Engineers say it might be possible to use tiny metal particles—similar in size to fine flour or icing sugar—to power external-combustion engines in vehicles on Earth and in space.
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 journal Applied Energy.
“Technologies to generate clean electricity—primarily solar and wind power—are being developed rapidly; but we can’t use that electricity for many of the things that oil and gas are used for today, such as transportation and global energy trade,” says Jeffrey Bergthorson, a McGill University professor and the study’s lead author.
“Biofuels can be part of the solution, but won’t be able to satisfy all the demand; hydrogen requires big, heavy fuel tanks and is explosive, and batteries are too bulky and don’t store enough energy for many applications,” says Bergthorson, a mechanical engineering professor.
“Using metal powders as recyclable fuels that store clean primary energy for later use is a very promising alternative solution.”
Used in Rockets and Fireworks
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—they’ve been used for centuries in fireworks, for instance. Since the mid-20th century, they’ve also been used in rocket propellants, such as the space shuttle’s 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 concept 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—unlike the CO2 emissions from burning fossil fuels that escape into the atmosphere.
Using a custom-built burner, the researchers demonstrated that a flame can be stabilized in a flow of tiny metal particles suspended in air. Flames from metal powders “appear quite similar” to those produced by burning hydrocarbon fuels, the researchers write.
