Fine cellular structures produced by marginal detonations

A new regime of unstable detonation near the propagation limits was observed experimentally in a Aat channel. Highly resolved, two-dimensional reactive Navier-Stokes numerical simulations with one-step Arrhenius kinetics were used to reproduce and analyze the detonation structures involved in this regime. The regime included three kinds of detonation instability: (1) the primary instability, which causes detonation waves moving in transverse directions (transverse detonations) to appear and disappear at regular intervals behind the leading shock; (2) the instability of the overdriven parts of the leading front, which is responsible for the formation of secondary detonation cells that coexist with transverse detonation waves; and (3) the instability of transverse detonations, which produces the fine structure called transverse detonation cells. Numerical simulations showed that transverse detonations appeared when a large induction zone formed behind the leading shock. The resulting reaction-zone structure was similar to that observed for spin detonations. The transverse detonation wave burned most of the material in the induction zone, thus preventing the Formation of large unreacted pockets and leaving behind only thin tails of unreacted material. The material involved in transverse detonations was compressed by two shocks, which makes transverse detonation waves more unstable than the overdriven parts of the leading detonation front.