Deflagration to detonation transition: Difference between revisions

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{{Short description|Type of explosion}}

{{more citations needed|date=February 2017}}

'''Deflagration to detonation transition''' ('''DDT''') refers to a phenomenon in [[Combustion|ignitable]] mixtures of a [[flammable]] gas and [[air]] (or [[oxygen]]) when a sudden transition takes place from a [[deflagration]] type of [[combustion]] to a [[detonation]] type of explosion.

==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 front 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>

and while existing theories are able to explain and model both deflagrations and detonations, there is no theory {{as of|2023|alt=at present}} which can predict the transition phenomenon.{{citation needed|date=February 2017}}

==Examples==

A deflagration to detonation transition has been a feature of several major [[industrial accident]]s:

* [[1970 Propanepropane vapourvapor cloud explosion in Port Hudson]]

* [[Flixborough disaster]]

* [[Phillips disaster of 1989]] in Pasadena, Texas

* Damage observed in the [[Buncefield fire]]

* [[2020 Beirut explosions|2020 Beirut Explosions]]

==Applications==

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==See also==

*[[Zeldovich spontaneous wave]]

*[[Dust explosion]]

*[[Pressure piling]]