Germany

High fluctuations in the combustion process from one cycle to another referred to as cycle-by-cycle variations can have adverse effects on internal combustion engine performances particularly in spark ignition (SI) engines. These effects encompass incomplete combustion the potential for misfires and adverse impacts on fuel economy. Furthermore the cycle-by-cycle variations can also affect a vehicle’s drivability and overall comfort especially when operating under lean-burn conditions. Although many cycle-by-cycle analyses have been investigated extensively in the past there is limited in-depth knowledge available regarding the causes of cycle-by-cycle (CbC) variations in hydrogen lean-burn SI engines. Trying to contribute to this topic the current study presents a comprehensive analysis of the CbC variations based on the cylinder pressure data. The study was carried out employing a hydrogen single-cylinder research SI engine. The experiments were performed by varying more than fifty operating conditions including the variations in lambda spark advance boost pressure and exhaust gas recirculation however the load and speed were kept constant throughout the experimental campaign. The results indicate that pressure exhibits significant variations during the combustion process and minor variations during non-combustion processes. In the period from the inlet valve close till the start of combustion pressure exhibits the least variations. The coefficient of variation of pressure (COVP) curve depicts three important points in H2-ICE as well: global minima global maxima and second local minima. The magnitude of the COVP curve changes across all the operating conditions however the shape of the COVP curve remains unchanged across all the operating conditions indicating its independence from the operating condition in an H2-ICE. This study presents an alternative approach for a quick combustion analysis of hydrogen engines. Without the need for more complex methodologies like heat release rate analysis the presented cylinder pressure cycle-by-cycle analysis enables a quick and precise identification of primary combustion features (start of combustion center of combustion end of combustion and operation condition stability). Additionally the engine control unit could implement these procedures to automatically adjust cycle-by-cycle variations therefore increasing engine efficiency.

This study identifies supply options for sustainable urban energy systems which are robust to external system changes. A multi-criteria optimization model is used to minimize greenhouse gas (GHG) emissions and financial costs of a reference system. Sensitivity analyses examine the impact of changing boundary conditions related to GHG emissions energy prices energy demands and population density. Options that align with both financial and emission reduction and are robust to system changes are called “no-regret” options. Options sensitive to system changes are labeled as “potential-risk” options.<br/>There is a conflict between minimizing GHG emissions and financial costs. In the reference case the emission-optimized scenario enables a reduction of GHG emissions (-93%) but involves higher costs (+160%) compared to the financially-optimized scenario.<br/>No-regret options include photovoltaic systems decentralized heat pumps thermal storages electricity exchange between sub-systems and with higher-level systems and reducing energy demands through building insulation behavioral changes or the decrease of living space per inhabitant. Potential-risk options include solar thermal systems natural gas technologies high-capacity battery storages and hydrogen for buildiing energy supply.<br/>When energy prices rise financially-optimized systems approach the least-emission system design. The maximum profitability of natural gas technologies was already reached before the 2022 European energy crisis.

Hydrogen storage is crucial to developing secure renewable energy systems to meet the European Union’s 2050 carbon neutrality objectives. However a knowledge gap exists concerning the site-specific performance and economic viability of utilizing underground gas storage (UGS) sites for hydrogen storage in Europe. We compile information on European UGS sites to assess potential hydrogen storage capacity and evaluate the associated current and future costs. The total hydrogen storage potential in Europe is 349 TWh of working gas energy (WGE) with site-specific capital costs ranging from $10 million to $1 billion. Porous media and salt caverns boasting a minimum storage capacity of 0.5 TWh WGE exhibit levelized costs of $1.5 and $0.8 per kilogram of hydrogen respectively. It is estimated that future levelized costs associated with hydrogen storage can potentially decrease to as low as $0.4 per kilogram after three experience cycles. Leveraging these techno-economic considerations we identify suitable storage sites.

Power-to-gas technology can be used to convert excess power from renewable energies to hydrogen by means of water electrolysis. This hydrogen can serve as “chemical energy storage” and be converted back to electricity or fed into the natural gas grid. In the presented study a leak in a household pipe in a single-family house with a 13 KW heating device was experimentally investigated. An admixture of up to 40% hydrogen was set up to produce a scenario of burning leakage. Due to the outflow and mixing conditions a lifted turbulent diffusion flame was formed. This led to an additional examination point and expanded the aim and novelty of the experimental investigation. In addition to the fire safety experimental simulation of a burning leakage the resulting complex properties of the flame namely the lift-off height flame length shape and thermal radiation have also been investigated. The obtained results of this show clearly that as a consequence of the hydrogen addition the main properties of the flame such as lifting height flame temperature thermal radiation and total heat flux densities along the flame have been changed. To supplement the measurements with thermocouples imaging methods based on the Sobel gradient were used to determine the lifting height and the flame length. In order to analyze the determined values a probability density function was created.

Limiting global warming to 1.5 ◦C is crucial to prevent the worst effects of climate change. This entails also the decarbonization of the aviation sector which is considered to be a “hard-to-abate” sector and thus requires special attention regarding its sustainability transition. However transition pathways to a potentially climateneutral aviation sector are unclear with different stakeholders having diverse imaginations of the sector's future. This paper aims to analyze socio-technical imaginaries of climate-neutral aviation as different perceptions of various stakeholders on this issue have not been sufficiently explored so far. In that sense this work contributes to the current scientific debate on socio-technical imaginaries of energy transitions for the first time studying the case of the aviation sector. Drawing on six decarbonization reports composed by different interest groups (e.g. industry academia and environmental associations) three imaginaries were explored following the process of a thematic analysis: rethinking travel and behavioral change (travel innovation) radical modernization and technological progress (fleet innovation) and transition to alternative fuels and renewable energy sources (fuel innovation). The results reveal how different and partly conflicting socio-technical imaginaries are co-produced and how the emergence and enforceability of these imaginaries is influenced by the situatedness of their creators indicating that the sustainability transition of aviation also raises political issues. Essentially as socio-technical imaginaries act as a driver for change policymakers should acknowledge the existence of alternative and counter-hegemonic visions created by actors from civil society settings to take an inclusive and equitable approach to implementing pathways towards climate-neutral aviation.

In the context of the German Energiewende the current government intends to install six million heat pumps by 2030. Replacing gas heating by power has significant implications on the infrastructure. One of the biggest advantages of using gas is the existing storage portfolio. It has not been clarified yet how power demand should be structured on an annual level—especially since power storage is already a problem and solar power is widely promoted to fuel heat pumps despite having an inverse profile. In this article three different solutions namely hydrogen batteries and carbon capture and storage are discussed with respect to resources energy and financial demand. It shows that relying solely on batteries or hydrogen is not solving the structuring problem. A combination of all existing technologies (including fossil fuels) is required to structure the newly generated electricity demand

This paper describes a model of hydrogen blowdown dynamics for storage tanks needed for hydrogen safety engineering to accurately represent incident scenarios. Heat transfer through a tank wall affects the temperature and pressure dynamics inside the storage vessel and therefore the characteristics of the resulting hydrogen jet in case of loss of containment. Available non-adiabatic blowdown models are validated only against experiments on hydrogen storages at ambient temperature. Effect of heat transfer for cryo-compressed hydrogen can be more significant due to a larger temperature difference between the stored hydrogen and surrounding atmosphere especially in case of failure of equipment insulation. Previous work by the authors demonstrated that the heat transfer through a discharge pipe wall can significantly affect the mass flow rate of cryogenic hydrogen releases. To the authors’ knowledge thoroughly validated models of non-adiabatic blowdown dynamics for cryo-compressed hydrogen are currently missing. The present work further develops the non-adiabatic blowdown model at ambient temperature using the under-expanded jet theory developed at Ulster University to expand it to cryo-compressed hydrogen storages. The non-ideal behaviour of cryo-compressed hydrogen is accounted through the high-accuracy Helmholtz energy formulations. The developed model includes effect of heat transfer at both the tank and discharge pipe wall. The model is thoroughly validated against sixteen tests performed by Pro-Science on blowdown of hydrogen storage tanks with initial pressure 0.5-20 MPa and temperature 80-310 K through release nozzle of diameter 0.5-4.0 mm. The model well reproduces the experimental pressure and temperature dynamics during the entire blowdown duration.

Due to climate change there is an urgent need to decarbonize high-emission industries. As coal-based operations predominate in primary steelmaking the steel industry offers an exceptionally high potential for reducing greenhouse gas emissions. Alternative processes for almost fully decarbonized primary steelmaking exist but require substantial investments by steelmakers for their implementation while maintaining desired production levels during the transformation periods. In this context the energy carriers required change such that the transformation of the steelmaking processes is deeply intertwined with the transformation of the background system. For the first time we evaluate potential transformation pathways from the steelmakers’ perspective using a prospective life cycle assessment approach. We find that hydrogen may facilitate a reduction of direct emissions by around 96 % compared to conventional steelmaking in 2050. However indirect emissions remain at a high level throughout the transformation period unless the upstream stages of the value chain are transformed accordingly.

Subcooled liquid hydrogen (sLH2) is an onboard storage as well as a hydrogen refueling technology that is currently being developed by Daimler Truck and Linde to boost the mileage of heavy-duty trucks while also improving performance and reducing the complexity of hydrogen refueling stations. In this article the key technical aspects advantages challenges and future developments of sLH2 at vehicle and infrastructure levels will be explored and highlighted.

Hydrogen is experiencing an unprecedented global hype. Hydrogen is globally discussed as a possible future energy carrier and regarded as the urgently needed building block for the much needed carbon-neutral energy transition of hard-to-abate sectors to mitigate the effects of global warming. This article provides synthesised measurable sustainability criteria for analysing green hydrogen production proposals and strategies. Drawn from expert interviews and an extensive literature review this article proposes that a sustainable hydrogen production should consider six impact categories; Energy transition Environment Basic needs Socio-economy Electricity supply and Project planning. The categories are broken down into sixteen measurable sustainability criteria which are determined with related indicators. The article concludes that low economic costs can never be the only decisive criterion for the hydrogen production; social aspects must be integrated along the entire value chain. The compliance with the criteria may avoid social and ecological injustices in the planning of green hydrogen projects and increases inter alia the social welfare of the affected population.