Deflagration to detonation transition: Difference between revisions

Revision as of 14:56, 12 December 2021

Revision as of 14:56, 12 December 2021

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==Description==

A [[deflagration]] is characterized by a [[Speed of sound|subsonic]] flame [[propagation velocity]], typically far below {{convert|100|m/s|mph}}, and relatively modest [[overpressure]]s, typically below {{convert|0.550|kPa|psi}}. The main mechanism of combustion propagation is of a flame front that moves forward through the gas mixture - in technical terms the reaction zone (chemical combustion) progresses through the medium by processes of [[diffusion]] of [[mass transfer|heat and mass]]. In its most benign form, a deflagration may simply be a [[flash fire]].

In contrast, a [[detonation]] is characterized by [[supersonic]] flame propagation velocities, perhaps up to {{convert|2000|m/s|mph}}, and substantial overpressures, up to {{convert|202|MPa|psi}}. The main mechanism of detonation propagation is of a powerful [[pressure]] wave that compresses the unburnt gas ahead of the wave to a [[temperature]] above the [[autoignition]] temperature. In technical terms, the reaction zone (chemical combustion) is a self-driven [[shock wave]] where the reaction zone and the shock are coincident, and the chemical reaction is initiated by the [[Compression heating ignition|compressive heating]] caused by the shock wave. The process is similar to ignition in a [[Diesel engine]], but much more sudden and violent.

Under certain conditions, mainly in terms of geometrical conditions (such as partial confinement and many obstacles in the flame path that cause turbulent flame eddy currents), a subsonic flame may accelerate to supersonic speed, transitioning from deflagration to detonation. The exact mechanism is not fully understood,<ref name=GexCon>{{cite web|title=Chapter 6: Detonation |url= http://www.gexcon.com/index.php?src=handbook/GEXHBchap6.htm |website=Gexcon AS |archive-date=October 4, 2011 |archive-url=https://web.archive.org/web/20111004174240/http://www.gexcon.com/handbook/GEXHBchap6.htm}}</ref>