“Abstract

Hydrogen is stored at high pressure making discharge a safety concern, including flame stability issue. Previous studies were focused on circular nozzles. However, actual incidents are more likely to involve slit-shaped openings. The experiments on hydrogen release from non-circular openings were conducted for nozzle cross-sectional areas equal to circular orifices of diameters 0.5, 0.6, 0.8 mm, with aspect ratios for rectangular orifices 1, 2, 4, 6, 8. For rectangular nozzles, expansion waves are generated from the corners in addition to those originating from the nozzle lip. These waves interfere causing an “axis-switching” phenomenon and formation of octagonal Mach disk, producing jet with wider velocity boundary, thus greater air entrainment and consequently 10–30 % shorter flame length. The lift-off length for rectangular openings, i.e. 10-15 mm was approximately half that of circular nozzles. The experimental and numerical study of non-combusting jet shed light on the flame stabilisation mechanism for rectangular nozzles identified as internal flame retention, i.e. anchoring the flame base at low-velocity region at the root of the cross-shaped velocity and hydrogen concentration distributions.”

 

The full report is accessible via: https://doi.org/10.1016/j.ijhydene.2025.152934

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

“Abstract

The maritime shipping sector is a significant contributor to global carbon dioxide (CO2) emissions, accounting for approximately 2.7%-3% of global emissions. In response, the International Maritime Organization (IMO) has set ambitious targets: a 30% reduction in emissions by 2030, 80% by 2040, and net-zero by 2050, relative to 2008 levels. Meeting these goals requires a comprehensive understanding of the full range of viable decarbonisation measures. Therefore, this study conducts a systematic review of maritime decarbonisation measures, applying the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) methodology. Unlike previous studies, this paper not only provides an updated overview of CO2 reduction measures but also maps them to specific vessel types based on data reported in the literature. Furthermore, the findings are compared with literature to highlight shifts in mitigation potential. A case study is also included to schematically demonstrate how these measures can be applied in practice. Following a rigorous analysis: (i) thirty-two individual CO2 mitigation measures were identified and classified into six categories, (ii) alternative fuels shown the highest long-term potential (5%–100% CO2 emission reduction), whereas hull design improvements show the lowest (1%–20%), (iii) the wide disparity in reported abatement values is attributed to inconsistent system boundaries, variability in fuel origin, partial-blend scenarios, and differing assumptions across studies, (iv) combinations of measures provide the most practical and realistic pathway to phased emissions reduction. These findings are expected to assist decision-makers in selecting effective, context-appropriate strategies to support global maritime decarbonisation and ensure long-term sectoral sustainability.”

 

The full report is accessible via: https://doi.org/10.1016/j.adapen.2025.100255

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

“Abstract

High-pressure composite tanks are widely used for gaseous hydrogen storage. A safety concern and knowledge gap is the potential overheating of components, including TPRD, during fast fuelling. This study presents a numerical investigation of the thermal response of a 12-litre tank with L/D = 9 under various fuelling conditions, e.g. tank orientation, and a fuelling failure scenario with excessive mass flow rate. The simulation demonstrated that, for a 3-min fuelling duration, the temperature non-uniformity (maximum–bulk difference) in horizontally oriented hydrogen tanks exceeds 29 °C. Vertical top-down fuelling reduces gradients by about 40 %, whereas bottom-up fuelling increases temperature non-uniformity and must be avoided. An extreme fuelling failure scenario with a mass flow rate of 50 g/s shows that hydrogen temperatures can exceed 300 °C. However, TPRD activation remains unlikely due to slow heat transfer to the sensing element. Monitoring only the average temperature is misleading as local temperature may exceed 85 °C and affect liner integrity.”

 

The full report is accessible via: https://doi.org/10.1016/j.ijhydene.2025.151376

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

“Abstract

Liquid hydrogen (LH₂) storage tanks are equipped with pressure relief devices (PRD) to vent hydrogen and avoid the pressure build-up in a tank due to heat transfer from the ambient, including in case of fire. In the event of a PRD failure, the tank structural integrity may be compromised leading to catastrophic rupture of the storage tank releasing the stored energy and producing destructive blast wave, fireball and projectiles. The present paper presents a CFD model to investigate the underlying physical processes of what is called “BLEVE” and assess the blast wave generated by an LH₂ storage tank rupture in a fire. The proposed CFD approach advances the previous model (Cirrone et al., 2023) to include the effect of flash evaporation of LH₂ during pressure drop after tank rupture and reproduce the multi-peak overpressure structure observed in experiments performed by BMW. Simulation results show that the observed maximum pressure peak is associated with the gaseous phase “explosion”, whereas the series of secondary pressure peaks, smaller in amplitude and of longer duration, are associated with the flash evaporation of the LH₂ fraction stored in the tank. Simulations can reproduce the minimum and maximum overpressures measured at 3 m from the storage tank in BMW experiments. The simulated maximum blast wave pressure is seen to increase with the storage pressure and volumetric fraction of the gaseous hydrogen phase in the tank prior to rupture.”

 

The full report is accessible via: https://www.cetjournal.it/index.php/cet/article/view/CET25116042

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