Day 2: Public Relations
Upon arriving at Kiruna yesterday, I was asked to prepare a presentation, along with the other investigators, for all the personnel assembled here at the Esrange Space Center. So, I spent this morning putting together the talk, and the early afternoon was a round-robin of talks from the scientists with the ESA, Swedish Space Corporation, and Airbus personnel as the audience. It is always a pleasure to hear other scientists talk about what they are working on, particularly those we will be sharing the MAXUS rocket ride to space with. Of particular interest to me (because I happen to like things that go fast) is a supersonic parachute experiment called SUPERMAX from the UK that will ride under our payload to space and then detach and reenter separately, which you can read more about here and here. I have a feeling that — if everything goes well with the launch — this team will win the coolest video competition, with a GoPro onboard observing the deployment of their parachute at Mach 2.
The rest of the afternoon was spent talking to the media from back home in Canada. The journalists I spoke with were mostly interested in the applications of metal combustion, which is understandable since they know the public will always ask what is the point of expending all this work and money for just a dozen minutes in space. I always enjoy discussing my research and particularly relish the problem of having to explain it in nontechnical terms, but the challenge in talking with the media is recognizing that it will all be distilled down to a 20 second sound bite. So, I will spend some words here to expand on the possible applications of our work.
The traditional application of metal combustion is in rocket propellants. It was not hard today to convince the other participants in the MAXUS 9 experiment of the importance of metal combustion: The fuel for our rocket ride this week is a solid propellant consisting of aluminum powder mixed with an oxidizer (ammonium perchlorate). Burning metal inside the rocket motor is going to create the hot, high pressure gas that will push us into space, which I’ve written about here.
Besides rockets, however, what else could metal combustion be used for? Ten years ago, even we would have scratched our heads at this question. But in the last decade, the idea of utilizing metal as fuels for ground-based power has picked up some attention, and my colleagues at McGill are working intensively on this application. The earliest suggestion I am aware of came from David Beach and his colleagues at the Oak Ridge National Laboratory in the US. They suggested that metallic nanoparticles, specifically iron, might be mixed in air and burned like a conventional hydrocarbon fuel. The products of combustion are iron oxide — essentially rust — and are also solid particles. They could be collected (not easily for nanoparticles, but doable in principle) and then recycled back into iron metal. So, rather than a fuel that is burned once, the iron would be a recyclable “energy carrier,” similar to a rechargeable battery.
If that is the case, why not just use a battery? Batteries have very low energy density, which is why electric vehicles need enormous batteries. The battery in a Prius, for example, weighs 600 pounds, but the amount of energy it stores is comparable to the amount of energy released when just a cupful of gasoline is burned. Even the most advanced electric cars still cannot compete with the range of a gasoline-powered vehicle. And iron, when burning in air, can release almost twice as much heat as gasoline when compared per liter of fuel, without any greenhouse gas emissions — or any other gasses for that matter. (The product of iron combustion, again, just being rust.)
We first learned of this concept from colleagues at the ESA, which has been one of the factors contributing to our research group’s collaborations with the ESA. Researchers at the ESA pointed out that iron powder is just about as expensive as gasoline, in terms of the heat you get out per dollar (well, euro) of fuel you buy. So, could you heat your home economically by buying and burning iron? Yes, but that is not quite how we envision using it.
My colleague Samuel Goroshin pioneered the ability to stabilize flames in suspensions of metal powders, and over the last 20 years demonstrated the ability the burn several different metal fuels in powder form on a Bunsen burner, just like you burn natural gas and air on the bench-top in chemistry class. Most importantly, Sam has shown you can do this with much larger, micron-sized powders, so we can avoid nanoscale particles entirely, which is good since nano-powders represent a potentially serious health risk. To give you an image: milled corn in your kitchen is made up of micron-sized particles, while cigarette smoke is nanometric. Using larger, micron-sized particles also makes collecting the iron oxide products much easier since a cyclone can be used, which is exactly how your bag-less Dyson vacuum cleaner works.
Around the time we first encountered this concept, my colleague Jeffrey Bergthorson was just joining our Mechanical Engineering Department at McGill. Jeff was hired to set-up a program at McGill in alternative energy, and he now supervises a lab developing the basic combustion science of novel fuels. His research focus has been biofuels, but Jeff’s extensive study of this problem has led him to conclude that, while biofuels have a role to play, they cannot be scaled up to address all our transportation energy needs without having unintended and potentially undesirable consequences. As a result, Jeff is now championing the metal energy carrier concept, and his research is making significant advances in demonstrating its feasibility.
The concept would work like this: Your car (or truck or ship or emergency generator) is fueled up with powdered iron. You burn the iron with air using Dr. Goroshin’s burner, and use the heat generated to power an external combustion engine, such as a Rankine or Stirling-cycle-based engine. With external combustion, you do not need to worry about the powder fuel jamming the piston/cylinder of traditional internal combustion engines. Several viable external combustion engine concepts have already been demonstrated that use particulate fuels. The exhaust coming out of the engine passes through a cyclone to collect the oxide products, and only warm nitrogen leaves the tailpipe. The next time you go to fuel up, you drop off the iron oxide your cyclone collected, which goes to a recycling center.
Now, the recycling center will need to consume energy to convert the iron oxide back to iron (you don’t get something for nothing, after all), but if this can be done using a renewable and green energy source of your choosing, then the entire cycle is completely free of any greenhouse gas emission. Can iron oxide be recycled back into pure iron on industrial scales? Yes, it already is. This is, to me, the real selling point of the concept: A world-wide infrastructure for the processing of iron powder already exists that has demonstrated much of the technical feasibility of the idea, although not yet with a green energy source. The same cannot be said of the much-touted “hydrogen economy.” Hydrogen is only handled — and handled with great care — in bulk quantities for applications such as launch vehicles like the Space Shuttle. Building a global infrastructure for hydrogen is a formidable challenge when compared to iron.
Finally, a word about the environmental impact if our civilization started using iron as a recyclable fuel. If you had a fuel spill before you recycle the iron oxide, no one would likely notice: Iron oxide already comprises a significant percentage of the earth’s crust and is largely innocuous. The iron is safe and won’t burn without being carefully dispersed in air. Iron itself (in metal form) is in fact good for you: Iron is a common food additive, as many people suffer from iron deficiency in their diet (as your doctor may have discussed with you). The iron powder added to your breakfast cereal is exactly same the candidate fuel I am discussing here.
So, as I told the journalists I talked to today, perhaps an answer to the double conundrum of the end of oil and global warming is a new Iron Age. If we are going to develop a new fuel, however, we need to make progress in the science of how it burns, and I will write more on this soon.
Bergthorson, J.M., Goroshin, S., Soo, M.J., Julien, P., Palecka, J., Frost, D.L., and Jarvis, D.J. “Direct combustion of recyclable metal fuels for zero-carbon heat and power.” Applied Energy 160:368–382 (2015).
Bergthorson, J.M., Yavor, Y., Palecka, J., Georges, W., Soo, M., Vickery, J., Goroshin, S., Frost, D.L., and Higgins, A.J. “Metal-water combustion for clean propulsion and power generation.” Applied Energy 186:13–27 (2017).