Deflagration to detonation transition: Difference between revisions

Revision as of 04:15, 6 August 2020

Revision as of 11:34, 1 December 2020

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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|20|bar|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 |archivedatearchive-date=October 4, 2011 |archiveurlarchive-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 at present which can predict the transition phenomenon.{{citation needed|date=February 2017}}

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==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==

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| 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]]