Thermophysical assessment of injection strategies for emerging fuels to guide new high-efficiency engine concepts

• Thermophysical fuel property assessment methodology, for low and zero carbon fuels. • Unified systematic comparison of hydrogen carriers, across injection locations. • Comprehensive fuel and injection comparative datasets, informs engine architecture. • Intra-cycle ammonia reforming, for a new high-efficiency split-cycle engine concept. • Hydrogen yields sufficient for staged ignition enhancement and flexible fuelling. Heavy-duty road and maritime transport accounts for 8 % of global GHG emissions, driving urgent efforts to decarbonise the sector. While low- and zero-carbon fuels such as methane, methanol, hydrogen, and ammonia offer promising pathways, their integration into current engine platforms varies in maturity and presents distinct technical, economic, and operational challenges. This work introduces a ‘fuel-property-driven methodology’ that uses thermophysical and combustion-relevant property assessment of alternative fuels, to systematically guide engine architecture development. The approach is demonstrated for both current platforms and emerging cycles, specifically the Recuperated Split Cycle Engine (RSCE), whose spatial and temporal decoupling of compression and expansion enables unique fuelling opportunities not feasible in conventional engines, particularly for staging low- and high-reactivity fuels. The methodology encompasses two stages. First, the thermophysical and combustion-relevant properties of hydrogen carrier fuels were evaluated for compatibility with four injection strategies − direct (IPA), port (IPB), fumigated (IPC), and early compression (IPD) − across both conventional and RSCE platforms. Second, insights from this mapping − specifically that ammonia is easier to store and well-suited to IPD, while hydrogen offers excellent combustion stability at IPB and IPA − were applied to develop an innovative RSCE variant: The Recuperated Reforming Split Cycle Engine (R 2 SCE). This unique concept integrates intra-cycle thermocatalytic ammonia reforming to generate hydrogen-rich reformate. To guide this, a thermophysical feasibility analysis was conducted to estimate reformate composition as a function of recuperator effectiveness under R 2 SCE-relevant temperatures and pressures, using a ruthenium-based catalyst, to significantly enhance the combustion characteristics of NH 3 -blended fuelling. By synthesising current knowledge into a ‘fuel-property-driven methodology’, this work uses thermophysical assessment to guide engine development. Demonstrated here through the R 2 SCE concept, the approach systematically links fuel properties to injection strategy suitability, providing a replicable framework for integrating hydrogen carriers into new high-efficiency engine architectures.