To prepare a decarbonated aviation with future hydrogen-fueled commercial aircraft, Pratt & Whitney launchedanHydrogen, Steam Injected, Inter-cooled Turbine Engine (HySIITE) project. With the aim to deliver increased efficiency and significantly reduced NOx emissions for future hydrogen-fueled commercial aircraft.

The principle of the proposed Pratt & Whitney engine architecture is a turbine powered by hydrogen and equipped with some additional features (see above picture).

Why hydrogen to power aircraft engines? The reaction between hydrogen H2 and Oxygen O2 releases energy and water, safe for environment.

Why steam injection? Mostly to reducenitrogen oxides Nox to an acceptable level when Nox which causes warming of Earth are a possible byproduct when H2 and air (O2, N2) are combined. (O2 needed for the chemical reaction with H2 is coming from air)

Why water intercooling?  To increase the mass being accelerated out of engine and thus increase thrust. As well as cooling the turbine.

In the frame of thisHySIITE project, rig tests of full-scale partial components conducted at the RTX Technology Research Center (East Hartford, CT) demonstrated positive results on 3keypoints: a 99.3% reduction in NOx compared to a current benchmark, condenser performed as expected and evaporator functioned effectively in an exhaust gas path.

Overall Pratt & WhitneyHySIITE architecture could enable up to 35% improved energy efficiency compared to a current state of the art propulsion system for single-aisle aircraft.

A hydrogen-enabled engine with water recovery and steam injection could triple net energy savings compared to equivalent of using power-to-liquid sustainable aviation fuel (PtL SAF).

Power to Liquid SAF (Sustainable Aviation Fuel) is an alternative to regular fuel currently used onaircraft engines but produced by catalytic conversion of green hydrogen coming from renewable energy and carbon dioxide. SAF is overall reducing CO2 emissions by 80%but is expensive to produce.

Pratt & WhitneyHySIITE architecture could also be combined with other improvements such as hybrid propulsion, use of advanced material technologies, addition of thermal energy recovery systems or GTF Geared Turbo Fan concept. (GTF turbine is a turbine with a gearbox between the front fan and the low-pressure core. This allows each section to operate at its optimal speed: the large front fan spins slower for maximum air intake efficiency, while the core with its compressor and turbine operates at a much faster speed for improved thrust generation. This design translates to significant performance gains, with an additional gearbox weight). Numerous exchanges are performed by Pratt & Whitney with some European universities or Research Center on this topic of H2 use to look for the best solution.

What’s left in front of us for an introduction timeframe around 2050 for this kind of H2 aircraft propulsion system:  further studies and testsas well as the existence of a viable commercial marketfor hydrogen fuel in aviation are to be addressed.Airplane hydrogen propulsion being full of promises for a greener world and suiting best with single aisle airplanes (the most numerous ones today), no doubt a lot of further efforts will be given by the whole industry into this direction.Pratt & WhitneyHySIITE project represents a significant contribution  into H2 use in commercial aviation.

Nadia Didelot for AeroMorning