Standard spark ignition systems cannot burn ultra-lean
mixtures, because combustion rate and stability deteriorate
rapidly as the mixture becomes lean. Jet ignition is one of the
main technologies that may overcome this problem by using
a different ignition process. The Hydrogen Assisted Jet Ignition
(HAJI) is a physico-chemical combustion enhancement
system developed at the University of Melbourne. The HAJI
device replaces the spark plug in otherwise standard four
stroke, spark ignition, internal combustion engines. The HAJI
system can ignite ultra-lean air/fuel mixtures which are far
beyond the stable ignition limit of a spark plug. Ultra-lean
combustion produces higher thermal efficiencies, reduced
combustion temperatures, heat transfer losses and a near
elimination of NOx emissions.