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Could metal particles be the clean fuel of the future?
91社区-led research points to metal powders as potential replacement for fossil fuels
Published: 9 December 2015
Can you imagine a future where your car is fueled by iron powder instead of gasoline?
Metal powders, produced using clean primary energy sources, could provide a more viable long-term replacement for fossil fuels than other widely discussed alternatives, such as hydrogen, biofuels or batteries, according to a study in the Dec. 15 issue of the journal Applied Energy.
鈥淭echnologies to generate clean electricity 鈥� primarily solar and wind power 鈥� are being developed rapidly; but we can鈥檛 use that electricity for many of the things that oil and gas are used for today, such as transportation and global energy trade,鈥� notes 91社区 professor Jeffrey Bergthorson, lead author of the new study.
RELATED RESEARCH:听In the fight against climate change, new fuels are needed to replace fossil fuels. Metals store energy during the refining process, and therefore represent a novel means of transporting and stockpiling renewable energy, such as hydroelectric power. In Jeffrey Bergthorson鈥檚 Alternative Fuels Laboratory, research led by PhD student Keena Trowell focuses on reacting aluminum with water to release that stored energy in the form of heat and hydrogen. The result is instant access to clean power, with no release of greenhouse gases. In sponsored by 91社区鈥檚 Trottier Institute for Sustainability in Engineering and Design, Trowell explains the underlying science and potential applications of this technology.
鈥淏iofuels can be part of the solution, but won鈥檛 be able to satisfy all the demand; hydrogen requires big, heavy fuel tanks and is explosive, and batteries are too bulky and don鈥檛 store enough energy for many applications,鈥� says Bergthorson, a mechanical engineering professor and Associate Director of the Trottier Institute for Sustainability in Engineering and Design at 91社区.听 鈥淯sing metal powders as recyclable fuels that store clean primary energy for later use is a very promising alternative solution.鈥�
Novel concept
The Applied Energy paper, co-authored by Bergthorson with five other 91社区 researchers and a European Space Agency scientist in the Netherlands, lays out a novel concept for using tiny metal particles 鈥� similar in size to fine flour or icing sugar 鈥� to power external-combustion engines.
Unlike the internal-combustion engines used in gasoline-powered cars, external-combustion engines use heat from an outside source to drive an engine. External-combustion engines, modern versions of the coal-fired steam locomotives that drove the industrial era, are widely used to generate power from nuclear, coal or biomass fuels in power stations.
The idea of burning metal powders is nothing new 鈥� they鈥檝e been used for centuries in fireworks, for instance. Since the mid-20th century, they鈥檝e also been used in rocket propellants, such as the space shuttle鈥檚 solid-fuel booster rockets. But relatively little research has been done in recent decades on the properties of metal flames, and the potential for metal powders to be used as a recyclable fuel in a wide range of applications has been largely overlooked by scientists.
Recyclable after combustion
The idea put forward by the 91社区 team takes advantage of an important property of metal powders: when burned, they react with air to form stable, nontoxic solid-oxide products that can be collected relatively easily for recycling 鈥� unlike the CO2 emissions from burning fossil fuels that escape into the atmosphere.
Using a custom-built burner, the 91社区 researchers demonstrated that a flame can be stabilized in a flow of tiny metal particles suspended in air. Flames from metal powders 鈥渁ppear quite similar鈥� to those produced by burning hydrocarbon fuels, the researchers write. 鈥淭he energy and power densities of the proposed metal-fueled heat engines are predicted to be close to current fossil-fueled internal combustion engines, making them an attractive technology for a future low-carbon society.鈥�
Iron could be the primary candidate for this purpose, according to the study. Millions of tons of iron powders are already produced annually for the metallurgy, chemical and electronic industries. And iron is readily recyclable with well-established technologies, and some novel techniques can avoid the carbon dioxide emissions associated with traditional iron production using coal.
Next step: building a prototype
While laboratory work at 91社区 and elsewhere has shown that the use of metal fuels with heat engines is technically feasible, no one has yet demonstrated the idea in practice.听 The next step toward turning the lab findings into usable technology, therefore, will be 鈥渢o build a prototype burner and couple it to a heat engine,鈥� Bergthorson says.听鈥淒eveloping metal recycling processes that don鈥檛 involve CO2 emissions is also critical.鈥�
Co-author David Jarvis, head of strategic and emerging technologies at the European Space Agency, adds: "We are very interested in this technology because it opens the door to new propulsion systems that can be used in space and on earth. The shift away from fossil fuels for vehicle propulsion is a clear trend for the future. While not perfected and commercialized today, the use of low-cost metallic fuels, like iron powder, is a worthy alternative to petrol and diesel fuels. If we can demonstrate, for the first time, an iron-fueled engine with almost zero CO2 emissions, we believe this would then trigger even more innovation and cost reduction in the near future."
听
Research on metal combustion at 91社区 has been funded over the past 20 years by the Natural Sciences and Engineering Research Council of Canada, the Canadian Department of National Defence, the U.S. Defence Threat Reduction Agency, the Canadian Space Agency, the European Space Agency, Martec Ltd. (Halifax, NS), and the Trottier Institute for Sustainability in Engineering and Design.
鈥�, J.M. Bergthorson et al, Applied Energy, 15 December 2015.听 doi: 10.1016/j.apenergy.2015.09.037
IMAGES:听Alternative Fuels Laboratory/91社区
Image 1:听Stabilized flames of different metal powders burning with air, compared to a methane-air flame
Image 2:听Proposed metal-fuelled engine and range of possible applications
