Comparative experimental and numerical investigation of engine-lubricant performance in hydrogen- and gasoline-fueled PFI SI engines
Hydrogen-fueled spark-ignition (SI) engines offer wide flammability limits, fast flame propagation, and carbon-free exhaust products, making them a promising route toward low-carbon transportation. However, their fast heat-release rates and elevated in-cylinder temperatures pose challenges for thermal management, friction control, and lubricant durability. While coolant and exhaust heat rejection have been extensively studied, lubrication-oil behavior—governing both frictional losses and local thermal regulation—remains insufficiently characterized. This study presents a combined experimental–numerical investigation of lubrication-oil performance in a single-cylinder SI engine fueled with hydrogen and gasoline under matched IMEP conditions. Oil-side heat transfer was quantified through direct measurements of oil-temperature rise and mass-flow rate, while a validated one-dimensional model coupling combustion, cooling, and lubrication subsystems was used for extended analysis. Results show that oil-circuit heat losses account for less than 7% of the total fuel energy for both fuels. Nevertheless, hydrogen operation can lead to increased lubricant thermal loading due to intensified near-wall heat transfer and potential reductions in lubricant-film stability. Consequently, hydrogen fueling leads to greater viscosity sensitivity and more pronounced additive depletion, despite a lower oil-heat-rejection. These findings deliver the first integrated experimental–numerical quantification of lubrication-oil performance in a hydrogen-fueled PFI SI engine, providing key insights for viscosity-grade selection, lubricant formulation, and future engine thermal-management strategies. While the present results are specific to PFI operation, they provide a useful reference framework for future investigations of hydrogen direct-injection (DI) engines, where lubricant-related thermal and chemical stresses may differ significantly.