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

In recent years, the progress of global warming and the response to environmental problems have become important global issues, and efforts are being made to achieve carbon neutrality. In this context, the automotive and energy industries, which are required to reduce carbon dioxide emissions, have an urgent need to move away from fossil fuels. Especially in small engines, efficiency and cleanliness are important themes, and the introduction of hydrogen fuel is attracting attention as one solution to this. Hydrogen does not emit carbon dioxide when combustion and is considered to be a clean energy source, but due to the difference in characteristics from hydrocarbon fuels used in the past, there are still many unclear points about its combustion behavior and application to engines, and this information is indispensable for improving the performance and efficient operation of hydrogen engines. Therefore, in this study, we investigated the effect of hydrogen on flame propagation and combustion characteristics of spark ignition engines. For the experiment, a side valve engine that can be optically visualized was used, the combustion process was photographed with a high-speed camera, and the flame propagation speed was calculated through in-cylinder data and camera image analysis. In the experiment, we investigated the difference in combustion characteristics when the hydrogen equivalents ratio and ignition timing are changed. From the experimental results, it was confirmed that the flame propagation speed of hydrogen is significantly faster than that of conventional gasoline, and it was also revealed that the ignition timing of hydrogen fuel can be burned over a wider range than conventional gasoline.