Publications

Alternative sources of energy are on the rise primarily because of environmental concerns in addition to the depletion of fossil fuel reserves. Currently there are many alternatives approaches and attempts to introduce alternative energy sources in the field of transport. This article centers around the need to explore additional energy sources beyond the current ones in use. It delves into individual energy sources that can be utilized for transportation including their properties production methods and the advantages and disadvantages associated with their use across different types of drives. The article not only examines the situation in the Czech Republic but also in other nations. In addition to addressing future mobility the thesis also considers how the utilization of new energy sources may impact the environment.

This paper investigates the performance of hydrogen-fueled spark-ignited single-cylinder Cooperative Fuel Research using experimental and numerical approaches. This study examines the effect of the air–fuel ratio on engine performance emissions and knock behaviour across different compression ratios. The results indicate that λ significantly affects both engine performance and emissions with a λ value of 2 yielding the highest efficiency and lowest emissions for all the tested compression ratios. Combustion analysis reveals normal combustion at λ ≥ 2 while knocking combustion occurs at λ < 2 irrespective of the tested compression ratios. The Livenwood–Wu integral approach was evaluated to assess the likelihood of end-gas autoignition based on fuel reactivity demonstrating that both normal and knocking combustion possibilities are consistent with experimental investigations. Combustion analysis at the ignition timing for maximum brake torque conditions demonstrates knock-free stable combustion up to λ = 3 with increased end-gas autoignition at lower λ values. To achieve knock-free combustion at those low λs the spark timings are significantly retarded to after top dead center crank angle position. Engine-out NOx emissions consistently increase in trend with a decrease in the air–fuel ratio of up to λ = 3 after which a distinct variation in NOx is observed with an increase in the compression ratio.

Compressed hydrogen storage is an energy-efficient alternative to liquefaction and in the absence of underground salt formations reservoirs like rock caverns mining shafts and cased boreholes are gaining traction. The limited reservoir volume constrained by excavation or drilling results in short high-pressure cycles. Thus effective temperature control is crucial to maintain integrity and maximize hydrogen density. This study presents a validated numerical model with open-access code for simulating heat exchange and predicting operating pressure and temperature for underground hydrogen storage in tanks or caverns. The validation encompasses analytical solutions and existing cylindrical models. Results highlight the heat transfer’s impact on hydrogen density and the limited penetration depth of the thermal perturbation underscoring the need for simulating heat transfer across multiple layers especially in restrictive media like cement. Managing injection and extraction flow rates is crucial to limit temperature peaks for larger radius reservoirs where heat transfer is less efficient.

The European Union is committed to a 55% reduction in greenhouse gas emissions by 2030 as outlined in the Green Deal and Climate Law initiatives. In response to geopolitical events the RePowerEU initiative aims to enhance energy self-sufficiency reduce reliance on Russian natural gas and promote hydrogen utilization. Hydrogen valleys localized ecosystems integrating various hydrogen supply chain elements play a key role in this transition particularly benefiting isolated regions like islands. This manuscript focuses on optimizing a Centralized Green Hydrogen Production Facility (CGHPF) on the island of Crete. A mixed-integer linear programming framework is proposed to optimize the CGHPF considering factors such as land area wind and solar potential costs and efficiency. Additionally an in-depth sensitivity analysis is conducted to explore the impact of key factors on the economic feasibility of hydrogen investments. The findings suggest that hydrogen can be sold in Crete at prices as low as 3.5 EUR/kg. Specifically it was found in the base scenario that selling hydrogen at 3.5 EUR/kg the net profit of the investment could be as high as EUR 6.19 million while the capacity of the solar and wind installation supplying the grid hydrogen facility would be 23.51 MW and 52.97 MW respectively. It is noted that the high profitability is justified by the extraordinary renewable potential of Crete. Finally based on our study a policy recommendation to allow a maximum of 20% direct penetration of renewable sources of green hydrogen facilities into the grid is suggested to encourage and accelerate green hydrogen expansion.

Green hydrogen presents a promising solution for transitioning from fossil fuels to a clean energy future particularly with the application of fuel cell electric vehicles (FCEVs). However the hydrogen refuelling process for FCEVs requires extensive pre-cooling to achieve fast filling times. This study presents experiments and simulations of a hydrogen refuelling station equipped with an adaptable cold-fill unit aiming to maximize fuelling efficiencies. For this purpose we developed and experimentally validated simulation models for a hydrogen tank and an aluminium block heat exchanger. Different pre-cooling parameters affect the final tank temperatures during the parallel filling of three 350 L type IV tanks. The results indicate significant potential for optimizing the required cooling energy with achievable savings of over 50 % depending on the pre-cooling strategy. The optimized pre-cooling strategies and energy savings aid in advancing the refuelling process for FCEVs effectively contributing to the transition to clean energy.

New hypotheses for reusing platforms reaching their end-of-life have been investigated in several works discussing the potential conversions of these infrastructures from recreational tourism to fish farming. In this perspective paper we discuss the conversion options that could be of interest in the context of the current energy transition with reference to the off-shore Italian scenario. The study was developed in support of the development of a national strategy aimed at favoring a circular economy and the reuse of existing infrastructure for the implementation of the energy transition. Thus the investigated options include the onboard production of renewable energy hydrogen production from seawater through electrolyzers CO2 capture and valorization and platform reuse for underground fluid storage in depleted reservoirs once produced through platforms. Case histories are developed with reference to a typical fictitious platform in the Adriatic Sea Italy to provide an engineering-based approach to these different conversion options. The coupling of the platform with the underground storage to set the optimal operational conditions is managed through the forecast of the reservoir performance with advanced numerical models able to simulate the complexity of the phenomena occurring in the presence of coupled hydrodynamic geomechanical geochemical thermal and biological processes. The results of our study are very encouraging because they reveal that no technical environmental or safety issues prevent the conversion of offshore platforms into valuable infrastructure contributing to achieving the energy transition targets as long as the selection of the conversion option to deploy is designed taking into account the system specificity and including the depleted reservoir to which it is connected when relevant. Socio-economic issues were not investigated as they were out of the scope of the project.

Thermodynamic modeling of hydrogen tank refueling i.e. 0 dimension (0D) model considers the gas in the tank as a single homogeneous volume. Based on thermodynamic considerations i.e. mass and energy balance equations the gas temperature and pressure predicted at each time step are volume-averaged. These models cannot detect the onset of the thermal stratification nor the maximum local temperature of the gas inside the tank.<br/>For safety reasons the temperature must be maintained below 85 °C in the composite tank. When thermal stratification occurs the volume-averaged gas temperature predicted by 0D models can be below 85 °C while local temperature may significantly exceed 85 °C. Then thermally stratified scenarios must be predicted to still employ 0D models safely.<br/>Up to now only computational fluid dynamics (CFD) approaches can predict the onset of the thermal stratification and estimate the amplitude of thermal gradients. However CFD approaches require much larger computational resources and CPU time than 0D models. This makes it difficult to use CFD for parametric studies or a live-stream temperature prediction for embedded applications. Previous CFD studies revealed the phenomenon of jet deflection during horizontal refueling of hydrogen tanks. The cold hydrogen injected into the warm gas bulk forms a round jet sinking down towards the lower part of the tank due to buoyancy forces. The jet breaks the horizontal symmetry and dumps the cold gas towards the lower part of the tank.<br/>The jet behavior is a key factor for the onset of the thermal stratification for horizontally filled tanks. Free round jets released in a homogeneous environment with a different density than the jet density were extensively investigated in the literature. A buoyant round jet modeling can be applied to predict the jet deflection in the tank. It requires initial conditions that can be provided by 0D refueling models. Therefore 0D models coupled with a buoyant round jet modeling can be used to predict the onset of the thermal stratification without CFD simulation. This approach clarifies the validity domain of 0D models and thus improves the safety of engineering applications

The impact of ship emission reductions can be maximised by considering climate health and environmental effects simultaneously and using solutions fitting into existing marine engines and infrastructure. Several options available enable selecting optimum solutions for different ships routes and regions. Carbon-neutral fuels including low-carbon and carbon-negative fuels from biogenic or non-biogenic origin (biomass waste renewable hydrogen) could resemble current marine fuels (diesel-type methane and methanol). The carbon-neutrality of fuels depends on their Well-to-Wake (WtW) emissions of greenhouse gases (GHG) including carbon dioxide (CO2) methane (CH4) and nitrous oxide emissions (N2O). Additionally non-gaseous black carbon (BC) emissions have high global warming potential (GWP). Exhaust emissions which are harmful to health or the environment need to be equally removed using emission control achieved by fuel engine or exhaust aftertreatment technologies. Harmful emission species include nitrogen oxides (NOx) sulphur oxides (SOx) ammonia (NH3) formaldehyde particle mass (PM) and number emissions (PN). Particles may carry polyaromatic hydrocarbons (PAHs) and heavy metals which cause serious adverse health issues. Carbon-neutral fuels are typically sulphur-free enabling negligible SOx emissions and efficient exhaust aftertreatment technologies such as particle filtration. The combinations of carbon-neutral drop-in fuels and efficient emission control technologies would enable (near-)zero-emission shipping and these could be adaptable in the short- to mid-term. Substantial savings in external costs on society caused by ship emissions give arguments for regulations policies and investments needed to support this development.

Low-carbon hydrogen could be an important component of a net-zero carbon economy helping to mitigate emissions in a number of hard-to-abate sectors. The United States recently introduced an escalating production tax credit (PTC) to incentivize production of hydrogen meeting increasingly stringent embodied emissions thresholds. Hydrogen produced via electrolysis can qualify for the full subsidy under current federal accounting standards if the input electricity is generated by carbon-free resources but may fail to do so if emitting resources are present in the generation mix. While use of behind-the-meter carbon-free electricity inputs can guarantee compliance with this standard the PTC could also be structured to allow producers using grid-supplied electricity to qualify subject to certain clean energy procurement requirements. Herein we use electricity system capacity expansion modeling to quantitatively assess the impact of grid-connected electrolysis on the evolution of the power sector in the western United States through 2030 under multiple possible implementations of the clean hydrogen PTC. We find that subsidized grid-connected hydrogen production has the potential to induce additional emissions at effective rates worse than those of conventional fossil-based hydrogen production pathways. Emissions can be minimized by requiring grid-based hydrogen producers to match 100% of their electricity consumption on an hourly basis with physically deliverable ‘additional’ clean generation which ensures effective emissions rates equivalent to electrolysis exclusively supplied by behind-the-meter carbon-free generation. While these requirements cannot eliminate indirect emissions caused by competition for limited clean resources which we find to be a persistent result of large hydrogen production subsidies they consistently outperform alternative approaches relying on relaxed time matching or marginal emissions accounting. Added hydrogen production costs from enforcing an hourly matching requirement rather than no requirements are less than $1 kg−1 and can be near zero if clean firm electricity resources are available for procurement.

Underground hydrogen storage in saline aquifers is a promising way to store large amounts of energy. Utilization of gas cushion enhances the deliverability of the storage and increases the volume of recovery gas. The key factor for the cushion characterization is cushion gas and storage gas mixing which can be used for simulation of mixing zone evolution. In this work coreflooding setup utilizing Raman spectroscopy is built and used for dispersion coefficient determination. Berea sandstone rock core is used as a test sample for setup validation and core entry/exit effects estimation. Dispersion for hydrogen and methane as displacing fluids is determined for 4 locations perspective for hydrogen storage in Poland is found. Reservoir structures most suitable for pure hydrogen or hydrogen/methane blend storage are selected.