Progress in Energy and Combustion Science最新文献

Metal-organic frameworks (MOFs) hold great potential as electrocatalysts for the reduction of carbon dioxide (CO₂), due to their highly tunable and porous structures. However, unlocking their full potential necessitates a comprehensive understanding of structure-performance relationships to guide rational design. This review provides a meticulous analysis of MOF electrocatalysts for electrocatalytic CO₂ reduction (ECR), emphasizing correlations between composition, morphology, and catalytic performance. Key structure-function aspects are explored across various MOF-derived materials, encompassing the impact of metal identity, organic linker chemistry, porosity, defect concentration, and particle morphology. Physicochemical properties related to substrate adsorption and active site availability are linked to catalytic activities, product selectivities, energy efficiencies, and overpotentials. The review identifies several performance-limiting factors, including suboptimally tuned active sites and weak structure-selectivity linkages. However, the modular nature of MOFs presents opportunities to address these challenges through synthetic tuning. Future prospects, involving advanced characterization techniques, are also discussed. Finally, a separate section is devoted to the potential (industrial) valorization of the process. This critical review aims to distill guiding principles for design and optimization from existing trends, facilitating the development of MOF electrocatalysts capable of driving sustainable CO₂ reduction at industrial scales. The realization of this promising technology holds the potential to provide renewable fuels and mitigate climate change through carbon capture and conversion utilizing intermittent renewable energy sources.

Premixed flame ignition is a fundamental issue in combustion. A basic understanding of this phenomenon is crucial for fire safety control and for the development of advanced combustion engines. Significant efforts have been devoted to understanding the mechanisms of ignition and determining critical ignition conditions, such as critical flame radius, minimum ignition energy, and minimum ignition power, which have remained challenging research topics for centuries. This review provides an in-depth investigation of the forced-ignition of laminar premixed flames in a quiescent flammable mixture, with emphasis on theoretical developments, particularly those based on activation energy analysis. First, the fundamental concepts are overviewed, including spark ignition, characteristic time scales, and critical ignition conditions. Then, the chronological development of premixed flame ignition theories is discussed, including homogeneous explosion, thermal ignition theory, flame ball theory, quasi-steady ignition theory, and, more importantly, transient ignition theory. Premixed flame ignition consists of three stages: flame kernel formation, flame kernel expansion, and transition to a self-sustaining flame. These stages are profoundly affected by the coupling of positive stretch with preferential diffusion, characterized by the Lewis number. Specifically, positive stretch makes the expanding ignition kernel weaker at larger Lewis numbers, consequently increasing the critical ignition radius and MIE. The premixed flame ignition process is dominated by flame propagation dynamics. Both quasi-steady and transient ignition theories demonstrate that the critical flame radius for premixed ignition differs from either flame thickness (by thermal ignition theory) or flame ball radius (by flame ball theory). Particularly, the transient ignition theory appropriately acknowledges the “memory effect” of external heating, offering the most accurate description of the evolution of the ignition kernel and the most sensible evaluation of minimum ignition energy. In addition, the effects of transport and chain-branching reactions of radicals, finite droplet vaporization, and repetitive heating pulses on premixed flame ignition are discussed. Finally, a summary of major advances is provided, along with comments on the applications of premixed flame ignition theory in ignition enhancement. Suggested directions for future research are presented.

Oxymethylene ethers (OME_x), are a promising renewable replacement fuel for compression ignition engines. OME_x are largely compatible with current engines, can help to significantly reduce engine-out and tail-pipe emissions while simultaneously reducing the transport sector’s net carbon emissions by gradually replacing fossil diesel fuel. This paper aims to compile and critically review recent research progress on OME_x, following the entire value chain from production to engine application. First, pathways for OME_x production are compiled and compared regarding energy efficiency, fuel production costs and life cycle CO₂ balance, showcasing advantages and disadvantages of more advanced production pathways with reduced hydrogen consumption. On the application side, chemical kinetics play a fundamental role in understanding OME_x combustion. Recent progress in understanding the decomposition and combustion of OME_x is discussed and resulting detailed chemical reaction mechanisms from the literature are investigated regarding their accuracy and capabilities. Furthermore, the liquid fuel properties of OME_x are presented and compared with conventional fossil diesel fuel as well as selected other renewable and surrogate fuels, pointing out possible issues and potentials for engine application. In particular, material compatibility is discussed, and suitable sealing materials are identified. Subsequently, the application of OME_x in CI engines is discussed in detail, including the fuel’s potential for engine efficiency increase and significant decrease in engine-out particulate and NO_x emissions. Necessary and possible changes to engine design and control, such as longer injection duration or larger injector holes, are outlined. Finally, on a high level, the potential for large-scale application of e-fuels such as OME_x is discussed, and necessary political incentives are pointed out.

The utilization of low calorific value gases (LCVG) in combustion devices presents particular challenges in terms of ignition and sustained combustion stability due to the presence of non-combustible components. Moderate or intense low-oxygen dilution (MILD) combustion has emerged as a promising technology for LCVG combustion, offering numerous advantages such as high combustion efficiency, reduced pollutant emissions, and increased fuel flexibility. However, the current body of research in this area is fragmented, making it challenging to draw meaningful comparisons between studies and hindering its practical application. This paper provides a comprehensive review of conventional and MILD combustion of LCVG. To understand the impact of composition on combustion, the fuels are classified based on their composition of hydrogen, carbon monoxide, methane, carbon dioxide, nitrogen, and water. We also delve into the chemical and physical effects of composition, including reaction kinetics and turbulence mixing, and provide an overview of the burners and methods used in establishing MILD combustion. Furthermore, computational fluid dynamics (CFD) models and chemical kinetics in MILD combustion are also thoroughly discussed.

The presence of a large amount of dilution gas in LCVG increases the self-ignition temperature and ignition delay time of the mixture, making preheating the reactants a critical consideration. In MILD combustion, it is crucial to have an inlet reactant temperature higher than the self-ignition temperature ($T_{\text{in}}>T_{\text{si}}$) to mitigate the difficulties associated with ignition and unstable combustion. The heat release in MILD combustion should be moderate to ensure that the combustion temperature does not become too high. The non-combustible components of LCVG are beneficial in this regard, as they allow for a temperature increase of less than the self-ignition temperature ($\Delta T<T_{\text{si}}$). Hydrogen is the most reactive component in LCVG, and its content directly impacts the establishment, efficiency, and pollutant emissions of MILD combustion. Carbon dioxide, nitrogen, and water act as diluents, helping to reduce NOx emissions in MILD combustion. Although a burner may have the potential to be used for MILD combustion, it must be optimised for LCVG with variable composition in order to achieve the lowest pollutant emissions. Further research is necessary to verify and improve simulation models and chemical kinetics. This article provides theoretical support for the practical application of MILD combustion of LCVG with variable composition.

Increasing global energy consumption has created an urgent need to address climate change and consequently, the need for sustainable and renewable energy has increased. Simultaneously, the pervasive presence of crude oil hydrocarbons in the ecosystem, stemming from exploration and extraction activities, underscores the urgency for developing effective and environment-friendly remediation technologies. Hence, here we describe use of non-edible second-generation energy crops for rhizoremediation of oil contaminated soil, to yield plant biomass for bioenergy and carbon sequestration. This could address the restoration of petroleum hydrocarbon contaminated soil, along with waste management for biofuel production. This strategy could also save the agricultural land that is under threat as a consequence of crude oil contamination. The strategies for enhanced rhizoremediation with bioenergy crops have been elaborated, including soil, and microbiome engineering. Furthermore, the article delves into recent technological advancements aimed at enhancing the efficiency of biofuel production with bioenergy crops, employing methodologies such as synthetic biology, systems biology, and metabolic engineering. Despite the promising aspects of this approach, challenges in biofuel production using bioenergy crops are acknowledged, including issues such as N₂O emissions, biodiversity loss, and water quality management. The article not only outlines these challenges but also proposes remedial strategies to address them. Through this comprehensive discussion, valuable insights are provided on the potential of petroleum hydrocarbon-contaminated soils for biomass production within the framework of achieving sustainable bioenergy generation. This approach has potential to mitigate CO₂ emissions, remediate polluted lands, and significantly contribute to the global effort to combat climate change.

Direct absorption solar collectors (DASCs) based on nanofluids offer a promising solution for achieving the dual goals of solar energy utilization: maximizing solar absorption and minimizing thermal losses. In contrast to conventional surface absorption solar collectors, which suffer from substantial heat losses, DASCs operate by replacing elevated-temperature absorption surfaces with nanofluid bulk for volumetric absorption. To bridge the gap between theoretical research and commercialization, a comprehensive understanding of DASCs is essential. This includes modeling approaches, the impact of design and operational parameters, recognizing limitations, and evaluating future prospects. This study provides a comprehensive review with a focus on resolving disagreements regarding low-flux DASC responses to specific design and operational variations that have sparked conflicting interpretations in the literature. This review, by addressing these discrepancies, serves as an invaluable resource for researchers seeking a more nuanced understanding of this evolving field, facilitating its advancement into practical applications.

This review comprehensively examines the field of DASCs across eight distinct sections. Section 1 provides an overview of solar energy's potential, the evolution of solar collectors, and the rationale for the review. Section 2 focuses on theoretical modeling approaches for simulating colloidal suspensions in solar thermal systems, including optical properties, radiative transport, and heat transfer mechanisms. The strengths and limitations of these models are critically evaluated to assist researchers in selecting the most suitable one for specific colloidal systems. Additionally, a critical assessment of analytical and numerical studies in the existing literature is presented in this section. Section 3 offers a detailed view and critical assessment of experimental efforts in the field. The stability of nanofluids is discussed in section 4, while sections 5 and 6 analyze the impact of operating conditions, geometry, design parameters, and flow properties on DASC performance criteria. We address contradictions and ambiguities in the effects of some operating variables in the DASC literature, considering state-of-the-art simulation techniques. Section 7 focuses on economic and environmental analyses related to DASCs, providing insights into their feasibility and sustainability. Finally, Section 8 synthesizes conclusions from the reviewed literature, identifies research gaps, and proposes future directions based on recent advancements in DASC technology.

Fischer-Tropsch Synthesis (FTS) allows the conversion of syngas to high-density liquid fuels, playing a key role in the petrochemical and global energy sectors over the last century. However, the current Global Challenges impose the need to recycle CO₂ and foster green fuels, opening new opportunities to adapt traditional processes like FTS to become a key player in future bioenergy scenarios. This review discusses the implementation of CO₂-rich streams and in tandem catalysis to produce sustainable fuels via the next generation of FTS. Departing from a brief revision of the past, present, and future of FTS, we analyse a disruptive approach coupling FTS to upstream and downstream processes to illustrate the advantages of process intensification in the context of biofuel production via FTS. We showcase a smart tandem catalyst design strategy addressing the challenges to gather mechanistic insights in sequential transformations of reagents in complex reaction schemes, the precise control of structure-activity parameters, catalysts aging-deactivation, optimization of reaction parameters, as well as reaction engineering aspects such as catalytic bed arrangements and non-conventional reactor configurations to enhance the overall performance. Our review analysis includes technoeconomic elements on synthetic aviation fuels as a case of study for FTS applications in the biofuel context discussing the challenges in market penetration and potential profitability of synthetic biofuels. This comprehensive overview provides a fresh angle of FTS and its enormous potential when combined with CO₂ upgrading and tandem catalysis to become a front-runner technology in the transition towards a low-carbon future.

Carbon capture and storage is recognized as one of the most promising solutions to mitigate climate change. Compared to conventional separation technologies, supersonic separation is considered a new generation of technology for gas separation and carbon capture thanks to its advantages of cleaning and efficient processes which are achieved using energy conversion in supersonic flows. The supersonic separation works on two principles which both occur in supersonic flows: the energy conversion to generate microdroplets and supersonic swirling flows to remove the generated droplets. This review seeks to offer a detailed examination of the cutting-edge technology for gas separation and carbon dioxide removal in the new-generation supersonic separation technology, which plays a role in carbon capture and storage. The evaluation discusses the design, performance, financial feasibility, and practical uses of supersonic separators, emphasizing the most recent progress in the industry. Theoretical analysis, experiments, and numerical simulations are reviewed to examine in detail the advances in the nucleation and condensation characteristics and the mechanisms of supersonic separation, as well as new applications of this technology including the liquefaction of natural gas. We also provide the perspective of the challenges and opportunities for further development of supersonic separation. This survey contributes to an improved understanding of sustainable gas removal and carbon capture by using the new-generation supersonic separation technology to mitigate climate change.

Solid oxide fuel cells (SOFCs) have witnessed significant advancements in recent years, emerging as potential alternatives to low-temperature fuel cells for mobile applications owing to their wide fuel flexibility and high efficiency. This paper offers a comprehensive assessment of the progress achieved thus far and the challenges faced in transitioning from stationary to mobility sectors. Three pivotal aspects are highlighted across different levels: enhancing fuel tolerance and flexibility at the anode level, achieving rapid start-up at the cell level, and realizing compact integration at the stack level. This review can lay a theoretical foundation for the development of SOFC systems tailored to unique requirements, such as high power density and rapid start-up, crucial for mobile applications. This review will facilitate commercial breakthroughs and advances in the mobility of SOFCs, which holds substantial strategic importance.