Poll

When will full-scale hot-fire testing of Raptor begin?

Component tests - 2017
2 (1.1%)
Component tests - 2018
8 (4.3%)
Integrated tests -  2017
12 (6.5%)
Integrated tests -  2018
136 (73.9%)
Integrated tests -  2019
18 (9.8%)
Raptor is not physically scaled up
7 (3.8%)
Never
1 (0.5%)

Total Members Voted: 184


Author Topic: ITS Propulsion The evolution of the SpaceX Raptor engine  (Read 150189 times)

Online abaddon

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Re: ITS Propulsion The evolution of the SpaceX Raptor engine
« Reply #700 on: 11/14/2017 01:20 PM »
I think it's TEA-TEB.  Spark igniters are external (?right?) and there's no evidence of one present.  There's also no illumination that would suggest sparks prior to ignition.  SpaceX is very comfortable with and experienced at using TEA-TEB.  The idea they would use it for the prototype engine seems very unsurprising to me as a result.

As far as the green flash in the middle of the previous fire, maybe some residue somehow?  That seems unlikely.  Or a leak.  That would be troubling, not really for the engine itself, but more for the test program.  So that's definitely a data point going the other direction.
« Last Edit: 11/14/2017 01:21 PM by abaddon »

Offline rakaydos

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Re: ITS Propulsion The evolution of the SpaceX Raptor engine
« Reply #701 on: 11/14/2017 02:59 PM »
As the green at the Raptor test stand or the merlin test stand? because we KNOW merlin uses TEA/TEB

Online abaddon

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Re: ITS Propulsion The evolution of the SpaceX Raptor engine
« Reply #702 on: 11/14/2017 03:01 PM »
Raptor.  As you say we know TEA-TEB is used for Merlin ignition.

Offline matthewkantar

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Re: ITS Propulsion The evolution of the SpaceX Raptor engine
« Reply #703 on: 11/14/2017 03:31 PM »
I think it's TEA-TEB.  Spark igniters are external 

I believe you are thinking of the pyros visible around the main engines at the base of STS. Those were not there to ignite the engines, their purpose was to burn any stray H2 before ignition. Raptor ignition device will be internal.

Matthew

Online acsawdey

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Re: ITS Propulsion The evolution of the SpaceX Raptor engine
« Reply #704 on: 11/14/2017 03:36 PM »
I think it's TEA-TEB.  Spark igniters are external (?right?) and there's no evidence of one present.  There's also no illumination that would suggest sparks prior to ignition.  SpaceX is very comfortable with and experienced at using TEA-TEB.  The idea they would use it for the prototype engine seems very unsurprising to me as a result.

As far as the green flash in the middle of the previous fire, maybe some residue somehow?  That seems unlikely.  Or a leak.  That would be troubling, not really for the engine itself, but more for the test program.  So that's definitely a data point going the other direction.

I rather imagine that the spark ignitors they'll use will be a torch type one like this:

https://twitter.com/fineri/status/930355129454178306


Also I think the green in the raptor startup sequence is a camera artifact (chromatic abberation, or sensor artifacts) due to the fact that when the main chamber lights the video is massively overexposed as the camera frantically dials down the exposure in the next few frames.


Offline notsorandom

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Re: ITS Propulsion The evolution of the SpaceX Raptor engine
« Reply #705 on: 11/15/2017 05:10 AM »
Could the green be a very slight engine rich combustion?

Offline jpo234

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Re: ITS Propulsion The evolution of the SpaceX Raptor engine
« Reply #706 on: 11/15/2017 08:45 AM »
Could the green be a very slight engine rich combustion?

Most likely it's just a camera artifact from the sudden increase in brightness.
You want to be inspired by things. You want to wake up in the morning and think the future is going to be great. That's what being a spacefaring civilization is all about. It's about believing in the future and believing the future will be better than the past. And I can't think of anything more exciting than being out there among the stars.

Offline Semmel

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Re: ITS Propulsion The evolution of the SpaceX Raptor engine
« Reply #707 on: 11/15/2017 08:37 PM »
Could the green be a very slight engine rich combustion?

Most likely it's just a camera artifact from the sudden increase in brightness.

I think so too. I remember distinctly that Elon said in the 2016 presentation that Raptor has a little torch inside that is spark ignited which in turn ignites the main combustion cycle. Creating a prototype with hypergolics makes no sense since this is one of the core problems in engine development.

Online acsawdey

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Re: ITS Propulsion The evolution of the SpaceX Raptor engine
« Reply #708 on: 11/15/2017 10:22 PM »
Could the green be a very slight engine rich combustion?

Most likely it's just a camera artifact from the sudden increase in brightness.

I think so too. I remember distinctly that Elon said in the 2016 presentation that Raptor has a little torch inside that is spark ignited which in turn ignites the main combustion cycle. Creating a prototype with hypergolics makes no sense since this is one of the core problems in engine development.

Also, with his Mars ambitions, Elon needs Raptor to be able to be restarted many times without servicing or refilling TEA/TEB supplies. And, spark ignition of an oxygen/methane mixture is a pretty well understood problem at this point -- millions of stoves, furnaces, and water heaters in service doing it every day.

Offline cscott

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Re: ITS Propulsion The evolution of the SpaceX Raptor engine
« Reply #709 on: 11/16/2017 11:56 AM »
FWIW there are plenty of kerosene/oxygen refrigerators out there in the world as well, although they tend to use pilot lights, not spark (or TEA/TEB!) ignition.

Online abaddon

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Re: ITS Propulsion The evolution of the SpaceX Raptor engine
« Reply #710 on: 11/16/2017 04:18 PM »
To be clear, nobody thinks that TEA/TEB might be used for the production engine.  We know it will use spark igniters.

I've mostly come around to it not being TEA/TEB in the prototype either.

Offline Semmel

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Re: ITS Propulsion The evolution of the SpaceX Raptor engine
« Reply #711 on: 11/23/2017 07:25 AM »
Spinning the wheel a bit further (pun intended), how does the Raptor actually start? I mean, spark ignition or not, it needs to spin up its turbines. Following the ongoing discussion on the Merlin:

[...]
The LOX and RP-1 tanks are pre pressurized with helium. 
High pressure helium spins up the turbo pump.  LOX and RP-1 are ignited by TEA-TEB in the gas generator and  takes over from the helium.  The propellants meet in the combustion chamber and are also ignited by TEA-TEB.
[...]

But the Raptor doesnt have high pressure helium available. Its tanks are autogenous pressurization. So how do the turbine wheels of Raptor start? I do have ideas how it could be done but I dont want to wildly speculate. Does anyone has info on that?

Offline docmordrid

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Re: ITS Propulsion The evolution of the SpaceX Raptor engine
« Reply #712 on: 11/23/2017 09:16 AM »
They said it uses autogenous  pressurization, so use some of those gases.

« Last Edit: 11/23/2017 09:18 AM by docmordrid »
DM

Offline Semmel

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Re: ITS Propulsion The evolution of the SpaceX Raptor engine
« Reply #713 on: 11/23/2017 10:43 AM »
They said it uses autogenous  pressurization, so use some of those gases.

I am pretty sure the tank pressure provided by autogenous pressurization system is not enough to start the spin of the turbines. If that was the case, F9 would be able to do the same with LOX and RP1 but they use high pressure helium instead. Probably a lot of it. But I am not an expert and happy to be proven wrong.

Offline hopalong

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Re: ITS Propulsion The evolution of the SpaceX Raptor engine
« Reply #714 on: 11/23/2017 11:23 AM »
IMHO the CH4 and Oxygen gas would be fed into the turbine combustion chamber and lit. The resulting combustion gases will spin the turbine. There may be a few ticks involved in getting enough initial pressure in the CH4 and GO2 supply lines to the pump turbines, but I understand that there is a lot of dark arts in starting a full flow engine.  :)

Online livingjw

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Re: ITS Propulsion The evolution of the SpaceX Raptor engine
« Reply #715 on: 11/23/2017 01:06 PM »
Spinning the wheel a bit further (pun intended), how does the Raptor actually start? I mean, spark ignition or not, it needs to spin up its turbines. Following the ongoing discussion on the Merlin:

[...]
The LOX and RP-1 tanks are pre pressurized with helium. 
High pressure helium spins up the turbo pump.  LOX and RP-1 are ignited by TEA-TEB in the gas generator and  takes over from the helium.  The propellants meet in the combustion chamber and are also ignited by TEA-TEB.
[...]

But the Raptor doesnt have high pressure helium available. Its tanks are autogenous pressurization. So how do the turbine wheels of Raptor start? I do have ideas how it could be done but I dont want to wildly speculate. Does anyone has info on that?

They said it was spark ignited. The sparks probably ignite ignition torches which in turn ignites the pre-burners and the main chamber.  You can see the ignition leads on their CAD model.

This ignition approach would make all Raptors restartable assuming their propellants had enough head pressure.
Head pressure and an electrical power source is all that is required to start.

The start sequence is something like the following:
- crack valves and dribble in propellants to pre-chill the engine.
- open valves and propellants flow into their respective pre-burners.
- spark ignites stoichiometric mixture in torches.
- torches ignite pre-burners
- pre-burner exhaust spins turbines attached to propellant pumps. (one for methane, one for LOX)
- main chamber torch ignites gaseous propellants entering chamber.
- pumps start increasing pressure above head pressure and quickly climb to design pressure.

This requires detailed understanding of the combustion processes and the dynamics of the pumps, turbines and valves. It is a tightly choreographed dance.

John


Offline Semmel

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Re: ITS Propulsion The evolution of the SpaceX Raptor engine
« Reply #716 on: 11/23/2017 08:48 PM »
This ignition approach would make all Raptors restartable assuming their propellants had enough head pressure.
Head pressure and an electrical power source is all that is required to start.

The start sequence is something like the following:
- crack valves and dribble in propellants to pre-chill the engine.
- open valves and propellants flow into their respective pre-burners.
- spark ignites stoichiometric mixture in torches.
- torches ignite pre-burners
- pre-burner exhaust spins turbines attached to propellant pumps. (one for methane, one for LOX)
- main chamber torch ignites gaseous propellants entering chamber.
- pumps start increasing pressure above head pressure and quickly climb to design pressure.

This requires detailed understanding of the combustion processes and the dynamics of the pumps, turbines and valves. It is a tightly choreographed dance.

John

Thats exactly what I am interested in. So initially, the propellant flows through the not-jet-rotating pumps until it reaches the preburner, is than ignited. It therefore puts pressure onto the turbine which starts to turn. But at the same time, the preburner also puts pressure back up the pumps and into the tanks. Because the pumps are not yet rotating. They are about to start rotating but they dont do it yet. It looks to me like a hen and a egg problem. How can you start the turbines/pumps under these conditions? Are there valves in front of the preburner that quickly close once some propellant is in the preburners and push it out the turbine only to open a fraction of a second later to allow new fuel to reach the preburner and further turn the turbine? And now my thought process looks like a moebius strip...
« Last Edit: 11/23/2017 08:48 PM by Semmel »

Offline rakaydos

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Re: ITS Propulsion The evolution of the SpaceX Raptor engine
« Reply #717 on: Today at 12:04 AM »
This ignition approach would make all Raptors restartable assuming their propellants had enough head pressure.
Head pressure and an electrical power source is all that is required to start.

The start sequence is something like the following:
- crack valves and dribble in propellants to pre-chill the engine.
- open valves and propellants flow into their respective pre-burners.
- spark ignites stoichiometric mixture in torches.
- torches ignite pre-burners
- pre-burner exhaust spins turbines attached to propellant pumps. (one for methane, one for LOX)
- main chamber torch ignites gaseous propellants entering chamber.
- pumps start increasing pressure above head pressure and quickly climb to design pressure.

This requires detailed understanding of the combustion processes and the dynamics of the pumps, turbines and valves. It is a tightly choreographed dance.

John

Thats exactly what I am interested in. So initially, the propellant flows through the not-jet-rotating pumps until it reaches the preburner, is than ignited. It therefore puts pressure onto the turbine which starts to turn. But at the same time, the preburner also puts pressure back up the pumps and into the tanks. Because the pumps are not yet rotating. They are about to start rotating but they dont do it yet. It looks to me like a hen and a egg problem. How can you start the turbines/pumps under these conditions? Are there valves in front of the preburner that quickly close once some propellant is in the preburners and push it out the turbine only to open a fraction of a second later to allow new fuel to reach the preburner and further turn the turbine? And now my thought process looks like a moebius strip...
I would expect the combustion chamber and turbine would be wider than the pipe into  the combustion chamber and pump connected to the turbine, so the shock wave only applies a few square CM of the pressure wave back toward the tanks, but many more times the pressure foreward toward the combustion chamber.

Online livingjw

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Re: ITS Propulsion The evolution of the SpaceX Raptor engine
« Reply #718 on: Today at 04:10 AM »
Everything downstream of the pumps has a lower pressure. That's why the propellants flow. This is true as long as there is pressure in the tanks even if the pumps are not rotating.

John

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