Project Summary

This project aims to deliver a technically rigorous and commercially grounded design and development plan for ammonia combustion in free-piston engine generators using advanced trajectory-based control. Ammonia is a carbon-free, hydrogen-derived fuel that is gaining momentum as a candidate for maritime decarbonisation due to its energy density, transportability and compatibility with existing port infrastructure. However, its slow flame speed, narrow flammability range and high ignition energy make it a difficult fuel to manage in conventional internal combustion engines.? The innovation proposed in this project addresses those barriers by leveraging the unique properties of free-piston engines, namely, their decoupled piston dynamics and software-defined motion profiles. By holding the piston near top dead centre for longer durations, the engine allows ammonia more time to burn fully, increasing combustion efficiency and stability. The project focuses on generating simulation models, detailed design and documentation, and a fully costed engineering and development plan that will enable investors, regulators and maritime technology adopters to assess the feasibility of commercialising ammonia-powered free-piston engine generators for port and vessel power systems. The work builds on previous studies with different fuels and reflects the growing urgency to deploy clean-fuel technologies in line with Maritime 2050 and the Clean Maritime Plan.

Project Achievements

During TRIG 25 we delivered a simulation-led feasibility assessment of ammonia HCCI operation in our free-piston engine platform, establishing the key operating dependencies and system implications for a credible development pathway. We built and exercised a validated chemical-kinetics modelling workflow to characterise auto-ignition behaviour across compression ratio, equivalence ratio, intake temperature and dilution, and used the results to define practical ignition boundaries and sensitivities. A central outcome was a quantified understanding of the emissions challenge for pure ammonia HCCI: once robust ignition is achieved, NOx remains intrinsically high and is strongly linked to peak gas temperature, informing the need for an integrated compliance strategy rather than relying solely on in-cylinder control. We also translated the modelling into engineering requirements for ancillary systems (thermal conditioning, exhaust after-treatment integration) and produced an initial costed bill of materials to support near-term design decisions, stakeholder engagement and follow-on funding discussions.

Conclusions

TRIG 25 confirmed that pure ammonia HCCI in a free-piston engine is technically feasible, but only within a constrained ignition envelope that is highly sensitive to charge temperature, dilution and operating conditions. The simulation work shows that achieving robust auto-ignition typically pushes peak gas temperatures into a regime where NOx formation remains high; therefore, trajectory control and in-cylinder optimisation alone are unlikely to deliver compliance. The practical route to deployment is an integrated system approach: (i) charge conditioning/thermal management to widen the stable operating range, and (ii) engineered after-treatment (with appropriate sensing and control) to meet regulated NOx limits while managing ammonia slip. The work provides a defensible basis for next-stage development, including trajectory optimisation against emissions objectives using higher-fidelity models, and sizing/packaging of the minimum viable thermal and after-treatment subsystems for a demonstrator.

Next Steps

Next we will move from feasibility to an engineered demonstrator plan. We will (1) extend the modelling stack beyond single-zone to include heat transfer, residual fraction and alternative volume histories, then optimise piston trajectory against a multi-objective target set (stability, efficiency, peak pressure, NOx and ammonia slip). (2) Define and size the minimum viable ancillary systems required for stable operation and compliance: charge conditioning/heat-recovery architecture, and a practical after-treatment package (SCR and ammonia slip management) with a clear sensor and control strategy. (3) Complete an ammonia-compatibility review for fuel-path materials, seals and safety functions (leak detection, purge, ventilation and shutdown). (4) Implement a minimal experimental validation loop (e.g., compression-only free-piston tests or a surrogate ignition-delay platform) to calibrate model assumptions and de-risk scale-up.