Research on evaluation of hydrogen jet behavior and assessment of cooling loss reduction by measuring local heat flux in direct injection hydrogen engines

The authors have proposed a new combustion process called the Plume Ignition Combustion Concept (PCC), in which a plume of the hydrogen jet is spark-ignited just after hydrogen is injected to accomplish combustion of a plume of rich mixture. With an optimal combination of injection timing, ignition timing and controlled jet geometry, this combustion process markedly improved thermal efficiency by reducing cooling loss which is an essential element to be reduced for improving thermal efficiency in hydrogen engine. In this study, in order to evaluate the cooling loss in hydrogen engine, characteristics of local cooling loss of PCC combustion are evaluated by measuring heat flux in two locations, one in the leading location and the others in the trailing location in the combustion chamber. As a result, it was found that local cooling heat flux in the leading direction of the jet injected showed extremely high level compare to trailing direction and spatially averaged cooling loss of the combustion chamber in injection angle of 15° of PCC combustion. By enlarging injection angle to 25°, thermal efficiency was improved and local heat flux in the leading direction is also mitigated. This result indicated that capturing local heat flux, especially in the leading direction of the injected jet, is a key to improve thermal efficiency.