Hypersonic flight means travelling at at least five times the speed of sound, and one of the main technological obstacles is currently overheating – a new catalyst could help. Hypersonic flight requires at least five times the speed of sound, and although we have had devices that have achieved and even exceeded this, we cannot talk about widespread commercial applications, not least because with the retirement of Concorde in 2003, even supersonic flights have been put on the back burner for a long time. (Incidentally, in June, United Airlines ordered 15 supersonic planes from Boom Supersonic – these will carry passengers from 2029).
Supersonic flight is a major technological challenge, and hypersonic flight even more so, because at the former speed the heat transfer between the flying object and the medium is negligible, but this is no longer the case for travel above Mach 5. In other words, in hypersonic flight, the problem is not only how to ensure adequate thrust, but also what to do about overheating. And to add to the difficulty, there is not much room for manoeuvring when it comes to cooling, as the weight of the aircraft has to be taken into account.
To address the problem of overheating, researchers have spent decades trying to develop a propellant that could also act as a coolant. It can only work if these materials have a very efficient heat transfer, which could be achieved by using catalysts to stimulate chemical processes. Researchers at RMIT University in Australia have developed just such a catalyst: a 3D-printed metal alloy coated with synthetic zeolites. 3D printing could be used to develop the most efficient form of catalyst for fuel combustion and cooling.
The researchers tested several different structures and subjected them to the extreme pressure and temperature conditions encountered during hypersonic flight in the laboratory. In practice, the way it worked was that the warming metal transferred excess heat to the zeolites, and the whole system started to act as a “miniature chemical reactor”. The researchers say that this method of using the fuel for cooling is one of the most promising experimental solutions to the problem. Researchers have yet to work out the exact proportions of alloys that will give the best possible performance, but once this is done, the solution will be applicable not only to hypersonic flight, but to all industrial processes where overheating has been a challenge. Scientists are also experimenting with catalysts to absorb pollutants from vehicles and could even be used in home appliances to clean the air.