Are chemical rockets really beyond 60% efficient?

https://en.wikipedia.org/wiki/Rocket_engine “Rocket engine nozzles are surprisingly efficient heat engines for generating a high speed jet, as a consequence of the high combustion temperature and high compression ratio. Rocket nozzles give an excellent approximation to adiabatic expansion which is a reversible process, and hence they give efficiencies which are very close to that of the Carnot cycle. Given the temperatures reached, over 60% efficiency can be achieved with chemical rockets.”

If they are really this efficient why can’t we have Aeopiles with hydrogen oxygen rockets on them, for high power to weight ratio electric generators, with similar efficiency as fuel cells? And we might not need precious metals for it. I don't mean we should try making a rocket-pile the size of a pair of opposing shuttle main engines but something much smaller like a hydrogen/air detonation engine. It would look something like the ancient Alexandrian engineer's version of the Aeopile.


1 Answer 1


why can’t we have [aeolipiles] with hydrogen oxygen rockets on them ...

Because efficiency is not the only consideration when designing a practical engine or generator. A rocket powered aeolipile would be:

  • An engineering nightmare - extreme temperatures and pressures in combustion chambers that are rotating at high speed
  • Extremely noisy due to supersonic exhaust
  • Very dangerous - volatile fuel components and high temperature exhaust going in all directions
  • $\begingroup$ excellent points, +1. -NN $\endgroup$ Mar 4, 2021 at 18:41
  • $\begingroup$ Can a rocket be 60% efficient at conveying force to a free moving payload? $\endgroup$
    – Ohiovr
    Mar 4, 2021 at 20:20

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