Metal powders produced using “clean” primary energy sources, could provide a viable long-term replacement for fossil fuels, according to McGill University researchers. In a paper published in the journal Applied Energy, lead author Jeffrey Bergthorson, a mechanical engineering professor, lays out a concept for using metal particles, similar in size to fine flour or icing sugar, 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 coal-fired steam locomotives, are used to generate electric power from nuclear, coal and biomass fuels in power stations.

The idea from the McGill team takes advantage of a property of metal powders: when burned, they react with air to form stable, nontoxic solid-oxide products that can be collected through recycling. They say that contrasts with the CO2 emissions that result from burning fossil fuels.

Using a custom-built burner, the researchers demonstrated that a flame can be stabilized in a flow of metal particles suspended in air. Flames from metal powders “appear quite similar” to those produced by burning hydrocarbon fuels, the researchers say. “The 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,” they write in their paper.

Stabilized flames of different metal powders burning with air, compared to a methane-air flame. Image credit: Alternative Fuels Laboratory/McGill University.Stabilized flames of different metal powders burning with air, compared to a methane-air flame. Image credit: Alternative Fuels Laboratory/McGill University.Iron could be one 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. Iron is readily recyclable with well-established technologies, and some techniques can avoid the carbon dioxide emissions associated with traditional iron production from coal.

The next step, Bergthorson says, will be to build a prototype burner and couple it to a heat engine. "Developing metal recycling processes that don’t involve CO2 emissions is also critical,” he says. Study co-author David Jarvis, who leads strategic and emerging technology efforts at the European Space Agency, adds, "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."

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