World Library  
Flag as Inappropriate
Email this Article

Deflagration to detonation transition

Article Id: WHEBN0023375296
Reproduction Date:

Title: Deflagration to detonation transition  
Author: World Heritage Encyclopedia
Language: English
Subject: Explosives engineering, Combustion, Pentaerythritol tetranitrate
Publisher: World Heritage Encyclopedia

Deflagration to detonation transition

Deflagration to detonation transition (DDT) refers to a phenomenon in 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 combustion. The effects of a detonation are usually devastating.

A deflagration is characterized by a subsonic flame propagation velocity, typically far below 100 m/s, and relatively modest overpressures, say below 0.5 bar. 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 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 2000 m/s, and substantial overpressures, up to 20 bars. The main mechanism of combustion 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 compressive heating caused by the shock wave.

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,[1] 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.

A deflagration to detonation transition has been a feature of several major industrial accidents

The phenomenon is exploited in pulse detonation engines 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.[2][3]

The mechanism has found military use in the thermobaric weapon.

A deflagration to detonation transition (DDT) has also been proposed for thermonuclear reactions responsible for supernovae initiation;[4] see also Carbon detonation. Apart from the name, this phenomenon is completely unrelated to the chemical combustion and flame acceleration phenomenon.

See also


  1. ^ "Gas explosion handbook". Gexcon AS, Norway. 
  2. ^ New, TH; PK Panicker; FK Lu; H M Tsai (2006). "Experimental Investigations on DDT Enhancements by Schelkin Spirals in a PDE". 44th AIAA Aerospace Sciences Meeting and Exhibit 9–12 January 2006, Reno, Nevada. 
  3. ^ Schultz, E; E Wintenberger; J Shepherd (1999). "Investigation of Deflagration to Detonation Transition for Application to Pulse Detonation Engine Ignition Systems". Proceedings of the 16th JANNAF Propulsion Symposium. 
  4. ^ Gamezo, Vadim N.; Oran ES (2008). "Mechanisms for Detonation Initiation in Type Ia Supernovae". American Astronomical Society, AAS Meeting #211, #162.08. 
  • Lea, CJ; HS Ledin (2002). A Review of the State-of-the-Art in Gas Explosion Modelling, HSL/2002/02. UK Health and Safety Laboratories. 
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.

Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.