Optical screening investigations of backfire in a large bore medium speed hydrogen engine

Further improvement of hydrogen combustion in port fuel injection engines is limited by backfire. To overcome this drawback of hydrogen port fuel injection engines it is essential to locate and understand the reasons for the inflammation of a backfiring cycle. To contribute to this understanding a minimal invasive lateral optical access was developed for a medium speed large bore engine. The access uses a UV enhanced endoscope to investigate the OH radical’s natural chemiluminescence to locate the inflammation of a backfiring cycle in the combustion chamber. The investigations are carried out at high engine load. The optical investigations were based on a thermodynamic screening. This included the variation of the start of the hydrogen port fuel injection and the engine’s backpressure. These experiments prove the influence of exhaust backpressure and the start of injection on the probability of backfire. As higher backpressure leads to an increased probability of backfire, the SoI strategy has also a decisive influence. An optimum start of injection timing with less backfire under high backpressure was experimentally determined at 300°CA with respect to 720°CA as FTDC. The conducted optical investigations show that backfire starts by ignition by hot residual gasses during the first cycle located under the exhaust valves. Furthermore, the results show ongoing combustion in the intake manifold leading to serious damage of the engine if not prohibited.