Fundamental Experimental Evaluation of Hydrogen Combustion with Low Injection Pressure Using the Focusing Compression Principle

In our laboratory, the focusing compression principle has been proposed, which is based on pulsed multi-jets of gas colliding around the chamber center. This aims to reduce the cooling loss on the chamber wall and the exhaust loss and improve the thermal efficiency. Our past studies focused on gasoline combustion experiments using the engine with the principle and suggested that the engine had the potential to achieve high thermal efficiency and knock resistance. Considering these past results and the growing interest in carbon-free fuels for net zero, in this paper, fundamental experimental evaluations of hydrogen combustion were principally conducted using the same engine with the focusing compression principle. The air was injected toward the chamber center from seven intake nozzles, while hydrogen gas was supplied from one intake nozzle, respectively. Hydrogen was injected with a relatively low pressure of 50 kPaG. This means that an injector with high injection pressure was not needed. Then, ignition timing and air excess ratio were set as variables, in order to investigate combustion properties depending on these factors. As a result, it can be found that for our prototype engine with the principle at fairly high compression ratios, any abnormal combustion such as backfiring and pre-ignition did not occur in the experiments. Then, potential of high indicated thermal efficiency on hydrogen combustion is also obtained under lean conditions of λ> 5.0, despite the small displacement (49.9 cc). These results show that the engine with our principle can be effective for hydrogen combustion, and lead to the practical use of it for hydrogen internal combustion engines.