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  • Valorization of hydrothermal liquefaction aqueous phase: pathways towards commercial viability
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2019-12-16
    Jamison Watson; Tengfei Wang; Buchun Si; Wan-Ting Chen; Aersi Aierzhati; Yuanhui Zhang

    Hydrothermal liquefaction (HTL) is a thermochemical conversion technology that shows promising commercial potential for the production of biocrude oil from wet biomass. However, the inevitable production of the hydrothermal liquefaction aqueous phase (HTL-AP) acts as a double-edged sword: it is considered a waste stream that without additional treatment clouds the future scale-up prospects of HTL technology; on the other hand, it also offers potential as an untapped nutrient and energy resource that could be valorized. As more researchers turn to liquefaction as a means of producing renewable fuel, there is a growing need to better understand HTL-AP from a variety of vantage points. Specifically, the HTL-AP chemical composition, conversion pathways, energy valorization potential, and the interconnection of HTL-AP conversion with biofuel production technology are particularly worthy of investigation. This paper extensively reviews the impact of HTL conditions and the feedstock composition on the energy and elemental distribution of process outputs with specific emphasis on the HTL-AP. Moreover, this paper also compares and contrasts the current state of value-added products separation along with biological (biomass cultivation, anaerobic fermentation, and bioelectrochemical systems) and thermochemical (gasification and HTL) pathways to valorize HTL-AP. Furthermore, life cycle analysis (LCA) and techno-economic assessments (TEA) are performed to appraise the environmental sustainability and economic implications of these different valorization techniques. Finally, perspectives and challenges are presented and the integration approaches of HTL-AP valorization pathways with HTL and biorefining are explored.

  • Nonprecious anodic catalysts for low-molecular-hydrocarbon fuel cells: Theoretical consideration and current progress
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2019-11-09
    Mohammad Ali Abdelkareem, Enas Taha Sayed, Hend Omar Mohamed, M. Obaid, Hegazy Rezk, Kyu-Jung Chae

    Fuel cells are electrochemical devices that convert chemical energy directly into electrical energy with high efficiency. The high cost of platinum catalysts and sluggish reaction kinetics are the main challenges in the development of low-temperature fuel cells. Although significant efforts have been made to prepare effective non-precious-metal-based oxygen reduction reaction (ORR) catalysts, suitable anodic catalysts are still far from realization. The reported onset potential of a nonprecious anodic catalyst toward low-molecular-weight hydrocarbons, such as methanol, ethanol, and urea, in alkaline media is approximately 0.35 V (vs. Ag/AgCl), which is far from the theoretical potentials of −0.61, −0.54, and −0.55 V (vs. Ag/AgCl), respectively. Therefore, some researchers concluded that nonprecious anodic catalysts are not practical, taking into account the ORR potential of 0.2 V (vs. Ag/AgCl) in alkaline media. Recently, however, several reports demonstrated an open-circuit voltage (OCV) of more than 0.8 V using non-precious-metal-based anodic catalysts, which contradicts expectations. Therefore, to answer these conflicting claims, this review intensively discusses the possibility of using nonprecious metals, for example Ni-based catalysts, for actual electricity generation in direct (methanol, ethanol, and urea) fuel cells, and the different methods applied to achieve the highest values of OCV. Also, the progress done in the preparation of nonprecious anodic catalysts is reviewed. Finally, conclusions and recommendations to prepare durable and active fuel cells using non-precious-metal-based anodic catalysts are presented.

  • Bioelectrochemical element conversion reactions towards generation of energy and value-added chemicals
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2019-11-21
    Min Sun, Lin-Feng Zhai, Yang Mu, Han-Qing Yu

    In the past decades, the bioelectrochemical system (BES) has developed into a versatile platform to sustain the conversion of various substances for the generation of energy and energy-efficient production of chemicals. Taking advantage of microbial extracellular electron transfer, the BES is able to perform a variety of value-added element conversion reactions, including production of electric energy from organic carbon, synthesis of chemicals from carbon dioxide, oxidation of sulfide into element sulfur, reduction of nitrate/nitrite into nitrous oxide and reduction of metal ions into solid metals and/or metal oxides. While the potential for using BES as an energy and resource factory has been fully recognized, governing the element conversion pathways into the desired energy and products in BES is still a great challenge. This review provides comprehensive insights into the microbial extracellular electron transfer principles as well as behaviors of key chemical elements in BESs. Individual element conversion processes and their integrations on the BES platform are analyzed. The physicochemical, chemical and microbial mechanisms involved in these processes are explored, and the coupling patterns of electron transfer and element conversion reactions are elucidated. Furthermore, the challenges to design, construct and operate a BES with improved electron transfer efficiency and product specificity are discussed, and research needs are proposed. Additionally, BES technologies from the perspectives of waste remediation, energy production, resource recovery and chemical synthesis are envisaged.

  • Battery warm-up methodologies at subzero temperatures for automotive applications: Recent advances and perspectives
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2019-11-25
    Xiaosong Hu, Yusheng Zheng, David A. Howey, Hector Perez, Aoife Foley, Michael Pecht

    Electric vehicles play a crucial role in reducing fuel consumption and pollutant emissions for more sustainable transportation. Lithium-ion batteries, as the most expensive but least understood component in electric vehicles, directly affect vehicular driving range, safety, comfort, and reliability. However, the overall performance of traction batteries deteriorates significantly at low temperatures due to the reduced electrochemical reaction rate and accelerated health degradation, such as lithium plating. Without timely and effective actions, this performance degradation causes operational difficulties and safety hazards for electric vehicles. Battery warm-up/preheating is of particular importance when operating electric vehicles in cold geographical regions. To this end, this paper reviews various battery preheating strategies, including external convective and conductive preheating, as well as the latest progress in internal heating solutions. The effects of low temperature on batteries from the perspectives of cell performance as well as materials properties are briefly summarized. Thermal science issues involved in warm-up are also elucidated. The framework of battery management systems (BTMS) at low temperatures, including the key design considerations at different battery integration levels and the overall classification of warm-up approaches into external and internal groups, are introduced in detail. Next, a comprehensive literature review on different warm-up strategies is presented, and the basic principles, advantages, disadvantages, and potential improvements of each strategy are elaborated. Finally, future trends of battery warm-up methods are discussed in terms of key technologies, promising opportunities, and challenges.

  • Mechanisms and occurrence of detonations in vapor cloud explosions
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2019-11-08
    Elaine S. Oran, Geoffrey Chamberlain, Andrzej Pekalski

    Not all accidental releases of flammable gases and vapors create explosions. Most releases do not find an ignition source, and of those that do ignite, most of them result in deflagrations that generate low or moderate overpressures. Under some circumstances, however, it is possible for deflagration-to-detonation transition (DDT) to occur, and this can be followed by a propagating detonation that quickly consumes the remaining detonable cloud. In a detonable cloud, a detonation creates the worst accident that can happen. Because detonation overpressures are much higher than those in a deflagration and continue through the entire detonable cloud, the damage from a DDT event is more severe. This paper first provides a brief summary of our knowledge to date of the fundamental mechanisms of flame acceleration and DDT. This information is then contrasted to and combined with evidence of detonations (detonation markers) obtained from large-scale tests and actual large vapor cloud explosions (VCEs), including events at Buncefield (UK), Jaipur (India), CAPECO (Puerto Rico), and Port Hudson (US). The major conclusion from this review is that detonations did occur in prior VCEs in at least part of the VCE accidents. Finally, actions are suggested that could be taken to minimize detonation hazards.

  • Mercury capture by native fly ash carbons in coal-fired power plants.
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2010-08-01
    James C Hower,Constance L Senior,Eric M Suuberg,Robert H Hurt,Jennifer L Wilcox,Edwin S Olson

    The control of mercury in the air emissions from coal-fired power plants is an on-going challenge. The native unburned carbons in fly ash can capture varying amounts of Hg depending upon the temperature and composition of the flue gas at the air pollution control device, with Hg capture increasing with a decrease in temperature; the amount of carbon in the fly ash, with Hg capture increasing with an increase in carbon; and the form of the carbon and the consequent surface area of the carbon, with Hg capture increasing with an increase in surface area. The latter is influenced by the rank of the feed coal, with carbons derived from the combustion of low-rank coals having a greater surface area than carbons from bituminous- and anthracite-rank coals. The chemistry of the feed coal and the resulting composition of the flue gas enhances Hg capture by fly ash carbons. This is particularly evident in the correlation of feed coal Cl content to Hg oxidation to HgCl2, enhancing Hg capture. Acid gases, including HCl and H2SO4 and the combination of HCl and NO2, in the flue gas can enhance the oxidation of Hg. In this presentation, we discuss the transport of Hg through the boiler and pollution control systems, the mechanisms of Hg oxidation, and the parameters controlling Hg capture by coal-derived fly ash carbons.

  • Premixed flames subjected to extreme turbulence: Some questions and recent answers
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2019-10-26
    James F. Driscoll, Jacqueline H. Chen, Aaron W. Skiba, Campbell D. Carter, Evatt R. Hawkes, Haiou Wang

    It has been predicted that several changes will occur when premixed flames are subjected to the extreme levels of turbulence that can be found in practical combustors. This paper is a review of recent experimental and DNS results that have been obtained for the range of extreme turbulence, and it includes a discussion of cases that agree or disagree with predictions. “Extreme turbulence” is defined to correspond to a turbulent Reynolds number (ReΤ, based on integral scale) that exceeds 2800 or a turbulent Karlovitz number that exceeds 100, for reasons that are discussed in Section 2.1. Several data bases are described that include measurements made at Lund University, the University of Sydney, the University of Michigan and the U.S. Air Force Research Lab. The data bases also include DNS results from Sandia National Laboratory, the University of New South Wales, Newcastle University, the California Institute of Technology and the University of Cambridge. Several major observations are: (a) DNS now can be achieved for a realistic geometry (of the Lund University jet burner) even for extreme turbulence levels, (b) state relations (conditional mean profiles) from DNS and experiments do tend to agree with laminar profiles, at least for methane-air and hydrogen-air reactants that are not preheated, and (c) regime boundaries have been measured and they do not agree with predicted boundaries. These findings indicate that the range of conditions for which flamelet models should be valid is larger than what was previously believed. Additional parameters have been shown to be important; for example, broken reactions occur if the “back-support” is insufficient due to the entrainment of cold gas into the product gas. Turbulent burning velocity measurements have been extended from the previous normalized turbulence levels (u’/SL) of 24 up to a value of 163. Turbulent burning velocities no longer follow the trend predicted by Shchelkin but they tend to follow the trend predicted by Damköhler. The boundary where flamelet broadening begins was measured to occur at ReTaylor = 13.8, which corresponds to an integral scale Reynolds number (ReT) of 2800. This measured regime boundary can be explained by the idea that flame structure is altered when the turbulent diffusivity at the Taylor scale exceeds a critical value, rather than the idea that changes occur when Kolmogorov eddies just fit inside a flamelet. A roadmap to extend DNS to complex chemistry and to higher Reynolds numbers is discussed. Exascale computers, machine learning, adaptive mesh refinement and embedded DNS show promise. Some advances are reviewed that have extended the use of line and planar PLIF and CARS laser diagnostics to studies that consider complex hydrocarbon fuels and harsh environments.

  • Chlorinated and brominated polycyclic aromatic hydrocarbons: Sources, formation mechanisms, and occurrence in the environment
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2019-10-08
    Rong Jin, Minghui Zheng, Gerhard Lammel, Benjamin A. Musa Bandowe, Guorui Liu

    Chlorinated and brominated polycyclic aromatic hydrocarbons (ClPAHs and BrPAHs; XPAHs) are carcinogenic organic pollutants which are mainly produced and emitted from combustion processes. In some environmental matrices, XPAHs display similar toxic properties and even higher toxic equivalent quantities (TEQs) than dioxins. Understanding the sources and formation mechanisms of XPAHs is important for controlling their emissions and human exposure to these ubiquitous pollutants. Nevertheless, comprehensive knowledge on the sources, formation mechanisms, and environmental characteristics of XPAHs, which are considered as emerging persistent organic pollutants (POPs) is lacking. Here, we review and discuss the knowledge on the primary sources (i.e. formation mechanisms, levels, composition pattern, emission factors in combustion and other anthropogenic sources), and secondary formation (i.e. formation from reactions between emitted PAHs and halogens in environmental compartments). Congener profiles of XPAHs released from various anthropogenic sources are evaluated for their possible application as source tracers of XPAHs. Regarding the chlorination of PAHs, we suggest and discuss two possible mechanisms, which result in the production of different congeners under different processes. Finally, knowledge on environmental exposure to XPAHs is reviewed. Research needs with regard to formation, emission, analytical methods, environmental exposure and environmental risk assessment are outlined.

  • Role of firebrand combustion in large outdoor fire spread
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2019-10-03
    Samuel L. Manzello, Sayaka Suzuki, Michael J. Gollner, A. Carlos Fernandez-Pello

    Large outdoor fires are an increasing danger to the built environment. Wildfires that spread into communities, labeled as Wildland-Urban Interface (WUI) fires, are an example of large outdoor fires. Other examples of large outdoor fires are urban fires including those that may occur after earthquakes as well as in informal settlements. When vegetation and structures burn in large outdoor fires, pieces of burning material, known as firebrands, are generated, become lofted, and may be carried by the wind. This results in showers of wind-driven firebrands that may land ahead of the fire front, igniting vegetation and structures, and spreading the fire very fast. Post-fire disaster studies indicate that firebrand showers are a significant factor in the fire spread of multiple large outdoor fires. The present paper provides a comprehensive literature summary on the role of firebrand mechanisms on large outdoor fire spread. Experiments, models, and simulations related to firebrand generation, lofting, burning, transport, deposition, and ignition of materials are reviewed. Japan, a country that has been greatly influenced by ignition induced by firebrands that have resulted in severe large outdoor fires, is also highlighted here as most of this knowledge remains not available in the English language literature. The paper closes with a summary of the key research needs on this globally important problem.

  • The fate of chlorine during MSW incineration: Vaporization, transformation, deposition, corrosion and remedies
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2019-09-26
    Wenchao Ma, Terrence Wenga, Flemming J. Frandsen, Beibei Yan, Guanyi Chen

    Municipal solid waste (MSW) incineration plays an important role in waste treatment systems throughout the world, due to the advantages of fast volume reduction by 80–90%, heat recovery, and power generation. However, waste-to-energy (WtE) plants have low electrical efficiency of 15–25%, due to the low steam temperature and pressure used in order to minimize boiler deposition and corrosion problems. Undoubtedly, the high Cl-content in MSW is the reason for the severe corrosion problem. Chlorine also forms volatile compounds with trace metals (e.g., Zn, Pb), and, influences the fate of other key elements, e.g., Na, K, and S. Different from alkali metals in biomass, which have been thoroughly investigated, the behavior of chlorine during MSW incineration has not been systematically and comprehensively studied. Up until now, there are few in-depth studies that have been conducted on the thermal behavior of chlorine or on the remedial measures against Cl-induced problems. An up-to-date review on the behavior of chlorine from incineration via freeboard chemistry to corrosive attack is therefore needed, in order to provide knowledge on process optimization and reactor design, thereby enabling high-efficient energy utilization and safe operation of large-scale WtE units. This review provides a critical summary of the progress of research on chlorine in MSW (origins, species, and analytical methods); the thermal behavior of chlorine, including chlorine vaporization, aerosol formation and transformation (freeboard chemistry), deposit formation, and Cl-initiated corrosion mechanisms. In addition, the interrelationship of chlorine with other key elements (S, Na, K, Zn, Pb), and, the chlorine roadmap in the incineration process is presented, along with the influence of feedstock composition and the temperature of both the flue gas and boiler tube metal on chlorine-induced deposition and corrosion. Mitigation measures against Cl-initiated problems such as Segher boiler prisms, mixed secondary air injection, and eco-tube systems, are also thoroughly discussed. Finally, challenges and further research questions, are identified.

  • A sustainable platform of lignin: From bioresources to materials and their applications in rechargeable batteries and supercapacitors
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2019-08-30
    Jiadeng Zhu, Chaoyi Yan, Xin Zhang, Chen Yang, Mengjin Jiang, Xiangwu Zhang
  • Dynamics of cool flames
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2019-08-01
    Yiguang Ju, Christopher B. Reuter, Omar R. Yehia, Tanvir I. Farouk, Sang Hee Won

    Cool flames play a critical role in ignition timing, burning rate, burning limits, engine knocking, and emissions in conventional and advanced combustion engines. This paper provides an overview of the recent progress in experimental and computational studies of cool flames. First, a brief review of low-temperature chemistry and classical studies of cool flames is presented. Next, the recent experimental and computational findings of cool flames in microchannels, microgravity droplet combustion, counterflow flames, and turbulent combustion environments are reviewed. The flammability diagrams of different low-temperature flames and their relations to hot flames in premixed and nonpremixed systems are discussed. The impact of cool flames on turbulent combustion and knock formation is also highlighted. Finally, future avenues in cool flame research, including the use of cool flames as a new platform for low-temperature kinetic model validation, are presented. It is concluded that the understanding and control of low-temperature combustion is critical for the development of future advanced engines and new fuels.

  • Solar fuels production: Two-step thermochemical cycles with cerium-based oxides
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2019-07-22
    Youjun Lu, Liya Zhu, Christos Agrafiotis, Josua Vieten, Martin Roeb, Christian Sattler

    Solar CO2/H2O splitting via two-step thermochemical cycles of metal oxides is a promising path for solar energy conversion to carbon-neutral, liquid hydrocarbons from virtually inexhaustible resources, water and (waste) carbon dioxide, with high theoretical efficiency potential. Cerium-based oxides have seen enormous interest and research efforts since they were proposed for this application, mainly due to their good stability at high temperatures and fast kinetics in redox reactions. The current state-of the-art review on the advancements of thermochemical cycles performed with the aid of cerium-based oxides is presented in this work, with emphasis on the latest developments during the last decade. Reaction principles, material modifications, reaction kinetics and finally solar reactors developed and operated are discussed in detail to provide a comprehensive understanding of the nature of the specific material and the factors impacting on the system efficiency. This efficiency depends on a combination of redox material/solar reactor/operation mode. With respect to the material issue, even though most studies have been targeted on improving the reduction conditions by suitable doping (e.g. Zr and Hf), the experience accumulated so far points to the direction of improving the oxidation step, provided the reduction step is performed below a critical, operationally feasible temperature. Thus the efficiency-optimal solar operation mode should be based on a trade-off between material reduction and oxidation performance and on another trade-off between solid and gas heat requirements and suitable recuperation strategies. The latter are highly dependent on the concept of solar reactor chosen and have to be demonstrated efficiently in real cyclic, field-test operation. The development of more effective oxygen removal strategies to lower the oxygen partial pressure during reduction may bring great improvement to efficiency.

  • Recent progress in the synthesis of graphene and derived materials for next generation electrodes of high performance lithium ion batteries
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2019-07-18
    Rajesh Kumar, Sumanta Sahoo, Ednan Joanni, Rajesh Kumar Singh, Wai Kian Tan, Kamal Krishna Kar, Atsunori Matsuda

    The importance of graphene and its derivatives for “clean energy” applications became apparent over the last few years due to their exceptional characteristics, especially regarding electrical, thermal and chemical properties. In this review article we examine the recent progress and some of the challenges in the syntheses and modification of graphene-based materials, including energy storage applications as electrodes in Li-ion batteries (LIBs). Various synthesis routes have been used for obtaining graphene using different kinds of carbon sources (graphite, non-graphitic carbon and carbon-containing materials). The most popular processing methods include epitaxial growth, liquid phase chemical/electrochemical exfoliation, mechanical exfoliation, chemical vapor deposition and laser-assisted synthesis. Taking the reduction approach, chemical, thermal, microwave and laser reduction methods have been applied to prepare graphene from graphene oxide/graphite oxide. Recent research has shown that graphene derivatives and hybrids/ nanocomposites using metal oxides/mixed metal oxides and metal sulfides/mixed metal sulphides can have a profound impact on the performance of energy storage devices. Closing the text, we speculate on the future prospects for the application of graphene and its derivatives in energy storage devices. We expect that this review article will help in generating new insights for further development and practical applications of graphene-based materials.

  • Recent advances in elevated-temperature pressure swing adsorption for carbon capture and hydrogen production
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2019-07-17
    Xuancan Zhu, Shuang Li, Yixiang Shi, Ningsheng Cai

    In this work, advanced technologies concerning warm gas carbon capture and hydrogen production from carbon-based fuels are reviewed, with a primary focus on the elevated-temperature pressure swing adsorption process coupled with the water gas shift reaction and in-situ CO2 adsorption. Key progress in the development of adsorption kinetic models, study of adsorption mechanisms, synthesis of efficient CO2 adsorbents, design and process optimization of adsorption/desorption reactors, and integration of purification systems, as well as major challenges and perspectives for the fundamental study and pilot-scale system development are discussed. This review provides a theoretical basis for the scaling-up of the next carbon capture system, and has scientific value and strategic significance for alleviating carbon emission pressure, developing hydrogen fuel cell energy system, and reducing energy consumption of hydrogen production in coal processing industries.

  • Reactor technologies for biodiesel production and processing: A review
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2019-07-04
    Meisam Tabatabaei, Mortaza Aghbashlo, Mona Dehhaghi, Hamed Kazemi Shariat Panahi, Arash Mollahosseini, Mehdi Hosseini, Mohamad Mojarab Soufiyan

    Diesel engines are preferred over spark ignition counterparts for heavy-duty applications and power generation plants because of their higher efficiency, durability, and productivity. Currently, the research interests have been propelled towards renewable and sustainable diesel fuels such as biodiesel in order to address the environmental and energy security challenges associated with these energy systems. However, the most challenging issue concerning large-scale production of biodiesel is its relatively high cost over fossil-based diesel owing to high feedstock and manufacturing costs. Therefore, cost-effective and eco-friendly biodiesel production technologies should be necessarily developed and continuously improved in order to make this biofuel more competitive vs. its petroleum counterpart. Accordingly, this paper comprehensively reviews biodiesel manufacturing techniques from natural oils and fats using conventional and advanced technologies with an in-depth state-of-the-art focus on the utmost important unit, i.e., transesterification reactor. The effects of the main influential parameters on the transesterification process are first discussed in detail in order to better understand the mechanisms behind each reactor technology. Different transesterification reactors; e.g., tubular/plug-flow reactors, rotating reactors, simultaneous reaction-separation reactors, cavitational reactors, and microwave reactors are then scrutinized from the scientific and practical viewpoints. Merits and limitations of each reactor technology for biodiesel production are highlighted to guide future R&D on this topic. At the end of the paper, the sustainability aspects of biodiesel production are comprehensively discussed by emphasizing on the biorefinery concept utilizing waste-oriented oils.

  • Soot formation in laminar counterflow flames
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2019-06-20
    Yu Wang, Suk Ho Chung

    Many practical soot-emitting combustion systems such as diesel and jet engines rely on diffusion flames for efficient and reliable operation. Efforts to mitigate soot emissions from these systems are dependent on fundamental understanding of the physicochemical pathways leading from fuel to soot in laminar diffusion flames. Existing diffusion flame−based soot studies focused primarily on over-ventilated coflow flame where the fuel gas (or vapor) issues from a cylindrical tube into a co-flowing oxidizer, and counterflow flame, where a reacting zone is established between two opposing streams of fuel and oxidizer. As a canonical diffusion flame configuration, laminar counterflow diffusion flames have been widely used as a highly controllable environment for soot research, enabling significant progress in the understanding of soot formation for several decades. In view of the possibility of fuel/oxidizer premixing in practical systems, counterflow partially premixed flames have also been studied. In the present work we intend to provide a comprehensive review of the researches on various aspects of soot formation utilizing counterflow flames. Major processes of soot formation (formation of gas phase soot precursors, soot inception and surface reactions, as well as particle-particle interactions) are examined first, with focus on the most recent (post-2010) research progress. Experimental techniques and associated challenges for the measurement of soot-related properties (some knowledge of which is helpful for full appreciation of the experimental data to be reviewed) are then introduced. This is followed by a detailed description of soot evolution in counterflow flames, which is complemented by a discussion on the similarity and differences of the sooting structures between counterflow and coflow diffusion flames. Parametric studies of the effects of fuel molecular structure, fuel additive, partial-premixing, pressure, temperature, stoichiometric mixture fraction, and residence time on soot formation in counterflow flames will then be addressed in detail. This review concludes with a summary of the knowledge and challenges gathered and demonstrated through decades of research, and an outlook on opportunities for future counterflow flame−based soot research towards a more complete understanding of soot formation and the development of novel techniques for soot mitigation in practical combustion devices.

  • Generalization of particle impact behavior in gas turbine via non-dimensional grouping
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2019-06-18
    Alessio Suman, Nicola Casari, Elettra Fabbri, Luca di Mare, Francesco Montomoli, Michele Pinelli

    Fouling in gas turbines is caused by airborne contaminants which, under certain conditions, adhere to aerodynamic surfaces upon impact. The growth of solid deposits causes geometric modifications of the blades in terms of both mean shape and roughness level. The consequences of particle deposition range from performance deterioration to life reduction to complete loss of power. Due to the importance of the phenomenon, several methods to model particle sticking have been proposed in literature. Most models are based on the idea of a sticking probability, defined as the likelihood a particle has to stick to a surface upon impact. Other models investigate the phenomenon from a deterministic point of view by calculating the energy available before and after the impact. The nature of the materials encountered within this environment does not lend itself to a very precise characterization, consequently, it is difficult to establish the limits of validity of sticking models based on field data or even laboratory scale experiments. As a result, predicting the growth of solid deposits in gas turbines is still a task fraught with difficulty. In this work, two non-dimensional parameters are defined to describe the interaction between incident particles and a substrate, with particular reference to sticking behavior in a gas turbine. In the first part of the work, historical experimental data on particle adhesion under gas turbine-like conditions are analyzed by means of relevant dimensional quantities (e.g. particle viscosity, surface tension, and kinetic energy). After a dimensional analysis, the data then are classified using non-dimensional groups and a universal threshold for the transition from erosion to deposition and from fragmentation to splashing based on particle properties and impact conditions is identified. The relation between particle kinetic energy/surface energy and the particle temperature normalized by the softening temperature represents the original non-dimensional groups able to represent a basis of a promising adhesion criterion.

  • A review of gas diffusion layers for proton exchange membrane fuel cells—With a focus on characteristics, characterization techniques, materials and designs
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2019-06-12
    Adnan Ozden, Samaneh Shahgaldi, Xianguo Li, Feridun Hamdullahpur

    Proton exchange membrane (PEM) fuel cells are at the dawn of commercialization. Their operation and design characteristics, hence their performance, are closely linked to the multiphase transport of mass, heat, and electricity in the cell constituents, a critical of which is the gas diffusion layer (GDL). The GDL's transport capability is represented by its effective transport properties: an effective diffusion coefficient for the diffusional transport of mass, absolute and relative permeabilities for the convective transport of mass, effective thermal conductivity for the heat transport, and effective electron conductivity for the electricity transport; in addition, surface wettability impacts the transport of liquid water. These transport properties depend on the GDL's mechanical, morphological, microstructural, and physical characteristics, which are in turn controlled by its materials and design parameters. This review article therefore focuses on the insights and comprehensive understanding of three critical issues of the GDLs: (i) their morphological, microstructural, and physical characteristics, (ii) ex- and in-situ characterization techniques for the determination of their effective transport and mechanical properties, and (iii) frequently used materials and design strategies and their relevant influences on the effective transport properties in order to achieve reliable and durable performance of PEM fuel cells with high power densities.

  • Mixed ionic-electronic conducting (MIEC) membranes for thermochemical reduction of CO2: A review
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2019-05-06
    Xiao-Yu Wu, Ahmed F. Ghoniem

    Intermediate temperature membrane-supported CO2 thermochemical reduction using renewable energy is a clean approach for reusing CO2. To implement this technology at scale, stable catalytic membrane materials with fast kinetics should be developed, and reactor designs and system integrations should be optimized. In this review, we highlight major advancements in experimental and numerical efforts on mixed ionic-electronic conducting (MIEC) membrane-supported CO2 thermochemical reduction, and discuss the connection among materials, kinetics, membranes and reactor design. First, we discuss the thermodynamics and kinetics of CO2 reduction and the working principles of membrane reactors. Two methods are compared: chemical looping (redox) and membrane supported CO2 reduction. Next, we compare CO2 conversion rates on various membrane materials and their stability. Strontium based perovskites, e.g., Nb2O5-doped SrCo0.8Fe0.2O3-δ (SCoF-82) show the highest CO2 reduction rates so far, but they suffer degradation mainly from carbonate formation. Mixed-phase membranes are promising, with high reduction rates and good stability. Surface modification can enhance the reduction rates and increase membrane stabilities. In order to accelerate the development in materials and membranes, kinetic parameters, e.g., conductivity and reaction rate constants should be obtained from high throughput benchtop reactors complemented by reduced physical models. The mechanisms and transport models for surface kinetics and bulk diffusion are summarized. Using these results, changes in membrane morphology and surface chemistry are proposed. Finally, we summarize methods and system-scaled analysis to integrate this membrane technology with renewable or waste heat sources for fuel production and energy storage.

  • Biomass-derived aviation fuels: Challenges and perspective
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2019-05-13
    Meng Wang, Raf. Dewil, Kyriakos Maniatis, John Wheeldon, Tianwei Tan, Jan Baeyens, Yunming Fang
  • Level set method for atomization and evaporation simulations
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2019-03-19
    Kun Luo, Changxiao Shao, Min Chai, Jianren Fan

    Atomization and evaporation processes have extensively existed in a variety of scientific and engineering applications, such as, rain formation, spray cooling, and spray combustion in propulsion devices. In spray combustion, atomization and evaporation processes govern the resultant liquid droplet characteristics, which strongly affect the combustion efficiency and pollutant emissions. However, atomization and evaporation are very complicated processes that involve convoluted interfaces as well as the breakup and coalescence of liquid masses, together with mass and heat transfers on the interface. Deep insights into atomization and evaporation put a significant challenge to the measuring techniques due to the harsh conditions and multi-scale nature of the problem within the apparatus. With the developments of computational algorithm and computer capacity, detailed numerical simulation of the atomization and evaporation processes has been a promising tool to explore the underlying physics. Level set method is such an interface capturing method, and tremendous progresses have been made for detailed numerical simulation of atomization and evaporation over the past few decades. In this article, we attempt to review the recent progresses in the development of the level set method and its applications to atomization and evaporation. Firstly, the fundamentals of the level set method are introduced and recent advances in improving the mass conservation are emphasized. Secondly, numerical issues for detailed numerical simulation of atomization and evaporation are summarized and the strategies for treating them are highlighted. We then review the state-of-the-art progresses in detailed numerical simulation of atomization and evaporation with the level set method. The challenges and future prospects are summarized in the end.

  • The effect of ozone addition on combustion: Kinetics and dynamics
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2019-02-27
    Wenting Sun, Xiang Gao, Bin Wu, Timothy Ombrello

    Ozone addition is a promising method to enhance and control combustion and ignition processes. It can be produced efficiently at atmospheric or elevated pressure conditions and its lifetime is sufficiently long to allow for remote production and transport to reaction zones. Over the past decades, the effect of ozone addition on ignition and combustion processes has been extensively studied from bench top fundamental burners to practical internal combustion engines. Ozone has shown the capability to accelerate ignition and control ignition timing, enhance flame propagation, improve flame stabilization, pre-process fuel to modify emission and reactivity characteristics, and reduce certain pollutant formation. Such enhancement is closely related to ozone chemistry, especially the decomposition of ozone to produce atomic oxygen and the rapid exothermic ozonolysis reactions with unsaturated hydrocarbons. The former requires elevated temperature to release atomic oxygen and initiate fuel/atomic oxygen reactions typically in the preheat zone, while the latter initiates low temperature (even room temperature) direct fuel/ozone reactions. These findings provide new opportunities in the development of strategies to enhance and control combustion/ignition processes. This article provides a comprehensive review of the basic principles of ozone enhanced reactive processes, including fundamental ozone chemistry, ozone generation and quantification, and the progress in the study of ozone addition in combustion systems.

  • A review on mercury in coal combustion process: Content and occurrence forms in coal, transformation, sampling methods, emission and control technologies
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2019-03-11
    Shilin Zhao, Deepak Pudasainee, Yufeng Duan, Rajender Gupta, Meng Liu, Jianhong Lu

    Mercury, as a global pollutant, has raised worldwide concern due to its high toxicity, long-distance transport, persistence, and bioaccumulation in the environment. Coal-fired power plants (CFPPs) are considered as the major anthropogenic mercury emission source to the atmosphere, especially for China, India, and the US. Studies on mercury in coal combustion process have been carried out for decades, which include content and occurrence forms of mercury in coal, mercury transformation during coal combustion, sampling, co-removal and emission of mercury in CFPPs, mercury removal technologies for CFPPs. This current review summarizes the knowledge and research developments concerning these mercury-related issues, and hopes to provide a comprehensive understanding of mercury in coal combustion process and guidance for future mercury research directions. The average mercury content in the coal from China, the US, and South Africa is 0.20, 0.17, and 0.20 mg/kg, respectively, which is higher than the world's coal average value of 0.1 mg/kg. In general, mercury in coal is in the forms of sulfide-bound mercury (mainly pyritic mercury, dominant), clay-bound mercury, and organic matter-bound mercury, which are influenced by diagenetic, coalification, and post-diagenetic conditions, etc. Mercury transformation in coal combustion includes homogeneous (without fly ash) and heterogeneous (with fly ash) reaction. The transformation is affected by the coal types, flue gas components, flue gas temperature, combustion atmosphere, coal ash properties, etc. The effects of chlorine, NOx, SO2, H2O, O2 NH3 on elemental mercury (Hg0) homogeneous oxidation and the influence of physical structure properties, unburned carbon, and metal oxides in fly ash as well as flue gas components on Hg0 heterogeneous transformation are systematically reviewed in detail. For the mercury transformation in oxy-coal combustion, O2 promotes Hg0 oxidation with Cl2 while NO and CO2 inhibit or do not favor that reaction. CO2 increases Hg0 oxidation in the atmosphere of NO and N2. SO2 will limit Hg0 oxidation, while HCl has a higher oxidation effect on Hg0 than that in air-coal combustion atmosphere. Fly ash plays an important role in Hg0 oxidation. SO3 inhibits mercury retention by fly ash while H2O promotes the oxidation. The sampling or analysis principle, sampling requirements, and advantages and disadvantages of the commonly used on-site mercury sampling methods, namely, Ontarion Hydro Method (OHM), US EPA Method 30B, and Hg-CEMS, are compared. The air pollution control devices (APCDs) in CFPPs also have the mercury co-removal ability besides the conventional pollutants, such as NOx, particulate matter (PM), SO2, and fine PM. Selective catalytic reduction (SCR) equipment, electrostatic precipitator (ESP) or fabric filter (FF), and wet flue gas desulfurization (WFGD) device are good at Hg0 oxidation, particulate mercury (Hgp) removal, and oxidized mercury (Hg2+) capture, respectively. The Hg0 oxidation rate for SCR equipment, and the total mercury (Hgt, Hgt = Hg0 + Hg2+ + Hgp) removal rate for ESP, FF, and WFGD device is 6.5–79.9%, 11.5–90.4%, 28.5–90%, and 3.9–72%, respectively. Wet electrostatic precipitator (WESP) can capture Hg0, Hg2+, and Hgp simultaneously. The mercury transformation process in SCR, ESP, FF, WFGD, and WESP is also discussed. Hgt removal in ESP+WFGD, SCR+ESP+WFGD, SCR+ESP+FF+WFGD, and SCR+ESP+WFGD+WESP is 35.5–84%, 43.8–94.9%, 58.78–73.32%, and 56.59–89.07%, respectively. The mercury emission concentration in the reviewed CFPPs of China, South Korea, Poland, the Netherlands, and the US is 0.29–16.3 µg/m3. Mercury in some fly ash and gypsum, and in most WFGD and WESP wastewater, is higher than the relevant limits, which needs to be paid attention to during their processing. Mercury removal technologies for CFPPs can be divided into pre-combustion (including coal washing technology and mild pyrolysis method), in-combustion (including low-NOx combustion technology, circulating fluidized bed combustion technology, and halogens addition into coal), and post-combustion (including existing commercial SCR catalyst improvement, inhibiting Hg0 re-emission in WFGD, mercury oxidizing catalysts, injecting oxidizing chemicals, carbon-based adsorbents, fly ash, calcium-based adsorbents, and mineral adsorbents) based on the mercury removal position. The mercury removal effects, mercury removal mechanism, and/or influencing factors are summarized in detail. One of the regenerable mercury removal adsorbents, the magnetic adsorbent modified by metal oxides or the metal halides, is the most promising sorbent for mercury removal from CFPPs. It has advantages of high mercury removal efficiency, low investment, easy separation from fly ash, and mercury recovery, etc. Lastly, further works about mercury transformation in coal combustion atmosphere, mercury co-removal by APCDs, the emission in CFPPs, and mercury removal technologies for CFPPs are noted.

  • Alternative designs of parabolic trough solar collectors
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2018-11-28
    Evangelos Bellos, Christos Tzivanidis

    Parabolic trough collector (PTC) is the most established solar concentrating technology worldwide. The conventional parabolic trough collectors are used in various applications of medium and high-temperature levels. However, there are numerous studies which investigate alternative designs. The reasons for examining different PTC configurations regard the thermal efficiency increase, the reduction of the manufacturing cost and the development of more compact designs. The objective of this review paper is to summarize the existing alternative designs of PTC and to suggest the future trends in this area. Optical and thermal modifications are examined, as well as the use of concentrating thermal photovoltaic collectors. The optical modifications include designs with secondary concentrators, stationary concentrators and strategies for achieving uniform heat flux. The thermal modifications regard the use of nanofluids, turbulators and the use of thermally modified receivers with insulation, double-coating and radiation shields. The concentrating thermal photovoltaics are systems with flat or triangular receivers which can operate in low or in medium temperature levels with the proper alternative designs. It has been found that there are many promising choices for designing PTC with higher thermal performance and lower cost. The conclusions of this work can be used as guidelines for future trends in linear parabolic concentrating technologies.

  • The multi-scale challenges of biomass fast pyrolysis and bio-oil upgrading: Review of the state of art and future research directions
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2018-11-23
    Mahdi Sharifzadeh, Majid Sadeqzadeh, Miao Guo, Tohid N. Borhani, N.V.S.N. Murthy Konda, Marti Cortada Garcia, Lei Wang, Jason Hallett, Nilay Shah

    Biomass fast pyrolysis is potentially one of the cheapest routes toward renewable liquid fuels. Its commercialization, however, poses a multi-scale challenge, which starts with the characterization of feedstock, products and reaction intermediates at molecular scales, and continues with understanding the complex reaction network taking place in different reactor configurations, and in the case of catalytic pyrolysis and upgrading on different catalysts. In addition, crude pyrolysis oil is not immediately usable in the current energy infrastructure, due to undesirable properties such as low energy content and corrosiveness as a result of its high oxygenate content. It, therefore, needs to be upgraded and fractionated to desired specifications. While various types of pyrolysis reactors and upgrading technologies are under development, knowledge transfer and closing the gap between theory and application requires model development. In-depth understanding of the reaction mechanisms and kinetics should be combined with the knowledge of multi-scale transport phenomena to enable design, optimization, and control of complex pyrolysis reactors. Finally, underpinning economic and environmental impacts of biofuel production requires expanding the system boundaries to include the overall process and supply chain. The present contribution aims at providing a comprehensive multi-scale review that discusses the state of the art of each of these aspects, as well as their multi-scale interactions. The study is mainly focused on fast pyrolysis, although reference to other types of pyrolysis technologies is made for the sake of comparison and knowledge transfer.

  • Lignin-derived platform molecules through TEMPO catalytic oxidation strategies
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2019-02-07
    Samira Gharehkhani, Yiqian Zhang, Pedram Fatehi

    Lignin is currently an under-used material of the pulping and cellulosic ethanol production plants. The first and foremost objective in dealing with lignin is to augment the use of this aromatic compound and financial profitability of lignin-based processes. Of particular interests are lignin oxidation and depolymerization methods that harvest either the aromatic subunits of polymers or monomeric/oligomeric aromatic products used as platform chemicals. In this context, many studies have focused on the catalytic processes in which a nitroxyl catalyst, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), was employed to oxidize hydroxyl groups in lignin structure and selectively depolymerize lignin via cleavage of the ether and CC bonds. In discussing the advanced studies especially over the last decade on the oxidation of lignin models with TEMPO catalyst systems, this review provides a description of promising methods that can be employed for authentic lignin conversion. In the present review, a particular emphasis is dedicated to the proposed mechanisms for the oxidation of lignin and lignin models.

  • Heat recirculating reactors: Fundamental research and applications
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2019-01-17
    Janet L. Ellzey, Erica L. Belmont, Colin H. Smith

    Worldwide emphasis on fuel efficiency, low emissions, and use of low-quality fuels such as biogas continues to drive the development of combustors that operate over a wider range of fuel/air ratios and with higher burning velocities than their conventional counterparts. Enhancement of reaction rates is required to increase burning velocities and widen fuel/air operating ranges over values achievable in conventional combustors, and extensive research over the last few decades has shown that transferring heat in a reactor from hot combustion products to incoming reactants can accomplish this enhancement without external energy addition. These reactors, called heat recirculating reactors, use various geometries and flow strategies to optimize the heat transfer. In this paper, research on heat recirculating reactors is reviewed with an emphasis on the most important designs and applications. The basic characteristics of a heat recirculating reactor are encompassed in a simple configuration: a flame stabilized in a tube with high thermal conductivity. More complex designs that have evolved to further optimize heat transfer and recirculation are then described, including porous reactors with or without flame stabilization and channel reactors consisting of parallel tubes or slots. Advanced designs introduce additional means of heat transfer, such as transverse heat transfer from hot products through channel walls to incoming reactants, thereby leading to the counter-flow channel reactor. The flexibility of heat recirculating reactors to operate on a variety of fuels and over wide operating ranges has led to many applications including fuel reformers, radiant heaters and thermal oxidizers, and important work on these applications is reviewed. Finally, future research directions are discussed.

  • A comparison of methodologies for the non-invasive characterisation of commercial Li-ion cells
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2019-01-14
    Anup Barai, Kotub Uddin, Matthieu Dubarry, Limhi Somerville, Andrew McGordon, Paul Jennings, Ira Bloom

    Lithium-ion cells currently power almost all electronic devices and power tools; they are a key enabling technology for electric vehicles and are increasingly considered to be the technology of choice for grid storage. In line with this increased applicability, there is also an increase in the development of new commercial lithium-ion cell technologies that incorporate innovative functional components (electrode material compositions and electrolyte formulations) and designs, leading to a diverse range of performance characteristics. The uniqueness of each technology in-turn gives rise to unique evolutions of cell performance as the cell degrades because of usage. Non-destructively measuring and subsequently tracking the evolution of lithium-ion cell characteristics is valuable for both industrial engineers and academic researchers. To proceed in this regard, stakeholders have often devised their own procedures for characterising lithium-ion cells, typically without considering unification, comparability or compatibility. This makes the comparison of technologies complicated. This comprehensive review for the first time has analysed and discusses the various international standards and regulations for the characterisation and electrical testing of lithium-ion cells, specifically for high-power automotive and grid applications.

  • Mesoscale modeling in electrochemical devices—A critical perspective
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2018-12-24
    Emily M. Ryan, Partha P. Mukherjee

    Electrochemical energy systems, such as batteries and fuel cells, are being developed for applications ranging from portable devices and electric vehicles to large-scale grid storage. These advanced energy conversion and storage technologies will be a critical aspect of a sustainable energy future and promise to provide cleaner, more efficient energy. Computational modeling at various scales from nanoscale ab initio modeling to macroscale system and controls level modeling, has been a central part of the electrochemical energy research. Much of the complex interactions due to the electrochemistry coupled transport phenomena occur at the interfaces and within the porous electrode microstructures. This is often referred to as the mesoscale and plays a critical role in the operation and efficiency of electrochemical devices. In this critical perspective, we discuss the state-of-the-art, challenges and path forward in mesoscale modeling of electrochemical energy systems and their application to various design and operational issues in solid oxide fuel cells, polymer electrolyte membrane fuel cells, lithium ion batteries and metal-air batteries. Particular focus is given to particle-based methods and fine-scale computational fluid dynamics based direct numerical simulation techniques, along with the challenges and advantages of these methods. Notable results from mesoscale modeling are presented along with discussions of the advantages, disadvantages and challenges facing mesoscale model development. This in-depth perspective is envisioned to serve as a primer to the critical role mesoscale modeling is poised to play in advancing the science and engineering of electrochemical energy systems.

  • Thermal decomposition of brominated flame retardants (BFRs): Products and mechanisms
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2018-11-03
    Mohammednoor Altarawneh, Anam Saeed, Mohammad Al-Harahsheh, Bogdan Z. Dlugogorski

    Brominated flame retardants (BFRs) are bromine-bearing hydrocarbons added or applied to materials to increase their fire resistance. As thermal treatment and recycling are common disposal methods for BFR-laden objects, it is essential to precisely describe their decomposition chemistry at elevated temperatures pertinent to their thermal recycling. Laboratory-level and pilot-scale investigations have addressed the thermal decomposition of pure BFRs and/or BFR-laden polymers under oxidative and pyrolytic environments, typically at temperatures of 280–900°C. These studies shed light on the effects of various factors influencing the decomposition behaviour of BFRs such as chemical character, polymer matrix, residence time, bromine input, oxygen concentration, and temperature. Although BFRs decomposition mainly occurs in a condensed phase, gas phase reactions also contribute significantly to the overall decomposition of BFRs. Exposing BFRs to temperatures higher than their melting points results in evaporation. Quantum chemical calculations have served to provide mechanistic and kinetic insights into the chemical phenomena operating in decomposition of BFRs and subsequent emissions of polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs). Under thermal conditions such as smouldering, municipal waste incineration, pyrolysis, thermal recycling, uncontrolled burning and fires, BFRs degrade and form brominated products of incomplete combustion (BPICs). Thermal degradation of BFRs often proceeds in the presence of bromine atoms which inhibit complete combustion. Major BPICs comprise brominated benzenes and phenols in addition to a wide range of brominated aromatics. Pyrolytic versus oxidative conditions seems to have very little influence on the thermal stability and decomposition behaviour of commonly-deployed BFRs. Thermal degradation of BFRs produces potent precursors to PBDD/Fs. Experimental studies have established inventories of PBDD/F emissions with alarming high yields for many BFRs. Co-combustion of BFRs-containing objects with a chlorine source (e.g. polyvinyl chlorides) results in the emission of significant concentrations of mixed halogenated dibenzo-p-dioxins and dibenzofurans (i.e. PXDD/Fs). Formation of PBDD/Fs from incomplete BFRs decomposition occurs primarily due to the condensations of gas phase precursors, including unaltered structural entities of some BFRs in their own right. Complete destruction of BFRs promotes PBDD/Fs formation via de novo synthesis. Bromination of PBDD/Fs in gas phase reactions is more prevalent if compared with chlorination mechanisms of PCDD/Fs, which is largely dominated by heterogeneous pathways. In uncontrolled burning and in simulated fly ash experiments, a strong correlation between congeners patterns of polybrominated diphenyl ethers (PBDEs) and PBDD/Fs indicate that PBDEs function as direct precursors for PBDD/Fs, even in the de novo synthesis route. In this review, we critically discuss current literature on BFRs thermal decomposition mechanisms; gather information regarding the contribution of homogenous and heterogeneous routes to overall BFRs decomposition; survey all studies pertinent to the emission of PBDD/Fs and their analogous mixed halogenated counterparts from open burning of e-waste, and finally, highlight knowledge gaps and potential directions that warrant further investigations.

  • Progress in non-intrusive laser-based measurements of gas-phase thermoscalars and supporting modeling near catalytic interfaces
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2018-11-03
    John Mantzaras

    Heterogeneous and combined hetero-/homogeneous chemical processes have attracted increased attention in many energy conversion systems, which include large-scale power generation, microreactors for portable power generation, household burners, fuel-processing technologies and automotive exhaust gas after treatment. Progress in such systems crucially depends on the development of catalysts with enhanced activity and thermal stability and on the comprehensive understanding of the fundamental processes occurring near gas–solid reacting interfaces. Recent advances in non-intrusive lased-based measurements of gas-phase thermoscalars over the catalyst boundary layer are reviewed. Such measurements, combined with theoretical analyses and numerical simulations, have fostered fundamental investigations of the catalytic and gas-phase chemical processes and their coupling at industrially-relevant operating conditions. The methodology for assessing local catalytic reaction rates and validating gas-phase reaction mechanisms under steady conditions using 1-D Raman and planar laser induced fluorescence (PLIF) of radical species, respectively, is presented first. Progress in the measurement of minor and major stable species using PLIF is outlined and the potential of this technique as a suitable method for assessing the catalytic reactivity under dynamic operating conditions is discussed. State of the art numerical modeling necessary for the interpretation of the measurements is presented in parallel with the laser-based techniques. Turbulence modeling, direct numerical simulation (DNS) and near-wall non-intrusive measurements of species concentrations and velocity have clarified aspects of the complex interplay between interphase turbulent transport and hetero-/homogeneous kinetics. Controlling parameters are the competition between the heterogeneous and homogeneous reaction pathways, diffusional imbalance of the deficient reactant, flow laminarization induced by the hot catalytic walls, and fuel leakage through the gaseous reaction zone that leads to concurrent catalytic and gas-phase combustion. Experimental needs for assessing turbulent fluctuations of catalytic reaction rates as well as for investigating intrinsic instabilities (heterogeneously or homogeneously driven) are discussed. Future directions for combining in situ surface science diagnostics with in situ non-intrusive gas-phase thermoscalar diagnostics and for advancing current numerical tools are finally proposed.

  • Towards sustainable and energy efficient municipal wastewater treatment by up-concentration of organics
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2018-10-27
    Huseyin Guven, Recep Kaan Dereli, Hale Ozgun, Mustafa Evren Ersahin, Izzet Ozturk
  • A current perspective on the accuracy of incoming solar energy forecasting
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2018-10-22
    Robert Blaga, Andreea Sabadus, Nicoleta Stefu, Ciprian Dughir, Marius Paulescu, Viorel Badescu
  • Forced response of laminar non-premixed jet flames
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2018-10-22
    Nicholas Magina, Vishal Acharya, Timothy Lieuwen
  • Methanol as a fuel for internal combustion engines
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2018-10-16
    Sebastian Verhelst, James WG Turner, Louis Sileghem, Jeroen Vancoillie
  • Recent trends in anaerobic co-digestion: Fat, oil, and grease (FOG) for enhanced biomethanation
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2018-09-29
    El-Sayed Salama, Shouvik Saha, Mayur B. Kurade, Subhabrata Dev, Soon Woong Chang, Byong-Hun Jeon
  • 更新日期:2018-09-27
  • Ammonia for power
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2018-09-11
    A Valera-Medina, H Xiao, M Owen-Jones, W.I.F. David, P.J. Bowen
  • Flameless combustion and its potential towards gas turbines
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2018-09-10
    André A.V. Perpignan, Arvind Gangoli Rao, Dirk J.E.M. Roekaerts

    Since its discovery, the Flameless Combustion (FC) regime has been seen as a promising alternative combustion technique to reduce pollutant emissions of gas turbine engines. This combustion mode is often characterized by well-distributed reaction zones, which can potentially decrease temperature gradients, acoustic oscillations and, consequently NOx emission. However, the application of FC to gas turbines is still not a reality due to the inherent difficulties faced in attaining the regime while meeting all the engine requirements. Over the past years, investigations related to FC have been focused on understanding the fundamentals of this combustion regime, the regime boundaries, its computational modelling, and combustor design attempts. This article reviews the progress achieved so far, discusses the various definitions of the FC regime, and attempts to point the directions for future research. The review suggests that modelling of the FC regime is still not capable of predicting intermediate species and pollutant emissions. Comprehensive experimental databases with conditions relevant to gas turbine combustors are not available, and moreover, many of the current experiments do not necessarily represent the FC regime. By analysing the latest developments in computational modelling, the review points to the most promising approaches for the prediction of reaction zones and pollutant emissions in FC. The lessons learned from previous design attempts provide valuable insights into the design of a successful gas turbine engine operating under the FC regime. The review concludes with some examples where the gas turbine architecture has been exploited to advance the possibilities of FC in gas turbines.

  • Thermodynamic analysis of integrated LNG regasification process configurations
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2018-09-09
    Mehdi Mehrpooya, Mohammad Mehdi Moftakhari Sharifzadeh, Mohammad H. Katooli

    Effective utilization of liquefied natural gas (LNG) cold energy during its regasification in both renewable and nonrenewable processes is discussed and analyzed. Conventional and non-conventional thermodynamic cycles, are described and categorized. Expressions for exergy and energy efficiencies are developed to facilitate evaluation of the processes. Finally suggestions for improving the efficiency of such systems are developed and the technical advantages and challenges are pointed out. The obtained results indicate that, among the considered cycles, the highest energy and exergy efficiencies are about 86.3% and 80.0% respectively; which is related to the combined cycles. Conversely the lowest energy and exergy efficiencies occur in other application of LNG cold energy cycles (i.e., production of hydrogen by a solar aid liquefied natural gas hybrid CO2 cycle) and Rankine cycle (i.e., CO2 transcritical geothermal power generation cycle) with the values of 7.39% and 7.95%; respectively.

  • Ash formation and deposition in coal and biomass fired combustion systems: Progress and challenges in the field of ash particle sticking and rebound behavior
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2018-05-24
    Ulrich Kleinhans, Christoph Wieland, Flemming J. Frandsen, Hartmut Spliethoff

    The purpose of this paper is to review the present knowledge on ash formation, ash particle transport and deposition during solid fuel combustion, with emphasis on particle sticking and rebound behavior. A substantial part of the fuel can be inorganic, forming inorganic vapors and ash particles. The impaction of solid, molten or partially molten particles on surfaces is dependent on the particle and surface characteristics. For instance, a particulate deposit might capture incoming particles or be removed due to erosion, while a molten layer will collect all impacting particles, no matter if they are sticky or not. The main properties affecting the particle stickiness are the viscosity and surface tension for silicate-rich ashes. On the contrary, the stickiness of salt-rich ashes – typical for herbaceous biomass and wood- or waste-based fuels – is often described using the liquid melt fraction. Furthermore, the particle kinetic energy and the angle of impaction, are crucial parameters. If all kinetic energy is dissipated during the impact, the particle will remain on the surface. This review presents an overview of major ash forming elements found in biomass and coal, and discusses the heterogeneity of particles’ inorganic composition. Ash transport and deposition mechanisms as well as their mathematical description are given and discussed, together with composition- and temperature-depended models for the estimation of ash particle and deposit properties. These properties are essential in order to describe the particle sticking and rebound behavior. Ash particle sticking and rebound criteria can be divided into three main groups, based on either: (1) the particle melt fraction, (2) the particle viscosity, or (3) the energy dissipation of a particle, upon impaction. Sticking criteria are presented, their required parameters are discussed and typical particle and surface properties found in combustion systems, are summarized. Eight different sticking criteria are implemented in a computational fluid dynamics code and computations are compared against measurements from an entrained flow reactor. Uniform sized soda-lime glass particles are applied instead of inhomogeneous fly ash particles, since soda-lime glass is known to behave similar to coal fly ash. Best agreement for the deposition rates on a clean tube is achieved using a criterion based on the work of Srinivasachar et al. [1]. In this model, the sticking and rebound threshold, is a function of the particle kinetic energy, the angle of impaction, and, the particle viscosity. Particularly, the particle viscosity is confirmed as a key parameter for silicate-rich ashes. It should be calculated using temperature- and composition-dependent correlations, being aware that there is a significant scattering in the results from such models and that the models are often only valid in narrow compositional ranges, and cannot be used outside these. A mechanistic model is used to explain results from glass particle experiments and their dependence on the particle kinetic energy. Therefore, the impaction process is subdivided in four steps, and the energy dissipation of each step is calculated. These theoretical considerations show that the contact angle of a molten droplet with the substrate is of minor importance, and that the majority of depositing particles are dominated by the work of deformation against viscosity, rather than surface tension effects. This review underlines the importance of the particle viscosity, and its accurate prediction for silicate-rich ashes. The proposed criterion is able to predict the sticking of small, solid particles below 10 µm diameter, as it is often observed in literature. Also, it is crucial to consider the surface structure and stickiness, in order to predict deposition rates in solid fuel-fired systems. Biomass ashes and their stickiness are more difficult, due to a different ash particle chemistry, compared to coal ashes. Salt-rich particles and their stickiness are controlled by the amount of liquid phase. Here, a link between the viscosity and amount of liquid phase is a promising approach, and should be addressed in future work. Furthermore, the viscosity of different ash particles – silicate-, salt- or Ca-rich – should preferentially be modeled from the chemical and physical structure instead of an empirical fitting procedure between fuel chemistry and viscosity measurements.

  • Transportation fuels from biomass fast pyrolysis, catalytic hydrodeoxygenation, and catalytic fast hydropyrolysis
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2018-06-22
    Trine M.H. Dabros, Magnus Zingler Stummann, Martin Høj, Peter Arendt Jensen, Jan-Dierk Grunwaldt, Jostein Gabrielsen, Peter M. Mortensen, Anker Degn Jensen

    This review presents and discusses the progress in combining fast pyrolysis and catalytic hydrodeoxygenation (HDO) to produce liquid fuel from solid, lignocellulosic biomass. Fast pyrolysis of biomass is a well-developed technology for bio-oil production at mass yields up to ∼75%, but a high oxygen content of 35–50 wt% strongly limits its potential as transportation fuel. Catalytic HDO can be used to upgrade fast pyrolysis bio-oil, as oxygenates react with hydrogen to produce a stable hydrocarbon fuel and water, which is removed by separation. Research on HDO has been carried out for more than 30 years with increasing intensity over the past decades. Several catalytic systems have been tested, and we conclude that single stage HDO of condensed bio-oil is unsuited for commercial scale bio-oil upgrading, as the coking and polymerization, which occurs upon re-heating of the bio-oil, rapidly deactivates the catalyst and plugs the reactor. Dual or multiple stage HDO has shown more promising results, as the most reactive oxygenates can be stabilized at low temperature prior to deep HDO for full deoxygenation. Catalytic fast hydropyrolysis, which combines fast pyrolysis with catalytic HDO in a single reactor, eliminates the need for reheating condensed bio-oil, lowers side reactions, and produces a stable oil with oxygen content, H/C ratio, and heating value comparable to fossil fuels. We address several challenges, which must be overcome for continuous catalytic fast hydropyrolysis to become commercially viable, with the most urgent issues being: (i) optimization of operating conditions (temperature, H2 pressure, and residence time) and catalyst formulation to maximize oil yield and minimize cracking, coke formation, and catalyst deactivation, (ii) development of an improved process design and reactor configuration to allow for continuous operation including pressurized biomass feeding, fast entrainment and collection of char, which is catalytically active for side reactions, efficient condensation of the produced oil, and utilization and/or integration of by-products (non-condensable gasses and char), and (iii) long-term tests with respect to catalyst stability and possible pathways for regeneration. By reviewing past and current research from fast pyrolysis and catalytic HDO, we target a discussion of the combined processes, including direct catalytic fast hydropyrolysis. By critically evaluating their potential and challenges, we finally conclude, which future steps are necessary for these processes to become industrially feasible.

  • A comprehensive review of measurements and data analysis of laminar burning velocities for various fuel+air mixtures
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2018-06-20
    Alexander A. Konnov, Akram Mohammad, Velamati Ratna Kishore, Nam Il Kim, Chockalingam Prathap, Sudarshan Kumar

    Accurate measurement and prediction of laminar burning velocity is important for characterization of premixed combustion properties of a fuel, development and validation of new kinetic models, and calibration of turbulent combustion models. Understanding the variation of laminar burning velocity with thermodynamic conditions is important from the perspective of practical applications in industrial furnaces, gas turbine combustors and rocket engines as operating temperatures and pressures are significantly higher than ambient conditions. With this perspective, a brief review of spherical flame propagation method, counterflow/stagnation burner method, heat-flux method, annular stepwise method, externally heated diverging channel method, and Bunsen method is presented. A direct comparison of power exponents for temperature (α) and pressure (β) obtained from different experiments and derived from various kinetic mechanisms is reported to provide an independent tool for detailed validation of kinetic schemes. Accurate prediction of laminar burning velocities at higher temperatures and pressures for individual fuels will help in closer scrutiny of the existing experimental data for various uncertainties due to inherent challenges in individual measurement techniques. Laminar burning velocity data for hydrogen (H2), gaseous alkane fuels (methane, ethane, propane, n-butane, n-pentane), liquid alkane fuels (n-heptane, isooctane, n-decane), alcohols (CH3OH, C2H5OH, n-propanol, n-butanol, n-pentanol) and di-methyl ether (DME) are obtained from literature of last three decades for a wide range of pressures (1–10 bar), temperatures (300–700 K), equivalence ratios and mixture dilutions. The available experimental and numerical data for H2 and methane fuels compares well for various pressures and temperatures. However, more experimental and kinetic model development studies are required for other fuels. Comparison of laminar burning velocity data obtained from different measurement techniques at higher initial pressures and temperatures showed significant deviations for all fuels. This suggests to conduct focused measurements at elevated pressure and temperature conditions for different fuels to enable the development of accurate kinetic models for wider range of mixtures and thermodynamic conditions.

  • Recyclable metal fuels for clean and compact zero-carbon power
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2018-06-18
    Jeffrey M. Bergthorson

    Metal fuels, as recyclable carriers of clean energy, are promising alternatives to fossil fuels in a future low-carbon economy. Fossil fuels are a convenient and widely-available source of stored solar energy that have enabled our modern society; however, fossil-fuel production cannot perpetually keep up with increasing energy demand, while carbon dioxide emissions from fossil-fuel combustion cause climate change. Low-carbon energy carriers, with high energy density, are needed to replace the multiple indispensable roles of fossil fuels, including for electrical and thermal power generation, for powering transportation fleets, and for global energy trade. Metals have high energy densities and metals are, therefore, fuels within many batteries, energetic materials, and propellants. Metal fuels can be burned with air or reacted with water to release their chemical energy at a range of power-generation scales. The metal-oxide combustion products are solids that can be captured and then be recycled using zero-carbon electrolysis processes powered by clean energy, enabling metals to be used as recyclable zero-carbon solar fuels or electrofuels. A key technological barrier to the increased use of metal fuels is the current lack of clean and efficient combustor/reactor/engine technologies to convert the chemical energy in metal fuels into motive or electrical power (energy). This paper overviews the concept of low-carbon metal fuels and summarizes the current state of our knowledge regarding the reaction of metal fuels with water, to produce hot hydrogen on demand, and the combustion of metal fuels with air in laminar and turbulent flames. Many important questions regarding metal-fuel combustion processes remain unanswered, as do questions concerning the energy-cycle efficiency and life-cycle environmental impacts and economics of metals as recyclable fuels. Metal fuels can be an important technology option within a future low-carbon society and deserve focused attention to address these open questions.

  • Refinery co-processing of renewable feeds
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2018-05-03
    Stella Bezergianni, Athanassios Dimitriadis, Oleg Kikhtyanin, David Kubička

    Biofuels are called upon to play an important role, not only in reducing the associated greenhouse-gases emissions, but also in enabling the gradual independence from fossil sources, rendering low-carbon-highly-sustainable fuels. Today, the involvement of biomass-derived sources into existing petroleum refineries has a growing interest due to the increasing unpredictability of oil prices, environmental concerns and the necessity to secure an energy supply. Petroleum refineries already have a well-developed infrastructure to produce fuels and base chemicals and, consequently, would not require additional intensive investments for processing of alternative feedstocks. From this point of view, co-processing of biomass-derived feedstocks with petroleum fractions is an attractive option, which has already been industrially demonstrated in some cases. There are two main technologies that could be used for co-processing of biomass feedstocks with petroleum fractions, the first one being catalytic hydroprocessing and the second one being fluid catalytic cracking (FCC). Both technologies are found in virtually any conventional refinery. It is obvious that the co-processing of biomass-based feedstocks with petroleum fractions has the potential to play an important role in the near future. There are several research studies in literature that examine both technologies for co-processing. However, while there are many technological reviews that focus on stand-alone biofuel production (e.g., FAME biodiesel, bioethanol, HVO etc.), a dedicated technological review on co-processing for production of hybrid fuels is still missing. Therefore, this paper is focused on presenting a state-of-the-art review on co-processing bio-based feedstocks with petroleum fractions via hydroprocessing and fluid catalytic cracking, looking at different potential feedstocks, catalysts, operating conditions, products and benefits in detail. As there is no specifically dedicated literature review in this field, the content of this review provides a guideline on co-processing of different bio-based feedstocks with petroleum fractions, aimed at delivering a technological assessment of the existing research efforts.

  • Review of arsenic behavior during coal combustion: Volatilization, transformation, emission and removal technologies
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2018-04-17
    Chunbo Wang, Huimin Liu, Yue Zhang, Chan Zou, Edward J. Anthony

    Growing public awareness of the environmental impact of coal combustion has raised serious concerns about the various hazardous trace elements produced by coal firing. Arsenic deserves special attention due to its toxicity, volatility, bioaccumulation in the environment, and potential carcinogenic properties. As the main anthropogenic source of arsenic is coal combustion, its behavior in power plants is of concern. Unlike mercury, arsenic behavior in coal combustion has not been subjected to systematic, in-depth research. Different researchers have reached opposing conclusions about the behavior of arsenic in combustion systems and, as yet, there is relatively little research on arsenic removal technologies. In this paper, the volatilization, transformation, and emission behavior of arsenic and its removal technologies are discussed in depth. Factors affecting the volatilization characteristics of arsenic are summarized, including temperature, pressure, mode of occurrence of arsenic, coal rank, mineral matter, and the sulfur and chlorine content of the fuel. The behavior of arsenic during oxy-fuel combustion and the effect of combustion atmosphere (O2, CO2, SO2 and H2O(g)) are also reviewed in detail. In order to better understand the pathways of arsenic in a power plant environment, a particular focus in this work is the transformation mechanism of ultra-fine ash particles and the partitioning behavior of arsenic. Finally, the effects of air pollution control devices (APCDs) on arsenic emissions are examined, along with the effectiveness of flue gas arsenic removal technologies with different kinds of adsorbents, including calcium-based adsorbents, metal oxides, activated carbon, and fly ash.

  • Bioethanol from corn stover – a review and technical assessment of alternative biotechnologies
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2018-04-07
    Yan Zhao, Anders Damgaard, Thomas H. Christensen

    Reviewing the literature from the last decade regarding the bioconversion of corn stover into ethanol, 474 references were identified containing 561 datasets. We found 144 datasets which were sufficiently consistent and detailed to address the current state of the art of corn stover conversion to bioethanol, and we were able to categorise 93% of these datasets into eight different technological configurations for the production of bioethanol, based on the pretreatment approaches used. After pretreating, the corn stover is subject to hydrolysis and fermentation, but these two process steps were largely identical in all datasets, albeit a range of operating conditions was reported. The final distillation of the ethanol was very rarely included in the datasets. By parameterising the bioethanol production by 26 parameters, including corn stover compositions, solid loadings, operational conditions, conversion efficiencies and material consumption, we were able to quantify the material flows for each technological configuration and estimate the uncertainty of the flows. The eight technological configurations produced 11–22% ethanol from the dry solid content of the corn stover. Technologies using alkaline-, solvent or ammonia-based pretreatments produced the largest amount of ethanol (19–22%), while fungi-based pretreatment produced much less (11%). All technological configurations resulted in large flows of solid as well as liquid residues, typically containing 60 to 70% of the dry solid corn stover content. Based on the selected datasets, statistical description is provided for all parameters, including mode, median, average and deviation, within each technological configuration. Bivariate correlation analysis across and within all technological configurations indicates that some operational parameters usually considered crucial in laboratory studies, e.g. pretreatment severity, show from a statistical perspective very little correlation with the yields. The review reveals that a great deal of research has addressed the challenge of converting corn stover into bioethanol, but a significant part of these studies is of limited value in terms of scope and documentation when addressing overall material flows and key parameters in a technological context.

  • Underground coal gasification – Part II: Fundamental phenomena and modeling
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2018-03-27
    Greg Perkins

    Underground coal gasification can convert deep coal into synthesis gas for use in the production of electricity, fuels and chemicals. This paper provides a review of the fundamental physical phenomena in underground coal gasification and associated modeling efforts. The relevant fundamentals of coal gasification are described and the phenomena of cavity growth at the sidewall and roof of the underground cavity are examined in detail. The transport phenomena and chemical reactions occurring in the permeable bed of char and ash and the void space are reviewed. The modeling of the transport of heat and mass, including contaminants, in the near- and far-fields surrounding an underground coal gasifier are also summarized. An overview of the geomechanical phenomena and the coupled interactions between transport and mechanical phenomena are provided. Finally, integrated UCG models are reviewed and recommendations for future model development are provided.

  • Two-stage electrostatic precipitators for the reduction of PM2.5 particle emission
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2018-03-27
    A. Jaworek, A. Marchewicz, A.T. Sobczyk, A. Krupa, T. Czech

    Electrostatic precipitator is the most efficient device used for the removal of fly ash particles from the flue gases produced by coal-fired boilers in power plants. However, the fractional collection efficiency of electrostatic precipitators steeply decreases for particles smaller than 1 μm, and particles in the size range of 200–500 nm are removed with lower collection efficiency than those outside this range. These particles are dangerous to humans and have detrimental environmental effects, so there is a need for novel more efficient technologies for their control. One of the answers to this challenge is the two-stage electrostatic precipitator, in which the electrostatic charging and precipitation processes have been separated. The PM2.5 particles (of a size < 2.5 μm) are electrically charged in a separate device (precharger) to a maximal possible electric charge, and then precipitated in a parallel plate collector, free of corona discharge. The electric field in the collection stage can be higher than in an electrostatic precipitator due to the lack of sharp discharge points. A higher electric field allows an increase of the collection efficiency for PM2.5 particles. Another solution is the agglomeration of submicron particles to form larger particles before their precipitation by a parallel-plate collector, conventional electrostatic precipitator or any other gas cleaning device. In some of the reviewed devices, both of these processes were combined in a single device that allowed further increases in the collection efficiency for submicron particles. Devices of this type have been tested in a lab- or semi-industrial scale for the removal of PM2.5 particles from flue gases or diesel engine exhausts. In this paper, various constructions of two-stage electrostatic precipitators, comprising a precharger and/or agglomerator in the first stage, and an electrostatic collector in the second stage, have been reviewed. Some of these devices were able to increase the mass collection efficiency above 95% for PM2.5 particles.

  • Progress in O2 separation for oxy-fuel combustion–A promising way for cost-effective CO2 capture: A review
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2018-05-08
    Fan Wu, Morris D. Argyle, Paul A. Dellenback, Maohong Fan
  • Underground coal gasification – Part I: Field demonstrations and process performance
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2018-03-16
    Greg Perkins

    Underground coal gasification can convert deep coal resources into synthesis gas for use in the production of electricity, fuels and chemicals. This paper provides a review of the various methods of undertaking underground coal gasification and observations from demonstrations of the process in the field. A general representation of the underground process is presented, along with an identification of the various zones and associated governing phenomena. The main factors affecting the performance of underground coal gasification, such as coal rank, depth and thickness and oxidant composition and injection rate are examined in detail. A brief assessment of the economic and environmental considerations relevant to underground coal gasification projects is presented. Finally, guidelines for site and oxidant selection are provided based on the learnings from prior demonstration projects.

  • Recent advances in the synthesis and modification of carbon-based 2D materials for application in energy conversion and storage
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2018-03-16
    Rajesh Kumar, Ednan Joanni, Rajesh K. Singh, Dinesh P. Singh, Stanislav A. Moshkalev

    Graphene, reduced graphene oxide (rGO) and derived materials have emerged as promising solutions for applications in renewable energy storage/conversion devices. No alternatives are known to simultaneously exhibit large specific surface area, high electrical conductivity, good chemical stability, high mechanical strength and flexibility. This review article is a collection of some of the most relevant research efforts published in the last few years focusing on the synthesis and modification of graphene/rGO as well as doped and hybrid bi-dimensional carbon materials. For research on graphene growth, the choice of precursor and physical state (gas, solid or liquid) has been proved to be as important as the environment and synthesis approach. On the other hand, research focused on graphene oxide reduction has relied on the development of simple and efficient techniques for rGO conversion and device structuring. Modifications applied to graphene (during synthesis) or rGO (during reduction) have included doping, decoration with nanoparticles and the formation of composite microstructures. Fabrication of electrodes based on graphene/rGO for application in energy storage and conversion has been reported, including relevant performance data from real devices (supercapacitors, lithium ion batteries, fuel cells or solar cells). This review concludes with a brief discussion of some of the possible directions for promising research in the area of graphene/rGO fabrication for energy conversion and storage devices.

  • Fuel reforming in internal combustion engines
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2018-03-16
    L. Tartakovsky, M. Sheintuch

    This article offers a comprehensive overview of research on fuel reforming in internal combustion engines (ICE). It includes a historical perspective of research in this field, a discussion on the considerations to be made prior to choosing a primary fuel for reforming purposes, and the main processes in fuel reforming. Steam reforming offers a moderate degree of thermochemical recuperation and is applicable to methanol and ethanol feeding. Reforming with air reduces the degree of recuperation, but opens up the use of heavier fuels such as gasoline and diesel fuel. Dry reforming (with CO2) offers the best recuperation but is prone to fast coking. The choice of catalyst and the expected side reactions for each fuel are also discussed. While there is extensive literature on steam reforming catalysts and kinetics at atmospheric pressure, studies at higher pressures and/or on decomposition reactions are very few. The thermodynamics of fuel reforming in ICE and simulation approaches are also discussed. The paper also reports on engineering aspects of fuel reformer design and provides an overview of engines with thermo-chemical recuperation (TCR), fuel supply, and load control strategies in ICE with TCR. In-cylinder fuel reforming as well as application of fuel reforming for performance improvement of emission aftertreatment systems are subsequently discussed. This overview reveals ongoing diverse research activities in the field of onboard fuel reforming. However, several problems, including reformate burning velocity at typical for ICE conditions, in-cylinder behavior of directly injected reformates and particle formation still need to be addressed. A discussion on some of these unresolved issues is attempted herein.

  • Advanced heat transfer fluids for direct molten salt line-focusing CSP plants
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2018-03-02
    Alexander Bonk, Salvatore Sau, Nerea Uranga, Marta Hernaiz, Thomas Bauer

    Concentrating solar power coupled to thermal energy storage (TES) is a vastly growing industrial process allowing for the generation of dispatchable and green electricity. This paper focuses on direct molten salt line-focusing technology using linear Fresnel and parabolic trough collector systems. Direct molten salt technology utilizes molten salt as heat transfer fluid in solar field and TES medium. Nitrate salts can be applied since they cover a wide temperature range. As storage medium Solar Salt, a binary NaNO3−KNO3 (60-40 wt%) mixture, is most commonly used but variations of this system have promising thermal properties in terms of a lower melting temperature to minimize the risk of undesired salt freezing events. These modified salts are typically ternary, ternary reciprocal or higher order systems formed by adding additional cations, anions or both. In this study five molten salt systems Solar Salt, HitecXL (CaKNa//NO3), LiNaK-Nitrate, Hitec (NaK//NO23) and CaLiNaK//NO23 are both investigated and critically reviewed. Their thermo-physical properties including phase diagrams, composition, melting ranges, melting temperature, minimum operation temperature, thermal stability, maximum operation temperature, density, heat capacity, thermal conductivity, viscosity and handling are evaluated and the most recommended values are discussed and highlighted. This review contributes to a better understanding of how the listed properties can be determined in terms of measurement conditions and provides temperature dependent data useful for future simulations of direct molten salt LF CSP plants.

  • Modeling nitrogen chemistry in combustion
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2018-02-22
    Peter Glarborg, James A. Miller, Branko Ruscic, Stephen J. Klippenstein

    Understanding of the chemical processes that govern formation and destruction of nitrogen oxides (NOx) in combustion processes continues to be a challenge. Even though this area has been the subject of extensive research over the last four decades, there are still unresolved issues that may limit the accuracy of engineering calculations and thereby the potential of primary measures for NOx control. In this review our current understanding of the mechanisms that are responsible for combustion-generated nitrogen-containing air pollutants is discussed. The thermochemistry of the relevant nitrogen compounds is updated, using the Active Thermochemical Tables (ATcT) approach. Rate parameters for the key gas-phase reactions of the nitrogen species are surveyed, based on available information from experiments and high-level theory. The mechanisms for thermal and prompt-NO, for fuel-NO, and NO formation via NNH or N2O are discussed, along with the chemistry of NO removal processes such as reburning and Selective Non-Catalytic Reduction of NO. Each subset of the mechanism is evaluated against experimental data and the accuracy of modeling predictions is discussed.

  • 更新日期:2018-07-12
  • Thermally stable polymers for advanced high-performance gas separation membranes
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2017-12-08
    Mashallah Rezakazemi, Mohtada Sadrzadeh, Takeshi Matsuura

    Polymeric membranes can be used for the energy-efficient and low-cost gas separation. However, their inability to resist high temperatures limits their use in certain industries. Some polymer membranes can be operated at some levels of the unpleasant environments, but the energy- and cost-efficiencies are offset by the necessity to severely cool hot streams. In many cases, such implementation is impossible or altogether impractical. Therefore, numerous studies have been focused on modifying polymers to create synthetic polymeric membranes which survive at high temperatures. Polymer scientists introduced many thermally stable polymers mostly based on carbocyclic and heterocyclic aromatic polymers, which exhibit enhanced thermal stability. However, the major problem with these polymers is their low processability, which is mainly due to their insolubility or high phase transition temperatures. So far, there has been little success in processing the high-temperature-resistant polymers to make membranes with acceptable separation and performance characteristics. The aim of this study is to review efforts which have been made to produce high-performance polymeric membranes with a focus on the preparation procedure; whereby, the main limitations and challenges to be faced were explored. The key factors discussed include the type of polymer, membrane preparation method, thermal analysis results and application of the prepared membranes. The primary purpose of this review is to lay out the basics for selecting polymer, solvent, additives and the appropriate preparation method to produce thermally stable polymeric membranes for gas separation. The future direction of research and development to fully exploit the potential usage of thermally stable polymeric membranes to achieve commercially viable processes was also shown.

  • A review of cavity-based trapped vortex, ultra-compact, high-g, inter-turbine combustors
    Prog. Energy Combust. Sci. (IF 26.467) Pub Date : 2017-12-16
    Dan Zhao, Ephraim Gutmark, Philip de Goey

    Trapped vortex combustor (TVC) is different from conventional swirl-stabilized combustors. It takes advantages of a cavity to stabilize the flame. When the cavity size of a TVC is well designed, a large rotating vortex can be formed in the cavity. The vortex cannot shed out the cavity and is thus named a “locked” or “stable” vortex. One of the main challenges for TVC design is fuel injection. Typically, fuel can be injected directly into the cavity or from the diffuser upstream. Injecting from the diffuser leads to the fuel being mixed with the air before it enters the combustor. When the fuel is injected directly into the cavity, it is desirable to supply the fuel in such way that the locked vortex in the cavity is reinforced. Furthermore, the fuel-air mixing in the cavity will be promoted, as the bypass air is directly added into the cavity. Since the recirculation zone anchored in the cavity is not exposed to the main incoming flow, stable combustion is achieved, even in the presence of a high speed main flow as typically expected in Ramjets and Scramjets. A well-designed trapped vortex combustor (TVC) enables a better fuel-air mixing, a better stabilized flame, lower emission, ultra-compact and high efficient combustion to be achievable. As a promising combustion concept, intensive scientific research has been conducted on TVC in the application areas of aerospace propulsion, power generation and waste incineration. In this work, we will firstly introduce the fundamental concepts, the development and evolution history of TVCs. The combustion, aerodynamics, and aeroacoustics features of trapped vortex combustion are then described. This includes reviewing and discussing the cavity flow/aerodynamics, fuel-air injection and mixing, trapped vortex combustion, emission and combustion of alternative fuels, and aeroacoustics characteristics. The ‘spin-off’ application of trapped vortex combustion concept for the design of ultra-compact and high-g combustors, inter-turbine burners, in-Situ and flameless TVC reheat combustors are then reviewed and discussed. Various practical applications of trapped vortex combustion concept in gas turbines, ramjets, scramjets and waste incinerators are discussed and summarized. Finally, the challenges and future directions of the design and implementation of TVCs are provided.

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上海纽约大学William Glover