“Abstract

Decarbonising the heavy-duty sector requires concepts that surpass the diesel cycle in efficiency while meeting increasingly stringent emissions standards. The recuperated split-cycle engine (RSCE) offers a potential pathway, combining quasi-isothermal compression (enabled with secondary working fluids, SWF) with internal exhaust heat recuperation. This work assesses hydrogen-diesel dual fuelling using single-cylinder RSCE experiments at a range of loads, supported by a validated Chemkin-Pro framework. The modelling extended the analysis using a reactor network and multizone model to evaluate high-load conditions, pre-ignition mixing and SWF carry-over. Experiments show stable dual-fuel operation, with light and controllable pre-ignition linked to elevated HO₂/H₂O₂/OH radicals. Model predictions at higher load indicate that, relative to a neat diesel baseline, BMEP is predicted to be maintained, with BSFC and CO₂ reduced by 33% and 43% at 10%Vol H₂. NOx is predicted to decrease by 23% at 5%Vol H₂, but to increase by 42% at 10%Vol H₂, as the H₂ energy share approaches 40%, consistent with faster premixed heat release and elevated O/OH driving thermal-NO. With efficient aftertreatment conversion, the 5%Vol case is predicted to meet 0.2 g/kWh NOx, whilst 10%Vol remains within the 0.26 g/kWh on-road benchmark. Furthermore, the model predicts that adding H₂O to the charge (SWF carry-over) could reduce NOx by 30% at 0.10% H₂O with a 3% BMEP penalty alongside an increase in HC due to temperature-limited oxidation. This combined experimental demonstration of expander port-injected H₂ in an RSCE, supported by a physically informed spatially resolved multizone modelling framework, supports the combustion feasibility for hydrogen-diesel dual fuelling and identifies the calibration and hardware levers required to achieve practical impact for Euro 7-class NOx alongside EU CO₂ reductions. Overall, these results position RSCE + H₂ as a potential mid-term route towards sustainable heavy-duty propulsion.”

 

The full article is accessible via:

https://doi.org/10.1177/14680874261461065

For related publications please see Resources – UK National Clean Maritime Research Hub

“Abstract

This study explores the macroscopic spray behaviour of methanol and its oxygenated blends MTBE5 (5 vol% methyl tert-butyl ether), A5 (5 vol% acetone), and E5 (5 vol% 2-ethylhexyl nitrate) at a fixed low ambient pressure of 40 mbar while varying liquid injection pressure from 40 to 100 bar. By keeping the flash-boiling environment and injector configuration fixed, the study provides a controlled comparison of how additive chemistry alters methanol spray development. High-speed Schlieren imaging and image-based analysis were used to examine, four key spray features; namely cone angle, spray penetration, spray area, and spray width. The results show that higher injection pressures generally promote broader and more uniform macroscopic spray development, however, the additive-specific response remained distinct under identical operating conditions. Among the blends, MTBE5 showed an approximate 8% increase in cone angle during injection, forming wide and stable sprays due to its favourable balance of low surface tension and sustained lateral plume growth. The A5 blend, by contrast, produced sprays with the strongest forward momentum and most consistent penetration, particularly at moderate pressures (40–80 bar), however, it showed reduced stability at the higher pressures. Pure methanol displayed narrower but moderately stable sprays, while E5 generated the widest sprays but with noticeable instability in the breakup region and spatial distribution. These results show that chemically distinct oxygenated additives do not modify methanol spray behaviour in the same way; rather, each additive produces a different balance of lateral expansion, axial penetration, and repeatability under the same flash-boiling condition. This provides a controlled basis for additive selection in methanol-fuelled injection systems.”

 

The full article is accessible via:

https://doi.org/10.1016/j.fuel.2026.140370

For related publications please see Resources – UK National Clean Maritime Research Hub

“Abstract

Direct ammonia-fuelled solid oxide fuel cells (DA-SOFCs) present a promising route for efficient, carbon-free energy conversion. While existing SOFC models can capture detailed cell-level behaviour, they typically lack integration of ammonia decomposition and thermal processes, limiting their suitability for system-level powertrain simulations. This study introduces a one-dimensional transient model that couples’ ammonia cracking kinetics with electrochemical processes, enabling both detailed transient analysis and integration into powertrain simulations. The model investigates the effects of startup conditions, operating pressure, temperature, inlet flow rate, and fuel concentration on steady-state and dynamic performance. Results show that low current and external heating are recommended abstract for the start-up to prevent sudden voltage drop and overcome the thermal threshold for ammonia decomposition. Once steady state is reached, the cell achieves heat balance and can operate without external heating. To ensure performance, maintaining ammonia concentration above 80% and fuel utilisation over 70% is a key to avoid fuel depletion or voltage interruption during load changes. Operating pressures up to 10 atm improve power density. However, further increases offer limited benefit and require higher operating temperatures to ensure complete ammonia decomposition. This numerical model offers cell-level mechanistic insights and provides a computationally efficient basis for future DA-SOFC stack- and system-level dynamic simulations.”

 

The full article is accessible via:

https://doi.org/10.1016/j.cej.2026.176840

For related publications please see Resources – UK National Clean Maritime Research Hub

“Abstract

Ammonia-fuelled engines have primarily targeted light-duty automotive internal combustion engines. However, ammonia can be a potential carbon-free fuel for large-bore marine engines to decarbonise the maritime sector. In this study, a CFD model was developed and validated to assess direct ammonia injection in a large-bore marine engine. The impacts of liquid ammonia energy ratios up to 77% and injection timings on combustion, engine performance, and emissions were examined. The results showed that the highest indicated thermal efficiency of 48.3% was achieved at SOI_NH3 − 40 CAD, where the main combustion occurred at TDC and overlapped with diesel ignition, leading to a shorter combustion duration. Varying ammonia injection timing revealed that the minimum NH₃ slip of 4.1 g/kWh was at SOI − 40 CAD and increased for both earlier and later ammonia injection timings. Liquid ammonia significantly reduced NO_X emissions from 7.7 g/kWh in the diesel case to just 1.3 g/kWh due to lower combustion temperature. Moreover, advancing ammonia SOI_NH3 from − 15 to − 50 CAD significantly reduced CO emissions from 9.1 to 2.7 g/kWh. The results also showed that N₂O primarily forms in thin mid-temperature NH₃-rich layers ahead of the flame front, and earlier ammonia injection expands these zones, increasing N₂O emissions.”

 

The full article is accessible via:

https://doi.org/10.1016/j.fuel.2026.139951

For related publications please see Resources – UK National Clean Maritime Research Hub