Detonation Explained

Detonation [1] is a type of combustion involving a supersonic exothermic front accelerating through a medium that eventually drives a shock front propagating directly in front of it. Detonations propagate supersonically through shock waves with speeds about 1 km/sec and differ from deflagrations which have subsonic flame speeds about 1 m/sec.[2] Detonation is an explosion of fuel-air mixture. Compared to deflagration, detonation doesn't need to have an external oxidizer. Oxidizers and fuel mix when deflagration occurs. Detonation is more destructive than deflagrations. In detonation, the flame front travels through the air-fuel faster than sound; while in deflagration, the flame front travels through the air-fuel slower than sound.

Detonations occur in both conventional solid and liquid explosives,[3] as well as in reactive gases. TNT, dynamite, and C4 are examples of high power explosives that detonate. The velocity of detonation in solid and liquid explosives is much higher than that in gaseous ones, which allows the wave system to be observed with greater detail (higher resolution).

A very wide variety of fuels may occur as gases (e.g. hydrogen), droplet fogs, or dust suspensions. In addition to dioxygen, oxidants can include halogen compounds, ozone, hydrogen peroxide, and oxides of nitrogen. Gaseous detonations are often associated with a mixture of fuel and oxidant in a composition somewhat below conventional flammability ratios. They happen most often in confined systems, but they sometimes occur in large vapor clouds. Other materials, such as acetylene, ozone, and hydrogen peroxide, are detonable in the absence of an oxidant (or reductant). In these cases the energy released results from the rearrangement of the molecular constituents of the material.[4] [5]

Detonation was discovered in 1881 by four French scientists Marcellin Berthelot and Paul Marie Eugène Vieille[6] and Ernest-François Mallard and Henry Louis Le Chatelier.[7] The mathematical predictions of propagation were carried out first by David Chapman in 1899[8] and by Émile Jouguet in 1905, 1906 and 1917.[9] The next advance in understanding detonation was made by John von Neumann and Werner Döring in the early 1940s and Yakov B. Zel'dovich and Aleksandr Solomonovich Kompaneets in the 1960s.

Theories

The simplest theory to predict the behaviour of detonations in gases is known as Chapman–Jouguet (CJ) theory, developed around the turn of the 20th century. This theory, described by a relatively simple set of algebraic equations, models the detonation as a propagating shock wave accompanied by exothermic heat release. Such a theory describes the chemistry and diffusive transport processes as occurring abruptly as the shock passes.

A more complex theory was advanced during World War II independently by Zel'dovich, von Neumann, and Döring.[10] [11] [12] This theory, now known as ZND theory, admits finite-rate chemical reactions and thus describes a detonation as an infinitesimally thin shock wave, followed by a zone of exothermic chemical reaction. With a reference frame of a stationary shock, the following flow is subsonic, so that an acoustic reaction zone follows immediately behind the lead front, the Chapman–Jouguet condition.[13] [14]

There is also some evidence that the reaction zone is semi-metallic in some explosives.[15]

Both theories describe one-dimensional and steady wavefronts. However, in the 1960s, experiments revealed that gas-phase detonations were most often characterized by unsteady, three-dimensional structures, which can only, in an averaged sense, be predicted by one-dimensional steady theories. Indeed, such waves are quenched as their structure is destroyed.[16] [17] The Wood-Kirkwood detonation theory can correct some of these limitations.[18]

Experimental studies have revealed some of the conditions needed for the propagation of such fronts. In confinement, the range of composition of mixes of fuel and oxidant and self-decomposing substances with inerts are slightly below the flammability limits and, for spherically expanding fronts, well below them.[19] The influence of increasing the concentration of diluent on expanding individual detonation cells has been elegantly demonstrated.[20] Similarly, their size grows as the initial pressure falls.[21] Since cell widths must be matched with minimum dimension of containment, any wave overdriven by the initiator will be quenched.

Mathematical modeling has steadily advanced to predicting the complex flow fields behind shocks inducing reactions.[22] [23] To date, none has adequately described how the structure is formed and sustained behind unconfined waves.

Applications

When used in explosive devices, the main cause of damage from a detonation is the supersonic blast front (a powerful shock wave) in the surrounding area. This is a significant distinction from deflagrations where the exothermic wave is subsonic and maximum pressures for non-metal specks of dust are approximately 7–10 times atmospheric pressure.[24] Therefore, detonation is a feature for destructive purposes while deflagration is favored for the acceleration of firearms' projectiles. However, detonation waves may also be used for less destructive purposes, including deposition of coatings to a surface[25] or cleaning of equipment (e.g. slag removal[26]) and even explosively welding together metals that would otherwise fail to fuse. Pulse detonation engines use the detonation wave for aerospace propulsion.[27] The first flight of an aircraft powered by a pulse detonation engine took place at the Mojave Air & Space Port on January 31, 2008.[28]

In engines and firearms

Unintentional detonation when deflagration is desired is a problem in some devices. In Otto cycle, or gasoline engines it is called engine knocking or pinging, and it causes a loss of power. It can also cause excessive heating, and harsh mechanical shock that can result in eventual engine failure.[29] In firearms, it may cause catastrophic and potentially lethal failure.

Pulse detonation engines are a form of pulsed jet engine that has been experimented with on several occasions as this offers the potential for good fuel efficiency.

See also

External links

Notes and References

  1. Web site: detonate . https://web.archive.org/web/20190222042210/https://en.oxforddictionaries.com/definition/detonate . dead . February 22, 2019 . Oxford Living Dictionaries . Oxford Living Dictionaries . British & World English . Oxford University Press . 21 February 2019 .
  2. Book: Handbook of Fire Protection Engineering . 2016 . Society of Fire Protection Engineers . 390 . 5 .
  3. Book: Fickett . Wildon . Davis . William C. . Detonation . University of California Press . 1979 . 978-0-486-41456-0 .
  4. Book: Stull, Daniel Richard . Fundamentals of fire and explosion . . Monograph Series . 10 . 73 . 1977 . 978-0-816903-91-7 .
  5. Book: Bretherick's Handbook of Reactive Chemical Hazards . Butterworths . London . 2006 . 978-0-123725-63-9 . Peter . Urben . Leslie . Bretherick . 7th .
  6. Berthelot, Marcellin; and Vieille, Paul Marie Eugène; « Sur la vitesse de propagation des phénomènes explosifs dans les gaz » ["On the velocity of propagation of explosive processes in gases"], Comptes rendus hebdomadaires des séances de l'Académie des sciences, vol. 93, pp. 18–22, 1881
  7. Mallard, Ernest-François; and Le Chatelier, Henry Louis; « Sur les vitesses de propagation de l’inflammation dans les mélanges gazeux explosifs » ["On the propagation velocity of burning in gaseous explosive mixtures"], Comptes rendus hebdomadaires des séances de l'Académie des sciences, vol. 93, pp. 145–148, 1881
  8. Chapman, David Leonard (1899). "VI. On the rate of explosion in gases", The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science, 47(284), 90-104.
  9. Jouguet, Jacques Charles Émile (1917). L'Œuvre scientifique de Pierre Duhem, Doin.
  10. Book: Zel'dovich . Yakov B. . Kompaneets . Aleksandr Solomonovich . Theory of Detonation . Academic Press . New York . 1960 . B000WB4XGE . 974679 .
  11. 1942 . von Neumann . John . Progress report on "Theory of Detonation Waves" . OSRD Report No. 549. Ascension number ADB967734 . 2017-12-22 . 2011-07-17 . https://web.archive.org/web/20110717145048/http://oai.dtic.mil/oai/oai?verb=getRecord . dead .
  12. Döring . Werner . Annalen der Physik . 43 . 421–436 . 1943 . 10.1002/andp.19434350605 . "Über den Detonationsvorgang in Gasen" . "On the detonation process in gases" . 6–7 . 1943AnP...435..421D .
  13. Chapman . David Leonard . On the rate of explosion in gases . Philosophical Magazine . London . Series 5 . 47 . 284 . 90–104 . January 1899 . 1941-5982 . sn86025845 . 10.1080/14786449908621243 .
  14. Jouguet . Jacques Charles Émile . Sur la propagation des réactions chimiques dans les gaz . Journal de mathématiques pures et appliquées . 6 . 1 . 347–425 . 1905 . "On the propagation of chemical reactions in gases" . dead . https://web.archive.org/web/20131019171453/http://math-doc.ujf-grenoble.fr/JMPA/PDF/JMPA_1905_6_1_A9_0.pdf . 2013-10-19 . 2013-10-19 . Continued in Jouguet . Jacques Charles Émile . Journal de mathématiques pures et appliquées . 6 . 2 . 5–85 . 1906 . Sur la propagation des réactions chimiques dans les gaz . "On the propagation of chemical reactions in gases" . dead . https://web.archive.org/web/20151016140100/http://sites.mathdoc.fr/JMPA/PDF/JMPA_1906_6_2_A1_0.pdf . 2015-10-16 .
  15. 10.1038/nphys806 . A transient semimetallic layer in detonating nitromethane . 2007 . Reed . Evan J. . Riad Manaa . M. . Fried . Laurence E. . Glaesemann . Kurt R. . Joannopoulos . J. D. . Nature Physics . 4 . 72–76 . 1 . 2008NatPh...4...72R .
  16. Edwards . D. H. . Thomas . G. O. . Nettleton . M. A. . amp . The Diffraction of a Planar Detonation Wave at an Abrupt Area Change . Journal of Fluid Mechanics . 95 . 1 . 79–96 . 1979 . 10.1017/S002211207900135X . 1979JFM....95...79E . 123018814 .
  17. 10.2514/5.9781600865497.0341.0357 . 75 . Progress in Astronautics & Aeronautics . 1981 . Diffraction of a Planar Detonation in Various Fuel-Oxygen Mixtures at an Area Change . 978-0-915928-46-0 . 341–357 . A. K. Oppenheim . N. Manson . R. I. Soloukhin . J. R. Bowen . Edwards . D. H. . Thomas . G. O. . Nettleton . M. A. .
  18. 10.1007/s00214-007-0303-9 . Improved Wood–Kirkwood detonation chemical kinetics . 2007 . Glaesemann . Kurt R. . Fried . Laurence E. . Theoretical Chemistry Accounts . 120 . 37–43 . 1–3 . 95326309 .
  19. Nettleton . M. A. . Detonation and flammability limits of gases in confined and unconfined situations . Fire Prevention Science and Technology . 0305-7844 . 29 . 1980 . 23 .
  20. Munday . G. . Ubbelohde . A. R. . Wood . I. F. . amp . Fluctuating Detonation in Gases . Proceedings of the Royal Society A . 306 . 171–178 . 1968 . 10.1098/rspa.1968.0143 . 1485 . 1968RSPSA.306..171M . 93720416 .
  21. Barthel . H. O. . Predicted Spacings in Hydrogen-Oxygen-Argon Detonations . Physics of Fluids . 17 . 8 . 1547–1553 . 1974 . 10.1063/1.1694932 . 1974PhFl...17.1547B .
  22. Book: Oran . Boris . Numerical Simulation of Reactive Flows . Elsevier Publishers . 1987 .
  23. Sharpe . G. J. . Quirk . J. J. . Nonlinear cellular dynamics of the idealized detonation model: Regular cells . Combustion Theory and Modelling . 12 . 1 . 1–21 . 2008 . 10.1080/13647830701335749 . 2008CTM....12....1S . 73601951 . live . https://web.archive.org/web/20170705073324/http://eprints.whiterose.ac.uk/7931/1/cells_revised.pdf . 2017-07-05.
  24. Book: Handbook of Fire Protection Engineering . 2016 . 5 . Society of Fire Protection Engineers . Table 70.1 Explosivity Data for representative powders and dusts, page 2770 .
  25. Nikolaev . Yu. A. . Vasil'ev . A. A. . Ul'yanitskii . B. Yu. . amp . Gas Detonation and its Application in Engineering and Technologies (Review) . Combustion, Explosion, and Shock Waves . 39 . 4 . 382–410 . 2003 . 10.1023/A:1024726619703 . 93125699 .
  26. Huque . Z. . Ali . M. R. . Kommalapati . R. . amp . Application of pulse detonation technology for boiler slag removal . Fuel Processing Technology . 90 . 4 . 558–569 . 2009 . 10.1016/j.fuproc.2009.01.004 .
  27. Kailasanath . K. . Review of Propulsion Applications of Detonation Waves . AIAA Journal . 39 . 9 . 1698–1708 . 2000 . 10.2514/2.1156 . 2000AIAAJ..38.1698K .
  28. Norris . G. . Pulse Power: Pulse Detonation Engine-powered Flight Demonstration Marks Milestone in Mojave . Aviation Week & Space Technology . 168 . 7 . 60 . 2008 .
  29. Web site: Don't Waste Your Time Listening for Knock... . High Performance Academy . Andre . Simon .

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