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.

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.