Abstract Metal fuels, as recyclable carriers of clean energy, are promising alternatives to fossil fuels in a future low-carbon economy. Fossil fuels are a convenient and widely-available source of stored solar energy that have enabled our modern society; however, fossil-fuel production cannot perpetually keep up with increasing energy demand, while carbon dioxide emissions from fossil-fuel combustion cause climate change. Low-carbon energy carriers, with high energy density, are needed to replace the multiple indispensable roles of fossil fuels, including for electrical and thermal power generation, for powering transportation fleets, and for global energy trade. Metals have high energy densities and metals are, therefore, fuels within many batteries, energetic materials, and propellants. Metal fuels can be burned with air or reacted with water to release their chemical energy at a range of power-generation scales. The metal-oxide combustion products are solids that can be captured and then be recycled using zero-carbon electrolysis processes powered by clean energy, enabling metals to be used as recyclable zero-carbon solar fuels or electrofuels. A key technological barrier to the increased use of metal fuels is the current lack of clean and efficient combustor/reactor/engine technologies to convert the chemical energy in metal fuels into motive or electrical power (energy). This paper overviews the concept of low-carbon metal fuels and summarizes the current state of our knowledge regarding the reaction of metal fuels with water, to produce hot hydrogen on demand, and the combustion of metal fuels with air in laminar and turbulent flames. Many important questions regarding metal-fuel combustion processes remain unanswered, as do questions concerning the energy-cycle efficiency and life-cycle environmental impacts and economics of metals as recyclable fuels. Metal fuels can be an important technology option within a future low-carbon society and deserve focused attention to address these open questions.

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可回收的金属燃料，用于清洁紧凑的零碳能源

摘要 金属燃料作为清洁能源的可回收载体，是未来低碳经济中极具潜力的化石燃料替代品。化石燃料是一种方便且广泛可用的储存太阳能来源，它使我们的现代社会成为可能；然而，化石燃料生产无法永远跟上不断增长的能源需求，而化石燃料燃烧产生的二氧化碳排放会导致气候变化。需要具有高能量密度的低碳能源载体来取代化石燃料的多种不可或缺的作用，包括用于发电和热力发电、为运输车队提供动力以及用于全球能源贸易。金属具有高能量密度，因此金属是许多电池、高能材料和推进剂中的燃料。金属燃料可以与空气一起燃烧或与水反应以在一系列发电规模下释放其化学能。金属氧化物燃烧产物是固体，可以被捕获，然后使用由清洁能源驱动的零碳电解工艺进行回收，使金属能够用作可回收的零碳太阳能燃料或电燃料。增加使用金属燃料的一个关键技术障碍是目前缺乏将金属燃料中的化学能转化为动力或电能（能量）的清洁高效的燃烧器/反应器/发动机技术。本文概述了低碳金属燃料的概念，并总结了我们对金属燃料与水反应以按需生产热氢的知识现状，以及金属燃料与空气在层流和湍流火焰中的燃烧。许多关于金属燃料燃烧过程的重要问题仍未得到解答，有关能量循环效率和生命周期环境影响以及金属作为可回收燃料的经济性的问题也没有得到解答。在未来的低碳社会中，金属燃料可能是一项重要的技术选择，值得关注解决这些悬而未决的问题。