Deflagration

A deflagration (from Latin deflagrare = to burn off) is a rapid combustion process in which the explosion pressure is only caused by the emerging and expanding gases . The propagation takes place through the heat released during the reaction, in other words the ignition of the unburned mixture takes place through the heating of the mixture in the flame front.

In the case of deflagration, the combustion pressure (in air under initial atmospheric conditions) is usually in the order of 1 MPa (10 bar), but can be higher depending on the fuel (e.g. in nuclear reactions; see also Supernova ). The combustion takes place at a speed that is lower than the speed of sound in the burning medium.

At higher speeds , one speaks of a detonation , whereby the combustion mechanism changes from the heating of the unburned mixture to shock wave-induced combustion. Detonations in pipelines can result in pressures that are many times higher than the explosion pressures in the case of deflagrations. During the detonation, the pressure wave is superimposed on the temperature-related volume expansion that occurs during the explosion reaction.

In the German-speaking world, deflagration is also the name given to the automatically continuous decomposition of a solid, which can be accompanied by the release of heat or gas.

Deflagration is also understood to mean a decomposition reaction in the absence of oxygen.

Deflagration

From a deflagration is spoken as it passes through the combustion reaction, although to a volume expansion, but does not come to a relevant pressure build-up. The speed of propagation and the associated expansion or compression of the gases produced can assume a speed of 0.01 m / s - 1 m / s. The previous definition of a maximum pressure of less than 100 kPa (1 bar) is no longer in use.

Examples are deflagrations in combustion systems, in which a dangerous explosive atmosphere can occur if there is no pre-ventilation (unburned fuel ) or due to incomplete combustion ( carbon monoxide formation). If this atmosphere is ignited on a hot surface or when the burner is started repeatedly, a pressure wave is created which is partially relaxed towards the chimney and possibly via explosion flaps. Since the combustion chambers are usually not designed for a pressure load, deflagrations can cause considerable damage.

See also

• Gas cloud explosion

literature

• Paul A. Tipler, Gene Mosca, Jenny Wagner (eds.): Physics for scientists and engineers. 7th edition. Springer Spektrum Fachverlag, Berlin / Heidelberg 2015, ISBN 978-3-642-54165-0 .
• Stephan Löhmer: Risk minimization through fire and explosion protection. ETH Verlag, Zurich 1995, ISBN 3-7281-2194-0 .
• Roy Bergdoll, Sebastian Breitenbach: Die Roten Hefte, Issue 1 - Burning and Extinguishing . 18th edition. Kohlhammer, Stuttgart 2019, ISBN 978-3-17-026968-2 .

Web links

• Basics of explosion protection for beginners (accessed on February 13, 2020)
• Deflagration-to-Detonation Transition and Detonation Propagation in H2-Air Mixtures with Transverse Concentration Gradients (accessed February 13, 2020)
• Flame Acceleration and Deflagration-to-Detonation Transition in Nuclear Safety (accessed February 13, 2020)
• Spread of deflagrations in closed long pipelines (accessed February 13, 2020)
• Analysis of the effects of disruptive material and energy releases in the process industry (accessed on February 13, 2020)

Individual evidence

1. ↑ Explosion. In: Schülerduden chemistry.