> The latest and greatest engines are not that far from the theoretical thermodynamic efficiency limit. So future designs are running into the hard part of the

> The latest and greatest engines are not that far from the theoretical thermodynamic efficiency limit. So future designs are running into the hard part of the asymptote. No. Even if an engine got to the Carnot efficiency, you can still improve it. Massively. You can push a certain quantity of air with a velocity v or 4 times that quantity with half the velocity. The second option produces twice the thrust, for the same fuel consumption. That's the reason engines are getting larger and larger, and going for higher and higher bypass ratios. Separately, the maximum theoretical (Carnot) efficiency depends on how hot the engine runs. GE has introduced turbines made of silicon carbide, which can withstand absurdly high temperatures. Silicon carbide melts at more than 2800 Celsius, but they don't push it to such limits. But they push it to more than 1300 Celsius [1]. Military jet engines run much hotter though. Exact numbers are classified, but according to [2] the temperature inside F35's engine might reach 2000 Celsius (the actual number is obviously classified). Of course, military jet engines are many times more expensive than civilian ones, with higher maintenance costs, and lifespan about 2 orders of magnitude shorter. Still the fact that they can run this hot means improvements for the civilian jet engines are possible. And they will happen. [1] https://www.ornl.gov/news/ceramic-matrix-composites-take-flight-leap-jet-engine https://www.ornl.gov/news/ceramic-matrix-composites-take-fli... [2] https://www.researchgate.net/publication/285727346_Fahrenheit_3600 https://www.researchgate.net/publication/285727346_Fahrenhei...