Effects of Injector Clogging and Hydrogen Energy Fraction on the Combustion and Emission Characteristics of a Four-Stroke Hydrogen/Diesel Dual Fuel Marine Engine at Different Intake Air Temperatures: A Numerical Study

This study numerically investigates the combined effects of injector clogging ratios (10%, 20%, 30%, 40%, 50%), hydrogen energy fractions (HEF20, HEF40, HEF60), and intake air temperatures (340 K, 351 K, 360 K) on the in-cylinder combustion and emission characteristics of a four-stroke hydrogen/diesel dual fuel marine engine. Based on an analysis of 45 different simulation scenarios, the study details in-cylinder pressure, heat release rate, mean temperature, and the mole fractions of NOX, HC, CO2, CO, CH2O, and OH. The research findings reveal that injector clogging is the most dominant parameter affecting engine performance changes; specifically, increasing the clogging ratio from 10% to 50% caused radical decreases of up to 17.3% in peak cylinder pressure and 42.4% in the maximum heat release rate. It was observed that the hydrogen enrichment strategy significantly compensated for this performance loss, as the HEF60/360 K configuration under 50% clogging outperformed the HEF20/340 K baseline at 10% clogging in terms of heat release performance. However, this improvement led to a 35% increase in NOX emissions compared to low HEF conditions. The clogging range between 30% and 40%, where heat release and OH radical concentrations exhibit non-linear degradation, is identified as a critical "fouling threshold." From a diagnostic perspective, the shifting of the peak CH2O value from near Top Dead Center (TDC) to approximately 20° Crank Angle after TDC with increasing clogging is presented to the literature as a characteristic "cool flame timing indicator." The suppression of the OH radical by up to 70% under severe clogging conditions makes this species the most sensitive indicator of combustion quality. The data obtained serve as a technical guide for condition-based maintenance planning and optimized hydrogen blending strategies in marine propulsion systems subject to IMO Tier III emission standards.