Progress in Energy and Combustion Science最新文献

The impact of ship emission reductions can be maximised by considering climate, health and environmental effects simultaneously and using solutions fitting into existing marine engines and infrastructure. Several options available enable selecting optimum solutions for different ships, routes and regions. Carbon-neutral fuels, including low-carbon and carbon-negative fuels, from biogenic or non-biogenic origin (biomass, waste, renewable hydrogen) could resemble current marine fuels (diesel-type, methane and methanol). The carbon-neutrality of fuels depends on their Well-to-Wake (WtW) emissions of greenhouse gases (GHG) including carbon dioxide (CO₂), methane (CH₄), and nitrous oxide emissions (N₂O). Additionally, non-gaseous black carbon (BC) emissions have high global warming potential (GWP). Exhaust emissions which are harmful to health or the environment need to be equally removed using emission control achieved by fuel, engine or exhaust aftertreatment technologies. Harmful emission species include nitrogen oxides (NO_x), sulphur oxides (SO_x), ammonia (NH₃), formaldehyde, particle mass (PM) and number emissions (PN). Particles may carry polyaromatic hydrocarbons (PAHs) and heavy metals, which cause serious adverse health issues. Carbon-neutral fuels are typically sulphur-free enabling negligible SO_x emissions and efficient exhaust aftertreatment technologies, such as particle filtration. The combinations of carbon-neutral drop-in fuels and efficient emission control technologies would enable (near-)zero-emission shipping and these could be adaptable in the short- to mid-term. Substantial savings in external costs on society caused by ship emissions give arguments for regulations, policies and investments needed to support this development.

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.

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.

Several advanced low-temperature combustion (LTC) strategies have been developed to reduce the harmful emissions from diesel engines. These LTC strategies, such as homogeneous charge compression ignition (HCCI), premixed charge compression ignition (PCCI), and reactivity-controlled compression ignition (RCCI), can reduce engine-out nitrogen oxides (NOx) and soot emissions simultaneously. LTC investigations exhibit several limitations of HCCI and PCCI combustion modes, such as lack of combustion control and other operational issues at higher engine loads, making their application in production-grade engines challenging. RCCI combustion mode exhibited promising results in combustion control, engine performance, and applicability at higher engine loads. The potential of the RCCI concept was demonstrated on different engine platforms, showing engine-out NOx levels below the limits proposed by the emissions regulations, together with ultra-low soot emissions, eliminating the need of after-treatment devices. However, the RCCI combustion mode has several challenges, such as excessive hydrocarbons (HC) and carbon monoxide (CO) emissions at low loads and excessive maximum pressure rise rate (MPRR) at high loads, which limit its effective operating range and practical applications. This review article includes recent advancements in RCCI combustion mode, its potential for using alternative fuels, the effects of different parameters on RCCI combustion mode and its optimization, and the ability of RCCI combustion mode to extend the engine operating limit to reach higher loads, which prevents the application of this concept in commercial applications. The findings of different optical diagnostics have also been included, which have been performed to understand the detailed chemical kinetics of the fuel-air mixtures and the effect of fuel reactivities on the RCCI combustion mode. The first part of this article focuses on these studies, which provide important outcomes that can be used for the practical implementation of RCCI combustion mode in production-grade engines. The second part of this article covers different RCCI combustion mode strategies that can be used to eliminate the restrictions of RCCI combustion mode at high loads. Among the different techniques, dual-mode concepts have been extensively investigated. The dual-mode concept is based on switching between two different combustion modes, typically an LTC mode and conventional compression ignition (CI) combustion mode, to cover the entire operational range of the engine. Many studies showed that the NOx and soot emissions from stationary engines with dual-mode RCCI/CI combustion had substantially improved versus a single-fueled CI combustion mode engine. Results related to the measurements of emissions and performance in transient conditions and driving cycles have also been included, whi