Minimum ignition energy

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The minimum ignition energy (MIE) E min. is a safety-related parameter for assessing the ignitability of explosive atmospheres. It describes the lowest energy that is sufficient during a discharge to ignite an explosive fuel-air mixture in its most flammable composition. Combustible gases and vapors as well as dispersed dust can be used as fuel. The minimum ignition energies of gases / vapors and dusts differ fundamentally. While gases and vapors can usually be ignited with ignition energies below 1 mJ, ignition energies in the millijoule to joule range are necessary for typical dusts. In the case of gases and vapors, almost any ignition source can be regarded as effective. For dust that is blown up, the minimum ignition energy is an important parameter for the system design, since in terms of the protection concept of avoiding ignition sources, it is possible to consider the probability of the occurrence of energetically different ignition sources and their ignition effectiveness.

The EN 13821 describes the experimental determination of the MIE as follows:

The minimum ignition energy of a gas and a vapor-air mixture is the smallest possible electrical energy that occurs when a capacitor is discharged, which is the most ignitable mixture of a gas or vapor with air at atmospheric pressure (1013.25 hPa) and 20 ° C able to ignite.

Ignition volume

Mixtures of flammable gases in air generally do not ignite spontaneously, but have to be ignited by means of an ignition source. The energy required for ignition depends on the pressure and temperature, the ignition volume and the composition of the mixture. The minimum ignition energy describes the minimum amount of energy that has to be supplied to the system under otherwise ideal conditions in order to achieve ignition. However, the concept of a minimum ignition energy density makes more sense, since the existing ignition volume must be heated to a sufficiently high temperature. Is the energy supply (minimum ignition power) - d. H. Increase in temperature - sufficiently large, the ignition is initiated and a self-sustaining flame spread occurs, the mixture explodes. Due to their importance both for safety technology and for engine combustion, various ignition sources have been examined in detail. In addition to ignition on hot surfaces and ignition using focused laser radiation, electrical spark ignition is of particular importance.

Combustible dusts - dust explosion

The minimum ignition energy depends heavily on the nature of the dust such as B. the composition, the grain size distribution, the surface structure and the moisture. In general, the minimum ignition energy decreases with decreasing grain size and decreasing humidity. According to their minimum ignition energy, dusts are in the areas of the minimum ignition energy

  • MIE> 10 mJ as normally sensitive to ignition
  • 10 mJ> MIE> 3 mJ as particularly sensitive to ignition
  • MIE <3 mJ as extremely sensitive to ignition

classified.

Flammable gases and vapors

The minimum ignition energies of gases and vapors are usually one to two powers of ten lower than that of dusts. Their value depends on the concentration. A roughly parabolic course is observed between the explosion limits, the minimum of which corresponds to the most ignitable mixture with the lowest minimum ignition energy. The following tables give the minimum ignition energies for important solvents and gases.

Minimum ignition energy of various solvent vapors
solvent acetone Butanone benzene Cyclohexane Diethyl ether Ethyl acetate Ethanol n-heptane Methanol Carbon disulfide ­
Minimum ignition energy in mJ 0.55 0.27 0.20 0.22 0.19 0.46 0.28 0.24 0.20 0.009
Most ignitable mixture in% by volume 6.5 5.3 4.7 3.8 5.1 5.2 6.4 3.4 14.7 7.8
Minimum ignition energy of various gases
gas ammonia n-butane Ethane Ethene Ethine Ethylene oxide methane Propyne Propylene oxide hydrogen
Minimum ignition energy in mJ 14th 0.25 0.25 0.082 0.019 0.061 0.28 0.11 0.13 0.016
Most ignitable mixture in% by volume 20th 4.7 6.5 8.0 7.7 10.8 8.5 6.5 7.5 22nd
Minimum ignition energy of various halogenated hydrocarbons
Halogenated hydrocarbons 1,2-dichloroethane Dichloromethane Tetrafluoroethylene 1,1,1-trichloroethane Trichlorethylene
Minimum ignition energy in mJ 1.0 9300 4.1 4800 510
Most ignitable mixture in% by volume 10.5 18th - 12 26th

The value of the minimum ignition energy decreases with increasing temperature, increasing pressure and increased oxygen content.

Individual evidence

  1. ^ A b E. Brandes, W. Möller: Safety-related parameters - Volume 1: Flammable liquids and gases , Wirtschaftsverlag NW - Verlag für neue Wissenschaft GmbH, Bremerhaven 2003.
  2. ↑ Explosion-related indicators: ATEX product directive 2014/34 / EU druckgeraete-online.de, accessed February 7, 2020.
  3. ↑ Ignition volume and ignition capacity
  4. ↑ a b c BG RCI-Merkblatt T 033 Avoidance of ignition hazards due to electrostatic charges , Jedermann-Verlag 2009, ISBN 978-3-86825-103-6 , PDF download .

literature

  • Wolfgang Bartknecht: Explosion Protection - Basics and Application , Springer-Verlag 1993, ISBN 3-540-55464-5 .
  • BG RCI Leaflet R003 Safety- related parameters , Jedermann-Verlag, Heidelberg, PDF download .
  • DIN-EN 13821 Explosive atmospheres - Explosion protection - Determination of the minimum ignition energy of dust / air mixtures
  • DIN EN ISO / IEC 80079-20-2 Explosive atmospheres - Part 20-2: Material properties - Test methods for combustible dusts
  • ASTM E582 Standard test Method for Minimum Ignition Energy and Quenching Distance in Gaseous Mixtures