Powdered metal could replace fossil fuels, eliminate greenhouse gas emissions

 One of the core problems with replacing fossil fuels throughout a modern industrial economy is the difficulty of finding replacement fuels for coal, oil, and natural gas. A new report from researchers at McGill University suggests that powdered metal fuels could be an effective replacement for the fossil fuels we currently rely on, while simultaneously slashing carbon emissions and environmental costs.
According to professor Jeffrey Bergthorson, the rise in renewable power is laudable, but only addresses part of the problem. Neither solar nor wind power provides enough electricity to directly drive a car, much less a freighter. Battery technology can fill this gap to some extent, but historic battery improvements simply aren’t growing quickly enough to meet the gap. As the chart below shows, battery energy density has only improved by roughly 3% per year since 1910.

Battery capacity over time. Don’t let the jumps fool you — the long-term trend is quite low.

Absent a massive and unexpected improvement in Li-ion technology, something else is needed. Enter powdered metal fuels.

Pow(d)ering the modern economy?

First, the good news: Unlike Li-ion batteries, which have absolutely miserable energy density whether you measure by weight or volume, powdered metal’s energy density per liter dwarfs any conventional fuel. The grains of powder in question would be quite fine — roughly equivalent to flour — and the engines themselves would rely on external combustion In an internal combustion engine, the expansion of gases applies force to the engine components directly — an external combustion engine contains a fluid that is heated by an external source. Both Stirling engines and steam engines are external combustion engines, though the former can be far more efficient than the latter.
In theory, powdered metal engines would have significant environmental advantages compared to conventional fossil fuels. The metal itself can potentially be recycled (the image below is from a separate story from 2005, but captures the theoretical recycling process):

The major announcement out of McGill today is that its research team has demonstrated that a stable flame can be sustained in a flow of metal particles suspended in the air. The team writes that “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.”
Despite the real potential of powdered metal, there are some substantial barriers to entry that McGill’s PR doesn’t really address. The first problem is that while powdered metals are quite efficient in terms of specific energy per liter, they don’t compare well at all in terms of specific energy per kilogram. This is particularly true of iron, which is often floated as the replacement fuel source thanks to its abundance and low cost. Other metals, like aluminum, are incredibly explosive in powdered form and are a non-option for stable combustion.

The other problem with the proposed use of powdered metal as a primary fuel source is that it would require a huge infrastructure investment in heavy mining equipment — investments that would not, themselves, be carbon neutral. Granted, this is true no matter what approach we take, since lithium mining isn’t exactly carbon neutral, either — but the processes required to turn iron ore into the fine-grained particulate required to use it as a fuel would require additional energy over and above simple smelting. The research team doesn’t address this at all, beyond noting that “some novel techniques can avoid the carbon dioxide emissions associated with traditional iron production using coal.”
Loosely translated, that means: “Nobody has figured out how to do this in a cost-competitive manner.” We’ve seen similar problems with hydrogen fuel cells. While hydrogen can theoretically be produced via the electrolysis of water using energy provided by renewable resources, it’s not remotely cost-competitive to do so. The hydrogen used in fuel cell vehicles today, what little there is of it, is typically produced by natural gas reformation — a decidedly non carbon-neutral process.
One of the intrinsic difficulties of trying to find better alternatives to existing infrastructure is that many improvements only address one aspect of the total ecosystem. Ideally, even these modest advances can be used to lower the environmental impact of the entire system — but all too often, costs and difficulty are offloaded into other areas.
Powdered metal has some interesting upsides, and it could provide an alternative in certain use cases — but it’s hard to imagine the technology emerging as a serious contender at this point. After all, GM once demonstrated (and confidently predicted) that vehicles would run on coal dust the consistency of flour, or even liquified coal by the turn the century.

The future is now! Unless it isn’t.

So far, that hasn’t exactly worked out.