Progress in Energy and Combustion Science最新文献

The introduction of downsized, turbocharged Gasoline Direct Injection (GDI) engines in the automotive market has led to a rapid increase in research on Low-speed Pre-ignition (LSPI) and super-knock as abnormal combustion phenomena within the last decade. The former is characterized as an early ignition of the fuel–air mixture, primarily initiated by an oil–fuel droplet or detached deposit. Meanwhile, super-knock is an occasional development from pre-ignition to high intensity knocking through detonation, which is either initiated by a shock wave interacting with a propagating reaction and cylinder surfaces or inside a hotspot with a suitable heat release and reactivity gradient. The phenomenon can be divided into four stages, including LSPI precursor initiation, establishment and propagation of a pre-ignited flame, autoignition of end-gases and development to a detonation. LSPI and super-knock are rare phenomena, difficult to observe optically in engines, and differences in methodologies and setups between steady-state experiments can lead to discrepancies in results. Experimental research has included more detailed approaches using glow plug-equipped engines, constant volume combustion chambers and rapid compression machines. In addition, the improved availability of mechanisms for fuel and lubricant surrogates has allowed researchers to model the oil–fuel interaction at the cylinder walls, evaporation and autoignition of oil–fuel droplets and regimes for different propagation modes of an autoignition reaction wave. This paper presents a comprehensive review of the underlying phenomena behind LSPI and its development to super-knock. Furthermore, it presents the methodology in experimental research and draws conclusions for mitigating strategies based on studies involving fuel, oil and engine parameters. Finally, it discusses the prerequisites for LSPI from oil–fuel droplets and the future needs of research as original equipment manufacturers (OEM) and lubricant industry have already adopted some proven solutions to their products.

It is accepted that the thermoacoustic behavior of a given combustion system can be analyzed by investigating how its natural acoustic modes are perturbed by the flame dynamics. As a result, the resonance frequency and structure of the resulting thermoacoustic mode – understood as a perturbed acoustic mode – are slightly modified with respect to the natural acoustic mode counterpart. However, experimental evidence shows that the frequency of unstable thermoacoustic modes sometimes lies far away from the natural acoustic frequencies of the system under study. In many cases, this frequency cannot be associated with hydrodynamic or entropy-related instabilities. In recent years, the intrinsic thermoacoustic (ITA) feedback loop has been formally recognized as the responsible mechanism in some of those situations. Theory and devoted experiments have been developed that have enormously contributed to the understanding of the particular behavior of intrinsic thermoacoustic instabilities.

The present review encapsulates in a single theoretical framework the theory presented in the collection of today existing ITA papers, which spread through different cases of study regarding acoustic boundaries – anechoic, partially or fully reflecting – and geometries – duct flames, combustors composed by three coaxial ducts and annular configurations. Several examples are shown that summarize the most relevant results on ITA theory to this day. This review paper also gives special attention to the categorization of ITA modes, given the fact that there is no current agreement on the definition of an ITA mode: one example in this review paper explicitly shows that the proposed categorization methods can indeed be contradictory. Of high interest is also the review of papers illustrating the coexistence of thermoacoustic modes of acoustic and ITA nature, which in turn relate to the recently discovered exceptional points in the thermoacoustic spectrum. Additionally, this paper discusses the ‘counter-intuitive’ evidence that shows that ITA modes can be destabilized when acoustic dissipative elements are added into the system. Finally, it is shown how a single-mode Galerkin expansion may be able to model some ITA eigenfrequencies. This result is suggested in some recent works and is not obvious. The practical relevance of ITA modes in industrial combustion chambers of gas turbines is also discussed together with suggestions for future studies.

Hydrogen (H₂) is currently considered a clean fuel to decrease anthropogenic greenhouse gas emissions and will play a vital role in climate change mitigation. Nevertheless, one of the primary challenges of achieving a complete H₂ economy is the large-scale storage of H₂, which is unsafe on the surface because H₂ is highly compressible, volatile, and flammable. Hydrogen storage in geological formations could be a potential solution to this problem because of the abundance of such formations and their high storage capacities. Wettability plays a critical role in the displacement of formation water and determines the containment safety, storage capacity, and amount of trapped H₂ (or recovery factor). However, no comprehensive review article has been published explaining H₂ wettability in geological conditions. Therefore, this review focuses on the influence of various parameters, such as salinity, temperature, pressure, surface roughness, and formation type, on wettability and, consequently, H₂ storage. Significant gaps exist in the literature on understanding the effect of organic material on H₂ storage capacity. Thus, this review summarizes recent advances in rock/H₂/brine systems containing organic material in various geological reservoirs. The paper also presents influential parameters affecting H₂ storage capacity and containment safety, including liquid–gas interfacial tension, rock–fluid interfacial tension, and adsorption. The paper aims to provide the scientific community with an expert opinion to understand the challenges of H₂ storage and identify storage solutions. In addition, the essential differences between underground H₂ storage (UHS), natural gas storage, and carbon dioxide geological storage are discussed, and the direction of future research is presented. Therefore, this review promotes thorough knowledge of UHS, provides guidance on operating large-scale UHS projects, encourages climate engineers to focus more on UHS research, and provides an overview of advanced technology. This review also inspires researchers in the field of climate change to give more credit to UHS studies.

Direct air capture (DAC) is gathering momentum since it has vast potential and high flexibility to collect CO₂ from discrete sources as “synthetic tree” when compared with current CO₂ capture technologies, e.g., amine based post-combustion capture. It is considered as one of the emerging carbon capture technologies in recent decades and remains in a prototype investigation stage with many technical challenges to be overcome. The objective of this paper is to comprehensively discuss the state-of-the-art of DAC and CO₂ utilization, note unresolved technology bottlenecks, and give investigation perspectives for commercial large-scale applications. Firstly, characteristics of physical and chemical sorbents are evaluated. Then, the representative capture processes, e.g., pressure swing adsorption, temperature swing adsorption and other ongoing absorption chemical loops, are described and compared. Methods of CO₂ conversion including synthesis of fuels and chemicals as well as biological utilization are reviewed. Finally, techno-economic analysis and life cycle assessment for DAC application are summarized. Based on research achievements, future challenges of DAC and CO₂ conversion are presented, which include providing synthesis guidelines for obtaining sorbents with the desired characteristics, uncovering the mechanisms for different working processes and establishing evaluation criteria in terms of technical and economic aspects.

This paper intends to provide a comprehensive state-of-art review of recent progresses and to formulate perspectives on window-ejected fire plumes, originating from under-ventilated compartment fires (known as ‘Regime I’ fires). Various external boundary conditions are considered, as they contribute to the fire and plume dynamics, and as such affect decisions on fire prevention and firefighting. Hence this is an important fire combustion topic of both fundamental and practical significance. After discussing the general fundamentals, the paper focuses particularly on recent progresses on quantifying the ejected fire plume behavior: constrained by the presence of walls; at sub-atmospheric pressure (for fires at high altitudes) and under complex flow conditions caused by wind. Experiments, theoretical scaling analysis and basic models are reviewed. The key points cover systematically: the compartment fire evolution (and hence criteria for flame ejection through the window); flame interaction and merging behavior from two windows; air entrainment mechanisms and characteristic parameters (flame structure/dimensions, temperature profile and heat flux) of window-ejected fire plumes. Meanwhile, the limitations of present research and future challenges are also discussed.