Detonation involves an exothermic front accelerating through a medium that eventually drives a shock front propagating directly in front of it. They are observed in both conventional solid and liquid explosives,[1] as well as in reactive gases. The velocity of detonations in solid and liquid explosives is much higher than that in gaseous ones, which allows far clearer resolution of the wave system in the latter.
Gaseous detonations normally occur in confined systems but are occasionally observed in large vapor clouds. Again, they are often associated with a gaseous mixture of fuel and oxidant of a composition, somewhat below conventional flammability limits. There is an extraordinary variety of fuels that may be present as gases, as droplet fogs and as dust suspensions. Other materials, such as acetylene, ozone and hydrogen peroxide are detonable in the absence of oxygen, fuller lists are given by both Stull[2] and Bretherick[3]. Oxidants include halogens, ozone, hydrogen peroxide and oxides of nitrogen and chlorine.
In terms of external damage, it is important to distinguish between detonations and deflagrations where the exothermic wave is subsonic and maximum pressures are at most a quarter[citation needed] of those generated by the former. Processes involved in the transition between deflagration and detonation are covered thoroughly by Nettleton.[4]
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French détoner, to explode; from Latin detonare, to expend thunder; from de-, ~off + tonare, to thunder
The simplest theory to predict the behavior 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]
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.[10][11]
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.[12] The influence of increasing the concentration of diluent on expanding individual detonation cells has been elegantly demonstrated.[13] Similarly their size grows as the initial pressure falls.[14] 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.[15][16] To date none has adequately described how structure is formed and sustained behind unconfined waves.
The main cause of damage from explosive devices is due to a supersonic blast front (a powerful shock wave) in the surrounding area. Therefore, the detonation is primarily associated with explosives and the acceleration of various projectiles. However, detonation waves may also be utilized for less-destructive purposes like deposition of coatings to a surface[17] or cleaning of equipment (i.e., slag removal[18]). Pulse detonation engines utilize the detonation wave for aerospace propulsion.[19] The first flight of an aircraft powered by a pulse detonation engine took place at the Mojave Air & Space Port on January 31, 2008.[20]
GALCIT Explosion Dynamics Laboratory Detonation Database
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Detonation f. (genitive Detonation, plural Detonationen)
Detonation is the explosion of an explosive. When an explosive detonates, it compresses the air around it, making a shock wave that can knock down buildings and kill people. The shock wave is made from the gases release when the explosive detonates.
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