Cryogenic closed-cycle linear engine integration for cold energy recovery in fuel cell trucks

This study investigated the integration of a Cryogenic Closed-cycle Free-piston Linear Joule Engine Generator (CCFLJEG) into a 100-kW hydrogen fuel cell truck to recover and convert cryogenic hydrogen cold energy into electricity. At 100% load and a hydrogen flow rate of 1.4 g/s, the CCFLJEG produced up to 2.9 kW of additional electrical power. Approximately 27% of the liquid hydrogen (LH2) regasification enthalpy was directly absorbed by helium in the cold heat exchanger, while a further 48.9% was indirectly utilised by enhancing hot-side energy recovery, giving an overall cold-energy utilisation of 76.2%. The system reduced annual energy demand from 131.04 MWh to 124.25 MWh (5.2% decrease), equivalent to a hydrogen saving of 333.3 kg. These results demonstrate that coupling CCFLJEG with fuel cell trucks provides an efficient pathway for exploiting cryogenic exergy while improving vehicle-scale energy efficiency. Economic analysis indicated that, when powered by green liquid hydrogen, the system achieved a net present value (NPV) of £23,355 and a payback time (PBT) of 0.7 years. With grey hydrogen, the PBT remained favourable at 1.4 years. Sensitivity analysis identified hydrogen purchase price as the most influential factor affecting NPV, while the capital cost of the CCFLJEG had the strongest influence on PBT. The findings indicated a positive outlook on the technical and economic viability of integrating CCFLJEG in fuel cell trucks, suggesting that it could offer a promising approach to improving energy efficiency and reducing hydrogen consumption in heavy-duty transport applications.