Energies, Volume 16, Issue 19 (October-1 2023) – 257 articles

As the electrification process of aircrafts continues to advance, the propulsion motor system, as its core component, has received more attention and research. This paper summarizes and analyzes the development status, research focus and typical cases in this field in recent years. Firstly, it analyzes the basic structure and principle of five common motors, summarizes the current status of their respective applications in electric aircrafts, and compares them to determine the most suitable type of motor for use as a propulsion motor, focusing on various performance indexes. Then, the optimized design of propulsion motors is generally divided into two categories, namely high power density and fault tolerance. Starting from the basic relationship equation of motor design, the basic method to improve the power density of motors is pointed out; at the same time, according to the basic principles and objectives of the fault tolerance of motors, the fault tolerance design is divided into two aspects, namely the redundant design and the design to improve the fault tolerance capability. Finally, this paper summarizes the current development status of the propulsion motor system and the existing problems and points out the main development direction of this field in the future, so as to provide reference for the further development of the electric propulsion system of aircraft. Full article

In the present work, a novel foam burner design is proposed and experimentally evaluated for operation with highly diluted syngas mixtures. The lab-scale burner consists of a purpose-built, square-shaped, high-temperature-grade stainless steel tubular reactor filled with square-sectioned siliconized silico carbide (SiSiC) foams. The assembly was installed in an electrical furnace. Spatially resolved temperature measurements were obtained along the reactor axis, while simultaneous measurements of CO, CO₂, H₂, O₂, and N₂ were taken at the burner exit and the water levels were recorded upstream and downstream of the reactor. The results clearly show that flames can be stabilized along the reactor for a range of foam characteristics and operating conditions. Hydrogen conversion efficiencies in excess of 98%, and overall thermal efficiencies close to 95% were achieved for the selected operating conditions. Overall, the denser 10 ppi foam demonstrated superior combustion characteristics in terms of stability, lower enthalpy rises, and a wider operating range at the expense of a very modest pressure drop penalty. Finally, scanning electron microscopy, coupled with energy dispersion spectroscopy (SEM/EDS) and Raman spectroscopy analyses, was used to determine the morphological and compositional characteristics of the pristine and aged foams. After more than 100 h of operation, no significant performance degradation was observed, even though the burner design was subjected to considerable thermal stress. Full article

This paper presents the development of a wind energy conversion system co-simulation based on the Functional Mock-up Interface standard aiming at contributing to the development of co-simulation of large electrical power systems by means of open-source and standardized computational tools. Co-simulation enables the computational burden of a monolithic simulation to be shared among several processing units, significantly reducing processing time. Through the Functional Mock-up Interface standard, developed models are encapsulated into Functional Mock-up Unit, providing an extra means for the protection of intellectual property, a very appealing feature for end users, both in industry and academia. To achieve the decoupling of the subsystems, the Bergeron ideal transmission line model will be used, with travel time equal to the simulation time-step. The computational performance and effectiveness of the proposed co-simulation technique was evaluated with a wind power plant with 50 wind turbines. The system digital models were developed into Modelica language, while co-simulation was implemented in Python. Full article

Definitions of methodologies to regulate the quality of electricity supply services are a topic under active discussion in Brazil and worldwide. There are various ways to define limits and quality service goals. In Brazil, the regulation of limit indicators for consumer unit sets is carried out by the National Electric Energy Agency. Its latest revision took place in 2014, under the framework of Public Announcement No. 29/2014. The primary contribution of this research is the proposition of an artificial intelligence-assisted methodology, specifically utilizing machine-learning techniques capable of organizing and selecting the most relevant attributes for representing similar consumer sets. Tests were conducted with real data from the 2020 system. The results demonstrated that this methodology can select attributes from different categories, achieving data representativeness and clustering scores superior to those attained with attributes selected by the current ANEEL methodology. Furthermore, the proposed methodology exhibits greater replicability compared to the current approach. These outcomes contribute to the modernization of quality regulation in the electricity distribution sector, benefiting all stakeholders in the industry. Full article

The shelf-life of catalyst ink for fabricating polymer electrolyte fuel cells (PEFCs) is relevant for large-scale manufacturing with unforeseen production stops. In this study, the storage effects on the physicochemical characteristics of catalyst ink (Pt/C, Nafion, 2-propanol, water) and subsequently manufactured catalyst layers are investigated. Sedimentation analysis showed that catalyst particles are not fully stabilized by charge interaction induced by Nafion. Acetone was found to be an oxidation product, even in freshly prepared ink with platinum catalyzing the reaction. Rotating disk electrode analysis revealed that the electrochemically active surface area is, overall, minimally increased by storage, and the selectivity towards water formation (4-electron pathway) is unharmed within the first 48 h of storage. MEAs prepared from stored ink reach almost the same current density level after conditioning via potential cycling. The open-circuit voltage (OCV) increases due to increased catalyst availability. Scanning electron microscopy and mercury intrusion porosimetry showed that with increasing acetone content, the pore structure becomes finer, with a higher specific surface area. Electrochemical impedance spectroscopy revealed that this results in a more hindered mass transfer but lowered charge transfer resistance. The MEA with the highest OCV and power output and the lowest overall cell resistance was fabricated from catalyst ink stored for a duration of four weeks. Full article

As the next generation of advanced adiabatic compressed air energy storage systems is being developed, designing a novel integrated system is essential for its successful adaptation in the various grid load demands. This study proposes a novel design framework for a hybrid energy system comprising a CAES system, gas turbine, and high-temperature solid oxide fuel cells, aiming for power generation and energy storage solutions. The overall model of the hybrid power generation system was constructed in Aspen Plus^TM, and the mass balance, energy balance, and thermodynamic properties of the thermal system were simulated and analyzed. The results demonstrate that the hybrid system utilizes the functional complementarity of CAES and solid oxide fuel cells (SOFCs), resulting in the cascade utilization of energy, a flexible operation mode, and increased efficiency. The overall round-trip efficiency of the system is 63%, and the overall exergy efficiency is 67%, with a design net power output of 12.5 MW. Additionally, thermodynamic analysis shows that it is advisable to operate the system under lower ambient temperatures of 25 °C, higher compressor and turbine isentropic efficiencies of 0.9, a higher fuel utilization of 0.62, and optimal SOFC/MGT split air flow rates of 1.1 kg/s. The results of this article provide guidance for designing innovative hybrid systems and system optimization. Full article

In the current work, the operating conditions for the Fischer–Tropsch process were optimized using experimental testing, kinetic modelling, simulation, and optimization. The experiments were carried out using a Ce-Co/SiO₂ catalyst to examine how operating parameters affected the conversion of CO and product selectivity. A power-law kinetic model was used to represent the reaction rates in a mathematical model that was created to replicate the Fischer–Tropsch synthesis (FTS). It was decided to estimate the kinetic parameters using a genetic optimization technique. The developed model was validated for a range of operating conditions, including a temperature range of 200–240 °C, a pressure range of 5–25 bar, a H₂/CO ratio of 0.5–4, and a space velocity range of 1000–5000 mL/g_cat·h. The mean absolute relative error (MARE) between the experimental and predicted results was found to be 11.7%, indicating good agreement between the experimental data and the predicted results obtained by the mathematical model. Optimization was applied to maximize the production of liquid biofuels (C₅₊₎. The maximum C₅₊ selectivity was 91.66, achieved at an operating temperature of 200 °C, reactor total pressure of 6.29 bar, space velocity of 1529.58 mL/gcat·h, and a H₂/CO feed ratio of 3.96. The practical implications of the present study are maximizing liquid biofuel production from biomass and municipal solid waste (MSW) as a renewable energy source to meet energy requirements, reducing greenhouse gas emissions, and waste management. Full article

Intelligent anomaly detection for wind turbines using deep-learning methods has been extensively researched and yielded significant results. However, supervised learning necessitates sufficient labeled data to establish the discriminant boundary, while unsupervised learning lacks prior knowledge and heavily relies on assumptions about the distribution of anomalies. A long short-term memory-based variational autoencoder Wasserstein generation adversarial network (LSTM-based VAE-WGAN) was established in this paper to address the challenge of small and noisy wind turbine datasets. The VAE was utilized as the generator, with LSTM units replacing hidden layer neurons to effectively extract spatiotemporal factors. The similarity between the model-fit distribution and true distribution was quantified using Wasserstein distance, enabling complex high-dimensional data distributions to be learned. To enhance the performance and robustness of the proposed model, a two-stage adversarial semi-supervised training approach was implemented. Subsequently, a monitoring indicator based on reconstruction error was defined, with the threshold set at a 99.7% confidence interval for the distribution curve fitted by kernel density estimation (KDE). Real cases from a wind farm in northeast China have confirmed the feasibility and advancement of the proposed model, while also discussing the effects of various applied parameters. Full article

The Smart Readiness Indicator (SRI) was included in the third version of the Energy Performance of Buildings Directive (EPBD) and has since been used in research involving a variety of building types and climate zones. While numerous studies highlighted the qualitative characteristics of the current SRI framework, this work describes a methodology for adding quantitative features to it. It uses indicators for each effect area and proposes multiple standards as rating assessment factors. We specify the integration of this crucial component enhancing the framework. This enhanced framework is applied to a hypothetical use case, and the outcomes are compared with those of the current framework. The results demonstrate that the SRI score was increased after adding quantitative elements to the SRI framework. Full article

This study provides an overview of new trends in the development of cooling systems for electric motors. It includes a summary of academic research and patents for cooling systems implemented by leading motor manufacturers at TRL9. New trends in the cooling management of air and liquid cooling systems are discussed and analyzed with a focus on temperature distribution and its influence on the power-to-dimension ratio of electric motors. The prevailing cooling method for synchronous and asynchronous motors is air cooling using external fins, air circulation ducts, air gaps, and fan impellers to enhance efficiency and reliability. Internal cooling with rotor and stator ducts, along with optimized air duct geometry, shows potential to increase the power-to-dimension ratio and reduce motor size. Liquid cooling systems offer a power-to-dimension ratio of up to 25 kW/kg, achieved through redesigned cooling ducts, stator heat exchangers, and cooling tubes. However, liquid cooling systems are complex, requiring maintenance and high ingress protection ratings. They are advantageous for providing high power-to-dimension ratios in vehicles and aircraft. Discussions on using different refrigerants to improve efficient motor cooling are underway, with ozone-friendly natural refrigerants like CO₂ considered to be promising alternatives to low-pressure refrigerants with high global warming potential. Full article

Driven by China’s long-term energy transition strategies, the construction of large-scale clean energy power stations, such as wind, solar, and hydropower, is advancing rapidly. Consequently, as a green, low-carbon, and flexible storage power source, the adoption of pumped storage power stations is also rising significantly. Operations management is a significant factor that influences the performance of pumped storage power stations in various domains, including environmental protection, economic benefits, and social benefits. While existing studies have highlighted the importance of stakeholder partnering in operations management, a systematic exploration of the causal relationships between partnering, operations management, and the performance of pumped storage power stations—especially from a multi-energy complementarity perspective—remains untouched. This paper strives to shed light on the vital role of stakeholder partnering in augmenting the operations management and overall performance of pumped storage power stations, thereby contributing to China’s dual carbon goals. A comprehensive conceptual model was developed by reviewing the relevant literature to empirically examine the causal relationships among partnering, operations management, and power station performance, which was validated using data from the Liaoning Qingyuan Pumped Storage Power Station, which is the largest of its kind in Northeast China. The findings suggest: (1) Effective partnering among stakeholders, particularly with grid companies, significantly influences the operations management of pumped storage power stations, with deficiencies in partnering mainly attributed to the lack of effective communication channels and problem-solving mechanisms. (2) The level of operations management in China’s pumped storage power stations is relatively high, averaging a central score around 4.00 (out of a full score of 5) on operations management indicators. However, there is a need to concentrate on enhancing multi-energy complementarity coordination, digital management system development, and profitability. (3) Path analysis further unveils that partnering not only improves operations management but also boosts the performance of pumped storage power stations. These findings suggest a wide range of practical strategies for operations managers at pumped storage power stations to forge partnerships with stakeholders and integrate complementary resources, aiming to achieve excellence in performance. Full article

Ammonia is considered one of the attractive alternatives for fossil fuels to realize carbon neutralization. However, low chemical reactivity limits its use in compression ignition (CI) engines. This study investigated dual-fuel combustion, involving the use of ammonia for port fuel injection (PFI) and diesel for direct injection (DI) in a heavy-duty engine. Unregular emissions, specifically HCN, were studied for the first time in an ammonia–diesel engine. The combustion and emission performance of the engine with pure diesel mode was also studied to reveal the influence on ammonia addition. The engine was consistently operated at a fixed condition of 0.556 MPa IMEP and 800 r/min. The findings reveal the successful achievement of stable dual-fuel combustion in the tested engine. The addition of ammonia led to delayed ignition and an extended combustion duration. Implementing early pilot injection timing (SOI₁) strategies significantly improved ammonia combustion efficiency, elevating it from 74% to 89%. This enhancement could be attributed to the diesel injected during pilot injection, which facilitated ammonia decomposition. However, early pilot injection had adverse effects on emissions, including CO, THC, NO_x, N₂O, and HCN. Advancing the main injection timing (SOI₂) within the early SOI₁ strategies accelerated the oxidation processes for CO, THC, N₂O, and HCN. Nevertheless, this adjustment resulted in increased thermal NO_x emissions. The highest HCN emission detected in this study was 9.2 ppm. Chemical kinetics analysis indicated that HCN production occurred within the temperature range of 1000 K to 1750 K under fuel-lean conditions. Furthermore, H₂CN played a significant role in HCN formation as temperatures increased. More HCN was formed by H₂CN as temperature rose. Strategies such as increasing pilot injection fuel quantity, raising premixed gas intake temperature, or advancing combustion phases close to TDC could potentially reduce HCN emissions. Full article

Bioethanol is the most widely used alternative transportation fuel to petrol. Bioethanol is considered a clean, renewable, and environmentally friendly fuel that can contribute to climate change mitigation, decreased environmental pollution, and enhanced energy security. Commercial bioethanol production is based on traditional agricultural crops such as corn, sugarcane, and sugarbeet, primarily used as food and feed. In order to meet the growing demand for this fuel and decrease competition in the food and biofuel sectors for the same feedstock, other raw materials and process technologies have been intensively studied. Lignocellulosic biomass is one of the most abundant renewable resources, with it being rich in compounds that could be processed into energy, transportation fuels, various chemical compounds, and diverse materials. Bioethanol production from lignocellulosic biomass has received substantial attention in recent decades. This review gives an overview of bioethanol production steps from lignocellulosic biomass and challenges in the production process. The following aspects of bioethanol production are covered here, including pretreatment methods, process strategies, strain development, ethanol isolation and purification, and technical hurdles. Full article

The current techniques utilized for estimating seasonal fluctuations in earthing system resistance, including artificial neural networks (ANNs) and correlation/correction factors, rely on resistance records, soil resistivity measurements, and meteorological data collected across broad areas. However, they frequently fail to consider the impact of soil conditions and properties at the actual earthing location. As a solution, this research introduces a new method that models atmospheric conditions as soil suction and incorporates hydraulic soil properties (soil water retention characteristics and hydraulic conductivity) to estimate the seasonal changes in earthing resistance and performance. To illustrate this approach, this study constructs geometric models of vertical earthing rods for three homogeneous soil textures (clayey, silty, and sandy) utilizing COMSOL Multiphysics software. By coupling the differential equations governing electric current and water flow using Archie’s formula and solving numerically with the finite element method (FEM) for various soil suctions, this research reveals that soil water retention and resistivity variations are notably influenced by soil texture. Sandy soil displays higher variability, silt soil demonstrates moderate changes, while clayey soil exhibits lower fluctuation. By linking soil resistivity changes to soil suction and hydraulic properties, this innovative method predicts seasonal trends in earthing resistance and performance. Full article

This is a comprehensive research endeavor focused on enhancing the efficiency of the proposed solar cell design. The integration of the simulation techniques, judicious material selection, and meticulous performance metrics showcase a methodical approach toward creating a solar cell capable of achieving high efficiency across a wide spectrum of light in the AM 1.5 G1 sun solar cell illumination spectrum. Having said this, many researchers are still working on the efficiency potential—based on external radiative efficiency (ERE), open-circuit voltage loss, and fill factor loss—of high-efficiency solar cells. The solar cell is built on aluminum-doped zinc oxide (ZnO) as a transparent conductive oxide layer; aluminum nitride (AlN) as the window layer (emitter); an SWCNT layer as the absorber layer; gallium phosphide (GaP) as the contact layer; and silicon as the substrate. The proposed solar cell transmission, reflection, and absorption relative to the variations in wavelength band spectrum are studied. The conduction and valence band energy diagrams of the solar cell design structure are simulated against the layer thickness variations for the suggested solar cell structure. Short-circuit current density and maximum power variations are clarified versus the bias voltage. Light current density is simulated versus the bias voltage (J/V characteristics curve) of the suggested solar cell design structure. The carrier generation–recombination rate is also simulated by the COMSOL simulation program versus the layer thickness of the suggested solar cell structure. The solar cell circuit design has a fill factor (FF) value of 74.31% and a power conversion efficiency value of 29.91%. Full article

We propose a network optimization model for smart energy market management in the context of an uncertain environment. The network optimization considers the stochastic programming approach to capture the randomness of the unknown demands. We utilize the particle swarm optimization technique in the proposed model to solve the proposed optimization problem. The present research is based on the inclusion of stochastic demands and uncertain energy prices. Optimizing produced energy is crucial for efficient usage and meeting the targets. The proposed model also focuses on addressing sustainability concerns by minimizing energy consumption in the scheduling process. An improved particle swarm optimization technique is implemented for energy-efficient production. Parameters such as number of particles, iterations, and energy usage specification are customized. A fitness function is taken that considers both completion time and energy consumption. The optimal of energy consumption is also visualized. The decision makers employ risk aversion in the objective function of the optimization problem to measure the risk deviation of the expected energy management. Full article

Progressive and increasingly noticeable climate change is forcing the search for new energy sources to reduce greenhouse gas emissions, especially carbon dioxide. One way to reduce greenhouse gas emissions is by gradually replacing fossil fuels with biofuels. The authors of this work addressed the production of second-generation biofuel. The purpose of this study was to produce second-generation biodiesel from babassu palm oil (BBuE) and first-generation biodiesel from rapeseed oil (RME), to study their properties, and to determine the effect of the addition of these biodiesels to diesel fuel on selected properties of “B” fuels that affect the fuel–air mixture formation process and the combustion process. Biodiesel from babassu oil was produced because it is non-edible and has a different composition than canola oil. Then, fuels were prepared that were mixtures of diesel oil and biodiesel containing from 10 to 40% (v/v) BBuE or RME (B10, B20, B30, and B40).Tests were conducted on selected physicochemical properties of the obtained fuels. “B” fuels prepared with BBuE and DF were shown to have more favorable fuel properties than those obtained from RME and DF. Fuels that are blends of BBuE and DF have slightly higher heating values, higher cetane number values, a more favorable distillation curve, lower dynamic viscosity values as a function of temperature, and marginally lower flash point values compared to the corresponding blends of RME and DF. Esters with shorter molecules have been shown to have more favorable fuel properties. Full article

Power distribution systems (PDS) comprise essential electrical components and infrastructure that facilitate the delivery of electrical energy from a power transmission system to end users. Typically, the topology of distribution systems is radial, so that power goes from the substations to end users through main lines or feeders. However, the expansion of new feeders to accommodate new users and ever-growing energy demand have led to higher energy losses and deterioration of the voltage profile. To address these challenges, several solutions have been proposed, including the selection of optimal conductors, allocation of voltage regulators, utilization of capacitor banks, implementation of distributed generation, and optimal reconfiguration. Although reconfiguring the network is the most cost-effective approach, this solution might not be sufficient to completely minimize technical losses and improve system performance. This paper presents a novel approach that combines optimal distribution network reconfiguration (ODNR) with optimal conductor selection (OCS) to minimize power losses and enhance the voltage profiles of PDS. The key contribution lies in the integration of the ODNR and OCS into a single MILP problem, ensuring the attainment of globally optimal solutions. The proposed model was tested with benchmark 33-, 69-, and 85-bus test systems. The results allowed us to conclude that the combined effect of ODNR and OCS presents better results than when any of these approaches are applied either separately or sequentially. Full article

The compatibility of shipping with environmental protection is a subject that the international community is becoming increasingly concerned about, considering the threat of climate change. The current study aims to assess the worldwide shipping sector’s eco-efficiency performance for the first time using the Dynamic Slack-Based assess non-oriented Data Envelopment Analysis methodology, while the visualization of the results has been made with the geographic information system of ArcGIS. The findings show that the most vibrant shipping sectors in the world, such as the Marshall Islands, present the lowest eco-efficiency levels due to the nations’ roles as tax havens for shipowners. Furthermore, traditional maritime economies such as the Chinese one show a great growth in the eco-efficiency score due to the strategies of the shipping companies that are headquartered in the region to invest and adopt Environmental, Social, and Governance principles, which help them to achieve high scores in eco-efficiency. Finally, nations with small fleets have the greatest eco-efficiency score, as local governments have engaged in sustainable activities and initiatives over the previous four to five years to enable their marine industry to thrive and dominate the market. Full article

Energy Transition is changing the renewable energy participation in new distributed generation systems like the Local Energy Markets. Due to its inherent intermittent and variable nature, forecasting production and consumption load profiles will be more challenging and demand more complex predictive models. This paper analyzes the production, consumption load profile, and storage headroom% of the Cornwall Local Energy Market, using advanced statistical time series methods to optimize the opportunity market the storage units provide. These models also help the Energy Community storage reserves to meet contract conditions with the Distribution Network Operator. With this more accurate and detailed knowledge, all sites from this Local Energy Market will benefit more from their installation by optimizing their energy consumption, production, and storage. This better accuracy will make the Local Energy Market more fluid and safer, creating a flexible system that will guarantee the technical quality of the product for the whole community. The training of several SARIMAX, Exponential Smoothing, and Temporal Causal models improved the fitness of consumption, production, and headroom% time series. These models properly decomposed the time series in trend, seasonality, and stochastic dynamic components that help us to understand how the Local Energy Market consumes, produces, and stores energy. The model design used all power flows and battery energy storage system state-of-charge site characteristics at daily and hourly granularity levels. All model building follows an analytical methodology detailed step by step. A benchmark between these sequence models and the incumbent forecasting models utilized by the Energy Community shows a better performance measured with model error reduction. The best models present mean squared error reduction between 88.89% and 99.93%, while the mean absolute error reduction goes from 65.73% to 97.08%. These predictive models built at different prediction scales will help the Energy Communities better contribute to the Network Management and optimize their energy and power management performance. In conclusion, the expected outcome of these implementations is a cost-optimal management of the Local Energy Market and its contribution to the needed new Flexibility Electricity System Scheme, extending the adoption of renewable energies. Full article

This paper utilizes a life cycle assessment (LCA) to evaluate three heating systems’ energy resources and environmental impacts. The first system uses an electric heat pump that exclusively relies on geothermal energy. The second system operates on a gas boiler system that utilizes non-renewable electricity and natural gas. Lastly, the third system incorporates an absorption heat pump utilizing geothermal energy and natural gas. In the first step, cradle-to-gate assessments were prepared for the renewable, conventional, and mixed systems. The second step involved comparing the system scenarios based on their loads and energy resources. Primary energy, material resources, emissions, and impact categories were normalized and weighted using the CML, ReCiPe, and EF 3.0 methods. Finally, models for environmental reliability and complex decision support were developed. The novelty of this research lies in analyzing the ecological burden and energy usage of a mixed energy system that incorporates both renewable and non-renewable energy sources. The results show that the gas boiler system has a higher load, primarily due to the depletion of abiotic fossil fuels. However, the acidification is higher when an electric heat pump is used. The absorption heat pump system falls between the renewable and conventional systems in terms of both fossil depletion and acidification. Full article

Using low-temperature (shallow) groundwater as a heat source or heat sink is a common practice to supply space heating or cooling, especially in the United States, Canada, China, and several European countries. The groundwater heat pump (GWHP) system has been extensively studied in recent decades using numerical approaches, which have some limitations in understanding the soil’s thermal behavior. Therefore, a laboratory-scale experimental study involving cooling tests was carried out to investigate the impact of GWHP on system performance and sustainability with varying groundwater flow velocities and injection and abstraction rates. The results demonstrated that groundwater flow velocity, as well as injection and abstraction rates, significantly impact thermal plume development. Higher injection and abstraction rates create a larger thermal plume, thereby decreasing abstraction temperature. However, groundwater flow prevents heat development around the well by dispersing the heat in the groundwater flow direction. Furthermore, the results indicate that the energy gain only increased by 81% and 107%, with a respective increase of 100% and 200% in injection and abstraction rates. Full article

Using carbon dioxide as a gasification agent for underground coal gasification (UCG) can not only reduce carbon dioxide emissions but is also expected to lead to a new natural gas technology revolution and ensure national energy security. To explore the effect of the oxygen content in oxygen-enriched carbon dioxide gasification agents on the results of gasification experiments, underground gasification experiments under different oxygen-enrichment conditions were designed, and quantitative parameters were used to analyze and evaluate the gas produced in the gasification experiments. The results showed that as the oxygen content in the oxygen-enriched carbon dioxide gasification agent increased, the CO and H₂ in the combustible gas gradually increased, and the calorific value of the combustible gas also slowly increased, reaching a peak value under the gasification condition of 60% oxygen concentration, and then decreased slightly; the product formation rate and the gas production per unit mass of coal fluctuated. The coal consumption rate increased with time and was relatively stable. According to theoretical calculations for the gasification energy recovery evaluation system, the overall energy recovery rate was 56.34%, and the energy utilization rate was relatively high. Research on quantitative indicators based on gas production data has good practical significance for evaluating the gasification efficiency of UCG, which can be used to better evaluate and control the reaction process of UCG. Full article

In recent years, the issue of energy security has been the subject of many studies, debates, and discussions. Undoubtedly, geopolitical crises in Eastern Europe and the actions of the EU as part of the continuous development of the EU’s climate and energy policy have contributed to the advancement of discussions in this area. Due to the growing role and importance of energy in the economic systems of individual countries, the need to guarantee energy security is commencing to be regarded as an element of the economic security of the state and therefore, national security. The legal solutions adopted in Poland in recent years and the launch of government support programs for the development of micro-installations and prosumer energy have led to the rapid development of this sector. The aim of this article is therefore to assess the conditions of renewable energy sources development in Poland on the example of photovoltaics in the line of energy security concept. The empirical results emphasize that the development of photovoltaic is so dynamic for several reasons, primarily due to lower technological costs, stakeholder cooperation, confidence in the regulatory environment, as well as the high interest of the Polish public in this issue. Full article

This study proposes the application of a precooler to the cascade mixed refrigerant Joule–Thomson (CMR J–T) cycle, herein referred to as the precooled CMR J–T (PCMR J–T) system. The purpose of the precooler is to utilize the temperature gradient characteristics within the two-phase region exhibited by the non-azeotropic mixed refrigerant. The precooler reduces the temperature of the high-temperature gas exiting the compressor by using cooling water from the condenser, thereby decreasing the capacity requirements of the high-temperature cycle (HTC). The working fluid comprises a nonflammable mixed refrigerant (R218, R23, R14, and Ar), and simulations were conducted by varying the HTC evaporation temperature and cooling water temperature for energy and exergy analysis. Under the analysis conditions, the capacity of each component in the HTC can be reduced by over 45%, leading to a maximum increase of 21.6% in the system’s coefficient of performance. Furthermore, the exergy destruction in the PCMR J–T system decreases along with the reduction in component capacity, with the most significant reduction occurring at the HTC expansion valve. The exergy efficiency of the system increases by up to 47.4%. Full article

We perform large-eddy simulations to study a cavitating flow over a two-dimensional hydrofoil section—a scaled-down profile (1:13.26) of guide vanes of a Francis turbine—using the Schnerr–Sauer cavitation model with an adaptive mesh refinement in intensive phase transition flow areas. In the test case, the guide vane is tilted at an angle of attack of $9^{°}$ to the direction of the flow, in which the Reynolds number, based on the hydrofoil chord length, equals $1.32\times {10}^6$, thus providing a strong adverse pressure gradient along the surface. The calculated time-averaged turbulence characteristics are compared with those measured by particle image velocimetry to verify that the flow is correctly reproduced in numerical simulations using the procedure of conditional averaging proposed and tested in our previous investigation. A re-entrant jet is identified as the primary source of vapor cloud shedding, and a spectral analysis of the cavitating flow over the profile midsection is conducted. Two characteristic frequencies corresponding to the cases, when an attached cavity detaches completely (as a whole) and two partially from the hydrofoil, are found in the flow. The study reveals that the natural frequency of partial cavity shedding is three times higher than that of full detachments. The examined regime exhibits an oscillatory system with two oscillation zones related to cavitation surge instability and unsteady cloud cavitation resulting from the re-entrant jet. Conditional averaging correlates cavitation structures with pressure distributions, forces, and torque on the guide vane. This modeling approach captures the fine details of quasi-periodic cavitation dynamics, providing insights into unsteady sheet/cloud cavitation and offering a method for developing control strategies. Full article

Particularly crucial throughout the mode transition procedure is the transmission properties of hydro–mechanical composite transmission devices. This paper describes a multipurpose power transmission device that integrates hydrostatic, hydro-mechanical, and mechanical transmission and mainly discusses the transmission characteristic optimization problem from the perspective of speed regulation characteristics, shift strategy, and efficiency characteristics. The kinematic and dynamic analysis of the transmission system, the assembly scheme, and relevant parameters of the power transmission device are analyzed, and the speed regulation characteristic curve is obtained. The shift strategy of power transmission devices involving clutches and brakes during the whole speed regulation process and the best switch time of each component are found. The efficiency expression of the static pressure system is obtained from the efficiency model of the pump-control-motor system, and the efficiency of the multi-purpose power transmission device is obtained using the efficiency definition method. The fitting curves of hydrostatic system efficiency are determined using experimental data, and the efficiency of the hydro–mechanical composite power transmission system is obtained using the conversion mechanism method. The results show that the shift quality of power transmission devices can be improved greatly by controlling the switch sequence of clutches and brakes reasonably. Full article

In recent years, the development of electronic chips has focused on achieving high integration and lightweight designs. As a result, pulsating heat pipes (PHPs) have gained widespread use as passive cooling devices due to their exceptional heat transfer capacity. Nevertheless, the erratic pulsations observed in slug flow across multiple channels constitute a significant challenge, hindering the advancement of start-up and heat dissipation capabilities in traditional PHP systems. In this paper, we introduce a flat plate pulsating heat pipe (PHP) featuring adaptive structured channels, denoted as ASCPHP. The aim is to enhance the thermal performance of PHP systems. These adaptive structured channels are specifically engineered to dynamically accommodate volume changes during phase transitions, resulting in the formation of a predictable and controllable two-phase flow. This innovation is pivotal in achieving a breakthrough in the thermal performance of PHPs. We experimentally verified the heat transfer performance of the ASCPHP across a range of heating loads from 10 to 75 W and various orientations spanning 0 to 90 degrees, while maintaining a constant filling ratio (FR) of 40%. In comparison to traditional PHP systems, the ASCPHP design, as proposed in this study, offers the advantage of achieving a lower evaporation temperature and a more uniform temperature distribution across the PHP surface. The thermal resistances are reduced by a maximum of 37.5% when FR is 40%. The experimental results for start-up characteristics, conducted at a heating power of 70 W, demonstrate that the ASCPHP exhibits the quickest start-up response and the lowest start-up temperature among the tested configurations. Furthermore, thanks to the guiding influence of adaptive structured channels on two-phase flow, liquid replenishment in the ASCPHP exhibits minimal dependence on gravity. This means that the ASCPHP can initiate the start-up process promptly, even when placed horizontally. Full article

The traveling wave protection of high voltage direct current (HVDC) transmission lines is susceptible to the influence of transition resistance. As a backup protection, current differential protection has absolute selectivity, but usually requires an increase in delay to avoid misoperation caused by distributed capacitance on the line, resulting in a longer action time. Based on this, a two-terminal directional protection method for HVDC transmission lines is proposed based on Sparrow Search Algorithm (SSA)-Variational Mode Decomposition (VMD) and Hilbert phase difference. On the basis of analyzing the directional characteristics of the current fault component at both ends of the rectifier and inverter sides under different faults, SSA is first used to optimize the parameters of VMD. The residual components representing the direction of the current fault component at both ends are extracted through VMD, and then the Hilbert phase difference of the residual components at both ends is calculated to identify faults inside and outside the line area. In addition, fault pole selection can be achieved based on the ratio of the sum of multi-band Hilbert energy of single-terminal voltage fault components at the positive and negative poles. Simulation experiments have shown that the proposed protection scheme can quickly and effectively identify fault and has good tolerance to transition resistance and noise interference. Full article

Water management is an important criterion in the operation of proton-exchange membrane fuel cells to maintain the high performance and reliability of the system. The water content in the cathode air that is supplied to the cathode channel contributes to the membrane humidification and the transport of protons inside the membrane structure. In automotive applications, the supply air is typically driven through an external membrane humidifier to absorb more moisture from the recirculated cathode exhaust. In the literature, humidifiers and fuel cell stacks have been separately investigated without considering whole-system configurations for water management. This study investigates changes in the cathode air characteristics through a membrane humidifier and compares two configurations using a humidifier bypass of the supply flow and exhaust flow to adjust the cathode inlet air relative humidity. Each component in the system was modeled using mathematical relations and converted into blocks of inputs and outputs in MATLAB/Simulink for simulation. The bypass valve was demonstrated to effectively reduce the relative humidity of the supply air from the saturation rate to above 60%, with a bypass fraction of up to 0.6 in both configurations. These adjustments provide system flexibility to accommodate load changes and prevent flooding in the stack channels. Bypassing the supply air through the humidifier effectively maintained consistent cathode inlet humidity across a wide operational range. A 0.4 bypass fraction on the supply side sustained a relative humidity of around 80% for the whole range of operating flow rates. In contrast, the exhaust-side bypass had a smaller impact, and the relative humidity of the cathode air was reduced when the flow rate and bypass fraction increased. This study further supports the control system design to regulate the bypass fraction according to load transients. Full article