Author Topic: SpaceX: Merlin 1D Updates and Discussion Thread 2  (Read 447167 times)

Offline aero

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #60 on: 02/20/2014 12:12 am »
yep - nothing there but light bouncing around.
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Offline malu5531

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #61 on: 02/24/2014 08:42 am »
I'm having a discussion with Aero to figure this Merlin 1D/1D+ model out.

It occurred to me that this particular document was not shared before, where I try to model Merlin 1D+ at thrust levels 30-100% in order to figure out constraints on throttling due to low exhaust pressure.

If anyone have some insights in modelling rocket engines, we would appreciate some feedback if there is something we've missed / misunderstood. My understanding of rocket engines is limited to the knowledge found here.

In particular I'm wondering; when an engine is throttled I have assumed the Mach number will stay constant, i.e., this number characterise a particular nozzle/throat/chamber design - and using this number one can calculate the exhaust pressure if given the chamber pressure (see spreadsheet for 90% throttle, for example).

Offline Proponent

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #62 on: 02/24/2014 10:25 am »
In particular I'm wondering; when an engine is throttled I have assumed the Mach number will stay constant, i.e., this number characterise a particular nozzle/throat/chamber design - and using this number one can calculate the exhaust pressure if given the chamber pressure (see spreadsheet for 90% throttle, for example).

That assumption isn't quite correct, because the Mach number will change as the ratio of specific heats changes, and that ratio, of course, changes with chamber pressure.

Offline MP99

Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #63 on: 02/24/2014 06:26 pm »
In particular I'm wondering; when an engine is throttled I have assumed the Mach number will stay constant, i.e., this number characterise a particular nozzle/throat/chamber design - and using this number one can calculate the exhaust pressure if given the chamber pressure (see spreadsheet for 90% throttle, for example).

That assumption isn't quite correct, because the Mach number will change as the ratio of specific heats changes, and that ratio, of course, changes with chamber pressure.

It's my understanding that flow through the throat is always exactly sonic, IE exactly Mach 1.0.

Mass flow (density of the exhaust through the throat) is presumably determined by chamber pressure.

I presume downstream pressure is related to throat pressure and expansion ratio (assuming no evolution of the molecular makeup during transit of the nozzle). [Is this what's referred to as "frozen flow"?]

Edit: and I further presume that exhaust velocity is related to pressure at the throat?

Cheers, Martin
« Last Edit: 02/24/2014 06:28 pm by MP99 »

Offline Proponent

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #64 on: 02/25/2014 03:12 pm »
It's true that flow at the throat is sonic.  But, of course, the absolute flow speed at the throat depends on throat temperature, which in turn depends on chamber temperature.

I haven't thought the problem through, but I think the approach would be to establish the area ratio of the nozzle, presumably by the above-discussed kremlinology on the available Merlin data.  Then, run a thermochemical code (e.g., RPA) for a variety of chamber pressures.  That will give a chamber temperature, molecular weight, and ratio of specific heats for each pressure.  Using the specific-heat ratio and the exit-to-throat area ratio, one can numerically determine the chamber-to-exit pressure ratio, and hence the exit pressure (going the other way, from pressure ratio to area ratio is easier: just plug the numbers into the formula, but to get an area ratio you have to solve the same equation numerically).  Once you've got the pressure ratio, it's easy to solve for all of the other quantities, including thrust and mass-flow rate.  Then you can tabulate these for various chamber pressures to establish the relationship between mass-flow rate and thrust, which I presume is ultimately what is of interest.

Offline Hobbes-22

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #65 on: 02/25/2014 03:40 pm »
kremlinology on the available Merlin data

 ;D You know, that's exactly how I felt trying to gather data for my Falcon 9 scale model.

Offline baldusi

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #66 on: 02/25/2014 03:54 pm »
Tom Muller had stated an expansion ratio of 16 for the 1D (14.5 for tge 1C). That might help.

Offline aero

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #67 on: 03/04/2014 03:50 am »
Has anyone else considered that SpaceX may modify the Merlin D in order to achieve Elon's projected 15% increase in thrust (12 to 17 % depending on how you figure)?

I have been wondering if maybe, just maybe they might convert the Merlin D engine fueling system to a staged combustion cycle. That would give them the performance and it is not totally unreasonable now that they are gaining experience in staged combustion by working on the Raptor engine. Building a smaller staged combustion engine than the Raptor makes some sense, and building one for LOX/RP-1 seems logical since they are familiar with and have available everything that goes into building and testing LOX/RP-1 engines.

What do you think about a staged combustion Merlin D+?

Would it be possible/practical/acceptable to test a SC Merlin D + on the Falcon 9 while leaving 8 of the engines as is?
« Last Edit: 03/04/2014 04:12 am by aero »
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Offline Lars_J

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #68 on: 03/04/2014 04:16 am »
A "staged combustion Merlin" would be a whole new engine. Not much would be in common.

Offline guckyfan

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #69 on: 03/04/2014 04:34 am »
I don't think a staged combustion RP-1 engine is likely at all. If they want to build a smaller SC-engine they would build a methane engine. It would make for a better upper stage engine of the Falcon 9 and gives experience for building the big one. I thought for a while they might do that but even that seems unlikely now.


Offline Wigles

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #70 on: 03/04/2014 06:12 am »
I wouldn't discount further changes to the 1D, possibly even a 1E model, due to the length of time they expect to continue operating the Falcon9 and F9R.

 But I doubt they would bother with an almost full redesign to include SC.

Offline aero

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #71 on: 03/04/2014 02:42 pm »
A "staged combustion Merlin" would be a whole new engine. Not much would be in common.

Well, the rocket would be in common. Seems like a lot of commonality to me.

I know that the prop pumps are a very expensive part of the engine and they would need to change the turbine/pumps and routing, but would they need to change the feeds and engine attachments, nozzle? Would an SC cycle engine even fit into the space available?

I think an important consideration is their long term plan for retaining the Falcon 9 in their operational inventory which I don't know.


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Offline cuddihy

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #72 on: 03/04/2014 03:50 pm »
I believe an RP1 and Methalox SC engine are entirely different beasts- the RP-1 has to run ox-rich preburner as does the RD-180 due to coking whereas methalox can run fuel-rich preburner due to simpler metallurgy &turbine construction. Either way they both operate at higher chamber pressures, have radically different piping and turbine requirements. Basically it'd be like re-constructing a Mustang to run on batteries--can be done, but it would be clunky& heavier than just starting fresh.

All that said, I'm convinced SpaceX is likely to first design a "Merlin sized" SC Methalox vacuum engine for upperstage use prior to doing booster Raptors...but now thats drifting OT.

Offline baldusi

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #73 on: 03/04/2014 03:53 pm »
A "staged combustion Merlin" would be a whole new engine. Not much would be in common.

Well, the rocket would be in common. Seems like a lot of commonality to me.

I know that the prop pumps are a very expensive part of the engine and they would need to change the turbine/pumps and routing, but would they need to change the feeds and engine attachments, nozzle? Would an SC cycle engine even fit into the space available?

I think an important consideration is their long term plan for retaining the Falcon 9 in their operational inventory which I don't know.
Would be two completely different engines with just (some) construction methods in common. For starters, they would have to use an oxygen rich preburner. So, the would go from burning 3% of the RP-1 to 100% of the Oxigen, which means the preburner will have to process 90 times more mass, in a highly corrosive oxygen environment. Then, the turbine will have to pass 90 times more mass, so it will have a lot more power. Since the pump has more power, but have a lot more pressure losses, the pump outlet pressure should be 2 to 3 times as high. And then the injector will have to mix gas (O2) with liquid (RP-1), instead of both liquid. And the main combustion chamber would work at least at 70% more pressure. Not to mention that they wouldn't have the GG exhaust.
So, I don't believe they could use anything save a few valves and may be some electronics. You can't get more different engines made by the same people with the same fuel.

Offline Lars_J

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #74 on: 03/04/2014 04:02 pm »
A "staged combustion Merlin" would be a whole new engine. Not much would be in common.

Well, the rocket would be in common. Seems like a lot of commonality to me.

But this is a *Merlin* thread. The rocket is called Falcon. The Falcon family could in theory have all different engines in a future version, but they wouldn't have to be called Merlin just because they are attached to a Falcon rocket. Does that make sense?

Offline MP99

Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #75 on: 03/04/2014 05:50 pm »
Has anyone else considered that SpaceX may modify the Merlin D in order to achieve Elon's projected 15% increase in thrust (12 to 17 % depending on how you figure)?

I have been wondering if maybe, just maybe they might convert the Merlin D engine fueling system to a staged combustion cycle. That would give them the performance and it is not totally unreasonable now that they are gaining experience in staged combustion by working on the Raptor engine. Building a smaller staged combustion engine than the Raptor makes some sense, and building one for LOX/RP-1 seems logical since they are familiar with and have available everything that goes into building and testing LOX/RP-1 engines.

What do you think about a staged combustion Merlin D+?

Would it be possible/practical/acceptable to test a SC Merlin D + on the Falcon 9 while leaving 8 of the engines as is?

I understand that would have to be ox-rich (ORSC) with RP-1, and at higher temps than you get away with on with methane.

No, don't see it.

Makes much more sense that they've left some margin on the table for now, and even then perhaps that 112% is for expendable flights only.

Cheers, Martin

Online TrevorMonty

Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #76 on: 03/04/2014 06:37 pm »
They may yet produce a M1E version, being engineering driven company I'd be surprised if they didn't tweek the M1D. Reducing the manufacturing cost of engine is one reason to make a new version, 3D printing may add significant cost savings if they are not already using it.

Offline DJPledger

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #77 on: 03/04/2014 07:18 pm »
They may yet produce a M1E version, being engineering driven company I'd be surprised if they didn't tweek the M1D. Reducing the manufacturing cost of engine is one reason to make a new version, 3D printing may add significant cost savings if they are not already using it.
Tom Mueller said a couple of years ago that there won't be a M1E. However the M1D is supposed to get a thrust upgrade to 165klbf at SL which has been discussed widely. SpaceX could have changed their mind over a possible M1E but I think it is still unlikely since SpaceX are moving on to their next gen. engine.

Is the TC of the production M1D additively manufactured? The TC of M1D has a matt finish which looks like the finish on the additively manufactured SD TC and the nozzle of M1D is shiny. The different finishes of the M1D TC and nozzle indicate different manufacturing processes being used for the TC and nozzle.

Offline Mader Levap

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #78 on: 03/04/2014 11:35 pm »
A "staged combustion Merlin" would be a whole new engine. Not much would be in common.
Well, the rocket would be in common. Seems like a lot of commonality to me.
Nonsensical argument. We are talking about comparing engines alone - Merlin 1D and mythical Merlin 1SC - and about commonality between them.
What rocket is attached to these engines is another matter, unrelated to comparison between engines.

So yes, forget about that. No staged combustion Merlin will happen.
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Offline aero

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Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
« Reply #79 on: 03/13/2014 07:21 pm »
While looking for Merlin data I came across this interesting little chalk talk by Tom Mueller on the Merlin 1C. Have your note pad ready, he gives numbers for the C model. I wonder how much they carry over to the D?

http://www.livescribe.com/cgi-bin/WebObjects/LDApp.woa/wa/MLSOverviewPage?sid=n7SMWV6PdG7r

The article where I found the link is here:

http://blog.linuxacademy.com/space/under-the-hood-with-the-spacex-merlin-engine/

JMO but I expect the numbers carry over reasonably well to the D model, better than the numbers that we don't have on the Merlin D.
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