Author Topic: Why is BE-4 ORSC instead of FRSC?  (Read 4592 times)

Offline hkultala

  • Full Member
  • ****
  • Posts: 1199
  • Liked: 748
  • Likes Given: 945
Why is BE-4 ORSC instead of FRSC?
« on: 06/15/2018 04:37 pm »
Kerosine has coking issues which is the reason kerosine-based SC engines are oxyge-rich,
and also the reasons there are no american SC kerosine engines as US did not previously have knowledge on the metallurgy for ORSC engines?

But BE-4 uses methanes instead of kerosine, with no coking issues?

So it could easily be FRSC?

Why go to ORSC which needs more exotic metallurgy etc.?

Offline kraisee

  • Expert
  • Senior Member
  • *****
  • Posts: 10560
  • Liked: 807
  • Likes Given: 40
Re: Why is BE-4 ORSC instead of FRSC?
« Reply #1 on: 06/15/2018 06:10 pm »
Basic question has been covered before, even quite recently in other threads.

Short answer is that Oxy is a heavier molecule than either C or H. By using more of it to drive the turbines in the turbopump, you can drive the turbines that much harder, which delivers higher pressures out of the pump side = higher overall engine performance.

There's more to it (isn't there always) but that's at the core of the whole FRSC/ORSC trade.

And methane fuels still contains Carbon, and some impurities that cause coking, just a lot less than kero. But still some. And coking always gets worse the higher your temperatures and pressures - and the purpose of staged combustion engines is to achieve *really* high temp and pressure. You can guess the rest.

The only fuel I'm aware of that doesn't coke at all, is H2, but its a lot harder to handle.

Ross.
« Last Edit: 06/15/2018 06:16 pm by kraisee »
"The meek shall inherit the Earth -- the rest of us will go to the stars"
-Robert A. Heinlein

Offline envy887

  • Senior Member
  • *****
  • Posts: 8148
  • Liked: 6808
  • Likes Given: 2965
Re: Why is BE-4 ORSC instead of FRSC?
« Reply #2 on: 06/15/2018 06:15 pm »
Methane does coke, if you get it hot enough. I think around 1300F. There was a discussion on this in the Raptor thread.

Offline gin455res

  • Full Member
  • ****
  • Posts: 510
  • bristol, uk
  • Liked: 42
  • Likes Given: 72
Re: Why is BE-4 ORSC instead of FRSC?
« Reply #3 on: 06/15/2018 08:46 pm »
Would ammonia coke?

Offline Steven Pietrobon

  • Member
  • Senior Member
  • *****
  • Posts: 39301
  • Adelaide, Australia
    • Steven Pietrobon's Space Archive
  • Liked: 32867
  • Likes Given: 8346
Re: Why is BE-4 ORSC instead of FRSC?
« Reply #4 on: 06/16/2018 12:05 am »
Would ammonia coke?

No, as there is no carbon in ammonia. NH3 decomposes into a nitrogen gas The problem is that CHx can decompose into carbon, which is a solid which has a very high melting point of 3727 C.
Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

Offline gin455res

  • Full Member
  • ****
  • Posts: 510
  • bristol, uk
  • Liked: 42
  • Likes Given: 72
Re: Why is BE-4 ORSC instead of FRSC?
« Reply #5 on: 06/16/2018 08:09 am »
Would ammonia coke?

No, as there is no carbon in ammonia. NH3 decomposes into a nitrogen gas The problem is that CHx can decompose into carbon, which is a solid which has a very high melting point of 3727 C.

To be honest, I knew that there was no carbon in ammonia. I was wondering if ammonia might be an interesting fuel for FFSC.




Offline Steven Pietrobon

  • Member
  • Senior Member
  • *****
  • Posts: 39301
  • Adelaide, Australia
    • Steven Pietrobon's Space Archive
  • Liked: 32867
  • Likes Given: 8346
Re: Why is BE-4 ORSC instead of FRSC?
« Reply #6 on: 06/16/2018 09:17 am »
To be honest, I knew that there was no carbon in ammonia. I was wondering if ammonia might be an interesting fuel for FFSC.

Ammonia and liquid fluorine makes for a very powerful propellant. Has an Isp of 4115 m/s and a density of 1.177 kg/L, giving an impulse density of 4843 Ns/L. Hydrolox is 1448 Ns/L and kerolox is 3663 Ns/L. Problem is dealing with the toxic hydrofluoric acid exhaust!
« Last Edit: 06/16/2018 09:18 am by Steven Pietrobon »
Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

Offline edzieba

  • Virtual Realist
  • Senior Member
  • *****
  • Posts: 6129
  • United Kingdom
  • Liked: 9376
  • Likes Given: 39
Re: Why is BE-4 ORSC instead of FRSC?
« Reply #7 on: 07/02/2018 04:43 pm »
Plus the few hundred tons of liquid fluorine sloshing about. The late John D. Clark would probably have some wise worlds about the practicality of that!
« Last Edit: 07/04/2018 01:20 pm by edzieba »

Offline Proponent

  • Senior Member
  • *****
  • Posts: 7282
  • Liked: 2783
  • Likes Given: 1462
Re: Why is BE-4 ORSC instead of FRSC?
« Reply #8 on: 07/03/2018 02:47 am »
[rant]
It's fluorine, not flourine.  And chemical elements' names are not capitalized.
[/rant]

Tags:
 

Advertisement NovaTech
Advertisement Northrop Grumman
Advertisement
Advertisement Margaritaville Beach Resort South Padre Island
Advertisement Brady Kenniston
Advertisement NextSpaceflight
Advertisement Nathan Barker Photography
1