inapplicable as the cell size approaches the characteristic transverse dimension of the geometry. === In the case of direct initiation or transmission of detonation from one geometry to another, the critical conditions are shown to be linked to the requirement for the diverging wave to exceed some minimum radius of curvature. Such radius is geometry dependent and satisfies the stream tube criterion. The role of the "initial conditions" in this type of problem is to guarantee survival of the wave until it achieves the minimum radius for which shock/reaction zone coupling, and hence self-substance, are possible.
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