Minimum ignition energy

Minimum ignition energy (MIE) is the minimum amount of energy required to ignite a combustible vapor, gas or dust cloud, for example due to an electrostatic discharge. Ignition of a fuel air mixture is possible only when the rate of liberation of heat near the ingnition zone is greater than or equal to the heat loss by conduction, thus ignition energy balances the heat loss by conduction. this is known as Minimum Ignition Energy. Heat loss due to radiation is not considered and the ignition process is assumed to be staedy and one-dimensional. MIE is measured in joules (J).

Explosives, hydrogen, unsaturated hydrocarbons and alkanes in oxygen have the lowest MIE – range of ×10⁻³ to ×10⁻¹ (mJ). Alkanes in air, distillate fuels, hybrid mixtures and extremely sensitive dusts have a MIE range of ×10⁻¹ to ×10¹ (mJ). Combustible dusts have a MIE range of ×10¹ to ×10⁴ (mJ).

For most materials, the lowest ignition energy value occurs at a concentration near the midpoint between those for the lower flammable limit (LFL) and the upper flammable limit (UFL).

See also

• Hydrogen safety
• Dust explosion
• Spark plug