A review on ignition in expanding gaseous media.

Fundamental research on detonation is relevant to industrial safety issues, propulsion and energy production applications, and internal combustion engines. Detonation waves are intrinsically unsteady and may rapidly decelerate under certain circumstances. Fluid elements traveling behind these waves can undergo strong gas dynamical volumetric expansion, which can ultimately lead to quenching. More generally, critical ignition in expanding media results from the competition between expansion and chemical energy release. While the pioneering work by Lundstrom and Oppenheim investigated the role of unsteadiness on detonation dynamics both experimentally and numerically, studies on ignition quenching by the volumetric expansion mechanism has been essentially limited to theoretical and numerical approaches. Studies have converged towards the concept of critical decay rate (CDR), and of critical Damköhler number. The CDR theory incorporates the ignition delay-time and the characteristic time of shock speed decay for identifying the threshold for successful ignition, while the Damköhler number is defined as the ratio of characteristic expansion time over characteristic chemical time. While the majority of early studies only considered globalized reaction models and investigated mixtures with a single step of heat release, more recent studies have employed detailed chemical mechanisms and included mixtures with non-monotonous energy release profiles. Practical consequences of ignition in expanding media under conditions relevant to water hammer, high-pressure hydrogen jet, and deflagration to detonation transition in obstructed channels are also summarized. [ABSTRACT FROM AUTHOR]