Simulation Study on the Effects of Hydrogen-Rich Gas Addition on the Performance and Emissions of Diesel Engines for Nearshore Fishing Vessels

This study investigates the influence of HHO gas enrichment on the combustion and emission characteristics of a diesel engine operating at 2200 rpm under various load conditions. Experimental measurements and AVL Boost simulations were conducted to evaluate the effects of hydrogen addition on in-cylinder pressure, air–fuel ratio, and key emission parameters. The results show that HHO, owing to its high flame speed, carbon-free composition, and additional oxygen content, significantly improves combustion quality and engine efficiency. Brake-specific fuel consumption decreased by 7–10% at medium loads, while CO and soot emissions were reduced by 20–35% and 30–40%, respectively, indicating more complete and cleaner combustion. However, NOx emissions increased slightly by about 10–15% at higher loads due to elevated peak temperatures. The air–fuel equivalence ratio (λ) decreased with increasing HHO proportion but remained above 1.2, ensuring stable operation. Overall, HHO enrichment proves to be a feasible and effective approach to enhancing the thermal efficiency and environmental performance of diesel engines, particularly by reducing soot and CO emissions while maintaining stable combustion behavior.