The hydrogen-fueled internal combustion engine faces a critical trade-off between high power density and low NOx emissions. This paper investigates water direct injection as a method to resolve this conflict in a multi-cylinder, port fuel injected hydrogen engine. A systematic experimental study was conducted to quantify the effects of injected water mass and timing on engine performance and emissions. The injection timing proved critical, with optimal results achieved during the intake and early compression stroke. The results further show that water direct injection in conjunction with spark retardation is a highly effective strategy for NOx reduction. Indicated specific nitrogen oxides emissions were minimized to a target value of approximately 1 g / kWh across the entire hydrogen-baseline engine operating map. Simultaneously, water direct injection enabled an extension of the maximum engine load by up to 20% while maintaining indicated efficiencies above 44% in large parts of the map, significantly outperforming solely spark retardation as a NOx mitigation method. While water direct injection enables clean, high-performance hydrogen internal combustion engine operation, the high water consumption in certain operating points poses a practical challenge for vehicle integration.
Grosse et al. (Tue,) studied this question.