Hydrogen tube vehicle for supersonic transport: 6. Density stages

A challenge of aerodynamic tunneling in hydrogen, and to a lesser extent other high-efficacy gases, with propeller propulsion is the long distance to accelerate to cruise speed. This problem is partly inherent to high-speed vehicles and is partly due to relatively low propeller thrust in the low density of hydrogen. A theory of “density stages” for ideal gases is developed. The idea is to span the distance from zero speed to terminal velocity by stages of successively decreasing gas density but increasing speed of sound. For constant acceleration within each stage and the condition that the product of gas density and propeller frequency forms a monotone decreasing sequence, I prove that the time and distance to reach terminal speed are decreasing functions of the number of stages. Density stages can substantially reduce the time and distance for acceleration or deceleration.     

Hydrogen tube vehicle for supersonic transport: 2. Speed and energy

The central concept of a new idea in high-speed transport is that operation of a vehicle in a hydrogen atmosphere, because of the low density of hydrogen, would increase sonic speed by a factor of 3.8 and decrease drag by 15 relative to air. A hydrogen atmosphere requires that the vehicle operate within a hydrogen-filled tube or pipeline, which serves as a phase separator. The supersonic tube vehicle (STV) can be supersonic with respect to air outside the tube while remaining subsonic inside. It breathes hydrogen fuel for its propulsion fuel cells from the tube itself. This paper, second in a series on the scientific foundations of the supersonic tube vehicle, tests the hypothesis that the STV will be simultaneously fast and energy efficient by comparing its predicted speed and energy consumption with that of four long-haul passenger transport modes: road, rail, maglev, and air. The study establishes the speed ranking STV ? airplane > maglev > train > coach (intercity bus) and the normalized energy consumption ranking Airplane ? coach > maglev > train > STV. Consistent with the hypothesis, the concept vehicle is both the fastest and lowest energy consuming mode. In theory, the vehicle can cruise at Mach 2.8 while consuming less than half the energy per passenger of a Boeing 747 at a cruise speed of Mach 0.81.     

Hydrogen tube vehicle for supersonic transport: 3. Atmospheric merit

To compare 24 common gases as potential operating atmospheres for tube vehicles, equations are derived for aerodynamic (tunneling) performance of the atmosphere and molar energy density of the tube vehicle. Aerodynamic performance is a function of the speed of sound and Reynolds number, and energy density is a function of the free energy of reduction or oxidation of the tube gas and the stoichiometric coefficients of the stored reactants. The product of these two parameters determines the rank of atmospheric merit. Hydrogen exhibits the highest aerodynamic performance, yields the fourth highest energy density, and has the highest overall merit. Acetylene, ammonia, and methane, in decreasing order, follow hydrogen in merit. Although superficially a promising tube gas, helium is below average in merit because of low energy density of the vehicle.     

Hydrogen tube vehicle for supersonic transport: 5. Aerodynamic tunneling

Aerodynamic tunneling is the process of transporting a vehicle from terrestrial point A to B via a closed tube containing an atmosphere more aerodynamically favorable than air. Equations are derived for “gas efficacy,” Γ, a measure of how well a gas increases Mach-1 speed or decreases drag of a vehicle. Theoretical results, Γ_p and its Mach-normalized form Γ₁, based on reducing the vehicle to a flat plate, allows efficacy to be calculated ab initio as a function of only four gas parameters: ratio of specific heats, pressure, density, and viscosity. Hydrogen has the highest normalized gas efficacy (Γ₁ = 48.5 s/kg). Ammonia, hydrocarbon gases, and helium have above-average efficacies. Xenon has the lowest (10.1 s/kg). Binary mixtures of hydrogen and methane (or natural gas) are proposed for lowering the upper flammability limit at a relatively small penalty in efficacy.     

Hydrogen/air supersonic combustion for future hypersonic vehicles

In this work, supersonic hydrogen combustion in the Hyshot II scramjet engine is investigated. In particular, fundamental physics of mixing, combustion and vorticity generation as well as the interaction between shock waves, boundary layer and heat release are analyzed by means of 3D Large Eddy Simulations (LES) using detailed chemistry. Results show very complex structures due to the interaction between the four sonic H₂ crossflow injections and the airstream flowing at M = 2.79. A bow shock forms ahead of each H₂ injector: the interaction between bow shocks and boundary layers leads to separation zones where H₂ recirculates. In these recirculation zones, OH radicals are produced, indicating that a flame already starts upstream of the injectors and downstream of the flow separation. The formation of barrel shocks due to the H₂ expansion and recompressions is also predicted. Comparison of pressure distribution along the wall centreline at 1.3 ms shows agreement with experimental results, mostly in the first part of the combustor, where the grid is very fine. The combustion is very fast and efficient: only 12.35% of hydrogen is found unburned at the combustor exit. This confirms that burning hydrogen is efficient and feasible also in supersonic flows and therefore it is a good candidate for hypersonic airbreathing applications.     

Hydrogen fuel and the Belgian transport sector: A critical assessment from an environmental and sustainable development perspective

This study provides an in-depth analysis of the potential role of hydrogen (H₂) in the Belgian transport sector in the context of sustainable and environmentally friendly growth. This paper starts by examining the energy-climate roadmap and the emission mitigation programme defined by the Belgian federal government in the context of environmental sustainability. Then, the Belgian situation is critically evaluated in light of the needs for H₂ fuel in the transport sector, as well as issues about a roadmap on environmental considerations for a sustainable future, while preserving the country's economic stakes. There are several key advances in this direction, especially as H₂ is seen as one of the best viable options for sustained development, unlike other possibilities. This paper also highlights some limitations that make it difficult to accelerate the transition to a sustainable H₂ energy future. Although there are many interests in favour of an advanced and non-polluting transport system, there are differing views on the approach to be taken in political decision-making at national level. Therefore, this study will help public authorities to better integrate environmental and sustainability issues in the context of a transition to a comprehensive hydrogen economy in the current transport sector.     

The impact of fuel cell vehicle deployment on road transport greenhouse gas emissions: The China case

Considerable attention has been paid to energy security and climate problems caused by road vehicle fleets. Fuel cell vehicles provide a new solution for reducing energy consumption and greenhouse gas emissions, especially those from heavy-duty trucks. Although cost may become the key issue in fuel cell vehicle development, with technological improvements and cleaner pathways for hydrogen production, fuel cell vehicles will exhibit great potential of cost reduction. In accordance with the industrial plan in China, this study introduces five scenarios to evaluate the impact of fuel cell vehicles on the road vehicle fleet greenhouse gas emissions in China. Under the most optimistic scenario, greenhouse gas emissions generated by the whole fleet will decrease by 13.9% compared with the emissions in a scenario with no fuel cell vehicles, and heavy-duty truck greenhouse gas emissions will decrease by nearly one-fifth. Greenhouse gas emissions intensity of hydrogen production will play an essential role when fuel cell vehicles' fuel cycle greenhouse gas emissions are calculated; therefore, hydrogen production pathways will be critical in the future.     

Liquid Organic Hydrogen Carriers as an efficient vector for the transport and storage of renewable energy

This contribution proposes the usage of Liquid Organic Hydrogen Carriers (LOHC) for the storage and subsequently the transport of renewable energy. It is expected that a significant share of future energy consumption will be satisfied with the import of energy coming from regions with high potential for renewable generation, e.g. the import of solar power from Northern Africa to Europe. In this context the transport of energy in form of chemical carriers is proposed supplementary to electrical transmission. Because of their high storage density and good manageability under ambient conditions Diesel-like LOHC substances could be transported within the infrastructure that already exists for the handling of liquid fossil fuels (e.g. oil tankers, tank trucks, pipelines, etc.). A detailed assessment of energy consumption as well as of transport costs is conducted that confirms the feasibility of the concept.     

Fuel cell electric vehicle as a power plant: Fully renewable integrated transport and energy system design and analysis for smart city areas

Reliable and affordable future zero emission power, heat and transport systems require efficient and versatile energy storage and distribution systems. This paper answers the question whether for city areas, solar and wind electricity together with fuel cell electric vehicles as energy generators and distributors and hydrogen as energy carrier, can provide a 100% renewable, reliable and cost effective energy system, for power, heat, and transport. A smart city area is designed and dimensioned based on European statistics. Technological and cost data is collected of all system components, using existing technologies and well-documented projections, for a Near Future and Mid Century scenario. An energy balance and cost analysis is performed. The smart city area can be balanced requiring 20% of the car fleet to be fuel cell vehicles in a Mid Century scenario. The system levelized cost in the Mid Century scenario is 0.09 €/kWh for electricity, 2.4 €/kg for hydrogen and specific energy cost for passenger cars is 0.02 €/km. These results compare favorably with other studies describing fully renewable power, heat and transport systems.     

Advanced reactor concept for complex hydrides: Hydrogen absorption from room temperature

Complex hydride materials (CxH) are potential candidates for hydrogen storage in automotive applications due to their high hydrogen storage capacities. However, the reaction rates of these materials are rather low at temperatures below 100 °C implying negative effects on absorption performance e.g. at a fuelling station. In this paper simulated and experimental results of a new reactor concept that can improve the dynamic reactor performance are presented. This concept is based on the combination of a metal hydride (MeH) and a CxH in one reactor, separated by a gas permeable layer. The storage capacity of available MeH materials is just ∼1 wt.%, however, they show very high reaction rates even at room temperature. Thus, the idea of this concept is to combine both: the high storage capacity of the CxH material and the high reaction rate of the MeH material. The two reference materials for this study are 2LiNH₂–1.1MgH₂–0.1LiBH₄–3 wt.%ZrCoH₃ (Li–Mg–N–H) and LaNi_4.3Al_0.4Mn_0.3 (MeH). In the first part, 2D simulation results are presented showing the development of a reaction front from the core to the annulus of the tubular reactor caused by the fast exothermal absorption reaction of the MeH material. In the second part, experimental results of a 50 g lab-scale reactor and simulated scenarios are presented and used for model validation. In the present scenario it has been possible to reduce the time to initiate the absorption reaction from room temperature by approximately 500 s.     

Emergency responders' perceptions of Hydrogen Fuel Cell Vehicle: A qualitative study on the U.K. fire and rescue services

Due to the fast growth of the Hydrogen Fuel Cell Vehicle (HFCV) market, the chances of these vehicles being involved in road crashes is also likely to increase. However, to date, studies into the Emergency Responders' perceptions of the HFCV have been limited. This paper investigates such perceptions of HFCVs through the interviews with firefighters. Through a pilot study results, initial findings suggest that firefighters are the ones who work next to the HFCV in post-crash scenarios, hence, they can provide more insightful information. As a result, 19 themes regarding their perceptions were discovered. The results show that the firefighters have different perceptions of the HFCV regarding the “economic cost”. Further analysis indicates the contradictions in their perceptions, and also shows they had more concerns about rescue-oriented safety rather than the fire-oriented safety. Finally, recommendations to address these concerns are discussed as well as the political implications of the results.     

Successful pathway for locally driven fuel cell electric vehicle adoption: Early evidence from South Korea

South Korea is an outstanding pioneer of fuel cell electric vehicle (FCEV) technology, an industry that is fundamental to the hydrogen ecosystem. This study aims to explore possible pathways for the successful adoption of FCEV in the local region. By using the fuzzy-set quality comparative analysis (fs/QCA) method, we identify three auspicious pathways based on the 16 regional cases in Korea. We find that, first, a large number of hydrogen (H₂) stations will lead to successful FCEV adoption (H₂ STATION→FCEV). Second, the combination of high levels of greenhouse gases(GHGs) and the local government-driven future construction plans of H₂ stations can also be a remarkable pathway (GHGs1 PLAN→FCEV). Lastly, a combination of high levels of GHGs and subsidies can be another compelling pathway (GHGs1 SUBSIDIES→FCEV). This study provides early evidence of FCEVs adoption and can be of use to latecomer countries to the hydrogen economy.     

Advanced reactor concept for complex hydrides: Hydrogen desorption at fuel cell relevant boundary conditions

Hydrogen storage in complex hydrides can be a storage option in automotive applications due to the high theoretical hydrogen storage capacities. As hydrogen is bonded by a chemical reaction to the solid state storage material, it is just released when heat is provided. In an automotive application for complex hydrides, this heat source can possibly be provided by the waste heat of a high temperature PEM fuel cell. However, for the application of existing complex hydride materials the temperature level of the fuel cell at 180 °C is still quite low leading to low desorption rates. A new reactor concept based on the addition of a metal hydride (MeH) to a complex hydride (CxH) reactor, separated by a gas permeable separation layer, can improve the desorption performance. In this paper, the effects of this reactor concept on desorption performance are studied using the two reference materials 2LiNH₂–1.1MgH₂–0.1LiBH₄–3 wt.%ZrCoH₃ and LaNi_4.3Al_0.4Mn_0.3. First, a model is developed and 2D simulations are performed using a driving scenario. Then, the model is validated by experimental data that has been obtained using a ∼600 g lab scale reactor. Concluding, there exist two main advantages of the combination reactor concept: The desorption time at a pressure above the fuel cell supply pressure is extended by a factor of 1.2, and 94 instead of 84% of the max. mass of hydrogen stored in the material can be desorbed at technically relevant boundary conditions.     

Hydrogen diffusion in Fe4N: Implication for an effective hydrogen diffusion barrier

The diffusion behavior of hydrogen in steel plays a significant role in understanding the mechanism of hydrogen embrittlement which may lead to the failure of steel. In the present work, density functional theory based first-principles calculations were performed to investigate the hydrogen diffusion in Fe₄N at atomic level. The results showed that the hydrogen atom in the Fe₄N structure didn't diffuse until the temperature increased up to 1350K, indicating a layer of Fe₄N covering on the iron could be a good candidate to trap the highly diffusive hydrogen atoms and prevent the aggregation of hydrogen which is the precursor of hydrogen embrittlement.     

Scenario analysis on alternative fuel/vehicle for China’s future road transport: Life-cycle energy demand and GHG emissions

The rapid growth of vehicles has resulted in continuing growth in China’s oil demand. This paper analyzes future trends of both direct and life cycle energy demand (ED) and greenhouse gas (GHG) emissions in China’s road transport sector, and assesses the effectiveness of possible reduction measures by using alternative vehicles/fuels. A model is developed to derive a historical trend and to project future trends. The government is assumed to do nothing additional in the future to influence the long-term trends in the business as usual (BAU) scenario. Four specific scenarios are used to describe the future cases where different alternative fuel/vehicles are applied. The best case scenario is set to represent the most optimized case. Direct ED and GHG emissions would reach 734 million tonnes of oil equivalent and 2384 million tonnes carbon dioxide equivalent by 2050 in the BAU case, respectively, more than 5.6 times of 2007 levels. Compared with the BAU case, the relative reductions achieved in the best case would be 15.8% and 27.6% for life cycle ED and GHG emissions, respectively. It is suggested for future policy implementation to support sustainable biofuel and high efficient electric-vehicles, and the deployment of coal-based fuels accompanied with low-carbon technology.     

Tourist preferences for fuel cell vehicle rental: going green with hydrogen on the island of Tenerife

Using a discrete choice experiment (DCE), a survey of international tourists on the island of Tenerife is conducted to examine preferences for fuel cell vehicle (FCV) rental while on vacation. Survey respondents were generally supportive of FCVs and willing to hire one as part of their trip but for most individuals this is contingent on an adequate fuel station infrastructure. A latent class model was used to identify three distinct groups; one of which potentially represent early adopters – they have a high willingness-to-pay (WTP) for green hydrogen and are more likely to accept a low number of fuel stations but it could be challenging to convince them to use FCVs if they are not run on green hydrogen.     

Hydrogen supply chain architecture for bottom-up energy systems models. Part 1: Developing pathways

The integration of hydrogen energy systems in the overall energy system is an important and complex subject for hydrogen supply chain management. The efficiency of the integration depends on finding optimum pathways for hydrogen supply. Accordingly, energy systems modelling methods and tools have been implemented to obtain the best configuration of hydrogen processes for a defined system. The appropriate representation of hydrogen technologies becomes an important stage for energy system modelling activities. This study, split in consecutive parts, has been conducted to analyse how representative hydrogen supply pathways can be integrated in energy systems modelling. The current paper, the first part of a larger study, presents stylised pathways of hydrogen supply chain options, derived on the basis of a detailed literature review. It aims at establishing a reference hydrogen energy system architecture for energy modelling tools. The subsequent papers of the study will discuss the techno-economic assumptions of the hydrogen supply chain components for energy modelling purposes.     

Hydrogen supply chain architecture for bottom-up energy systems models. Part 2: Techno-economic inputs for hydrogen production pathways

This article is the second paper of a serial study on hydrogen energy system modelling. In the first study, we proposed a stylized hydrogen supply chain architecture and its pathways for the representation of hydrogen systems in bottom-up energy system models. In this current paper, we aim to present and assess techno-economic inputs and bandwidths for a hydrogen production module in bottom-up energy system models. After briefly summarizing the current technological status for each production method, we introduce the parameters and associated input data that are required for the representation of hydrogen production technologies in energy system modelling activities. This input data is described both as numeric values and trend line modes that can be employed in large or small energy system models. Hydrogen production technologies should be complemented with hydrogen storage and delivery pathways to fully understand the system integration. In this context, we will propose techno-economic inputs and technological background information for hydrogen delivery pathways in later work, as the final paper of this serial study.     

The possibility of an accidental scenario for marine transportation of fuel cell vehicle: Hydrogen releases from TPRD by radiant heat from lower deck

In case fires break out on the lower deck of a car carrier ship or a ferry, the fuel cell vehicles (FCVs) parked on the upper deck may be exposed to radiant heat from the lower deck. Assuming that the thermal pressure relief device (TPRD) of an FCV hydrogen cylinder is activated by the radiant heat without the presence of flames, hydrogen gas will be released by TPRD to form combustible air-fuel mixtures in the vicinity. To investigate the possibility of this accident scenario, the present study investigated the relationship between radiant heat and TPRD activation time and evaluated the possibility of radiant heat causing hydrogen releases by TPRD activation under the condition of deck temperature reaching the spontaneous ignition level of the tires and other automotive parts. It was found: a) the tires as well as polypropylene and other plastic parts underwent spontaneous ignition before TPRD was activated by radiant heat and b) when finally TPRD was activated, the hydrogen releases were rapidly burned by the flames of the tires and plastic parts on fire. Consequently it was concluded that the explosion of air-fuel mixtures assumed in the accident scenario does not occur in the real world.     

Safety approach for composite pressure vessels for road transport of hydrogen. Part 1: Acceptable probability of failure and hydrogen mass

Hydrogen is a promising alternative for current energy carriers. Compressed gas cylinders are the storage systems closest to the commercialization of hydrogen in vehicles. The safety factors in current standards are seen as restrictive for further growth and competitiveness of hydrogen infrastructure. A probabilistic approach can be employed in order to give a rational background to the safety factors. However, an acceptable probability of failure needs to be estimated before calculating the safety factors. The discussion of determining the acceptable probability must include the mass of hydrogen since this determines the consequences of an accident. It is concluded that an annual probability of failure of 10⁻⁷ would be appropriate for small pressure vessels containing a few kilograms of hydrogen. Larger pressure vessels of a few hundred kilograms or more should be designed for an annual probability 10⁻⁸.