In order to establish hydrogen engines for practical use, it is important to overcome difficulties caused by unique characteristics of hydrogen fuel. A hydrogen engine with direct injection right before top dead center(TDC) and spark ignition has advantages such as prevention of abnormal combustion and realization of high power output near the stoichiometric air-fuel ratio, in comparison with an engine with external mixture. On the other hand, it has been pointed out that ignition and combustion for this type of hydrogen engines should be improved and that further studies on mixture formation of air and injected hydrogen are necessary for the improvement.
For the direct injection hydrogen engine, mixture is formed both by air flow inside the combustion chamber and by injected hydrogen jet. In the present study, to investigate the effect of the hydrogen jet, the jet flow under various injection conditions and with different nozzle geometries have been analyzed and its effects on ignition and combustion have been clarified. The hydrogen jet was visualized by Schlieren method, and the local concentration measurement in the jet was carried out by Rayleigh scattering method.
Since self-ignition temperature of hydrogen is 580°C [1], which is much higher than diesel fuel, the hydrogen engine for the present study is using a spark plug as an igniter[2]. In this system, stable ignition under various operating conditions is very important, and therefore wider range of stable ignition timing is required. In this paper, measured hydrogen concentration profiles in the jet will be reported as a function of injection pressure, nozzle ratio, and nozzle port geometry. The concentration profiles revealed difference in jet flow composition and provided indication as to characteristics of spark plug ignition.