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  • RESEARCH ARTICLE
    Mahmoud BAKRY, Jinhui LI, Xianlai ZENG
    Frontiers in Energy, 2023, 17(2): 286-293. https://doi.org/10.1007/s11708-022-0823-y

    Metal, as the indispensable material, is functioning the society from technology to the environment. Niobium (Nb) is considered a unique earth metal as it is related to many emerging technologies. The increasing economic growth exerts an increasing pressure on supply, which leads to its significance in the economic sector. However, few papers have addressed Nb sustainability, which forms the scope of this paper in order to start the process of Nb market forecasting based on some previous data and some assumptions. Therefore, this paper will discuss different thoughts in material substitution and the substance flow of Nb throughout a static flow using Nb global data to have a better understanding of the process of Nb from production to end of life. This shall lead to the identification of the market needs to determine its growth which is around 2.5% to 3.0%. Moreover, due to China’s huge Nb consumption which comes from the continuous development that is happening over the years, it will also briefly mention the Nb situation as well as its growth which according to statistics will grow steadily till 2030 by a rate of 4.0% to 6.0%. The results show that there should be some enhancement to Nb recycling potentials out of steel scrap. In addition, there should be more involvement of Nb in different industries as this would lead to less-used materials which can be translated to less environmental impact.

  • REVIEW ARTICLE
    Qiao MA, Shan WANG, Yan FU, Wenlong ZHOU, Mingwei SHI, Xueting PENG, Haodong LV, Weichen ZHAO, Xian ZHANG
    Frontiers in Energy, 2023, 17(3): 400-411. https://doi.org/10.1007/s11708-023-0862-z

    Carbon capture, utilization, and storage (CCUS) is estimated to contribute substantial CO2 emission reduction to carbon neutrality in China. There is yet a large gap between such enormous demand and the current capacity, and thus a sound enabling environment with sufficient policy support is imperative for CCUS development. This study reviewed 59 CCUS-related policy documents issued by the Chinese government as of July 2022, and found that a supporting policy framework for CCUS is taking embryonic form in China. More than ten departments of the central government have involved CCUS in their policies, of which the State Council, the National Development and Reform Commission (NDRC), the Ministry of Science and Technology (MOST), and the Ministry of Ecological Environment (MEE) have given the greatest attention with different focuses. Specific policy terms are further analyzed following the method of content analysis and categorized into supply-, environment- and demand-type policies. The results indicate that supply-type policies are unbalanced in policy objectives, as policy terms on technology research and demonstration greatly outnumber those on other objectives, and the attention to weak links and industrial sectors is far from sufficient. Environment-type policies, especially legislations, standards, and incentives, are inadequate in pertinence and operability. Demand-type policies are absent in the current policy system but is essential to drive the demand for the CCUS technology in domestic and foreign markets. To meet the reduction demand of China’s carbon neutral goal, policies need to be tailored according to needs of each specific technology and implemented in an orderly manner with well-balanced use on multiple objectives.

  • RESEARCH ARTICLE
    Chao TANG, Yong GENG, Xue RUI, Guimei ZHAO
    Frontiers in Energy, 2023, 17(2): 294-305. https://doi.org/10.1007/s11708-022-0819-7

    China’s aluminum (Al) production has released a huge amount of greenhouse gas (GHG) emissions. As one of the biggest country of primary Al production, China must mitigate its overall GHG emission from its Al industry so that the national carbon neutrality target can be achieved. Under such a background, the study described in this paper conducts a dynamic material flow analysis to reveal the spatiotemporal evolution features of Al flows in China from 2000 to 2020. Decomposition analysis is also performed to uncover the driving factors of GHG emission generated from the Al industry. The major findings include the fact that China’s primary Al production center has transferred to the western region; the primary Al smelting and carbon anode consumption are the most carbon-intensive processes in the Al life cycle; the accumulative GHG emission from electricity accounts for 78.14% of the total GHG emission generated from the Al industry; China’s current Al recycling ratio is low although the corresponding GHG emission can be reduced by 93.73% if all the primary Al can be replaced by secondary Al; and the total GHG emission can be reduced by 88.58% if major primary Al manufacturing firms are transferred from Inner Mongolia to Yunnan. Based upon these findings and considering regional disparity, several policy implications are proposed, including promotion of secondary Al production, support of clean electricity penetration, and relocation of the Al industry.

  • RESEARCH ARTICLE
    Tongbin ZHAO, Zhe REN, Kai YANG, Tao SUN, Lei SHI, Zhen HUANG, Dong HAN
    Frontiers in Energy, 2023, 17(5): 664-677. https://doi.org/10.1007/s11708-021-0787-3

    The combustion characteristics and emission behaviors of RP-3 jet fuel were studied and compared to commercial diesel fuel in a single-cylinder compression ignition (CI) engine. Engine operational parameters, including engine load (0.6, 0.7, and 0.8 MPa indicating the mean effective pressure (IMEP)), the exhaust gas recirculation (EGR) rate (0%, 10%, 20%, and 30%), and the fuel injection timing (−20, −15, −10, and −5 ° crank angle (CA) after top dead center (ATDC)) were adjusted to evaluate the engine performances of RP-3 jet fuel under changed operation conditions. In comparison to diesel fuel, RP-3 jet fuel shows a retarded heat release and lagged combustion phase, which is more obvious under heavy EGR rate conditions. In addition, the higher premixed combustion fraction of RP-3 jet fuel leads to a higher first-stage heat release peak than diesel fuel under all testing conditions. As a result, RP-3 jet fuel features a longer ignition delay (ID) time, a shorter combustion duration (CD), and an earlier CA50 than diesel fuel. The experimental results manifest that RP-3 jet fuel has a slightly lower indicated thermal efficiency (ITE) compared to diesel fuel, but the ITE difference becomes less noticeable under large EGR rate conditions. Compared with diesel fuel, the nitrogen oxides (NOx) emissions of RP-3 jet fuel are higher while its soot emissions are lower. The NOx emissions of RP-3 can be effectively reduced with the increased EGR rate and delayed injection timing.

  • RESEARCH ARTICLE
    Juntian NIU, Cunxin ZHANG, Haiyu LIU, Yan JIN, Riguang ZHANG
    Frontiers in Energy, 2023, 17(4): 545-554. https://doi.org/10.1007/s11708-023-0867-7

    The effect of oxygen vacancies on the adsorption and activation of CO2 on the surface of different phases of ZrO2 is investigated by density functional theory (DFT) calculations. The calculations show that the oxygen vacancies contribute greatly to both the adsorption and activation of CO2. The adsorption energy of CO2 on the c-ZrO2, t-ZrO2 and, m-ZrO2 surfaces is enhanced to 5, 4, and 3 folds with the help of oxygen vacancies, respectively. Moreover, the energy barrier of CO2 dissociation on the defective surfaces of c-ZrO2, t-ZrO2, and m-ZrO2 is reduced to 1/2, 1/4, and 1/5 of the perfect surface with the assistance of oxygen vacancies. Furthermore, the activation of CO2 on the ZrO2 surface where oxygen vacancies are present, and changes from an endothermic reaction to an exothermic reaction. This finding demonstrates that the presence of oxygen vacancies promotes the activation of CO2 both kinetically and thermodynamically. These results could provide guidance for the high-efficient utilization of CO2 at an atomic scale.

  • RESEARCH ARTICLE
    Qiang LI, Qian WANG, Jian HOU, Jiansheng ZHANG, Yang ZHANG
    Frontiers in Energy, 2023, 17(2): 306-316. https://doi.org/10.1007/s11708-021-0736-1

    Coal water slurry gasification is a main source of hydrogen in the developing hydrogen economy. Moreover, biomass and waste can be added, making gasification process greener. To expand the application of coal water slurry and gasification process, it is necessary to understand the micro-structure in this large particle suspension system. In this paper, the micro-structure in coal water slurry was studied by extended DLVO (eDLVO) theory and fractal dimension, which is used to explain the mechanism of stability in large particle suspension systems. The interaction between two coal particles was characterized from the interparticle potential and energy barrier based on the eDLVO theory. The rheology and stability between different types of coals are measured and explained by the aggregating structure and fractal dimension in coal water slurry. The results indicated that there would be an aggregating structure in high rank coals, due to the interparticle potential caused by the surface properties, but probably not in low rank coals. This aggregating structure can be described and characterized by fractal dimension. The aggregation of particles is the source of the stability for high rank coals, as the close-packed 3D network structure in large particle suspension can support coal particles from settling down. The results have demonstrated that the combination of the eDLVO theory and rheological measurement is an effective way to investigate the stability of large particle suspension systems.

  • RESEARCH ARTICLE
    Jianfa WU, Haoran HU, Cheng CHANG, Deliang ZHANG, Jian ZHANG, Shengxian ZHAO, Bo WANG, Qiushi ZHANG, Yiming CHEN, Fanhua ZENG
    Frontiers in Energy, 2023, 17(3): 428-445. https://doi.org/10.1007/s11708-023-0865-9

    In this work, using fractured shale cores, isothermal adsorption experiments and core flooding tests were conducted to investigate the performance of injecting different gases to enhance shale gas recovery and CO2 geological storage efficiency under real reservoir conditions. The adsorption process of shale to different gases was in agreement with the extended-Langmuir model, and the adsorption capacity of CO2 was the largest, followed by CH4, and that of N2 was the smallest of the three pure gases. In addition, when the CO2 concentration in the mixed gas exceeded 50%, the adsorption capacity of the mixed gas was greater than that of CH4, and had a strong competitive adsorption effect. For the core flooding tests, pure gas injection showed that the breakthrough time of CO2 was longer than that of N2, and the CH4 recovery factor at the breakthrough time () was also higher than that of N2. The of CO2 gas injection was approximately 44.09%, while the of N2 was only 31.63%. For CO2/N2 mixed gas injection, with the increase of CO2 concentration, the increased, and the for mixed gas CO2/N2 = 8:2 was close to that of pure CO2, about 40.24%. Moreover, the breakthrough time of N2 in mixed gas was not much different from that when pure N2 was injected, while the breakthrough time of CO2 was prolonged, which indicated that with the increase of N2 concentration in the mixed gas, the breakthrough time of CO2 could be extended. Furthermore, an abnormal surge of N2 concentration in the produced gas was observed after N2 breakthrough. In regards to CO2 storage efficiency (), as the CO2 concentration increased, also increased. The of the pure CO2 gas injection was about 35.96%, while for mixed gas CO2/N2 = 8:2, was about 32.28%.

  • RESEARCH ARTICLE
    Yi ZUO, Xingang ZHAO
    Frontiers in Energy, 2023, 17(2): 266-285. https://doi.org/10.1007/s11708-021-0752-1

    Tradable green certificate (TGC) scheme promotes the development of renewable energy industry which currently has a dual effect on economy and environment. TGC market efficiency is reflected in stimulating renewable energy investment, but may be reduced by the herding behavior of market players. This paper proposes and simulates an artificial TGC market model which contains heterogeneous agents, communication structure, and regulatory rules to explore the characteristics of herding behavior and its effects on market efficiency. The results show that the evolution of herding behavior reduces information asymmetry and improves market efficiency, especially when the borrowing is allowed. In addition, the fundamental strategy is diffused by herding evolution, but TGC market efficiency may be remarkably reduced by herding with borrowing mechanism. Moreover, the herding behavior may evolve to an equilibrium where the revenue of market players is comparable, thus the fairness in TGC market is improved.

  • RESEARCH ARTICLE
    Mingkuan ZHANG, Xudong ZHANG, Luna GUO, Xuan LI, Wei RAO
    Frontiers in Energy, 2023, 17(6): 796-810. https://doi.org/10.1007/s11708-023-0877-5

    Liquid metal-based microchannel heat sinks (MCHSs) suffer from the low heat capacity of coolant, resulting in an excessive temperature rise of coolant and heat sink when dealing with high-power heat dissipation. In this paper, it was found that expanded space at the top of fins could distribute the heat inside microchannels, reducing the temperature rise of coolant and heat sink. The orthogonal experiments revealed that expanding the top space of channels yielded similar temperature reductions to changing the channel width. The flow and thermal modeling of expanded microchannel heat sink (E-MCHS) were analyzed by both using the 3-dimensional (3D) numerical simulation and the 1-dimensional (1D) thermal resistance model. The fin efficiency of E-MCHS was derived to improve the accuracy of the 1D thermal resistance model. The heat conduction of liquid metal in Z direction and the heat convection between the top surface of fins and the liquid metal could reduce the total thermal resistance (Rt). The above process was effective for microchannels with low channel aspect ratio, low mean velocity (Um) or long heat sink length. The maximum thermal resistance reduction in the example of this paper reached 36.0%. The expanded space endowed the heat sink with lower pressure, which might further reduce the pumping power (P). This rule was feasible both when fins were truncated (h2 < 0, h2 is the height of expanded channel for E-MCHS) and when over plate was raised (h2 > 0).

  • NEWS & HIGHLIGHTS
    Xavier MOYA, Neil D. MATHUR
    Frontiers in Energy, 2023, 17(4): 447-449. https://doi.org/10.1007/s11708-022-0854-4

    The widespread need to pump heat necessitates improvements that will increase energy efficiency and, more generally, reduce environmental impact. As discussed at the recent Calorics 2022 Conference, heat-pump devices based on caloric materials offer an intriguing alternative to gas combustion and vapor compression.

  • PERSPECTIVE
    Yue ZHOU, Jianzhong WU, Wei GAN
    Frontiers in Energy, 2023, 17(2): 189-197. https://doi.org/10.1007/s11708-023-0873-9

    Peer-to-peer (P2P) energy trading is an emerging energy supply paradigm where customers with distributed energy resources (DERs) are allowed to directly trade and share electricity with each other. P2P energy trading can facilitate local power and energy balance, thus being a potential way to manage the rapidly increasing number of DERs in net zero transition. It is of great importance to explore P2P energy trading via public power networks, to which most DERs are connected. Despite the extensive research on P2P energy trading, there has been little large-scale commercial deployment in practice across the world. In this paper, the practical challenges of conducting P2P energy trading via public power networks are identified and presented, based on the analysis of a practical Local Virtual Private Networks (LVPNs) case in North Wales, UK. The ongoing efforts and emerging solutions to tackling the challenges are then summarized and critically reviewed. Finally, the way forward for facilitating P2P energy trading via public power networks is proposed.

  • REVIEW ARTICLE
    Muhammad Tauseef NASIR, Mirae KIM, Jaehwa LEE, Seungho KIM, Kyung Chun KIM
    Frontiers in Energy, 2023, 17(3): 332-379. https://doi.org/10.1007/s11708-023-0863-y

    In modern times, worldwide requirements to curb greenhouse gas emissions, and increment in energy demand due to the progress of humanity, have become a serious concern. In such scenarios, the effective and efficient utilization of the liquified natural gas (LNG) regasification cold energy (RCE), in the economically and environmentally viable methods, could present a great opportunity in tackling the core issues related to global warming across the world. In this paper, the technologies that are widely used to harness the LNG RCE for electrical power have been reviewed. The systems incorporating, the Rankine cycles, Stirling engines, Kalina cycles, Brayton cycles, Allam cycles, and fuel cells have been considered. Additionally, the economic and environmental studies apart from the thermal studies have also been reviewed. Moreover, the discussion regarding the systems with respect to the regassification pressure of the LNG has also been provided. The aim of this paper is to provide guidelines for the prospective researchers and policy makers in their decision making.

  • RESEARCH ARTICLE
    Haoqing WU, Yaoyuan ZHANG, Shijie MI, Wenbin ZHAO, Zhuoyao HE, Yong QIAN, Xingcai LU
    Frontiers in Energy, 2023, 17(5): 678-691. https://doi.org/10.1007/s11708-022-0859-z

    Gasoline compression ignition (GCI) combustion faces problems such as high maximum pressure rise rate (MPRR) and combustion deterioration at high loads. This paper aims to improve the engine performance of the GCI mode by regulating concentration stratification and promoting fuel-gas mixing by utilizing the double main-injection (DMI) strategy. Two direct injectors simultaneously injected gasoline with an octane number of 82.7 to investigate the energy ratio between the two main-injection and exhaust gas recirculation (EGR) on combustion and emissions. High-load experiments were conducted using the DMI strategy and compared with the single main-injection (SMI) strategy and conventional diesel combustion. The results indicate that the DMI strategy have a great potential to reduce the MPRR and improve the fuel economy of the GCI mode. At a 10 bar indicated mean effective pressure, increasing the main-injection-2 ratio (Rm-2) shortens the injection duration and increases the mean mixing time. Optimized Rm-2 could moderate the trade-off between the MPRR and the indicated specific fuel consumption with both reductions. An appropriate EGR should be adopted considering combustion and emissions. The DMI strategy achieves a highly efficient and stable combustion at high loads, with an indicated thermal efficiency (ITE) greater than 48%, CO and THC emissions at low levels, and MPRR within a reasonable range. Compared with the SMI strategy, the maximum improvement of the ITE is 1.5%, and the maximum reduction of MPRR is 1.5 bar/°CA.

  • REVIEW ARTICLE
    Yawen ZHENG, Lin GAO, Song HE, Hongguang JIN
    Frontiers in Energy, 2023, 17(3): 390-399. https://doi.org/10.1007/s11708-023-0864-x

    CO2 capture and storage (CCS) has been acknowledged as an essential part of a portfolio of technologies that are required to achieve cost-effective long-term CO2 mitigation. However, the development progress of CCS technologies is far behind the targets set by roadmaps, and engineering practices do not lead to commercial deployment. One of the crucial reasons for this delay lies in the unaffordable penalty caused by CO2 capture, even though the technology has been commonly recognized as achievable. From the aspects of separation and capture technology innovation, the potential and promising direction for solving this problem were analyzed, and correspondingly, the possible path for deployment of CCS in China was discussed. Under the carbon neutral target recently proposed by the Chinese government, the role of CCS and the key milestones for deployment were indicated.

  • RESEARCH ARTICLE
    Weishuo SHI, Jinwei HE
    Frontiers in Energy, 2023, 17(2): 228-238. https://doi.org/10.1007/s11708-022-0852-6

    In this paper, a fault-tolerant control method for an input-series output-parallel modular grid-tied pulse-width modulation (PWM) current source inverter is proposed to address the most commonly seen single symmetrical gate-commutated thyristor (SGCT) open-circuit fault problems. This method actively offsets the neutral point of the current space vector to ensure a sinusoidal output of the grid current, and it can achieve the upper limit power of the inverter under the condition of a single SGCT open-circuit fault. In addition, an active damping control method based on grid harmonic current feedback is proposed after analyzing the influence of the transformer ferromagnetic resonance caused by the neutral point offset on the power quality of the grid current. It has been demonstrated that the proposed method effectively suppresses the resonance caused by the transformer and the modified modulation, improving the grid current’s power quality.

  • RESEARCH ARTICLE
    Hanyi WANG, Renjie LUO, Qun YU, Zhiyi LI
    Frontiers in Energy, 2023, 17(2): 211-227. https://doi.org/10.1007/s11708-022-0847-3

    With multiple microgrids (MGs) integrated into power distribution networks in a distributed manner, the penetration of renewable energy like photovoltaic (PV) power generation surges. However, the operation of power distribution networks is challenged by the issues of multiple power flow directions and voltage security. Accordingly, an efficient voltage control strategy is needed to ensure voltage security against ever-changing operating conditions, especially when the network topology information is absent or inaccurate. In this paper, we propose a novel data-driven voltage profile improvement model, denoted as system-wide composite adaptive network (SCAN), which depends on operational data instead of network topology details in the context of power distribution networks integrated with multiple MGs. Unlike existing studies that realize topology identification and decision-making optimization in sequence, the proposed end-to-end model determines the optimal voltage control decisions in one shot. More specifically, the proposed model consists of four modules, Pre-training Network and modified interior point methods with adversarial networks (Modified IPMAN) as core modules, and discriminator generative adversarial network (Dis-GAN) and Volt convolutional neural network (Volt-CNN) as ancillary modules. In particular, the generator in SCAN is trained by the core modules in sequence so as to form an end-to-end mode from data to decision. Numerical experiments based on IEEE 33-bus and 123-bus systems have validated the effectiveness and efficiency of the proposed method.

  • REVIEW ARTICLE
    Yuan LIN, Jiazheng HAO, Kaiming QIAO, Yihong GAO, Fengxia HU, Jing WANG, Tongyun ZHAO, Baogen SHEN
    Frontiers in Energy, 2023, 17(4): 463-477. https://doi.org/10.1007/s11708-023-0860-1

    Solid state refrigeration based on caloric effect is regarded as a potential candidate for replacing vapor-compression refrigeration. Numerous methods have been proposed to optimize the refrigeration properties of caloric materials, of which single field tuning as a relatively simple way has been systemically studied. However, single field tuning with few tunable parameters usually obtains an excellent performance in one specific aspect at the cost of worsening the performance in other aspects, like attaining a large caloric effect with narrowing the transition temperature range and introducing hysteresis. Because of the shortcomings of the caloric effect driven by a single field, multifield tuning on multicaloric materials that have a coupling between different ferro-orders came into view. This review mainly focuses on recent studies that apply this method to improve the cooling performance of materials, consisting of enlarging caloric effects, reducing hysteresis losses, adjusting transition temperatures, and widening transition temperature spans, which indicate that further progress can be made in the application of this method. Furthermore, research on the sign of lattice and spin contributions to the magnetocaloric effect found new phonon evolution mechanisms, calling for more attention on multicaloric effects. Other progress including improving cyclability of FeRh alloys by introducing second phases and realizing a large reversible barocaloric effect by hybridizing carbon chains and inorganic groups is described in brief.

  • RESEARCH ARTICLE
    Chao SHEN, Wei GU, Enbo LUO
    Frontiers in Energy, 2023, 17(2): 239-250. https://doi.org/10.1007/s11708-022-0856-2

    Grid-forming converters (GFMs) are faced with the threat of transient inrush current and synchronization instability issues when subjected to grid faults. Instead of disconnecting from the grid unintentionally, GFMs are required to have fault ride through (FRT) capability to maintain safe and stable operation in grid-connected mode during grid fault periods. In recent studies, different FRT control strategies with distinguishing features and that are feasible for different operation conditions have been proposed for GFMs. To determine their application scope, an intuitive comparison of the transient performance of different FRT control strategies is presented in this paper. First, three typical FRT control strategies (virtual impedance, current limiters, and mode-switching control) are introduced and transient mathematical models are established. A detailed comparison analysis on transient inrush current and transient synchronization stability is then presented. The results will be useful for guiding the selection and design of FRT control strategies. Finally, simulation results based on PSCAD/EMTDC are considered to verify the correctness of the theoretical analysis.

  • RESEARCH ARTICLE
    Kongkuai YING, Wang YIN, Yinong WU, Zhenhua JIANG, Jiantang SONG, Shaoshuai LIU, Haifeng ZHU
    Frontiers in Energy, 2023, 17(4): 516-526. https://doi.org/10.1007/s11708-022-0844-6

    A two-stage gas-coupled Stirling/pulse tube refrigerator (SPR), whose first and second stages respectively involve Stirling and pulse tube refrigeration cycles, is a very promising spaceborne refrigerator. The SPR has many advantages, such as a compact structure, high reliability, and high performance, and is expected to become an essential refrigerator for space applications. In research regarding gas-coupled regenerative refrigerator, the energy flow distribution between the two stages, and optimal phase difference between the pressure wave and volume flow, are two critical parameters that could widely influence refrigerator performance. The effects of displacer displacement on the pressure wave, phase difference, acoustic power distribution, and inter-stage cooling capacity shift of the SPR have been investigated experimentally. Notably, to obtain the maximum first-stage cooling capacity, an inflection point in displacement exists. When the displacer displacement is larger than the inflection point, the cooling capacity could be distributed between the first and second stages. In the present study, an SPR was designed and manufactured to work between the liquid hydrogen and liquid oxygen temperatures, which can be used to cool small-scale zero boil-off systems and space detectors. Under appropriate displacer displacement, the SPR can reach a no-load cooling temperature of 15.4 K and obtain 2.6 W cooling capacity at 70 K plus 0.1 W cooling capacity at 20 K with 160 W compressor input electric power.

  • PERSPECTIVE
    Tianyi CAI, Mengshi WANG, Xiaoping CHEN, Ye WU, Jiliang MA, Wu ZHOU
    Frontiers in Energy, 2023, 17(3): 380-389. https://doi.org/10.1007/s11708-023-0872-x

    Alkali carbonate-based sorbents (ACSs), including Na2CO3- and K2CO3-based sorbents, are promising for CO2 capture. However, the complex sorbent components and operation conditions lead to the versatile kinetics of CO2 sorption on these sorbents. This paper proposed that operando modeling and measurements are powerful tools to understand the mechanism of sorbents in real operating conditions, facilitating the sorbent development, reactor design, and operation parameter optimization. It reviewed the theoretical simulation achievements during the development of ACSs. It elucidated the findings obtained by utilizing density functional theory (DFT) calculations, ab initio molecular dynamics (AIMD) simulations, and classical molecular dynamics (CMD) simulations as well. The hygroscopicity of sorbent and the humidity of gas flow are crucial to shifting the carbonation reaction from the gas−solid mode to the gas−liquid mode, boosting the kinetics. Moreover, it briefly introduced a machine learning (ML) approach as a promising method to aid sorbent design. Furthermore, it demonstrated a conceptual compact operando measurement system in order to understand the behavior of ACSs in the real operation process. The proposed measurement system includes a micro fluidized-bed (MFB) reactor for kinetic analysis, a multi-camera sub-system for 3D particle movement tracking, and a combined Raman and IR sub-system for solid/gas components and temperature monitoring. It is believed that this system is useful to evaluate the real-time sorbent performance, validating the theoretical prediction and promoting the industrial scale-up of ACSs for CO2 capture.

  • RESEARCH ARTICLE
    Tao JIANG, Xinru DONG, Rufeng ZHANG, Xue LI, Houhe CHEN, Guoqing LI
    Frontiers in Energy, 2023, 17(2): 251-265. https://doi.org/10.1007/s11708-022-0857-1

    Advances in natural gas-fired technologies have deepened the coupling between electricity and gas networks, promoting the development of the integrated electricity-gas network (IEGN) and strengthening the interaction between the active-reactive power flow in the power distribution network (PDN) and the natural gas flow in the gas distribution network (GDN). This paper proposes a day-ahead active-reactive power scheduling model for the IEGN with multi-microgrids (MMGs) to minimize the total operating cost. Through the tight coupling relationship between the subsystems of the IEGN, the potentialities of the IEGN with MMGs toward multi-energy cooperative interaction is optimized. Important component models are elaborated in the PDN, GDN, and coupled MMGs. Besides, motivated by the non-negligible impact of the reactive power, optimal inverter dispatch (OID) is considered to optimize the active and reactive power capabilities of the inverters of distributed generators. Further, a second-order cone (SOC) relaxation technology is utilized to transform the proposed active-reactive power scheduling model into a convex optimization problem that the commercial solver can directly solve. A test system consisting of an IEEE-33 test system and a 7-node natural gas network is adopted to verify the effectiveness of the proposed scheduling method. The results show that the proposed scheduling method can effectively reduce the power losses of the PDN in the IEGN by 9.86%, increase the flexibility of the joint operation of the subsystems of the IEGN, reduce the total operation costs by $32.20, and effectively enhance the operation economy of the IEGN.

  • RESEARCH ARTICLE
    Chunqiu XIA, Wei LI, Xiaomin CHANG, Ting YANG, Albert Y. ZOMAYA
    Frontiers in Energy, 2023, 17(2): 198-210. https://doi.org/10.1007/s11708-023-0874-8

    The increasing use of distributed energy resources changes the way to manage the electricity system. Unlike the traditional centralized powered utility, many homes and businesses with local electricity generators have established their own microgrids, which increases the use of renewable energy while introducing a new challenge to the management of the microgrid system from the mismatch and unknown of renewable energy generations, load demands, and dynamic electricity prices. To address this challenge, a rank-based multiple-choice secretary algorithm (RMSA) was proposed for microgrid management, to reduce the microgrid operating cost. Rather than relying on the complete information of future dynamic variables or accurate predictive approaches, a lightweight solution was used to make real-time decisions under uncertainties. The RMSA enables a microgrid to reduce the operating cost by determining the best electricity purchase timing for each task under dynamic pricing. Extensive experiments were conducted on real-world data sets to prove the efficacy of our solution in complex and divergent real-world scenarios.

  • PERSPECTIVE
    Xiangwan DU
    Frontiers in Energy, 2023, 17(3): 324-331. https://doi.org/10.1007/s11708-023-0883-7

    First, a brief introduction is made to the four basic judgments and understandings of the goals of “carbon peaking and carbon neutrality.” Then, an in-depth elaboration is provided on the eight major strategies for achieving the goals of “carbon peaking and carbon neutrality,” including conservation and efficiency priority, energy security, non-fossil energy substitution, re-electrification, resource recycling, carbon sequestration, digitalization and cooperation between countries. Next, eight major implementation paths for achieving the goals of “carbon peaking and carbon neutrality” are discussed in detail, including industrial restructuring; building a clean, low-carbon, safe and efficient energy system, and renewing the understanding of China’s energy resource endowment; accelerating the construction of a new-type power system with a gradually growing proportion of new energy, and realizing the “possible triangle” of high-quality energy system development; utilizing electrification and deep decarbonization technologies to promote the orderly peaking and gradual neutralization of carbon emissions in the industrial sector; promoting the low-carbon transition of transportation vehicles to achieve carbon peaking and carbon neutrality in the transportation sector; focusing on breaking through key green building technologies to achieve zero carbon emissions from building electricity and heat; providing a strong technical support for carbon removal to achieve carbon neutrality; accelerating the construction of the integrated planning and assessment mechanism for pollution and carbon reduction, establishing a sound strategy, planning, policy and action system, and optimizing the carbon trading system. Afterwards, it is particularly pointed out that the realization of the goals of “carbon peaking and carbon neutrality” cannot be separated from the support of sci-tech innovation. Finally, it is stressed that carbon neutrality is not the end, but an important milestone. If viewed from the perspective of future energy, the significance and historical status of the goals of “carbon peaking and carbon neutrality” will be more understandable.

  • REVIEW ARTICLE
    Zhang WEN, Liangzhong YAO, Fan CHENG, Jian XU, Beilin MAO, Rusi CHEN
    Frontiers in Energy, 2023, 17(5): 611-634. https://doi.org/10.1007/s11708-023-0876-6

    Wind power (WP) is considered as one of the main renewable energy sources (RESs) for future low-carbon and high-cost-efficient power system. However, its low inertia characteristic may threaten the system frequency stability of the power system with a high penetration of WP generation. Thus, the capability of WP participating in the system frequency regulation has become a research hotspot. In this paper, the impact of WP on power system frequency stability is initially presented. In addition, various existing control strategies of WP participating in frequency regulation are reviewed from the wind turbine (WT) level to the wind farm (WF) level, and their performances are compared in terms of operating principles and practical applications. The pros and cons of each control strategy are also discussed. Moreover, the WP combing with energy storage system (ESS) for system frequency regulation is explored. Furthermore, the prospects, future challenges, and solutions of WP participating in power system frequency regulation are summarized.

  • REVIEW ARTICLE
    Yu CAI, Qiang LI, Feihong DU, Jiawang FENG, Donglin HAN, Shanyu ZHENG, Shihao YANG, Yingjing ZHANG, Binbin YU, Junye SHI, Xiaoshi QIAN
    Frontiers in Energy, 2023, 17(4): 450-462. https://doi.org/10.1007/s11708-022-0858-0

    Electrocaloric refrigeration represents an alternative solid-state cooling technology that has the potential to reach the ultimate goal of achieving zero-global-warming potential, highly efficient refrigeration, and heat pumps. To date, both polymeric and inorganic oxides have demonstrated giant electrocaloric effect as well as respective cooling devices. Although both polymeric and inorganic oxides have been identified as promising cooling methods that are distinguishable from the traditional ones, they still pose many challenges to more practical applications. From an electrocaloric material point of view, electrocaloric nanocomposites may provide a solution to combine the beneficial effects of both organic and inorganic electrocaloric materials. This article reviews the recent advancements in polymer-based electrocaloric composites and the state-of-the-art cooling devices operating these nanocomposites. From a device point of view, it discusses the existing challenges and potential opportunities of electrocaloric nanocomposites.

  • RESEARCH ARTICLE
    Shixian XIONG, Hongcheng KE, Lei CAO, Yu WANG, Qian ZHU, Liqin ZHONG, Lanlan FAN, Feng GU
    Frontiers in Energy, 2023, 17(4): 555-566. https://doi.org/10.1007/s11708-023-0882-8

    Exploring cathode materials that combine excellent cycling stability and high energy density poses a challenge to aqueous Zn-ion hybrid supercapacitors (ZHSCs). Herein, polyaniline (PANI) coated boron-carbon-nitrogen (BCN) nanoarray on carbon cloth surface is prepared as advanced cathode materials via simple high-temperature calcination and electrochemical deposition methods. Because of the excellent specific capacity and conductivity of PANI, the CC@BCN@PANI core-shell nanoarrays cathode shows an excellent ion storage capability. Moreover, the 3D nanoarray structure can provide enough space for the volume expansion and contraction of PANI in the charging/discharging cycles, which effectively avoids the collapse of the microstructure and greatly improves the electrochemical stability of PANI. Therefore, the CC@BCN@PANI-based ZHSCs exhibit superior electrochemical performances showing a specific capacity of 145.8 mAh/g, a high energy density of 116.78 Wh/kg, an excellent power density of 12 kW/kg, and a capacity retention rate of 86.2% after 8000 charge/discharge cycles at a current density of 2 A/g. In addition, the flexible ZHSCs (FZHSCs) also show a capacity retention rate of 87.7% at the current density of 2 A/g after 450 cycles.

  • RESEARCH ARTICLE
    Guodong LIU, Thomas B. OLLIS, Maximiliano F. FERRARIL, Aditya SUNDARARAJAN, Yang CHEN, Mohammed M. OLAMA, Kevin TOMSOVIC
    Frontiers in Energy, 2023, 17(3): 446-446. https://doi.org/10.1007/s11708-022-0851-7
  • NEWS & HIGHLIGHTS
    Li REN, Yinghui LI, Xi LIN, Wenjiang DING, Jianxin ZOU
    Frontiers in Energy, 2023, 17(3): 320-323. https://doi.org/10.1007/s11708-023-0889-1
  • NEWS
    Ruiqin LIU
    Frontiers in Energy, 2023, 17(3): 317-319. https://doi.org/10.1007/s11708-023-0888-2
  • RESEARCH ARTICLE
    Jinlong WANG, Jin XIAO, Yingdong CHENG, Zhen HUANG
    Frontiers in Energy, 2023, 17(6): 811-821. https://doi.org/10.1007/s11708-022-0848-2

    Free-piston engine generators (FPEGs) can be applied as decarbonized range extenders for electric vehicles because of their high thermal efficiency, low friction loss, and ultimate fuel flexibility. In this paper, a parameter-decoupling approach is proposed to model the design of an FPEG. The parameter-decoupling approach first divides the FPEG into three parts: a two-stroke engine, an integrated scavenging pump, and a linear permanent magnet synchronous machine (LPMSM). Then, each of these is designed according to predefined specifications and performance targets. Using this decoupling approach, a numerical model of the FPEG, including the three aforementioned parts, was developed. Empirical equations were adopted to design the engine and scavenging pump, while special considerations were applied for the LPMSM. A finite element model with a multi-objective genetic algorithm was adopted for its design. The finite element model results were fed back to the numerical model to update the LPMSM with increased fidelity. The designed FPEG produced 10.2 kW of electric power with an overall system efficiency of 38.5% in a stable manner. The model provides a solid foundation for the manufacturing of related FPEG prototypes.