Applications & Pathways

This paper focuses on the conceptual design optimization of liquid hydrogen aircraft and their performance in terms of climate impact cash operating cost and energy consumption. An automated multidisciplinary design framework for kerosene-powered aircraft is extended to design liquid hydrogen-powered aircraft at a conceptual level. A hydrogen tank is integrated into the aft section of the fuselage increasing the operating empty mass and wetted area. Furthermore the gas model of the engine is adapted to account for the hydrogen combustion products. It is concluded that for medium-range narrow-body aircraft using hydrogen technology the climate impact can be minimized by fying at an altitude of 6.0 km at which contrails are eliminated and the impact due to NOx emissions is expected to be small. However this leads to a deteriorated cruise performance in terms of energy and operating cost due to the lower lift-to-drag ratio (– 11%) and lower engine overall efciency (– 10%) compared to the energy-optimal solutions. Compared to cost-optimal kerosene aircraft the average temperature response can be reduced by 73–99% by employing liquid hydrogen depending on the design objective. However this reduction in climate impact leads to an increase in cash operating cost of 28–39% when considering 2030 hydrogen price estimates. Nevertheless an analysis of future kerosene and hydrogen prices shows that this cost diference can be signifcantly decreased beyond 2030.

Due to the aviation energy sector's increasing contribution to climate change and the impact of climate change on the aviation sector determining key energy policy and economic research priorities for enabling an effective and equitable aviation climate action is becoming an increasingly important topic. In this perspective we address this research need using a four-pronged methodology. It includes (i) identifying topical matters highlighted in the media (news); (ii) formulating novel and feasible policy and economic research challenges that pertain to these contemporary issues; (iii) cross-referencing the proposed research challenges with academic literature to confirm their novelty and refining them as necessary; and (iv) validating the importance novelty and feasibility of these research challenges through consultation with a diverse group of aviation experts in fuel policy technology and infrastructure fields. Our results highlight twelve main themes. Among these the top emerging policy and economic research challenges as prioritized by expert input are – (i) frameworks for equitable responsibility allocation between developed and developing country airlines for future emissions; (ii) cost analysis of airlines' net-zero by 2050 commitments; (iii) effectiveness and opportunity cost of airlines investing in offsetting relative to reduction measures; (iv) EU aviation policies' historical and potential effects on airfares demand emissions EU air carriers' competitiveness passenger traffic through EU hubs regional economies and social climate funds' ability to mitigate distributional effects of EU aviation policies. These identified priorities can steer both industry and academic research toward creating practical recommendations for policymakers and industry participants. When it comes to future research the ever-changing nature of the challenges in achieving aviation climate action means that our findings might need regular updates.

This review sets out to investigate the detrimental impacts of hydrogen gas (H2 ) on critical boiler components and provide appropriate state-of-the-art mitigation measures and future research directions to advance its use in industrial boiler operations. Specifically the study focused on hydrogen embrittlement (HE) and high-temperature hydrogen attack (HTHA) and their effects on boiler components. The study provided a fundamental understanding of the evolution of these damage mechanisms in materials and their potential impact on critical boiler components in different operational contexts. Subsequently the review highlighted general and specific mitigation measures hydrogen-compatible materials (such as single-crystal PWA 1480E Inconel 625 and Hastelloy X) and hydrogen barrier coatings (such as TiAlN) for mitigating potential hydrogen-induced damages in critical boiler components. This study also identified strategic material selection approaches and advanced approaches based on computational modeling (such as phase-field modeling) and data-driven machine learning models that could be leveraged to mitigate potential equipment failures due to HE and HTHA under elevated H2 conditions. Finally future research directions were outlined to facilitate future implementation of mitigation measures material selection studies and advanced approaches to promote the extensive and sustainable use of H2 in industrial boiler operations.

With the large-scale deployment of renewable energy the issue of wind power consumption has become increasingly prominent leading to serious wind energy abandonment. In order to promote energy sustainability this paper proposes a low-carbon economic scheduling model of an integrated energy system (IES) that combines the flexible supply–demand response with the diversified utilization of hydrogen energy. A mixedinteger linear programming model is developed and solved using the commercial solver GUROBI to obtain the scheduling scheme that minimizes total costs. First decoupling analysis is performed for combined heat and power (CHP) units and the organic Rankine cycle (ORC) is introduced to enable dynamic output adjustments. On the demand side a flexible demand response mechanism is introduced which allows various types of loads to transfer within the scheduling cycle or substitute for each other within the same period. Additionally combining the clean characteristics of hydrogen this paper introduces hydrogen-doped CHP and other utilization strategies and develops a diversified utilization structure of hydrogen. A small IES is used for case analysis to verify the effectiveness of the above strategies. The results show that the proposed strategy can entirely consume wind power reduce total cost by 21.32% and decrease carbon emissions by 44.83% thereby promoting low-carbon economic operation and sustainable energy development of the system.

Hydrogen energy as a zero-carbon emission type of energy is playing a significant role in the development of future electricity power systems. Coordinated operation of hydrogen and electricity will change the direction and shape of energy utilization in the power grid. To address the evolving power system and promote sustainable hydrogen energy development this paper initially examines hydrogen preparation and storage techniques summarizes current research and development challenges and introduces several key technologies for hydrogen energy application in power systems. These include hydrogen electrification technology hydrogen-based medium- and long-term energy storage and hydrogen auxiliary services. This paper also analyzes several typical modes of hydrogen–electricity coupling. Finally the future development direction of hydrogen energy in power systems is discussed focusing on key issues such as cost storage and optimization.

Shipping corridors act as the arteries of the global economy. The maritime shipping sector is also a major source of greenhouse gas emissions accounting for 2.9% of the global total. The international nature of the shipping sector combined with issues surrounding the use of battery technology means that these emissions are considered difficult to eliminate. This work explores the transition to renewable fuels by examining the use of electrofuels (in the form of liquid hydrogen methane methanol ammonia and Fischer-Tropsch fuel) to decarbonise large container ships from a technical economic and environmental perspective. For an equivalent range to current fossil fuel vessels the cargo capacity of vessels powered by electrofuels decreases by between 3% and 16% depending on the fuel of choice due to the lower energy density compared with conventional marine fuels. If vessel operators are willing to sacrifice range cargo space can be preserved by downsizing onboard energy storage which necessitates more frequent refuelling. For a realistic green hydrogen cost of €3.5/kg (10.5 €c/kWh) in 2030 the use of electrofuels in the shipping sector results in an increase in the total cost of ownership of between 124% and 731% with liquid hydrogen in an internal combustion engine being the most expensive and methanol in an internal combustion engine resulting in the lowest cost increase. Despite this we find that the increased transportation costs of some consumer goods to be relatively small adding for example less than €3.27 to the cost of a laptop. In general fuels which do not require cryogenic storage and can be used in internal combustion engines result in the lowest cost increases. For policymakers reducing the environmental impact of the shipping sector is a key priority. The use of liquid hydrogen which results in the largest cost increase offers a 70% reduction in GHG emissions for an electricity carbon intensity of 80 gCO2e/ kWh which is the greatest reduction of all fuels assessed in this work. A minimum carbon price of €400/tCO2 is required to allow these fuels to reach parity with conventional shipping operations. To meet European Union emissions reductions targets electricity with an emissions intensity below 40 gCO2e/kWh is required which suggests that for electrofuels to be truly sustainable direct connection with a source of renewable electricity is required.

The introduction of gaseous hydrogen (H2) into the intake air of a heavy-duty diesel engine results in H2-diesel dual-fuel (HDDF) combustion which offers a near-term pathway to reduce CO2 emissions in heavy-duty longhaul trucking. Since H2 introduction impacts oxygen availability combustion characteristics and emissions simultaneously it is imperative to appropriately optimize and control the input parameters including intake air pressure diesel injection timing and EGR ratio. This study investigates the impacts of these controlling parameters on the combustion characteristics limiting factors and emissions of an HDDF engine. Experimental tests were conducted on a 2.4 L single-cylinder research engine under medium load and speed conditions (1200 rpm 8 bar brake mean effective pressure) with varying H2 fractions. The results show that engine performance and combustion parameters are not solely influenced by H2 introduction. Instead the key factor is how H2 introduction affects combustion phasing and fuels equivalence ratio at various intake air pressures and diesel injection timings. The findings demonstrate that technical challenges in HDDF combustion such as combustion harshness (indicated by maximum rate of pressure rise) and unburned H2 (“H2 slip”) can be addressed through coordinated control of intake air pressure diesel injection timing and EGR ratio based on H2 energy ratio. At high H2 energy ratios adding 20% EGR effectively reduced combustion harshness by up to 40% and NOx emissions by 68% with negligible impact on brake thermal efficiency and H2 slip. At a given EGR level precise control of combustion phasing and intake pressure enabled the introduction of 40% H2 energy ratio resulting in 40% reduction in CO₂ emissions and 55% reduction in particulate matter emissions with no increase in NOx levels compared to the baseline diesel operation. These outcomes establish simultaneous adjustment of key engine control parameters as a practical strategy to maximize H2 introduction while addressing technical challenges in HDDF combustion. This ensures comparable engine performance with significantly lower CO2 emissions compared to conventional heavy-duty diesel engines.

The transport sector in France accounts for 30% of national emissions and will require significant decarbonization effort to achieve carbon neutrality in 2050. Various technological solutions from electric vehicles to renewable fuel such as biofuels and e-fuels as well as changes in demand are envisioned to reach this target. We build three technological foresight scenarios and two sufficiency variants mainly based on different readings of the European regulations banning the sale of internalcombustion-engine vehicles and setting Sustainable Aviation Fuel incorporation rates. The transport hydrogen and biomass sectors are modeled in system dynamics to assess the detail impacts of these scenarios on biomass resources and energy consumption. In all scenarios the total electricity demand increases drastically regardless of the technological choices made for the vehicle fleets mainly due to the production of e-fuels for aviation. None of the technological scenarios studied suggest that biomass supply is unfeasible. However in a scenario with low electrification there is a potentially increased dependence on imports for waste oils and fats and competing uses or tensions with other demand sectors may arise over some biomass for anaerobic digestion and lignocellulosic resources. To reduce these potential tensions and the demand for electricity sufficiency measures seem necessary in addition to technological advancements.

The steel industry is one of the major sources of greenhouse gas emissions with significant energy demand. Currently 73% of the world’s steel is manufactured through the coal-coke-based blast furnace-basic oxygen furnace route (BF-BOF) emitting about two tonnes of CO2 per tonne of steel produced. This review reports the major technologies recent developments challenges and technoeconomic comparison of steelmaking technol ogies emphasising the integration of hydrogen in emerging and established ironmaking and steelmaking pro cesses. Significant trials are underway especially in Germany to replace coal injected in the tuyeres of the blast furnace with hydrogen. However it is not clear that this approach can be extended beyond 30% replacement of coke because of the associated technical challenges. Direct smelting and fluidised bed technologies can emit 20%–30% less CO2 without carbon capture and storage utilisation. The implications of hydrogen energy in these technologies as a substitute for natural gas and coal are yet to be fully explored. A hydrogen-based direct reduction of iron ore (DRI) and steel scrap melting in an electric arc furnace (EAF) appeared to be the most mature technological routes to date capable of reducing CO2 emission by 95% but rely on the availability of rich iron concentrates as feed materials. Shaft furnace technologies are the common DRI-making process with a share of over 72% of the total production. The technology has been developed with natural gas as the main fuel and reductant. However it is now being adapted to operate predominantly on hydrogen to produce a low-carbon DRI product. Plasma and electrolysis-based iron and steelmaking are some of the other potential technologies for the application of hydrogen with a CO2 reduction potential of over 95%. However these technologies are in the preliminary stage of development with a technology readiness level of below 6. There are many technological challenges for the application of hydrogen in steel manufacturing such as challenges in distributing heat due to the endothermic H2 reduction process balancing carbon content in the product steel (particularly using zerocarbon DRI) removal of gangue materials and sourcing of cost-competitive renewable hydrogen and highquality iron ore (65>Fe). As iron ore quality degrades worldwide several companies are considering melting DRI before steelmaking possibly using submerged arc technology to eliminate gangue materials. Hence sig nificant laboratory and pilot-scale demonstrations are required to test process parameters and product qualities. Our analysis anticipates that hydrogen will play an instrumental role in decarbonising steel industries by 2035.

The derivation of an efficient operational strategy for storing intermittent renewable energies using a hybrid battery-hydrogen energy storage system is a difficult task. One approach for deriving an efficient operational strategy is using mathematical optimization in the context of model predictive control. However mathematical optimization derives an operational strategy based on a non-exact mathematical system representation for a specified prediction horizon to optimize a specified target. Thus the resulting operational strategies can vary depending on the optimization settings. This work focuses on evaluating potential improvements in the operational strategy for a hybrid batteryhydrogen energy storage system using mathematical optimization. To investigate the operation a simulation model of a hybrid energy storage system and a tailor-made mixed integer linear programming optimization model of this specific system are utilized in the context of a model predictive control framework. The resulting operational strategies for different settings of the model predictive control framework are compared to a rule-based controller to show the potential benefits of model predictive control compared to a conventional approach. Furthermore an in-depth analysis of different factors that impact the effectiveness of the model predictive controller is done. Therefore a sensitivity analysis of the effect of different electricity demands and resource sizes on the performance relative to a rule-based controller is conducted. The model predictive controller reduced the energy consumption by at least 3.9 % and up to 17.9% compared to a rule-based controller. Finally Pareto fronts for multi-objective optimizations with different prediction and control horizons are derived and compared to the results of a rule-based controller. A cost reduction of up to 47 % is achieved by a model predictive controller with a prediction horizon of 7 days and perfect foresight. Keywords: Model Predictive Control Optimization Mixed Integer Linear Programming Hybrid Battery-Hydrogen Energy Storage System