Numerical Investigation on Hydrogen Enrichment and EGR on In-Cylinder Soot and NOx Formation in Dual-Fuel CI-Engine

To mitigate the NOx emissions from diesel engines, the adoption of exhaust gas recirculation (EGR) has gained widespread acceptance as a technology. Employing EGR has the drawback of elevating soot emissions. Using hydrogen-enriched air with EGR in a diesel engine (dual-fuel operation), offers the potential to decrease in-cylinder soot formation while simultaneously reducing NOx emissions. The present study numerically investigates the effect of hydrogen energy share and engine load on the formation and emission of soot and NOx from hydrogen-diesel dual-fuel engines. The numerical investigation uses an n-heptane/H₂ reduced reaction mechanism with a two-step soot model in ANSYS FORTE. A reduced n-heptane reaction mechanism is integrated with a hydrogen reaction mechanism using CHEMKIN to enhance the accuracy of predicting dual-fuel combustion in a hydrogen dual-fuel engine. The results show that hydrogen enrichment plays a significant role by decreasing the soot precursor concentration by increasing the hydroxyl (OH) radical and suppressing soot formation by enhancing oxidation. Hydrogen enrichment in dual-fuel operation significantly reduces soot and NOx emissions under low load conditions. Adding hydrogen in diesel engines decreases the concentration of acetylene (C₂H₂), locally inside the combustion chamber, which inhibits soot formation. The findings highlight the synergistic benefits of combining hydrogen and EGR in a dual-fuel engine, offering a viable strategy for achieving lower NOx levels without compromising on soot emissions. This research contributes to the advancement of cleaner and more efficient propulsion technologies, especially in the context of heavy-duty applications where stringent emissions standards are a critical concern.