Maximizing hydrogen utilization in CI engines: An investigation of dual fuel and RCCI combustion approaches under low and mid-load conditions in a medium duty automotive engine

This investigation explored maximum hydrogen fuel utilization in a medium-duty, twin-cylinder engine under low and mid-load conditions (2 and 4 bar BMEP). The impact of increasing hydrogen energy share on combustion, performance, and emissions was assessed for conventional dual fuel and RCCI combustion modes. Hydrogen served as the primary fuel, with diesel fuel employed solely for ignition. Both modes achieved 90% hydrogen fuel contribution at low load without combustion instabilities, constrained only by fuel injection limitations. Substantial emission reductions were observed without performance compromise, with RCCI demonstrating superior emissions compared to dual fuel. Mid-load operation was restricted to 40% hydrogen due to knock, leading to reduced emissions except for NOx. At low load with 90% hydrogen, both modes exhibited zero NOx and minimal smoke. Brake thermal efficiency improved with increasing hydrogen share, with RCCI surpassing dual fuel at mid load. While this study highlights the potential for significant emission reductions through high hydrogen fuel utilization, especially at low load, challenges related to knock at higher loads and fuel injector technology must be addressed for widespread adoption.