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Deflagration (Lat: de + flagrare, 'to burn down') is subsonic combustion in which a pre-mixed flame propagates through an explosive or a mixture of fuel and oxidizer. [ 1 ] [ 2 ] Deflagrations in high and low explosives or fuel–oxidizer mixtures may transition to a detonation depending upon confinement and other factors.
The Chapman–Jouguet condition holds approximately in detonation waves in high explosives.It states that the detonation propagates at a velocity at which the reacting gases just reach sonic velocity (in the frame of the leading shock wave) as the reaction ceases.
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.
A schematic diagram of a shock wave situation with the density , velocity , and temperature indicated for each region.. The Rankine–Hugoniot conditions, also referred to as Rankine–Hugoniot jump conditions or Rankine–Hugoniot relations, describe the relationship between the states on both sides of a shock wave or a combustion wave (deflagration or detonation) in a one-dimensional flow in ...
The simplest theory to predict the behaviour of detonations in gases is known as the Chapman–Jouguet (CJ) condition, 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.
The velocity of detonation is an important indicator for overall energy and power of detonation, and in particular for the brisance or shattering effect of an explosive which is due to the detonation pressure. The pressure can be calculated using Chapman-Jouguet theory from the velocity and density.
A high explosive violent reaction (HEVR) includes reactions ranging from a fast deflagration of the high explosive (HE), up to and including a detonation of the high explosive. The explosive wave may be subsonic or supersonic.
A substance is characterized by a burn rate vs. pressure chart and burn rate vs temperature chart. Higher burn rate than the speed of sound in the material (usually several km/s): "detonation" A few meters per second: "deflagration" A few centimeters per second: "burn" or "smolder" 0.01 mm/s to 100 mm/s: "decomposing rapidly" to characterise it.