Direct combustion of recyclable metal fuels for zero-carbon heat and power J.M. Bergthorson a,⇑ , S. Goroshin a , M.J. Soo a , P. Julien a , J. Palecka a , D.L. Frost a , D.J. Jarvis b a Department of Mechanical Engineering, McGill University, Montreal, Quebec, Canada b European Space Agency, Noordwijk, The Netherlands highlights  Metals are promising high-energy density, low-emission, recyclable energy carriers.  Metal fuels can be burned with air to produce heat for many applications.  A novel combustor that can burn metal fuels is proposed.  Metal-oxide combustion products can be captured and recycled.  Use of clean power sources to recycle metals enables low-net-carbon emissions. graphical abstract Concept drawing of a metal-fuelled combustor and its possible applications at a range of power- generation scales. article info Article history: Received 27 April 2015 Received in revised form 4 August 2015 Accepted 7 September 2015 Keywords: Metal fuels External-combustion engines Zero carbon Energy carrier Energy vector Solar fuel abstract It is becoming widely recognized that our society must transition to low-carbon energy systems to com- bat global climate change, and renewable energy sources are needed to provide energy security in a world with limited fossil-fuel resources. While many clean power-generation solutions have been pro- posed and are being developed, our ability to transition to a low-carbon society is prevented by the pre- sent lack of clean and renewable energy carriers that can replace the crucial roles that fossil fuels play, due to their abundance, convenience and performance, in global energy trade and transportation. Any future low-carbon energy carriers that aim to displace or supplement fossil fuels must have high energy densities for convenient trade and storage, and should be consumable within efficient high-power- density engines for transportation, heavy machinery, and other off-grid energy applications. Hydrogen and batteries have been widely studied but they are not suitable for use as international energy-trading commodities and they cannot provide the energy density and safety demanded by soci- ety. Metal fuels, produced using low-carbon recycling systems powered by clean primary energy, such as solar and wind, promise energy densities that are competitive to fossil fuels with low, or even negative, net carbon dioxide emissions. To date, however, few practical high-power-density end-use devices for generating heat or power from metal fuels have been proposed. http://dx.doi.org/10.1016/j.apenergy.2015.09.037 0306-2619/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: jeffrey.bergthorson@mcgill.ca (J.M. Bergthorson). Applied Energy 160 (2015) 368–382 Contents lists available at ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy