Zero-Carbon Port Fueling for Heavy Propulsion through a Recuperated Split Cycle Engine

Upcoming global emissions regulations demand innovation in heavy-duty road and marine transport. This research explores emissions-compliant concepts using both experiments and simulations focused on the Recuperated Split Cycle Engine (RSCE), which separates compression and expansion to enable internal heat recovery and quasi-isothermal compression. A single-cylinder research engine representing the expansion cylinder of an RSCE demonstrated direct injection diesel and port injection hydrogen co-firing. A validated Chemkin-Pro Multi-Zone model first reproduced, then extended this work, evaluating partial diesel substitution with hydrogen or ammonia alongside secondary working fluids (SWF’s liquid N₂, H₂O, NH₃). For the extension, two variants of the split cycle architecture were employed; the RSCE in combination with hydrogen fueling for the heavy-duty road sector, and the novel recuperated reformed split cycle engine (R²SCE), a new architectural and simulation contribution enabling on-board ammonia reforming and dual-role use of SWFs for the maritime sector. In the RSCE configuration, 10%Vol H₂ with H₂O as SWF delivered 13% NOx and 45% CO₂ reductions, along with a 33% improvement in brake specific fuel consumption (BSFC). System-level evaluation of this configuration demonstrated the potential of Euro 7 compliant NOx with typical after-treatments. In the R²SCE configuration, while SWFs N₂ and H₂O reduced thermal NOx via dilution, the use of NH₃ as a dual role SWF - combined with a Recuperator-Reformer (59% NH₃-to-H₂ conversion) - delivered a 4% increase in total fuel energy and reduced NOx emissions across all tested NH₃ injection levels. The R²SCE system level comparison between 6%Vol NH₃ and diesel-only operation showed 10% and 43% reduction in BSFC and CO₂ per unit work, with NOx within maritime regulatory targets with typical after-treatments. These quantified outcomes serve as reference points for performance benchmarking, demonstrating how, compared to a contemporary conventional engine, the increased flexibility offered by the novel R²SCE concept can maximise fuel-to-power conversion for zero-carbon fuels.