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, saytypically below {{convert|0.550|barkPa|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|barMPa|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 current]]scurrents), 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=GasChapter explosion6: handbookDetonation |url= http://www.gexcon.com/index.php?src=handbook/GEXHBchap6.htm|work= |publisherwebsite= Gexcon AS, Norway |accessdatearchive-date=}}{{DeadOctober 4, 2011 link|datearchive-url=May 2018https://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]]

==Applications==

The phenomenon is exploited in [[pulse detonation engine]]s, because a detonation produces a more efficient combustion of the reactants than a deflagration does, i.e. giving a higher yields. Such engines typically employ a [[Shchelkin spiral]] in the [[combustion chamber]] to facilitate the deflagration to detonation transition.<ref>{{cite conference | first = TH | last = New | authorlink = |author2=PK Panicker |author3=FK Lu |author4=H M Tsai | year = 2006| title = Experimental Investigations on DDT Enhancements by Schelkin Spirals in a PDE | conference = 44th AIAA Aerospace Sciences Meeting and Exhibit 9–12 January 2006, Reno, Nevada | url = http://arc.uta.edu/publications/cp_files/aiaa-2006-7958.pdf | format = | accessdate = | doi = | id = | oclc =}}</ref><ref>{{cite conference | first = E | last = Schultz | authorlink = |author2=E Wintenberger |author3=J Shepherd | year = 1999 | title = Investigation of Deflagration to Detonation Transition for Application to Pulse Detonation Engine Ignition Systems | conference = Proceedings of the 16th JANNAF Propulsion Symposium | url = http://www.galcit.caltech.edu/EDL/publications/reprints/jannaf99_paper.pdf | format = | accessdate = | doi = | id = | oclc =}}</ref>

The mechanism has also found military use in [[thermobaric weapon]]s.

==Related phenomena==

An analogous deflagration to detonation transition (DDT) has also been proposed for thermonuclear reactions responsible for [[supernovae]] initiation.<ref>{{cite conference | first = Vadim N. | last = Gamezo | authorlink = |author2=Oran ES | year = 2008 | title = Mechanisms for Detonation Initiation in Type Ia Supernovae | conference = American Astronomical Society, AAS Meeting #211, #162.08 | bibcode = 2008AAS...21116208G | format = | accessdate = | doi = | id = | oclc =}}</ref> This process has been called a "[[carbon detonation]]".

==See also==

*[[Zeldovich spontaneous wave]]

*[[Dust explosion]]

*[[Pressure piling]]

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==References==

{{reflist|30em}}

* {{cite book

| last = Lea

| first = CJ

| authorlink =

|author2=HS Ledin

| title = A Review of the State-of-the-Art in Gas Explosion Modelling, HSL/2002/02

| publisher = UK Health and Safety Laboratories

| year = 2002

| ___location =

| pages =

| url = http://www.hse.gov.uk/research/hsl_pdf/2002/hsl02-02.pdf

}}

| doi =

| id =

| isbn = }}

[[Category:Combustion]]