Hydrogen minimum ignition energy

Relationship between minimum ignition energy and equivalence ratio for hydrogen-air and methane-air mixtures. 

Hydrogen is produced or used in gas or liquid form in a number of processes. Hydrogen is a colorless, odorless gas that is easily ignited over a wide flammable range. Hydrogen burns very rapidly and cleanly in air with a nearly invisible clear blue flame. It has flammable limits of 4-74% in air and minimum ignition energy of 0.02 mj, compared to 0.25 mj for typical hydrocarbons. 

Ono, R., Nifuku, M., Fujiwara, S., Horiguchi, S., Oda, T., 2(X)7. Minimum ignition energy of hydrogen-air mixture effects of humidity and spark duration. Journal of Electrostatics 65 (2), 87-93. 

In hydrogenous diluted mixtures, in particular, in (H2 + CO2) mixtures, the laser ignition energy measured data also correspond to a U-shaped relation. It follows from Fig. 4.19 that the minimum ignition energy increases and the area of the measured data narrows when the mixture is diluted by CO2. 

The explosion of an unconfined hydrogen gas doud in the presence of a weak ignition source was never observed to have turned into a detonation [45]. The ignition energy required for a direct detonation can only be provided by either an intensive turbulent hot gas jet or by an explosive. For a stoichiometric mixture, the minimum energy was experimentally determined to be 4.7 kJ ( 1 g TNT). A methane-air mixture even requires... 

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