Author Topic: SpaceX: Merlin 1D Updates and Discussion Thread 3  (Read 57991 times)

Online Coastal Ron

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 3
« Reply #180 on: 11/23/2017 01:22 AM »
The turbine is started with high pressure helium if I'm not mistaken.

Helium is used to pressurize the LOX tank, which then forces LOX into the turbo pump.

For anyone that has not seen it:

- YouTube
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Offline Jim

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 3
« Reply #181 on: 11/23/2017 03:08 AM »
Sorry for me ignorance, but I have a hard time understanding the ignition sequence of the Merlin 1D engine.
I have carefully read this article, and I really do miss pieces of the puzzle on this part:

Quote
To start the engine, LOX is flowed through the rocket injector into the chamber from the vehicle's tank, TEA-TEB is injected into the chamber to create ignition, then RP-1 (fancy kerosene) is flowed in from the vehicle tank to start burning. The flows are increased, thrust is made, and the rocket launches.

I have several questions about this:
1) How does the LOX come into the chamber if its turbopump is stopped ? With the tank pressure delivered by the COPVs ?
2) If the TEA-TEB burns into the (main?) chamber with LOX, how does that lead to a startup of the turbine ? As I understand the architecture of the engine, a combustion in the chamber has basically no way to accelerate the turbopumps.
3) How is the pre-burner ignited ?

In brief, what I first intuitively thought was that the hypergolic fuels were introduced into the preburner (or elsewhere) to start the turbines, then the turbopumps, then the engine. But as it is written that it is introduced into the chamber, and that this is the only way to start the engine (no cartridge to run the turbine), I'm lost.

Thanks

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.

There is no preburner since this is not a staged combustion engine.  There is only a has generator
« Last Edit: 11/23/2017 03:11 AM by Jim »

Offline S.Paulissen

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 3
« Reply #182 on: 11/23/2017 12:49 PM »
Thank you Jim. This is exactly how I understood it but didn't feel confident enough to say much without a lot of qualification.

The propellant tank pressurization is primarily to provide rigidity to the airframe and provide adequate inlet conditions at the turbopump so there is no cavitation.
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Offline Boost

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 3
« Reply #183 on: 12/07/2017 09:52 PM »
One more question that remains unclear to me: in the following video:


The gas generator exhaust is clearly (or darkly ;)) visible, but I have a hard time observing them in any of the SpaceX flights. Where are these GG nozzles located in the octaweb ?
« Last Edit: 12/07/2017 10:00 PM by Boost »

Offline Lars-J

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 3
« Reply #184 on: 12/07/2017 10:01 PM »
One more question that remains unclear to me: in the Merlin 1D qualification test vidéo, the gas generator exhaust is clearly (or darkly ;)) visible, but I have a hard time observing them in any of the SpaceX flights. Where are these GG nozzles located in the octaweb ?

The GG exhausts are on the inside of each engine - see image.  (before and after flight) The one for the center engine can be partially seen in the 2nd image.
« Last Edit: 12/07/2017 10:02 PM by Lars-J »

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 3
« Reply #185 on: 12/07/2017 10:01 PM »
The turbopump exhaust is in inside of the octaweb:
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Offline Boost

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 3
« Reply #186 on: 12/07/2017 10:02 PM »
Thank you. And where is the central one's ?

Offline Lars-J

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 3
« Reply #187 on: 12/07/2017 10:03 PM »
Thank you. And where is the central one's ?

Look at the 2nd image I posted, it is there. (partially obscured by the nozzle)

Offline Boost

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 3
« Reply #188 on: 12/07/2017 10:10 PM »
Yes indeed, it is visible. What's the purpose of the grids at the exit of the nozzles ?

Offline jpo234

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 3
« Reply #189 on: 12/07/2017 10:15 PM »
One more question that remains unclear to me: in the following video:


The gas generator exhaust is clearly (or darkly ;)) visible, but I have a hard time observing them in any of the SpaceX flights. Where are these GG nozzles located in the octaweb ?

I think it's visible during landings when only the center engine is active.
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Offline Lars-J

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 3
« Reply #190 on: 12/07/2017 10:21 PM »
Yes indeed, it is visible. What's the purpose of the grids at the exit of the nozzles ?

Presumably to prevent debris from entering and blocking the exhaust during re-entry and landing. (not many rockets fly backwards, so it is not necessary for those) ;) But there could be another reason.
« Last Edit: 12/07/2017 10:26 PM by Lars-J »

Offline John Alan

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 3
« Reply #191 on: 12/07/2017 11:31 PM »
If you watch an F9 launch, and fixate on the area in and around the nozzles...
From about T+ 0:50 to T+1:20 or so... on CRS-12 for example
The open area right under the GG exhausts back to the rocket nozzle faces...
You see random flames that dance and flicker in that area...
Mostly hidden by the nozzles... 
But seen as a dull orange fire ring above the white hot rocket plume...

I have come to think these flames are the carbon rich exhausts from the GG exhausts catching fire and burning.
The radiate heat from the hell storm below the nozzle faces catches the carbon dust smoke afire and away it goes.
Is it hurting anything?... Nah, I don't think so...  :)

Much later edit... added pic of above
« Last Edit: 12/08/2017 04:30 AM by John Alan »

Offline cambrianera

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 3
« Reply #192 on: 12/08/2017 07:42 PM »
Yes indeed, it is visible. What's the purpose of the grids at the exit of the nozzles ?

Metal wire grid can act as flame stopper, preventing ignition of the flow upstream.
This is the case of safety lamps for mines.
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