Progress in Energy and Combustion Science最新文献

The shift in the energy sector toward green resources makes fuel cells increasingly relevant as a supplier of green and sustainable energy. However, factors such as expensive catalysts, anodic poisoning, and fuel crossover reduce the lifetime and performance of the fuel cells, necessitating catalysis improvement. This review article presents the unique capabilities of metal chalcogenides (MC) as tailored catalysts, elucidating their synthesis, testing techniques, and performance evaluations. MC catalysts are matured via various physical and chemical methods to control their morphology, quantity, dimension, and size. Upon synthesis, the catalyst performance is quantified using three-electrode cells, followed by tests in fuel-cell prototypes. As anodic catalysts, MCs oxidize various fuels such as methanol, ethanol, urea, and impure H₂ at high current densities and low onset potentials, while hindering the poisoning species. As cathodic catalysts, MCs exhibit current values similar to that exhibited by their noble metal counterparts while reducing oxygen selectively in the vicinity of the fuels via four electron transfers at a wide range of potentials.

This is a comprehensive, critical, and pedagogical review of volumetric emission tomography for combustion processes. Many flames that are of interest to scientists and engineers are turbulent and thus inherently three-dimensional, especially in practical combustors, which often contain multiple interacting flames. Fortunately, combustion leads to the emission of light, both spontaneously and in response to laser-based stimulation. Therefore, images of a flame convey path-integrated information about the source of light, and a tomography algorithm can be used to reconstruct the spatial distribution of the light source, called emission tomography. In a carefully designed experiment, reconstructions can be post-processed using chemical kinetic, spectroscopic, and/or transport models to extract quantitative information. This information can be invaluable for benchmarking numerical solutions, and volumetric emission tomography is increasingly relied upon to paint a more complete picture of combustion than point, linear, or planar tools. Steady reductions in the cost of optical equipment and computing power, improvements in imaging technology, and advances in reconstruction algorithms have enabled a suite of three-dimensional sensors that are regularly used to characterize combustion. Four emission modalities are considered in this review: chemiluminescence, laser-induced fluorescence, passive incandescence, and laser-induced incandescence. The review covers the reconstruction algorithms, imaging models, camera calibration techniques, signal physics, instrumentation, and post-processing methods needed to conduct volumetric emission tomography and interpret the results. Limitations of each method are discussed and a survey of key applications is presented. The future of volumetric combustion diagnostics is considered, with special attention paid to the advent and promise of machine learning as well as spectrally-resolved volumetric measurement techniques.

Biomass is a promising renewable source that can reduce fossil fuel consumption and associated greenhouse gas emissions, but some of its characteristics make it difficult to use in its raw form. Torrefaction has been proposed as a thermochemical pretreatment to upgrade biomass for direct applications such as combustion and gasification, biochar and chemicals production, while reducing its transportation cost and increasing its shelf-life. Research, development, and demonstration of biomass torrefaction technologies have advanced during the last few decades, but many science and engineering fundamentals as well as technological challenges remain, especially in the areas of reaction thermodynamics and kinetics, reactor models and design, large-scale implementation, and environmental performance. In this paper we present a comprehensive review of recent developments in biomass torrefaction research and technology focusing on kinetics, particle and reactor scale models, and reactor designs. The impacts of torrefaction as a pretreatment of biomass on subsequent conversion processes, and the novel applications of torrefied biomass are discussed. The energy management, environmental impacts, economic and market potential of the technology as well as the deployment options are also addressed. There is no best universal torrefaction reactor and hence the choice should be made based on the biomass feedstock and the expected production rate and application. To reduce process costs and competition with other uses of biomass, the utilization of either waste or environmentally sustainable, more abundant, and faster growing biomass should be targeted for this technology. Torrefied biomass produced at higher temperatures resemble pyrolysis biochar in several properties thereby making it suitable for most biochar applications. Finally, considering the need to identify the bottlenecks that potentially could limit the use of torrefaction, and its preceding or subsequent processes, the future prospects, challenges, and opportunities of torrefaction technology are presented.

Metal fuels are attractive for solid/hybrid rocket propulsion and energy-conversion applications, because of their high energy densities. Boron powder (B), due to its high gravimetric (58.30 MJ·kg⁻¹) and volumetric heats of combustion (136.44 kJ·cm⁻³), is ideally one of the most promising fuel candidates for fuel-rich solid propellant (SP). However, from an application perspective, amorphous B has drawbacks of high ignition temperatures and incomplete combustion, resulting in low energy-release rate and efficiency. Thus, there is growing interest in employing B-based composite energetic materials (B-CEMs) in SP, explosives, and pyrotechnics. The present work provides a comprehensive review of the advances made over the past few decades in the areas of preparation, combustion, and applications of B-CEMs. The preparation methods of various types of B-CEMs are introduced, and the physicochemical properties of B-CEMs are systematically discussed particularly with regards to achieving advantages over B and other metal powders in a broad range of applications. The ignition and combustion behavior of different energetic formulations with B-CEMs are reviewed. Finally, the existing problems and future challenges in our understanding of the field (prospects) are discussed.

Global warming is one of the most pressing environmental concerns which correlates strongly with anthropogenic CO₂ emissions so that the CO₂ decreasing strategies have been meaningful worldwide attention. As an option, natural gas hydrate reservoirs have steadily emerged as a potent source of energy which would simultaneously be the proper places for CO₂ sequestration if the method of CO₂/CH₄ replacement could be developed. On the flip side, CO₂ hydrates as safe and non-flammable solid compounds without an irreversible chemical reaction would contribute to different industrial processes if their approaches could be improved. Toward developing substantial applications of CO₂ hydrates, laboratory experiments, process modelling, and molecular dynamics (MD) simulations can aid to understand their characteristics and mechanisms involved. Therefore, the current review has been organized in form of four distinct sections. The first part reviews the studies on sequestering CO₂ into the natural gas hydrate reservoirs. The next section gives an overview of process flow diagrams of CO₂ hydrate-based techniques in favour of CO₂ Capture and Sequestration & Utilization (CCS&U). The third section summarizes the merits, flaws, and different effects of hydrate promoters as well as porous media on CO₂ hydrate systems at macroscopic and mesoscopic levels, and also how these components can improve CO₂ hydrate properties, progressing toward the more feasibility of CO₂ hydrate industrial applications. The final sector recapitulates the MD frameworks of CO₂ clathrate and semiclathrate hydrates in terms of new insights and research findings to elucidate the fundamental properties of CO₂ hydrates at the molecular level.

High lipid content and excellent CO₂ fixation capability of microalgae by photosynthesis have made microalgal biodiesel (BD) a promising carbon-neutral fuel. Nonetheless, the commercialization of BD has not yet been realized because of expensive and energy-intensive cultivation, pretreatment, and BD conversion processes in reference to 1^st generation BD production. To resolve the issues, this study comprehensively reviewed the current technical developments of microalgal BD production process and suggested promising future studies. Current microalgal BD production processes highly rely on the processes developed from 1^st generation BD process, namely base-catalyzed transesterifications. However, the base-catalyzed suffers from saponification reaction and low production yield due to high water and free fatty acid contents in microalgae. Vigorous pretreatments such as dewatering, drying, esterification of free fatty acid, and purification are required for high yield of microalgal BD production, making this process economically not attractive. As efforts to construct new transesterification platform, novel approaches tolerant to impurities such as thermally induced non-catalytic transesterifications were suggested. The thermally induced reactions allowed in situ conversion of microalgal lipid into BD (≥ 95 wt.% yield) within 1 min of reaction at ≥ 350 ˚C. This process resists to presence of water and free fatty acids and does not require lipid extraction process. To make this process more promising, it was suggested lowering reaction temperature for thermally induced transesterifications. In addition, pilot study, in-depth life cycle assessment, and economic analysis were suggested to assess economic viability and environmental impacts.