Hydrogen has very low ignition energy. The amount of energy
needed to ignite hydrogen is about one order of magnitude
less than that required for gasoline. This enables hydrogen
engines to ignite lean mixtures and ensures prompt ignition.
Unfortunately, the low ignition energy means that hot gases
and hot spots on the cylinder can serve as sources of ignition,
creating problems of premature ignition and flashback.
Preventing this is one of the challenges associated with running
an engine on hydrogen. The wide flammability range of hydrogen means that almost any mixture can be ignited by a
hot spot