Numerical investigation of low-load performance improvement in a marine PFI hydrogen–diesel dual-fuel engine via elevated compression ratio and split injection

Low-load operation of marine hydrogen–diesel dual-fuel engines may deteriorate engine performance and hydrogen combustion efficiency. To address this issue, this study proposes a strategy that combines an increased compression ratio with split diesel injection to restore engine performance and reduce NOx emissions. A CFD model of a 10.5 MW-rated marine engine was developed and validated against experimental data for both diesel and hydrogen-diesel dual-fuel operation. The effects of compression ratio, diesel injection timing, and diesel split injection control were examined both individually and in combination at 20% load. The results show that the combination of elevated compression ratio and advanced diesel injection timing enables performance comparable to the diesel baseline at 60% hydrogen substitution ratio (HSR), but with a NOx penalty, whereas the individual strategies are insufficient to recover baseline performance. The most effective strategy is the combination of high compression ratio (CR = 19) and diesel split injection. At the recommended control point of 60% HSR, this strategy achieves a hydrogen combustion efficiency of 96.5% and an indicated thermal efficiency of 53.9%, corresponding to a 3.0% improvement over the diesel baseline, while reducing NOx emissions by 1.59 g/kWh. This study demonstrates the performance potential of low-load operation and offers insights into the stable and efficient operation of hydrogen-fueled marine engine under varying loads.