1
$\begingroup$

On a sea-Level engine, what is the average nozzle ratio? What about an upper-stage vacuum engine?

$\endgroup$

1 Answer 1

4
$\begingroup$

It varies widely with the chamber pressure and other details of the engine design. Some examples of first-stage engines with their approximate nozzle ratios:

For ideal performance, the expansion should reduce the exhaust pressure to be equal to the ambient atmospheric pressure, but since first-stage engines operate over a range of altitudes, the expansion ratio must be a compromise.

Note that the SSME on the shuttle burns from liftoff all the way to orbit, so it is tuned more towards vacuum performance than the others, with a higher expansion ratio.

Some upper stage engines:

Since upper stage engines exhaust into near-vacuum, extremely high expansion ratios would be ideal for performance, but the nozzle sizes are constrained by mass and space limitations.

$\endgroup$
2
  • $\begingroup$ This does answer the direct question, but I wouldn't mind seeing a brief discussion (or link to such) as to the optimum expansion vs. atmospheric density. $\endgroup$ Nov 11, 2019 at 17:04
  • $\begingroup$ Added a bit of info. $\endgroup$ Nov 11, 2019 at 17:36

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy