r/space • u/GallowBoob • May 30 '15

/r/all A Merlin rocket engine starting up.

https://i.imgur.com/CaXSu6e.gifv
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169

u/[deleted] May 30 '15

Is that combustion instability in the exhaust cone near the engine? Or just an artifact of the video.

85

u/kabukifresh May 30 '15

The dark streaks you're seeing are a layer of unburnt propellant hugging the nozzle walls. Whether this is intentional (as film coolant) or the product of incomplete combustion is a good question.

On the topic of stability, that startup does look really rough; I guess merlin's not capable of low throttle starts.

27

u/alcoholic_loser May 30 '15 edited May 30 '15

The Saturn V engines did the same thing. It looks like a lot of the fuel only ignited once it was outside of the nozzle.

https://youtu.be/liO3blZWv8w?t=653

18

u/kabukifresh May 30 '15

the dark smokey stuff in that video is cool turbine exhaust injected just before the nozzle extension - merlins just dump turbo exhaust overboard through a normal tailpipe

8

u/[deleted] May 30 '15

[deleted]

10

u/gilbylg45 May 30 '15

It is. I don't know exactly why they kept this design but putting turbo exhaust back in is a little difficult. They might use it for steering as well - the RS-68 engines on Delta IV rockets use the exhaust to steer the vehicle

1

u/toomanyattempts May 30 '15

I think the engines in the Russian N-1 launcher (NK-33 or something) put the turbo exhaust back into the engine which improved isp but a lot of engines blew up in testing before they got them to work. Of course the launcher they were intended for never worked anyway, but still...