Mitigating NOx Emissions in Hydrogen Engines Through Fuel Cell-Assisted Oxygen-Diluted Combustion

While hydrogen offers a zero-carbon pathway for energy generation, its use in combustion systems is challenged by NOₓ formation. We propose an integrated hybrid solution combining a Solid Oxide Fuel Cell (SOFC) with a hydrogen engine (H₂ICE) via Oxygen-Diluted Combustion (ODC). In this configuration, the SOFC operates in an air-deficient regime to directly control the oxygen content of the ICE intake air, effectively suppressing NOₓ formation mechanisms with negligible efficiency penalties. Using 0D and 1D system modeling, we demonstrate that the hybrid ODC architecture achieves an 80% reduction in NOₓ emissions with less than a 3% efficiency penalty compared to a conventional hybrid system (overall efficiency ~60%). The analysis further shows that air utilization factors between 20–40% enable effective SOFC operation for intake-air dilution, whereas values exceeding 60%, corresponding to approximately 9.6% oxygen in the off-gas, result in substantial performance degradation. Although the approach incurs a modest efficiency loss relative to standard hybrid operation, it delivers a significant reduction in NOₓ emissions and surpasses standalone configurations in terms of combined emissions compliance and high-load capability.