The Hydrogen Assisted let ignition (HAJI) is a physico-chemical combustion enhancement system developed at the University of Melbourne. jet ignition can ignite ultra-lean air/fuel mixtures which are far beyond the stable ignition limit of a spark plug. jet ignition may further enhance the combustion properties of hydrogen enabling the development of a diesel-like, almost throttle-less, control of load by quantity of fuel injected for higher thermal efficiencies all over the range of loads. The object of this paper is to show the benefits of jet ignition and present the latest results obtained on a four cylinder engine having the jet ignition coupled with cryogenic hydrogen injection and turbo charging. (C) 2009 International Association for Hydrogen Energy, Published by Elsevier Ltd. All rights reserved.