Countries around the world are making long-term efforts to reduce greenhouse gas emissions in response to global climate change, with a target of Zero greenhouse gas emissions by 2050.
In the automotive sector, discussions are ongoing on carbon-free powertrains in the future. Hydrogen is a fuel that can achieve zero carbon emissions and production, and is positioned as a key technology that is expected to play an active role in a wide range of fields, including power generation, transportation, and industry. Hydrogen engines are attracting increasing attention because conventional engine components can be diverted. In particular, hydrogen direct injection engines are attracting attention in order to achieve high power and high efficiency. In a hydrogen direct injection engine, the generation of backfire can be suppressed by injecting high-pressure hydrogen in the compression process, but it is known that the formation of air-fuel mixture in the cylinder becomes difficult, which greatly affects the engine performance. The exposure time of the hydrogen mixture to the hot spot in the cylinder can be reduced by retarding the hydrogen injection timing. Furthermore, the injection retard can reduce the compression work, and the stratification of the mixture and the in-cylinder turbulence intensity can improve the initial flame growth. The reduction of heat loss can also be expected by reducing the rich area near the combustion chamber wall by stratification. (3) On the other hand, stratification has the possibility of increasing heat loss, and the occurrence of hot spots also increases the possibility, and consequently it can be a factor of preignition.
A hydrogen mono-firing operation was conducted using a research single-cylinder engine, and a clear change in combustion was observed when the injection timing was delayed from the time when the intake valve was closed. It is clear that the mixing state of hydrogen and air in the cylinder changes with the change of the injection timing and affects the combustion. In order to examine the details, it is necessary to make a CFD model and grasp the hydrogen mixing state in the cylinder. It is necessary to construct a detailed hydrogen jet model for a CFD model of a hydrogen direct injection engine. The jet generated by a hydrogen direct injection injector was visualized by the schlieren method, and an injector analysis model was constructed. The effect of the injection timing on hydrogen combustion is examined by CFD analysis in the engine cylinder using the injector analysis model.