Gaseous Detonation. I. Initiation of Detonation

Abstract

By means of piezoelectric gauges, a study has been made of the development of detonation from a shock wave propagated into a mixture. With a sufficiently strong shock, detonation above the stable velocity is immediately established which decays smoothly to the steady state. When the shock is weaker than required for detonation the phenomena which ensue depend upon the strength of the shock wave and the nature of the medium. A zone of combustion, accompanied by a build‐up of the pressure, develops in the wake of the shock front. This may lead to a smooth acceleration of the latter until detonation is established; shock waves may be formed which overtake the front and cause detonation; or the initial shock may decay without detonation. The hydrodynamic properties of the medium are particularly important in determining the sequence of events. Composition and pressure limits are observed beyond which detonation cannot be initiated in any case. Near these limits there is always ``spin'' in the detonation, which appears on the pressure records as a periodic oscillation of the pressure for some distance behind the wave front. In these experiments the initiating shock wave was produced by a detonating mixture such as 2H₂–O₂ contained behind a Cellophane diaphragm. The strength of the shock wave was very much increased when this mixture was diluted with hydrogen.