Suppressing pre-ignition and knock in hydrogen direct injection spark ignition engines with variable valve timing and split injection

Abnormal combustion phenomena pose significant challenges for the application of hydrogen direct injection engines. This study investigates the suppression of these issues in pure hydrogen direct injection engines through the use of variable valve timing and split injection strategies. The research addresses a critical gap in the current literature, as these strategies have not been widely explored in hydrogen direct injections, despite their successful application in gasoline engines. Results demonstrated that significant reductions in pre-ignition at early-mid compression-stroke events by up to 38 % were observed with specific valve timing adjustments, alongside decreased in knock intensity by 34.5 % and knock probability by 38.6 % with optimal intake valve closing timing set at 227 degrees crank angle before top dead center. Furthermore, configurations utilizing split end of injection timing at 30 degrees crank angle before top dead center and split injection ratio of 0.6 achieved a substantial 64 % reduction in specific pre-ignition events and split injection ratio of 0.7 resulted in a 63.0 % and 63.7 % decrease in knock intensity and knock probability, respectively, compared to initial valve timing and single injection. However, it was found that higher split injection ratio values, while effective in reducing abnormal combustion, led to diminishing returns in brake thermal efficiency. Achieving optimal performance required a careful balance between suppressing pre-ignition at early-mid compression-stroke events and knock phenomena while maintaining or improving brake thermal efficiency. The findings offer critical insights for advancing hydrogen direct injection engine technology, promoting decarbonization in transportation, and supporting global carbon neutrality goals. Future research should focus on optimizing variable valve timing and split injection strategies for various operational conditions and explore their integration with other advanced technologies, such as turbocharging and exhaust gas recirculation, to further enhance hydrogen combustion stability.