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Frontiers in Energy

ISSN 2095-1701 (Print)
ISSN 2095-1698 (Online)
CN 11-6017/TK
Postal Subscription Code 80-972
Formerly Known as Frontiers of Energy and Power Engineering in China
2018 Impact Factor: 1.701

, Volume 13 Issue 4

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Theoretical and technological exploration of deep in situ fluidized coal mining
Heping XIE, Yang JU, Shihua REN, Feng GAO, Jianzhong LIU, Yan ZHU
Front. Energy. 2019, 13 (4): 603-611.
Abstract   HTML   PDF (2145KB)

Mining industries worldwide have inevitably resorted to exploiting resources from the deep underground. However, traditional mining methods can cause various problems, e.g., considerable mining difficulty, environmental degradations, and frequent disastrous accidents. To exploit deep resources in the future, the concept of mining must be reconsidered and innovative new theories, methods, and technologies must be applied. To effectively acquire coal resources deeper than 2000 m, new theoretical and technological concepts about deep in situ fluidized mining are required. The limits of mining depth need to be broken to acquire deep-coal resources in an environmentally friendly, safe, and efficient manner. This is characterized by ‘There are no coal on the ground and no men in the coal mine’. First, this paper systematically explains deep in situ fluidized coal mining. Then, it presents a new theoretical concept, including the theories of mining-induced rock mechanics, three-field visualization, multi-physics coupling for in situ transformation, and in situ mining, transformation and transport. It also presents key technological concepts, including those of intelligent, unmanned, and fluidized mining. Finally, this paper presents a strategic roadmap for deep in situ fluidized coal mining. In summary, this paper develops new theoretical and technological systems for accomplishing groundbreaking innovations in mining technologies of coal resources in the deep underground.

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Understanding high-emitting households in the UK through a cluster analysis
Xinfang WANG, Ming MENG
Front. Energy. 2019, 13 (4): 612-625.
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Anthropogenic climate change is a global problem that affects every country and each individual. It is largely caused by human beings emitting greenhouse gases into the atmosphere. In general, a small percentage of the population is responsible for a large amount of emissions. This paper focuses on high emitters and their CO2 emissions from energy use in UK homes. It applies a cluster approach, aiming to identify whether the high emitters comprise clusters where households in each cluster share similar characteristics but are different from the others. The data are mainly based on the Living Cost and Food survey in the UK. The results show that after equivalising both household emissions and income, the high emitters can be clustered into six groups which share similar characteristics within each group, but are different from the others in terms of income, age, household composition, category and size of the dwelling, and tenure type. The clustering results indicate that various combinations of socioeconomic factors, such as low-income single female living in an at least six-room property, or high-income retired couple owning a large detached house, could all lead to high CO2 emissions from energy use at home. Policymakers should target each high-emitter cluster differently to reduce CO2 emissions from energy consumption at home more effectively.

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Promoting Si-graphite composite anodes with SWCNT additives for half and NCM811 full lithium ion batteries and assessment criteria from an industrial perspective
Jingning SHAN, Xiaofang YANG, Chao YAN, Lin CHEN, Fang ZHAO, Yiguang JU
Front. Energy. 2019, 13 (4): 626-635.
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Single wall carbon nanotube (SWCNT) additives were formulated into µm-Si-graphite composite electrodes and tested in both half cells and full cells with high nickel cathodes. The critical role of small amount of SWCNT addition (0.2 wt%) was found for significantly improving delithiation capacity, first cycle coulombic efficiency (FCE), and capacity retention. Particularly, Si (10 wt%)-graphite electrode exhibits 560 mAh/g delithiation capacity and 92% FCE at 0.2 C during the first charge-discharge cycle, and 91% capacity retention after 50 cycles (0.5 C) in a half cell. Scanning electron microscope (SEM) was used to illustrate the electrode morphology, compositions and promoting function of the SWCNT additives. In addition, full cells assembled with high nickel-NCM811 cathodes and µm-Si-graphite composite anodes were evaluated for the consistence between half and full cell performance, and the consideration for potential commercial application. Finally, criteria to assess Si-containing anodes are proposed and discussed from an industrial perspective.

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Performance and emission characteristics of a diesel engine operating on different water in diesel emulsion fuels: optimization using response surface methodology (RSM)
Seyed Saeed HOSEINI, Mohammad Amin SOBATI
Front. Energy. 2019, 13 (4): 636-657.
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The nitrogen oxide (NOx) release of diesel engines can be reduced using water in diesel emulsion fuel without any engine modification. In the present paper, different formulations of water in diesel emulsion fuels were prepared by ultrasonic irradiation. The water droplet size in the emulsion, polydisperisty index, and the stability of prepared fuel was examined, experimentally. Afterwards, the performance characteristics and exhaust emission of a single cylinder air-cooled diesel engine were investigated using different water in diesel emulsion fuels. The effect of water content (in the range of 5%–10% by volume), surfactant content (in the range of 0.5%–2% by volume), and hydrophilic-lipophilic balance (HLB) (in the range of 5–8) was examined using Box-Behnken design (BBD) as a subset of response surface methodology (RSM). Considering multi-objective optimization, the best formulation for the emulsion fuel was found to be 5% water, 2% surfactant, and HLB of 6.8. A comparison was made between the best emulsion fuel and the neat diesel fuel for engine performance and emission characteristics. A considerable decrease in the nitrogen oxide emission (–18.24%) was observed for the best emulsion fuel compared to neat diesel fuel.

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Exergy losses in premixed flames of dimethyl ether and hydrogen blends
Tongbin ZHAO, Jiabo ZHANG, Dehao JU, Zhen HUANG, Dong HAN
Front. Energy. 2019, 13 (4): 658-666.
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A second-law thermodynamic analysis was conducted for stoichiometric premixed dimethyl ether (DME)/hydrogen (H2)/air flames at atmospheric pressure. The exergy losses from the irreversibility sources, i.e., chemical reaction, heat conduction and species diffusion, and those from partial combustion products were analyzed in the flames with changed fuel blends. It is observed that, regardless of the fuel blends, chemical reaction contributes most to the exergy losses, followed by incomplete combustion, and heat conduction, while mass diffusion has the least contribution to exergy loss. The results also indicate that increased H2 substitution decreases the exergy losses from reactions, conduction, and diffusion, primarily because of the flame thickness reduction at elevated H2 substitution. The decreases in exergy losses by chemical reactions and heat conduction are higher, but the exergy loss reduction by diffusion is slight. However, the exergy losses from incomplete combustion increase with H2 substitution, because the fractions of the unburned fuels and combustion intermediates, e.g., H2 and OH radical, increase. The overall exergy losses in the DME/H2 flames decrease by about 5% with increased H2 substitution from 0% to 100%.

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Key problems and solutions in supercritical CO2 fracturing technology
Haizhu WANG, Gensheng LI, Bin ZHU, Kamy SEPEHRNOORI, Lujie SHI, Yong ZHENG, Xiaomei SHI
Front. Energy. 2019, 13 (4): 667-672.
Abstract   HTML   PDF (1026KB)

Supercritical CO2 fracturing is considered to be a new method for efficient exploitation of unconventional reservoirs, such as shale gas, coal bed methane, and tight sand stone gas. Supercritical CO2 has many special properties including low viscosity, high diffusion coefficient, and lack of surface tension, which brings about great advantages for fracturing. However, these properties also cause several problems, such as difficulty in proppant transportation, high friction loss, and high pump displacement. In this paper, the above problems were analyzed by combining field test with laboratory study and specific solutions to these problems are given. The high frictionloss in the pipeline could be reduced by developing a new drag reducing agent and selecting large-size casing. Besides, for the problem of poor capacity in proppant carrying and sand plug, the methods of adding tackifier into supercritical CO2, increasing pump displacement and selecting ultra-low density proppants are proposed. Moreover, for the problem of fast leak-off and high requirement for pump displacement, the displacement can be increased or the pad fluid can be injected into the reservoir. After solving the above three problems, the field test of supercritical CO2 fracturing can be conducted. The research results can promote the industrialization process of supercritical CO2 fracturing.

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Effects of critical geometric parameters on the optical performance of a conical cavity receiver
Hu XIAO, Yanping ZHANG, Cong YOU, Chongzhe ZOU, Quentin FALCOZ
Front. Energy. 2019, 13 (4): 673-683.
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The optical performance of a receiver has a great influence on the efficiency and stability of a solar thermal power system. Most of the literature focuses on the optical performance of receivers with different geometric shapes, but less research is conducted on the effects of critical geometric parameters. In this paper, the commercial software TracePro was used to investigate the effects of some factors on a conical cavity receiver, such as the conical angle, the number of loops of the helical tube, and the distance between the focal point of the collector and the aperture. These factors affect the optical efficiency, the maximum heat flux density, and the light distribution in the conical cavity. The optical performance of the conical receiver was studied and analyzed using the Monte Carlo ray tracing method. To make a reliable simulation, the helical tube was attached to the inner wall of the cavity in the proposed model. The results showed that the amount of light rays reaching the helical tube increases with the increasing of the conical angle, while the optical efficiency decreases and the maximum heat flux density increases. The increase in the number of loops contributed to an increase in the optical efficiency and a uniform light distribution. The conical cavity receiver had an optimal optical performance when the focal point of the collector was near the aperture.

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Roles of various Ni species on TiO2 in enhancing photocatalytic H2 evolution
Xiaoping CHEN, Jihai XIONG, Jinming SHI, Song XIA, Shuanglin GUI, Wenfeng SHANGGUAN
Front. Energy. 2019, 13 (4): 684-690.
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Low-cost nickels can be used as cocatalyst to improve the performance of photocatalysts, which may be promising materials applied in the field of photocatalytic water splitting. In this study, different nickel species Ni, Ni(OH)2, NiO, NiOx, and NiS are used to modified titanium dioxide (P25) to investigate their roles on the photocatalytic hydrogen evolution activities. UV-visible, X-ray diffraction (XRD), Brunner-Emmet-Teller (BET) measurements, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) analysis etc. are employed to characterize the physical and chemical properties of catalysts. The results indicate that all the nickel species can improve the photocatalytic hydrogen production activity of P25. The P25 modified with NiOx and NiS has more superior photocatalytic hydrogen evolution activities than those modified with other nickel species. The reason for this is that NiOx and NiS can form p-n junctions with P25 respectively. In addition, NiOx can be selectively deposited on the active sites of P25 via in situ the photodeposition method and NiS is beneficial for H+ reacting with photo-excited electrons.

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Improvement of engine performance with high compression ratio based on knock suppression using Miller cycle with boost pressure and split injection
Haiqiao WEI, Jie YU, Lei ZHOU
Front. Energy. 2019, 13 (4): 691-706.
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In theory, high compression ratio has the potential to improve the thermal efficiency and promote the power output of the SI engine. However, the application of high compression ratio is substantially limited by the knock in practical working process. The objective of this work is to comprehensively investigate the application of high compression ratio on a gasoline engine based on the Miller cycle with boost pressure and split injection. In this work, the specific optimum strategies for CR10 and CR12 were experimentally investigated respectively on a single cylinder DISI engine. It was found that a high level of Miller cycle with a higher boost pressure could be used in CR12 to achieve an effective compression ratio similar to CR10, which could eliminate the knock limits at a high compression ratio and high load. To verify the advantages of the high compression ratio, the fuel economy and power performance of CR10 and CR12 were compared at full and partial loads. The result revealed that, compared with CR10, a similar power performance and a reduced fuel consumption of CR12 at full load could be achieved by using the strong Miller cycle and split injection. At partial load, the conditions of CR12 had very superior fuel economy and power performance compared to those of CR10.

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Phenomena identification and ranking table exercise for thorium based molten salt reactor-solid fuel design
Xiaojing LIU, Qi WANG, Zhaozhong HE, Kun CHEN, Xu CHENG
Front. Energy. 2019, 13 (4): 707-714.
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Thorium based molten salt reactor-solid fuel (TMSR-SF) design is an innovative reactor concept that uses high-temperature tristructural-isotropic (TRISO) fuel with a low-pressure liquid salt coolant. In anticipation of getting licensed applications for TMSR-SF in the future, it is necessary to fully understand the significant features and phenomena of TMSR-SF design, as well as its transient behavior during accidents. In this paper, the safety-relevant phenomena, importance, and knowledge base were assessed for the selected events and the transient of TMSR-SF during station blackout scenario is simulated based on RELAP/SCDAPSIM Mod 4.0.

The phenomena having significant impact but with limited knowledge of their history are core coolant bypass flows, outlet plenum flow distribution, and intermediate heat exchanger (IHX) over/under cooling transients. Some thermal hydraulic parameters during the station blackout scenario are also discussed.

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Smart residential energy management system for demand response in buildings with energy storage devices
Front. Energy. 2019, 13 (4): 715-730.
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In the present scenario, the utilities are focusing on smart grid technologies to achieve reliable and profitable grid operation. Demand side management (DSM) is one of such smart grid technologies which motivate end users to actively participate in the electricity market by providing incentives. Consumers are expected to respond (demand response (DR)) in various ways to attain these benefits. Nowadays, residential consumers are interested in energy storage devices such as battery to reduce power consumption from the utility during peak intervals. In this paper, the use of a smart residential energy management system (SREMS) is demonstrated at the consumer premises to reduce the total electricity bill by optimally time scheduling the operation of household appliances. Further, the SREMS effectively utilizes the battery by scheduling the mode of operation of the battery (charging/floating/discharging) and the amount of power exchange from the battery while considering the variations in consumer demand and utility parameters such as electricity price and consumer consumption limit (CCL). The SREMS framework is implemented in Matlab and the case study results show significant yields for the end user.

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Investigation of wind energy potentials in Brunei Darussalam
Front. Energy. 2019, 13 (4): 731-741.
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Conventional power generation mainly depends on natural gas and diesel oil in Brunei Darussalam. The power utility company is now thinking of power generation using natural wind. In this paper, wind energy, being one of the most readily available renewable energy sources, was studied. The wind characteristic, velocity and directions were studied using Weibull distribution based on the measurement of wind speed at two different locations in Brunei Darussalam. These wind speed distributions were modeled using the Wind Power program. The wind rose graph was obtained for the wind direction to analyze the wind power density onshore and offshore. Based on this analysis, it has been found that the wind speed of 3 to 5 m/s has a probability of occurrence of 40%. Besides, the annual energy production at a wind speed of 5 m/s has been found to be in the range between 1000 and 1500 kWh for both the locations in Brunei Darussalam.

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Novel power capture optimization based sensorless maximum power point tracking strategy and internal model controller for wind turbines systems driven SCIG
Front. Energy. 2019, 13 (4): 742-756.
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Under the trends to using renewable energy sources as alternatives to the traditional ones, it is important to contribute to the fast growing development of these sources by using powerful soft computing methods. In this context, this paper introduces a novel structure to optimize and control the energy produced from a variable speed wind turbine which is based on a squirrel cage induction generator (SCIG) and connected to the grid. The optimization strategy of the harvested power from the wind is realized by a maximum power point tracking (MPPT) algorithm based on fuzzy logic, and the control strategy of the generator is implemented by means of an internal model (IM) controller. Three IM controllers are incorporated in the vector control technique, as an alternative to the proportional integral (PI) controller, to implement the proposed optimization strategy. The MPPT in conjunction with the IM controller is proposed as an alternative to the traditional tip speed ratio (TSR) technique, to avoid any disturbance such as wind speed measurement and wind turbine (WT) characteristic uncertainties. Based on the simulation results of a six KW-WECS model in Matlab/Simulink, the presented control system topology is reliable and keeps the system operation around the desired response.

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Large-scale geo-energy development: sustainability impacts
Li JIANG, Liandong ZHU, Erkki HILTUNEN
Front. Energy. 2019, 13 (4): 757-763.
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Geothermal energy is a renewable and alternative energy with the potential to replace fossil fuels and help mitigate global warming. However, the development of geothermal energy has environmental, economic and social-cultural consequences, which needs to be predicted beforehand and then mitigated. To guarantee a sustainable development, it is, therefore, essential to consider the relative potential impacts. From a sustainability point of view, in the present study, a comprehensive analysis of consequences of geothermal energy development is conducted, including environmental, economic and societal & cultural dimensions. The geothermal energy industry will prosper only if sustainable aspects can be integrally considered.

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Structural optimal design of a swing vane compressor
Junjie MA, Xiang CHEN, Zongchang QU
Front. Energy. 2019, 13 (4): 764-769.
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In this paper, a novel swing vane rotary compressor (SVC) was introduced, which had significant advantages—simple mechanism, reduced frictional loss, reliable operation, and a comparatively higher compression ratio. Based on the swing vane compressor geometry model, thermodynamic model and kinetic model, the mathematical model of optimum design was established, and further theoretical and experimental studies were conducted. The length of the cylinder, radius of the rotor and cylinder were defined as design variables and the reciprocal of EER as objective function. The complex optimization method was adopted to study the structure of the swing vane compressor. The theoretical model could provide an effective method for predicting compressor performance, which would also contribute to structural optimization of the SVC. The study shows that the friction loss of the compressor are greatly reduced by optimized design in a given initial value, and the EER increased by 8.55%.

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Latest development of double perovskite electrode materials for solid oxide fuel cells: a review
Shammya AFROZE, AfizulHakem KARIM, Quentin CHEOK, Sten ERIKSSON, Abul K. AZAD
Front. Energy. 2019, 13 (4): 770-797.
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Recently, the development and fabrication of electrode component of the solid oxide fuel cell (SOFC) have gained a significant importance, especially after the advent of electrode supported SOFCs. The function of the electrode involves the facilitation of fuel gas diffusion, oxidation of the fuel, transport of electrons, and transport of the byproduct of the electrochemical reaction. Impressive progress has been made in the development of alternative electrode materials with mixed conducting properties and a few of the other composite cermets. During the operation of a SOFC, it is necessary to avoid carburization and sulfidation problems. The present review focuses on the various aspects pertaining to a potential electrode material, the double perovskite, as an anode and cathode in the SOFC. More than 150 SOFCs electrode compositions which had been investigated in the literature have been analyzed. An evaluation has been performed in terms of phase, structure, diffraction pattern, electrical conductivity, and power density. Various methods adopted to determine the quality of electrode component have been provided in detail. This review comprises the literature values to suggest possible direction for future research.

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Energy conservation in China’s coal-fired power industry by installing advanced units and organized phasing out backward production
Weiliang WANG, Junfu LYU, Zheng LI, Hai ZHANG, Guangxi YUE, Weidou NI
Front. Energy. 2019, 13 (4): 798-807.
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Coal-fired power is the main power source and the biggest contributor to energy conservation in the past several decades in China. It is generally believed that advanced technology should be counted on for energy conservation. However, a review of the decline in the national average net coal consumption rate (NCCR) of China’s coal-fired power industry along with its development over the past few decades indicates that the up-gradation of the national unit capacity structure (including installing advanced production and phasing out backward production) plays a more important role. A quantitative study on the effect of the unit capacity structure up-gradation on the decline in the national average NCCR suggests that phasing out backward production is the leading factor for the decline in the NCCR in the past decade, followed by the new installation, whose sum contributes to approximately 80% of the decline in the national average NCCR. The new installation has an effective affecting period of about 8 years, during which it would gradually decline from a relatively high value. Since the effect of phasing out backward production may remain at a certain degree given a continual action of phasing out backward capacity, it is suggested that the organized action of phasing out backward production should be insisted on.

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17 articles