Maybe they're going liquid hydrogen for the fuel? Or another cryogenic? That gives you a lot of "waste cold" that you can use for cooling charge air and the res

Maybe they're going liquid hydrogen for the fuel? Or another cryogenic? That gives you a lot of "waste cold" that you can use for cooling charge air and the rest of the engine. I'm a big fan of LH2 planes. Tupolev actually built one just before the wall fell [1]. Airbus did a big concept study in the 2000s that indicated it would be on par with normal airliners once you eked out all the optimizations. Then everyone decided to go gradual biofuel phase-in instead, which I'm decidedly skeptical of. Sure I get that the CAPEX of going LH2 is a lot worse, so for someone optimizing on a < 10 year horizon it looks better. But are biofuels really going to get us all the way we need to go eventually? [1] https://en.wikipedia.org/wiki/Tupolev_Tu-155 https://en.wikipedia.org/wiki/Tupolev_Tu-155