Abstract
Keywords Thermal efficiency, nitrogen oxides, lean burn, alternative fuels, hydrogen assisted ignition
Abstract Over a decade of research has gone into the development of combustion initiated with hydrogen assisted jet ignition (HAJI). This paper reviews the research from its original conception to the latest achievements. HAJI uses a small pre-chamber built into a standard spark plug body into which a hydrogen is injected late in the compression process. On ignition the OH and H rich jets traversing the combustion chamber accelerate lean main-chamber flames by up to six times their normal flame speed, allowing repeatable ignition of mixtures as lean as lambda five for hydrocarbons and seven for hydrogen. Thus HAJI has many of the desirable virtues of HCCI engine but with ability to operate without throttling over the entire load-speed range. Application is described in this paper to two research engines. Homogeneous charge preparation and direct liquid and gaseous fuel injection have been compared. With DI, HC emissions have been reduced to one third those of a stoichiometric homogenous fuelling, with gaseous fuelling (LPG, hydrogen and natural gas) lower emissions had higher efficiency have been obtained. A peak thermal efficiency of 42% was achieved. Moreover, 0.6 g/kWh HC and 0.005 g/kWh NOx was obtained with CNG injected at 6 MPa and an improvement of 40% in thermal efficiency at the 1500 rev/min, 300 kPa IMEP world-wide mapping point speed and load condition.