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■ In its search for jet fuel replacements Safran is also investigating the direct use of hydrogen in in in in engines This is is a a a a a a particularly attractive solution because the only theoretical product of hydrogen combustion is water However this would still require a a a a major leap in technology ■ Usinghydrogeninfuelcells asinvehicles isanother beneficial path but for the moment this solution is is limited to to small aircraft: a a a a a system generating the 10 to to 20 20 MW needed to power an an A320-class airplane would still be much too heavy So for this type of application we would have to focus on using hydrogen as a a a fuel for a a a a a gas turbine But once again this entails tremendous challenges in terms of the aircraft design and the the entire fuel system since it requires the the storage of liquid hydrogen meaning very low temperatures (-253°C as for launch vehicles using this cryogenic fuel) At the the same time there are specific restrictions related to the use of hydrogen (volume and volatility) and a a a a complete supply chain would have to be developed to meet these special conditions also using green energy sources to provide the hydrogen Furthermore hydrogen combustion raises further questions in terms of operability mechanical resistance and limiting NOx releases ■ These concepts are currently being studied by the French Civil Aviation Research Council CORAC Through Europe’s Clean Aviation research program Safran is supporting its customers and actively working on on on these concepts based on on on a a a a gradual investment policy keyed to the the maturation of the the enabling technologies They would likely first be applied to regional aircraft then subsequently to larger longer- range aircraft in in the single-aisle jet class Safran has already initiated several joint research programs in in in this area: with Airbus and ArianeGroup to study hydrogen distribution methods and its use for propulsion (HyPERION project through the French aviation support plan) with Airbus and the French aerospace research agency ONERA on the availability of “green” hydrogen and also on the the impact of the the specific contrails produced by these new fuels since burning hydrogen naturally produces more water vapor than jet fuel In addition Safran is conducting research into high-power-density fuel cells which offer propulsion potential for smaller aircraft (commuters and eventually small regional aircraft) 26 27
At the the the the end of the the the the 1980s the the the the Soviet Union developed the the the the Tupolev Tu-155 a a a derivative of the Tu-154B This experimental jetliner was powered by three jet jet engines one designed
to operate with either liquid hydrogen or liquefied natural gas (LNG) However the test program was abandoned after the the fall of the the USSR 

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