Detonation

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Detonation of TNT, and shock wave TNT detonation on Kaho'olawe Island during Operation Sailor Hat, shot Bravo, 1965.jpg
Detonation of TNT, and shock wave

Detonation (from Latin detonare  'to thunder down/forth') [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 in the range of 1 km/sec and differ from deflagrations which have subsonic flame speeds in the range of 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.

Contents

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, [9] 1906 and 1917. [10] The next advance in understanding detonation was made by John von Neumann [11] and Werner Döring [12] in the early 1940s and Yakov B. Zel'dovich and Aleksandr Solomonovich Kompaneets in the 1960s. [13]

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. [13] [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. [14] [9]

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

A controlled bomb disposal in Iraq, 2006; detonating the bomb causes fire and smoke to propel upward. Iraqi Bomb Disposal Company DVIDS19881.jpg
A controlled bomb disposal in Iraq, 2006; detonating the bomb causes fire and smoke to propel upward.

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[ citation needed ].

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[ citation needed ].

See also

Related Research Articles

<span class="mw-page-title-main">Explosive</span> Substance that can explode

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<span class="mw-page-title-main">Ammonium nitrate</span> Chemical compound with formula NH4NO3

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<span class="mw-page-title-main">Shock wave</span> Propagating disturbance

In physics, a shock wave, or shock, is a type of propagating disturbance that moves faster than the local speed of sound in the medium. Like an ordinary wave, a shock wave carries energy and can propagate through a medium but is characterized by an abrupt, nearly discontinuous, change in pressure, temperature, and density of the medium.

In spark-ignition internal combustion engines, knocking occurs when combustion of some of the air/fuel mixture in the cylinder does not result from propagation of the flame front ignited by the spark plug, but when one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front. The fuel–air charge is meant to be ignited by the spark plug only, and at a precise point in the piston's stroke. Knock occurs when the peak of the combustion process no longer occurs at the optimum moment for the four-stroke cycle. The shock wave creates the characteristic metallic "pinging" sound, and cylinder pressure increases dramatically. Effects of engine knocking range from inconsequential to completely destructive.

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<span class="mw-page-title-main">Deflagration</span> Combustion that leads on to an explosion

Deflagration is subsonic combustion in which a pre-mixed flame propagates through an explosive or a mixture of fuel and oxidizer. Deflagrations in high and low explosives or fuel–oxidizer mixtures may transition to a detonation depending upon confinement and other factors. Most fires found in daily life are diffusion flames. Deflagrations with flame speeds in the range of 1 m/s differ from detonations which propagate supersonically with detonation velocities in the range of km/s.

<span class="mw-page-title-main">Shock tube</span> Instrument

The shock tube is an instrument used to replicate and direct blast waves at a sensor or a model in order to simulate actual explosions and their effects, usually on a smaller scale. Shock tubes can also be used to study aerodynamic flow under a wide range of temperatures and pressures that are difficult to obtain in other types of testing facilities. Shock tubes are also used to investigate compressible flow phenomena and gas phase combustion reactions. More recently, shock tubes have been used in biomedical research to study how biological specimens are affected by blast waves.

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Explosive velocity, also known as detonation velocity or velocity of detonation (VoD), is the velocity at which the shock wave front travels through a detonated explosive. Explosive velocities are always faster than the local speed of sound in the material.

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<span class="mw-page-title-main">Chapman–Jouguet condition</span>

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<span class="mw-page-title-main">Flame arrester</span> Device to stop the burning of a fuel

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<span class="mw-page-title-main">Explosion</span> Sudden release of heat and gas

An explosion is a rapid expansion in volume of a given amount of matter associated with an extreme outward release of energy, usually with the generation of high temperatures and release of high-pressure gases. Explosions may also be generated by a slower expansion that would normally not be forceful, but is not allowed to expand, so that when whatever is containing the expansion is broken by the pressure that builds as the matter inside tries to expand, the matter expands forcefully. An example of this is a volcanic eruption created by the expansion of magma in a magma chamber as it rises to the surface. Supersonic explosions created by high explosives are known as detonations and travel through shock waves. Subsonic explosions are created by low explosives through a slower combustion process known as deflagration.

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The ZND detonation model is a one-dimensional model for the process of detonation of an explosive. It was proposed during World War II independently by Y. B. Zel'dovich, John von Neumann, and Werner Döring, hence the name.

Jacques Charles Émile Jouguet was a French engineer and scientist, whose name is attached to the Chapman–Jouguet condition.

<span class="mw-page-title-main">Fickett–Jacobs cycle</span>

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<span class="mw-page-title-main">Pressure gain combustion</span>

Pressure gain combustion (PGC) is the unsteady state process used in gas turbines in which gas expansion caused by heat release is constrained. First developed in the early 20th century as one of the earliest gas turbine designs, the concept was mostly abandoned following the advent of isobaric jet engines in WWII.

References

  1. ↑ Oxford Living Dictionaries. "detonate". British & World English. Oxford University Press. Archived from the original on February 22, 2019. Retrieved 21 February 2019.
  2. ↑ Handbook of Fire Protection Engineering (5 ed.). Society of Fire Protection Engineers. 2016. p. 390.
  3. ↑ Fickett, Wildon; Davis, William C. (1979). Detonation. University of California Press. ISBN   978-0-486-41456-0.
  4. ↑ Stull, Daniel Richard (1977). Fundamentals of fire and explosion. Monograph Series. Vol. 10. American Institute of Chemical Engineers. p. 73. ISBN   978-0-816903-91-7.
  5. ↑ Urben, Peter; Bretherick, Leslie (2006). Bretherick's Handbook of Reactive Chemical Hazards (7th ed.). London: Butterworths. ISBN   978-0-123725-63-9.
  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. 1 2 Jouguet, Jacques Charles Émile (1905). "Sur la propagation des réactions chimiques dans les gaz" ["On the propagation of chemical reactions in gases"](PDF). Journal de mathématiques pures et appliquées. 6. 1: 347–425. Archived from the original (PDF) on 2013-10-19. Retrieved 2013-10-19. Continued in Jouguet, Jacques Charles Émile (1906). "Sur la propagation des réactions chimiques dans les gaz" ["On the propagation of chemical reactions in gases"](PDF). Journal de mathématiques pures et appliquées. 6. 2: 5–85. Archived from the original (PDF) on 2015-10-16.
  10. ↑ Jouguet, Jacques Charles Émile (1917). L'Œuvre scientifique de Pierre Duhem, Doin.
  11. 1 2 von Neumann, John (1942). Progress report on "Theory of Detonation Waves" (Report). OSRD Report No. 549. Ascension number ADB967734. Archived from the original on 2011-07-17. Retrieved 2017-12-22.
  12. 1 2 Döring, Werner (1943). ""Über den Detonationsvorgang in Gasen"" ["On the detonation process in gases"]. Annalen der Physik. 43 (6–7): 421–436. Bibcode:1943AnP...435..421D. doi:10.1002/andp.19434350605.
  13. 1 2 Zel'dovich, Yakov B.; Kompaneets, Aleksandr Solomonovich (1960). Theory of Detonation. New York: Academic Press. ASIN   B000WB4XGE. OCLC   974679.
  14. ↑ Chapman, David Leonard (January 1899). "On the rate of explosion in gases". Philosophical Magazine. Series 5. 47 (284). London: 90–104. doi:10.1080/14786449908621243. ISSN   1941-5982. LCCN   sn86025845.
  15. ↑ 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. Bibcode:2008NatPh...4...72R. doi:10.1038/nphys806.
  16. ↑ Edwards, D. H.; Thomas, G. O. & Nettleton, M. A. (1979). "The Diffraction of a Planar Detonation Wave at an Abrupt Area Change". Journal of Fluid Mechanics. 95 (1): 79–96. Bibcode:1979JFM....95...79E. doi:10.1017/S002211207900135X. S2CID   123018814.
  17. ↑ Edwards, D. H.; Thomas, G. O.; Nettleton, M. A. (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: 341–357. doi:10.2514/5.9781600865497.0341.0357. ISBN   978-0-915928-46-0.
  18. ↑ Glaesemann, Kurt R.; Fried, Laurence E. (2007). "Improved Wood–Kirkwood detonation chemical kinetics". Theoretical Chemistry Accounts. 120 (1–3): 37–43. doi:10.1007/s00214-007-0303-9. S2CID   95326309.
  19. ↑ Nettleton, M. A. (1980). "Detonation and flammability limits of gases in confined and unconfined situations". Fire Prevention Science and Technology (23): 29. ISSN   0305-7844.
  20. ↑ Munday, G.; Ubbelohde, A. R. & Wood, I. F. (1968). "Fluctuating Detonation in Gases". Proceedings of the Royal Society A. 306 (1485): 171–178. Bibcode:1968RSPSA.306..171M. doi:10.1098/rspa.1968.0143. S2CID   93720416.
  21. ↑ Barthel, H. O. (1974). "Predicted Spacings in Hydrogen-Oxygen-Argon Detonations". Physics of Fluids. 17 (8): 1547–1553. Bibcode:1974PhFl...17.1547B. doi:10.1063/1.1694932.
  22. ↑ Oran; Boris (1987). Numerical Simulation of Reactive Flows. Elsevier Publishers.
  23. ↑ Sharpe, G. J.; Quirk, J. J. (2008). "Nonlinear cellular dynamics of the idealized detonation model: Regular cells" (PDF). Combustion Theory and Modelling. 12 (1): 1–21. Bibcode:2008CTM....12....1S. doi:10.1080/13647830701335749. S2CID   73601951. Archived (PDF) from the original on 2017-07-05.
  24. ↑ Handbook of Fire Protection Engineering (5 ed.). Society of Fire Protection Engineers. 2016. Table 70.1 Explosivity Data for representative powders and dusts, page 2770.
  25. ↑ Nikolaev, Yu. A.; Vasil'ev, A. A. & Ul'yanitskii, B. Yu. (2003). "Gas Detonation and its Application in Engineering and Technologies (Review)". Combustion, Explosion, and Shock Waves. 39 (4): 382–410. doi:10.1023/A:1024726619703. S2CID   93125699.
  26. ↑ Huque, Z.; Ali, M. R. & Kommalapati, R. (2009). "Application of pulse detonation technology for boiler slag removal". Fuel Processing Technology. 90 (4): 558–569. doi:10.1016/j.fuproc.2009.01.004.
  27. ↑ Kailasanath, K. (2000). "Review of Propulsion Applications of Detonation Waves". AIAA Journal. 39 (9): 1698–1708. Bibcode:2000AIAAJ..38.1698K. doi:10.2514/2.1156.
  28. ↑ Norris, G. (2008). "Pulse Power: Pulse Detonation Engine-powered Flight Demonstration Marks Milestone in Mojave". Aviation Week & Space Technology. 168 (7): 60.
  29. ↑ Simon, Andre. "Don't Waste Your Time Listening for Knock..." High Performance Academy.
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