Contrails could be dissipated by airborne microwave emitter: research

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Dissipation of contrails with a powerful microwave beam aligned behind aircraft engines is being touted as a possible solution to help address air transport's effects on the climate.

Speaking on 19 November at the Towards Sustainable Aviation Propulsion event organised by the Institution of Mechanical Engineers, Cranfield University's Frank Noppel described how his research led sponsor Rolls-Royce to file a patent on what he believes could be a cost-effective contrail avoidance technology.

Noppel told delegates that ice particles could be prevented from forming, or be evaporated once formed, by remotely heating them, together with condensation nuclei such as soot in the exhaust plume.

Contrails form as the engine exhaust mixes with ambient air, the temperature drops and humidity levels reach super-saturation, leading to the formation of ice particles. Contrails are also more likely to form as a result of increasingly-efficient engine architecture.

An influential Intergovernmental Panel on Climate Change special report in 1999 on aviation and the global atmosphere attributed the second-largest climate effect of aviation-specific emissions to linear - or young - contrails, with contrail cirrus thought to have an even more significant effect.

"The remote heating of condensation nuclei could be achieved by applying electromagnetic radiation, such as microwaves," says Noppel. "Depending on assumptions made, calculation shows that the power required for such a device could be as little as 0.1% of the engine power."

"With theoretically low energy requirements and associated weight penalty, existing aircraft could possibly be retrofitted and new aircraft equipped with this technology," he adds.

Speaking at the same event, German aerospace centre DLR's Klaus Gierens agreed that manipulating the contrail composition of, for example, the number and size of emitted soot particles could produce fewer ice crystals - making the contrail optically thinner and reducing its lifespan.

Photo credit: Glenn Peters