Browsing by Author "Holborn, Paul"

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    Enabling cryogenic hydrogen-based CO2-free air transport: meeting the demands of zero carbon aviation
    (IEEE, 2022-06-02) Sethi, Vishal; Sun, Xiaoxiao; Nalianda, Devaiah; Rolt, Andrew Martin; Holborn, Paul; Wijesinghe, Charith; Xisto, Carlos; Jonsson, Isak; Grönstedt, Tomas; Ingram, James; Lundbladh, Anders; Isikveren, Askin; Williamson, Ian; Harrison, Tom; Yenokyan, Anna
    Flightpath 2050 from the European Union (EU) sets ambitious targets for reducing the emissions from civil aviation that contribute to climate change. Relative to aircraft in service in year 2000, new aircraft in 2050 are to reduce CO2 emissions by 75% and nitrogen oxide (NOx) emissions by 90% per passenger kilometer flown. While significant improvements in asset management and aircraft and propulsion-system efficiency and are foreseen, it is recognized that the Flightpath 2050 targets will not be met with conventional jet fuel. Furthermore, demands are growing for civil aviation to target zero carbon emissions in line with other transportation sectors rather than relying on offsetting to achieve “net zero.” A more thorough and rapid greening of the industry is seen to be needed to avoid the potential economic and social damage that would follow from constraining air travel. This requires a paradigm shift in propulsion technologies. Two technologies with potential for radical decarbonization are hydrogen and electrification. Hydrogen in some form seems an inevitable solution for a fully sustainable aviation future. It may be used directly as a fuel or combined with carbon from direct air capture of CO2 or other renewable carbon sources, to synthesize drop-in replacement jet fuels for existing aircraft and engines. As a fuel, pure hydrogen can be provided as a compressed gas, but the weight of the storage bottles limits the practical aircraft ranges to just a few times that is achievable with battery power. For longer ranges, the fuel needs to be stored at lower pressures in much lighter tanks in the form of cryogenic liquid hydrogen (LH2).
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    Modelling studies of the hazards posed by liquid hydrogen use in civil aviation
    (IOP Publishing, 2022-02-15) Holborn, Paul; Ingram, J. M.; Benson, C. B.
    As part of the ENABLEH2 project, modelling studies have been carried out to examine liquid hydrogen release and dispersion behaviour for different LH2 aircraft and airport infrastructure leak/spill accident scenarios. The FLACS CFD model has been used to simulate the potential hazard effects following an accidental LH2 leak, including the extent of the flammable LH2 clouds formed, magnitude of explosion overpressures and pool fire radiation hazards. A comparison has also been made between the relative hazard consequences of using LH2 with conventional Jet A/A-1 fuel. The results indicate that in the event of accidental fuel leak/spill LH2 has some safety advantages over Jet A/A-1 but will also introduce additional hazards not found with Jet A/A-1 that will need to be carefully managed and mitigated against.
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    Performance evaluation of nitrogen for fire safety application in aircraft
    (Elsevier, 2020-05-26) Dinesh, Akhil; Benson, C. M.; Holborn, Paul; Sampath, Suresh; Xiong, Yifang
    Fire suppression is an important safety certification requirement for aircraft as it is for all safety critical systems. Risk analyses are required at the design and certification stages to determine the probabilities and means of mitigating such risks. [18] shows an approach for spacecraft, [19] for passenger ships and [30] for reactors. An important analysis tool for aircraft is the Zonal Analysis process [31]. Such analyses include investigation of means of fire suppression for which the use of Halon 1301 was a popular choice. The production of Halon and several halocarbons were banned under the Montreal Protocol in 1994, which necessitates an investigation for use of environmental-friendly agents for this application. The primary objective of this paper is to determine the ‘design concentration’1 of nitrogen required for fire suppression. Computational Fluid Dynamics (CFD), in combination with experimental verification is described in this paper. The air flow rate in the cup-burner model was varied between 10 L/min and 40 L/min for a low-speed numerical model and was validated against the BS ISO 14520 cup burner test [1] to determine the extinguishing concentration of nitrogen. The study revealed that the design concentration of nitrogen was 34% (14% oxygen concentration). Further investigation suggested that at low air flow rates (10L/min and 20 L/min case), distortions produced in the flow led to erroneous measurement of oxygen concentration in experiments. The fire suppression model was extended to an n-heptane pool fire in a large enclosure. The recorded design concentration was approximately 39% additional nitrogen corresponding to 13% oxygen concentration by volume. It was observed that the weight of nitrogen required increased by 7.5 times compared to Halon 1301 use for this model. Future work can be explored in aircraft cargo and engine bay fire safety systems through Minimum Performance Standard (MPS) testing and simulations with nitrogen as the agent. Such work will feed directly into system safety assessments during the early design stages, where analyses must precede testing.
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    Preliminary assessment of a hydrogen farm including health and safety and capacity needs
    (MDPI, 2024-12-02) Alssalehin, Esmaeil; Holborn, Paul; Pilidis, Pericles
    The safety engineering design of hydrogen systems and infrastructure, worker education and training, regulatory compliance, and engagement with other stakeholders are significant to the viability and public acceptance of hydrogen farms. The only way to ensure these are accomplished is for the field of hydrogen safety engineering (HSE) to grow and mature. HSE is described as the application of engineering and scientific principles to protect the environment, property, and human life from the harmful effects of hydrogen-related mishaps and accidents. This paper describes a whole hydrogen farm that produces hydrogen from seawater by alkaline and proton exchange membrane electrolysers, then details how the hydrogen gas will be used: some will be stored for use in a combined-cycle gas turbine, some will be transferred to a liquefaction plant, and the rest will be exported. Moreover, this paper describes the design framework and overview for ensuring hydrogen safety through these processes (production, transport, storage, and utilisation), which include legal requirements for hydrogen safety, safety management systems, and equipment for hydrogen safety. Hydrogen farms are large-scale facilities used to create, store, and distribute hydrogen, which is usually produced by electrolysis using renewable energy sources like wind or solar power. Since hydrogen is a vital energy carrier for industries, transportation, and power generation, these farms are crucial in assisting the global shift to clean energy. A versatile fuel with zero emissions at the point of use, hydrogen is essential for reaching climate objectives and decarbonising industries that are difficult to electrify. Safety is essential in hydrogen farms because hydrogen is extremely flammable, odourless, invisible, and also has a small molecular size, meaning it is prone to leaks, which, if not handled appropriately, might cause fires or explosions. To ensure the safe and dependable functioning of hydrogen production and storage systems, stringent safety procedures are required to safeguard employees, infrastructure, and the surrounding environment from any mishaps.