3
$\begingroup$

The new Ariane 6's upper stage engine "Vinci" is expected to challenge the RL-10C, which is currently the most efficient chemical rocket engine on the market. The European aerospace conglomerate aims at achieving a much better thrust-to-weight ratio while realizing approximately the same specific impulse.

While that sounds great, the published test run video does not look good at all, at least from my armchair engineer perspective:

The exhaust looks very unstable, especially during the close-up side views. This is in contrast to the test run of the comparable ISRO engine CE20 (same fuel, approximately same thrust) which looks much more steady and smooth:

Is a deep-throttled state of operation the only possible explanation for the appearance of the exhaust in the Vinci video? Or is it the lack of a propper nozzle? What's the most likely explanation?

$\endgroup$
  • 7
    $\begingroup$ The RL-10-C is an engine for upper stages, a ground test is done at a much higher pressure than at a flight test. There is overexpansion, see. $\endgroup$ – Uwe Mar 20 at 21:42
  • 7
    $\begingroup$ The Vinci engine in that test stand doesn't appear to have a nozzle at all really, just a hemispherical blast shield kind of thing. That video looks reminiscent to me of preburner or powerhead tests where the exit flow isn't properly expanded. That said, I have no knowledge of the Vinci engine. $\endgroup$ – Organic Marble Mar 20 at 21:59
  • 1
    $\begingroup$ @Uwe: Both engines are upper-stage only, so they should (on that basis) undergo similar effects. $\endgroup$ – Nathan Tuggy Mar 22 at 5:12
  • 1
    $\begingroup$ @OrganicMarble I believe it is the most underrated engine at the moment. $\endgroup$ – Everyday Astronaut Mar 22 at 8:56
  • 1
    $\begingroup$ @EverydayAstronaut I'm a bit late to the party but you might want to watch more recent footage of the Vinci engine test firing. I think both engine do look about the same comparing "stability". With the CE20 test you only see the exhaust right at the end of the combustion chamber which is really stable. With the Vinci test you see the really stable "beginning" of the exhaust and the unstable (because not in vacuum) "tail". Fun fact: ArianeGroup is a part supplier for the RL-10 engine. And I also think it is a highly underrated engine. $\endgroup$ – GittingGud Jun 26 at 13:41
2
$\begingroup$

If I were the engineer responsible the RL-10-C engine development, and I had this kind of good-looking test in that stage of engine development, at sea level pressure, I'd be a very happy engineer.

Addressing @EverydayAstronaut's request for clarification: three factors that contribute to me saying "looks good":

  1. continuous combustion (I don't have the readout of the various measurement instruments and sensors; we can assume they're all at nominal values, though)
  2. the engine is designed for operation in a vacuum, not at sea-level pressure; so I'd have asked my people, beforehand, to compute the maximum (order of magnitude of) plume instability; it doesn't look dramatic to me
  3. the engine is designed to be restartable, and this wasn't its first test: all good. This not being a final acceptance test, it's all green.

There's nothing to be worried about here. Next thing I would be pressing for a vacuum test, to make my bliss complete.

$\endgroup$
  • 1
    $\begingroup$ Thanks for your comment. Would you mind elaborating on your view? Why do you think so, and is there any reference you could include in order to support your view? $\endgroup$ – Everyday Astronaut Aug 26 at 6:03
  • 1
    $\begingroup$ @uhoh Thanks - I was not conscious of the temporary nature of comments. Edited my answer correspondingly. $\endgroup$ – Jan van Oort Aug 26 at 9:18
  • $\begingroup$ looks good, thanks! $\endgroup$ – uhoh Aug 26 at 10:04
  • $\begingroup$ @EverydayAstronaut the answer has been edited per your comment. $\endgroup$ – uhoh Aug 26 at 10:05
  • 1
    $\begingroup$ @uhoh Thanks for the heads-up. I'll read that, as soon as I have some leisure time on my hands, and certainly before my next major answer :-) $\endgroup$ – Jan van Oort Aug 27 at 9:17

Your Answer

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

Not the answer you're looking for? Browse other questions tagged or ask your own question.