Analysis of Flame Propagation Characteristics in a Hydrogen Engine using an Optically Accessible Engine

This study focused on the effects of hydrogen on the flame propagation characteristics and combustion characteristics of a small spark-ignition engine. The combustion flame in the cylinder was observed using a side-valve engine that allowed optical access. The fundamental characteristics of hydrogen combustion were investigated based on combustion images photographed in the cylinder with a high-speed camera and measured cylinder pressure waveforms. Experiments were conducted under various ignition timings and equivalence ratios and comparisons were made with the characteristics of an existing hydrocarbon liquid fuel. The hydrogen flame was successfully photographed, although it has been regarded as being difficult to visualize, thus enabling calculation of the flame propagation speed. As a result, it was found that the flame propagation speed of hydrogen was much faster than that of the existing hydrocarbon fuel. On the other hand, it was difficult to photograph the hydrogen flame directly in the lean region. In future studies, it will be necessary to reduce the shooting speed or to conduct investigations based on spectroscopic measurements.

Regarding hydrogen combustion, it was found that the combustible range of hydrogen was broad even when the experimental conditions were substantially varied. It was also found that the combustible period was much shorter than that of the existing hydrocarbon fuel. Misfiring and after-firing were observed in hydrogen combustion where the ignition timing was close to top dead center as well as under a lean condition. This confirmed that there are issues concerning hydrogen combustion stability under such conditions.