In April 2018, the International Maritime Organisation adopted an ambitious plan to contribute to the global efforts to reduce the Greenhouse Gas emissions, as set by the Paris Agreement, by targeting a 50% reduction in shipping’s Green House Gas emissions by 2050, benchmarked to 2008 levels. To meet these challenging goals, the maritime industry must introduce environmentally friendly fuels with negligible, or low SO_X, NO_X and CO₂ emissions. Ammonia use in maritime applications is considered promising, due to its high energy density, low flammability, easy storage and low production cost. Moreover, ammonia can be used as fuel in a variety of propulsors such as fuel cells and can be produced from renewable sources. As a result, ammonia can be used as a versatile marine fuel, exploiting the existing infrastructure, and having zero SO_X and CO₂ emissions. However, there are several challenges to overcome for ammonia to become a compelling fuel towards the decarbonisation of shipping. Such factors include the selection of the appropriate ammonia-fuelled power generator, the selection of the appropriate system safety assessment tool, and mitigating measures to address the hazards of ammonia. This paper discusses the state-of-the-art of ammonia fuelled fuel cells for marine applications and presents their potential, and challenges.

One of the tasks of the HySafe Network of Excellence was the evaluation of available CFD tools and models for dispersion and combustion in selected hydrogen release scenarios identified as “standard benchmark problems” (SBEPs). This paper presents the results of the HySafe standard benchmark problem SBEP-V11. The situation considered is a high pressure hydrogen jet release from a compressed gaseous hydrogen (CGH2) bus in an underpass. The bus considered is equipped with 8 cylinders of 5 kg hydrogen each at 35 MPa storage pressure. The underpass is assumed to be of the common beam and slab type construction with I-beams spanning across the highway at 3 m centres (normal to the bus), plus cross bracing between the main beams, and light armatures parallel to the bus direction. The main goal of the present work was to evaluate the role of obstructions on the underside of the bridge deck on the dispersion patterns and assess the potential for hydrogen accumulation. Four HySafe partners participated in this benchmark, with 4 different CFD codes, ADREA-HF, CFX, FLACS and FLUENT. Four scenarios were examined in total. In the base case scenario 20 kg of hydrogen was released in the basic geometry. In Sensitivity Test 1 the release position was moved so that the hydrogen jet could hit directly the light armature on the roof of the underpass. In Sensitivity Test 2 the underside of the bridge deck was flat. In Sensitivity Test 3 the release was from one cylinder instead of four (5 kg instead of 20). The paper compares the results predicted by the four different computational approaches and attempts to identify the reasons for observed disagreements. The paper also concludes on the effects of the obstructions on the underside of the bridge deck.

A comparative study has been made for the modelling of a passive release from an L-shaped building, in the presence of wind, using dispersion models of various complexities. Selected for the comparison were the one- and two-dimensional shallow layer models DISPLAY-1 and DISPLAY-2 and the full three-dimensional model ADREA-HF, all being part of the Dense Gas Dispersion Code Package, jointly developed by NCSR-DEMOKRITOS and JRC-ISPRA. For the shallow layer models, turbulence is modelled by means of the entrainment velocity concept, while for the three-dimensional model, a one-equation turbulence closure is used, according to which the turbulent kinetic energy conservation equation is solved. Length scales depend on the local and global flow characteristics of the L-shaped building. Concepts of volume porosity and area permeability are used. The pressure drop due to the building is taken into account by adding resistance terms in the shallow momentum equations. For model validation, the EMU-A1 wind tunnel experiment has been selected. The model results are compared against the experimental concentrations, using a statistical evaluation approach. The results clearly demonstrate the applicability of the model ADREA-HF for the present complex topography. For the shallow layer models acceptable results were obtained in CPU times much lower than ADREA-HF. Further improvements of the model for additional entrainment due to the presence of obstacles is necessary.

Accidental release from a hydrogen car tank in a confined space like a tunnel poses safety concerns. This Computational Fluid Dynamics (CFD) study focuses on the first seconds of such a release, which are the most critical. Hydrogen leaks through a Thermal Pressure Relief Device (TPRD), forms a high-speed jet that impinges on the street, spreads horizontally, recirculates under the chassis and fills the area below it in about one second. The “fresh-air entrainment effect” at the back of the car changes the concentrations under the chassis and results in the creation of two “tongues” of hydrogen at the rear corners of the car. Two other tongues are formed near the front sides of the vehicle. In general, after a few seconds, hydrogen starts moving upwards around the car mainly in the form of buoyant blister-like structures. The average hydrogen volume concentrations below the car have a maximum of 71%, which occurs at 2 s. The largest “equivalent stoichiometric flammable gas cloud size Q9” is 20.2 m³ at 2.7 s. Smaller TPRDs result in smaller hydrogen flow rates and smaller buoyant structures that are closer to the car. The investigation of the hydrogen dispersion during the initial stages of the leak and the identification of the physical phenomena that occur can be useful for the design of experiments, for the determination of the TPRD characteristics, for potential safety measures and for understanding the further distribution of the hydrogen cloud in the tunnel.