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Hydrogen can be used as a fuel for internal combustion engines to realize a carbon-neutral transport society. By extending the lean limit of spark ignition engines, their efficiency, and emission characteristics can be improved. In this study, stratified charge combustion (SCC) using monofueled hydrogen direct injection was used to extend the lean limit of a spark ignition engine. The injection and ignition timing were varied to examine their effect on the SCC characteristics. An engine experiment was performed in a spray-guided single-cylinder research engine, and the nitrogen oxide and particulate emissions were measured. Depending on the injection timing, two different types of combustion were characterized: mild and hard combustion. The advancement and retardation of the ignition timing resulted in a high and low combustion stability, respectively. The lubricant-based particulate emission was attributed to the in-cylinder temperature and area of the flame surface. Therefore, the results of the study suggest that the optimization of the hydrogen SCC based on the injection and ignition timing could contribute to a clean and efficient transport sector.

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