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Clean Sky’s PIPS harnesses space tech for plane de-icing

As much as three percent of an aircraft’s fuel-burn is spent on deicing the engine intakes and the wings’ leading edges during flight. What if some of that energy could be saved? Clean Sky’s Passive Ice Protection System (PIPS) project uses technology originally developed for orbiting space satellites to bring fuel savings and reduced CO2 emissions for aviation.

Ice poses a potential threat to flight operations at all stages of the journey and can occur unexpectedly – pre-flight, at altitude whenever ambient temperatures drop below 10 degrees Celsius, or when flying through clouds containing tiny water droplets within a certain temperature range that can quickly freeze as they attach to the aircraft. Ice accumulating on aircraft distorts their aerodynamic profile, resulting in drag, reduced lift, impaired maneuverability and higher stall speeds. Furthermore, ice ingested into jet engines compromises their performance and can cause undue wear. All of this means greater fuel consumption and an increase in CO2 emissions.

Current measures deployed to prevent ice build-up include the use of bleed-air (whereby hot air is bled off from the engine’s compressor stage) which is ducted internally to parts of the aircraft that are prone to freezing; through the use of pneumatic ’boots’ on the leading edges of wings which inflate and contract to physically break the ice up; or by the use of electro-thermal systems which electrically heat the parts of the wings and engine cowlings where ice is prone to lurk. But all these systems, one way or another, take their toll on the aircraft’s fuel supply.

”Existing de-icing systems use a lot of energy and the primary aim of Clean Sky’s PIPS (Passive Ice Protection System) project is to increase the efficiency and reliability of the anti-icing system in the aircraft while using less energy”, says Elena Pedone, Clean Sky’s Project Administrator for PIPS. The specific objective of this project is to attain a TRL6 anti-icing solution which will help Europe’s aeronautical industry to produce more efficient aircraft with less environmental impact, and to this end ”the PIPS solution will be a bit lighter and more efficient than existing systems, which in the long term will all add up to a significant reduction in the CO2 emissions” says Pedone.

EHP (Euro Heat Pipes), a Belgian company specialising in ’two-phase’ (also known as biphasic) thermal control systems for orbiting space satellites, is steering the PIPS program through its paces and has drawn on its niche expertise in maintenance-free passive heat management technologies to address the issue of aircraft icing. Airbus DS is the project’s topic manager and has defined the scenarios in which the system will ultimately operate, such as phases when the aircraft is on the ground, at altitude, hot weather, cold weather, ascending, descending, and so on. The program kicked off in June 2016 and runs until March 2020.

”Sometimes you can spend up to 3% of the plane’s energy on anti-icing, and there are two main zones where this occurs: the leading edge of the wings and the air intake of the aircraft engine” says EHP’s design engineer Romain Rioboo. ”The technology we’re using in PIPS is the Capillary Pump Loop (CPL) which is used by orbiting space satellites to manage temperature changes without using energy, because in space you have no choice – you cannot put any pump or have maintenance – you need a system which is passive. This concept was developed by the Americans and Russians at the end of the 1960s and it’s commonly used in space applications”.

Though the principles of the system have been proven for use in satellites, adapting them for use in aviation for this specific engine de-icing task has been a significant undertaking, explains Rioboo: ”We spent two and a half years at the very beginning of the project because when we answered the Clean Sky call we were thinking about all the various two-phase systems – but they weren’t strong enough to transport enough heat, so we modified them more and more and took a lot of time perfecting the performance. We also spent a lot of time with the proof-of-concept, which we did on a full-scale system because in such an application the technology is also dependent on the dimensions”.

”In PIPS we’re working on the air intake in order to protect it from icing up using a ’twophase’ system. We need to have a heat source – which in this case is the hot air coming from the engine – and the idea is to bring this heat up to the air intake zone that we have to protect, as well as further inside the front of the engine where you have a large zone which is about 1.5 metre long and 0.9 metre square that you have to de-ice” says Rioboo.

The PIPS system is comprised of five elements: an evaporator; a fluid reservoir; a condenser; fluid transport lines; and fluid inside the system to transport the heat between the evaporator and the condenser through the transport lines.

”You have a zone which is called the evaporator. The evaporator is in contact with a heat source and inside you have the heat exchange fluid. This fluid turns from liquid to vapour because it receives the heating from the engine. The vapour then goes to another zone which is the condenser (the cold zone) where you have condensation of the fluid. And because of the condensation of the fluid the heat is released. Then, at the evaporator the fluid is in contact with porous metallic media while it evaporates; this porous metallic media acts as a pump while the vapour is let go to the condenser making the fluid’s journey circular from the evaporator to the condenser and then back to the evaporator. And it works autonomously, you just need a difference of temperature between your evaporator and the condenser – the condenser is the cold zone and the evaporator is the hot zone”, explains Rioboo.

A significant milestone was announced in September 2018 when a test of the complete system was successfully undertaken to validate the analytical performances model of the system prior to construction of the system to be fitted in an engine air intake and nacelle mockup.

In the meantime EHP, having collated the final proof-of-concept data from last Summer’s complete system test, is now modelling it to extrapolate and define what the operational limits of the technology are, says Rioboo: ”We now have a model which is rough and not precise which is working stationery and we saw that the system has to work in a non-stationery way. So we have to model and understand all that – this is now our main focus.”

As the PIPS project progresses, further tests will be conducted in the Icing Wind Tunnel at Rail Tech Arsenal in Austria in the framework of another Clean Sky 2 project, I3PS (Integrated Innovative Ice Protection System), by the beginning of 2020.