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Detonation

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Title: Detonation  
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Detonation

Detonation of a 500-ton TNT explosive charge during Operation Sailor Hat. The initial shock wave is visible on the water surface, and a shock condensation cloud is visible overhead.

Detonation (from Latin detonare, meaning "to expend thunder") 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 occur in both conventional solid and liquid explosives,[1] as well as in reactive gases. 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).

An extraordinary variety of fuels may occur as gases, droplet fogs, or dust suspensions. Oxidants include halogens, 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 oxygen; a more complete list is given by both Stull[2] and Bretherick.[3]

Processes involved in the transition between deflagration and detonation are covered thoroughly for gases by Nettleton.[4]

Contents

  • Theories 1
  • Applications 2
  • In engines and firearms 3
  • Etymology 4
  • See also 5
  • References 6
  • External links 7

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 confines the chemistry and diffusive transport processes to an infinitely thin zone.

A more complex theory was advanced during World War II independently by Zel'dovich, von Neumann, and W. Doering.[5][6][7] This theory, now known as ZND theory, admits finite-rate chemical reactions and thus describes a detonation as an infinitely 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.[8][9] There is also some evidence that the reaction zone is semi-metallic in some explosives.[10]

Both theories describe one-dimensional and steady wave fronts. 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.[11][12] The Wood-Kirkwood detonation theory can correct for some of these limitations.[13]

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.[14] The influence of increasing the concentration of diluent on expanding individual detonation cells has been elegantly demonstrated.[15] Similarly their size grows as the initial pressure falls.[16] 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.[17][18] To date, none has adequately described how 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 are at most one quarter as great. Therefore, detonation is most often used for explosives and the acceleration of projectiles. However, detonation waves may also be used for less destructive purposes, including deposition of coatings to a surface[19] and cleaning of equipment (e.g. slag removal[20]). Pulse detonation engines use the detonation wave for aerospace propulsion.[21] The first flight of an aircraft powered by a pulse detonation engine took place at the Mojave Air & Space Port on January 31, 2008.[22]

In engines and firearms

Unintentional detonation when deflagration is desired is a problem in some devices. In internal combustion engines it is called engine knocking or pinging or pinking, and it causes a loss of power and excessive heating of certain components. In firearms, it may cause catastrophic and potentially lethal failure.

Etymology

Classical Latin detonare means "to stop thundering", as in weather. The modern meaning developed later.

See also

References

  1. ^ Fickett; Davis (1979). Detonation. Univ. California Press.  
  2. ^ Stull (1977). Fundamentals of fire and explosion. Monograph Series 10. A.I.Chem.E. p. 73. 
  3. ^ Bretherick (1979). Handbook of Reactive Chemical Hazards. London: Butterworths.  
  4. ^ Nettleton (1987). Gaseous Detonations: Their Nature, Effects and Control. London: Butterworths.  
  5. ^ Zel'dovich; Kompaneets (1960). Theory of Detonation. New York: Academic Press.  
  6. ^ von Neumann. Progress report on the theory of detonation waves, OSRD Report No. 549 (Report). 
  7. ^ Doring, W. (1943). "Über den Detonationsvorgang in Gasen". Annalen der Physik 43 (6–7): 421.  
  8. ^ Chapman, David Leonard (January 1899). "On the rate of explosion in gases". Philosophical Magazine. Series 5 (London: Taylor & Francis) 47 (284): 90–104.  
  9. ^ Jouguet, Jacques Charles Emile (1905). "Sur la propagation des réactions chimiques dans les gaz" [On the propagation of chemical reactions in gases] (PDF). Journal des Mathématiques Pures et Appliquées. 6 1: 347–425.  Continued in Continued in Jouguet, Jacques Charles Emile (1906). "Sur la propagation des réactions chimiques dans les gaz" [On the propagation of chemical reactions in gases] (PDF). Journal des Mathématiques Pures et Appliquées. 6 2: 5–85. 
  10. ^ Reed, Evan J.; Riad Manaa, M.; Fried, Laurence E.; Glaesemann, Kurt R.; Joannopoulos, J. D. (2007). "A transient semimetallic layer in detonating nitromethane". Nature Physics 4 (1): 72–76.  
  11. ^ Edwards, D.H., Thomas, G.O., and Nettleton, M.A. (1979). "The Diffraction of a Planar Detonation Wave at an Abrupt Area Change". Journal of Fluid Mechanics 95 (1): 79–96.  
  12. ^ D. H. Edwards; G. O. Thomas; M. A. Nettleton (1981). A. K. Oppenheim; N. Manson; R.I. Soloukhin; J.R. Bowen, eds. "Diffraction of a Planar Detonation in Various Fuel-Oxygen Mixtures at an Area Change". Progress in Astronautics & Aeronautics 75: 341.  
  13. ^ Glaesemann, Kurt R.; Fried, Laurence E. (2007). "Improved wood–kirkwood detonation chemical kinetics". Theoretical Chemistry Accounts 120 (1–3): 37–43.  
  14. ^ Nettleton, M. A. (1980). "Detonation and flammability limits of gases in confined and unconfined situations". Fire prevention science and technology (Fire Prevention Society (UK)) (23): 29.  
  15. ^ Munday, G., Ubbelohde, A.R., and Wood, I.F. (1968). "Fluctuating Detonation in Gases". Proceedings of the Royal Society A 306 (1485): 171–178.  
  16. ^ Barthel, H. O. (1974). "Predicted Spacings in Hydrogen-Oxygen-Argon Detonations". Physics of Fluids 17 (8): 1547–1553.  
  17. ^ Oran; Boris (1987). Numerical Simulation of Reactive Flows. Elsevier Publishers. 
  18. ^ Sharpe, G.J., and Quirk, J.J. (2008). "Nonlinear cellular dynamics of the idealized detonation model: Regular cells". Combustion Theory and Modelling 12 (1): 1–21.  
  19. ^ Nikolaev, Yu.A., Vasil'ev, A.A., and Ul'yanitskii, B.Yu. (2003). "Gas Detonation and its Application in Engineering and Technologies (Review)". Combustion, Explosion, and Shock Waves 39 (4): 382–410.  
  20. ^ Huque, Z., Ali, M.R., and Kommalapati, R. (2009). "Application of pulse detonation technology for boiler slag removal". Fuel Processing Technology 90 (4): 558–569.  
  21. ^ Kailasanath, K. (2000). "Review of Propulsion Applications of Detonation Waves". AIAA Journal 39 (9): 1698–1708.  
  22. ^ Norris, G. (2008). "Pulse Power: Pulse Detonation Engine-powered Flight Demonstration Marks Milestone in Mojave". Aviation Week & Space Technology 168 (7): 60. 

External links

  • Youtube video demonstrating physics of a blast wave
  • GALCIT Explosion Dynamics Laboratory Detonation Database
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