HAJI is a physio-chemical combustion enhancement system developed by the Transport Energy Group 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.
Ignition stability is achieved by relocating the spark plug electrodes to a small prechamber which is connected to the combustion chamber via a shaped orifice. A minute quantity of hydrogen is injected into the prechamber prior to ignition, thus increasing flame kernal growth dramatically. The hydrogen rich combustion within the prechamber causes a highly turbulent jet containing chemically active species to eject from the orifice and spread into the main chamber. This physically and chemically active jet enhances the combustion of the mixture in the main chamber, providing extra-ordinary tolerance of main chamber conditions.
HAJI has been successfully used with a variety of gaseous and liquid fuels and due to its extremely stable nature is expected to allow engines to operate efficiently even on poorer quality renewable fuels. HAJI has been installed and tested on a standard16 valve SI engine, resulting in ultra lean low NOx operation. The group is also studying the cause of hydrocarbon emissions under ultra lean conditions, and working on a direct injection protoype to reduce emissions even further.
To assist in gaining understanding over the HAJI combustion process we are also working on some computational models. A quasi-dimensional model has been written based on fractal dimensions of the flame front measured using the optical access engine. Work has also been carried out with KIVA3 - a 3D-CFD code from Los Almos National Labs. An update on the progress of the KIVA simulations is available here.
