Author Topic: New methane SC engine.  (Read 324619 times)

Offline baldusi

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New methane SC engine.
« on: 10/06/2011 04:45 PM »
Considering that:
* When SpaceX President talked in the FH presentation, she stated that the Raptor Engine was a back burner project with something like just four people working on it.
* Elon, when doing his AIAA presentation, mentioned a "super efficient staged combustion methane engine".
* When Space X responded to an Air Force RFP, who where asking for a 300klbf to 500klb, 300s SL isp, reusable, RP-1/LOX engines, they specifically asked if they could submit a methane engine that they were working on "for other customer".
* When he answered questions in the Reddit about the future fuels for space, he specifically talked about "light hydrocarbons, like methane".
So, all things here, point to a staged combustion, reusable, methane engine.
This 2005 paper by the NPO Energomash, shows an evolution of the RD-191 to a fuel rich, staged combustion methane engine, that did:
PropellantRG-1/LOXCH4/LOXCH4/LOX
SchemeOxidizer-rich SCOxidizer-rich SC
fuel nozzle cooling
Fuel-rich SC
fuel nozzle cooling
Mixture ratio2.753.53.5
Diameter of a throat, mm262,4262,4262,4
Diameter of the nozzle exit, mm143014301430
Sea Level thrust, MN1.9221.9221.971
Vacuum thrust, MN2.0852.0852.136
Specific impulse SL, sec311324332
Specific impulse in vacuum, sec337.5356,9360
% of fuel consumption for chamber cooling1002727
Pressure of gas in the preburner, MPa52.76047.4646.68
Temperature of gas in preberner, C264.9210.9202.9
Pressure ratio on the turbine2.051.211.95

The more important numbers there are the isp. NPO Energomash has demonstrated that fuel rich methane can do 330s SL and 360 vacuum, for a SL optimized engine. So, if doing a big nozzle allows you to have an extra 40s of isp (at least that's what SpaceX claimed for the Merlin 1C), that could give you close to 400s for a vacuum version.
Why is this important? Because with methane, at this levels of efficiency, you could have a single engine and 330s SL, and 360s vac for the first stage, and 400s in the upper stage.

So, I did a small simulation with Shillings'
CaseAll RP-1RP-1+H2All CH4
First Stage-FuelRP-1RP-1CH4
First Stage-Fuel Fraction (%)96.6%96.6%95%
First Stage-Dry Mass (kg)12,24512,24518,007
First Stage-Fuel Mass (kg)347,899347,899342,137
First Stage-Thrust (kN)5 6005 6005 600
First Stage-ISP (vacuum sec)310310360
Upper Stage-FuelRP-1H2CH4
Upper Stage-Fuel Fraction (%)92%85%88%
Upper Stage-Dry Mass (kg)3,8427,2035,762
Upper Stage-Fuel Mass (kg)44,17840,81642,257
Upper Stage-Thrust (kN)667667667
Upper Stage-ISP (vacuum sec)350470400
Payload to LEO13,51917,17218,188
Payload to GTO4,5056,2856,598
Payload to TLI2,9394,2514,505
Fairing Weight: 1000kg
Fairing Sep: 200s
Launch Site: Cape Canaveral
LEO: 200km x 28d
GTO: 35786km x 185km x 28d
TLI: C3=-1.8 (185km x 28d)

And what I got was that an all methane rocket would be superior to an all RP-1 AND RP-1/H2, for the same wet weight. Since there's a lot of margin of error, and my numbers were totally pulled out of thin air, you should take this with a grain of salt.
But the interesting part is that, at those efficiencies, an all methane solution might give you the performance of a mixed RP-1/H2 rocket, with just a single engine, one fuel, and only one tank type (currently LOX is cryogenic while RP-1 isn't). And you have a lot less coking problems, so it might help for reusability. What's more, with some technology added you could make it space storable.
Overall, my analysis from all this development is that they are working towards an all methane future.
Then, I did other calculation. From the afore mentioned RFP, SpaceX talked about the "other customer". I'm sure they couldn't know that the SLS boosters would be competed. But, if their intention was to develop an AJ-500 competitor, and they might have been thinking about the SLS boosters.
From what oldAtlas_Eguy said in this thread, I started thinking. If they have something in the 300klbf to 500klbf, they could build an SLS booster with 4 to 6 engines, since the Thrust limit of the SLS booster attachment point appear to be 2mlbf. The other relevant limitation is that they have to fit within the pad's flame trench, and the ML attachment points (designed for the original solids).
This means that whatever they do, they have to fit it within a maximum width of 4m. A 2 x 3 engine arrangement would seem to fit, and allow 2m per engine (this should account for nozzle attitude spacing and such). If I take the area of the 2m available, and the 1.25m of the Merlin 1, and multiply by the Merlin 1D's 140klbf (SL), I arrive at a 360klbf (SL) engine should be possible in the 2m available. So, a 333klbf (SL) engine should fit within said envelope. And also fit the requirement of the Air Force's request.
And if it could be rated from 333 to 400, they could make a Falcon X like rocket with 9 of those.
All this wild speculation gives me the idea that SpaceX has two possible methane engines.
1) A straight 120~150klbf straight Merlin 1 replacement.
2) A bigger 333~425klbf that they will try to get paid by the SLS contract.
They might try for NASA to pay for the Grashopper RLV, too. Which would make a very interesting offering, overall. If I were they, I would ask to be paid to "demonstrate" a big methane engine, and offer the Returnable as an option, that SpaceX will pay to develop. So NASA can invest in the "low" risk engine, while getting the change of having a truly Reusable Booster. What's more importantly, SpaceX, if it got that contract (again, wild speculation), would be getting, basically, a Falcon X development for free.

Edit: Attached the paper due to deletion from the URL.
« Last Edit: 03/15/2014 01:07 AM by baldusi »

Offline Jim

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Re: New methane SC engine.
« Reply #1 on: 10/06/2011 04:54 PM »
NASA has no need to pay for the Grashopper RLV.

Offline starsilk

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Re: New methane SC engine.
« Reply #2 on: 10/06/2011 05:02 PM »
could you add an 'all H2' set of numbers to the list? same assumptions, so equal sized grain of salt..

Offline baldusi

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Re: New methane SC engine.
« Reply #3 on: 10/06/2011 05:11 PM »
NASA has no need to pay for the Grashopper RLV.
I'm sorry I didn't made myself clear. I said they might try. But what I expected them to do is to ask to get payed to demonstrated the methane engine. And offer to demonstrate the Grashopper technology as an option for a Reusable evolution. But it would improve their standing since they would be putting "skin in the game" and developing a "disruptive" technology. As usual, pure economist speculation.

Offline TrueBlueWitt

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Re: New methane SC engine.
« Reply #4 on: 10/06/2011 05:52 PM »
Would one of these engines be suitable to getting a manned vehicle off the mars surface and back to Orbit?  If you're doing in-situ Methane/Lox production of course.   Elon's far reaching goals would seemingly be better served by al Methane over combinations of other fuels.

Offline baldusi

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Re: New methane SC engine.
« Reply #5 on: 10/06/2011 06:00 PM »
There's that, too. Mars ISRU.
And another thing, that maybe I didn't made clear. Only the Russians have develop a metallurgy able to make Oxygen Rich Stage Combustion. Both Rocketdyne and Aerojet, due to their RD-180 and NK-33 contracts have access to this technology. But, as far as I'm aware, SpaceX isn't. The beauty of methane, according to the Energomash paper, is that fuel rich is more efficient. And you have lower pressure losses if you use it as the chamber cooling liquid. So, apparently, SpaceX wouldn't need to develop any significant advancement in metallurgy to use fuel rich combustion if using methane. I guess that's the key of the analysis.

Offline Robotbeat

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Re: New methane SC engine.
« Reply #6 on: 10/06/2011 07:01 PM »
There's that, too. Mars ISRU.
And another thing, that maybe I didn't made clear. Only the Russians have develop a metallurgy able to make Oxygen Rich Stage Combustion. Both Rocketdyne and Aerojet, due to their RD-180 and NK-33 contracts have access to this technology. But, as far as I'm aware, SpaceX isn't. The beauty of methane, according to the Energomash paper, is that fuel rich is more efficient. And you have lower pressure losses if you use it as the chamber cooling liquid. So, apparently, SpaceX wouldn't need to develop any significant advancement in metallurgy to use fuel rich combustion if using methane. I guess that's the key of the analysis.
SpaceX does have access to staged combustion tech (they bought access to a US research engine using staged combustion), not sure if it's oxygen-rich, though.
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Offline notsorandom

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Re: New methane SC engine.
« Reply #7 on: 10/06/2011 07:09 PM »
There's that, too. Mars ISRU.
And another thing, that maybe I didn't made clear. Only the Russians have develop a metallurgy able to make Oxygen Rich Stage Combustion. Both Rocketdyne and Aerojet, due to their RD-180 and NK-33 contracts have access to this technology. But, as far as I'm aware, SpaceX isn't. The beauty of methane, according to the Energomash paper, is that fuel rich is more efficient. And you have lower pressure losses if you use it as the chamber cooling liquid. So, apparently, SpaceX wouldn't need to develop any significant advancement in metallurgy to use fuel rich combustion if using methane. I guess that's the key of the analysis.
SpaceX does have access to staged combustion tech (they bought access to a US research engine using staged combustion), not sure if it's oxygen-rich, though.
The RS-84 is oxygen-rich if thats the engine you are talking about.

Offline Robotbeat

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Re: New methane SC engine.
« Reply #8 on: 10/06/2011 07:12 PM »
There's that, too. Mars ISRU.
And another thing, that maybe I didn't made clear. Only the Russians have develop a metallurgy able to make Oxygen Rich Stage Combustion. Both Rocketdyne and Aerojet, due to their RD-180 and NK-33 contracts have access to this technology. But, as far as I'm aware, SpaceX isn't. The beauty of methane, according to the Energomash paper, is that fuel rich is more efficient. And you have lower pressure losses if you use it as the chamber cooling liquid. So, apparently, SpaceX wouldn't need to develop any significant advancement in metallurgy to use fuel rich combustion if using methane. I guess that's the key of the analysis.
SpaceX does have access to staged combustion tech (they bought access to a US research engine using staged combustion), not sure if it's oxygen-rich, though.
The RS-84 is oxygen-rich if thats the engine you are talking about.
Yeah, that's it. I think SpaceX has access to that engine's design.

Not saying they'll do anything with it.
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Offline baldusi

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Re: New methane SC engine.
« Reply #9 on: 10/06/2011 07:31 PM »
...
SpaceX does have access to staged combustion tech (they bought access to a US research engine using staged combustion), not sure if it's oxygen-rich, though.
The RS-84 is oxygen-rich if thats the engine you are talking about.
Yeah, that's it. I think SpaceX has access to that engine's design.

Not saying they'll do anything with it.
I've seen that said, but never any actual document or company statement regarding those rights. I've also seen the TR-107 quoted. Does anyone have a source for that?
Going back to the methane engine, what's the speculation of the more knowledgeable?

could you add an 'all H2' set of numbers to the list? same assumptions, so equal sized grain of salt..
The big issue is the mass fraction of the first stage. Methane requires 28% extra volume than RP-1. But you can use common bulkhead tanks, and the same tank insulation for both LOX and LCH4. The LH2/LOX combination requires three times more volume. And the LH2 required insulation is significantly more than LOX's, since it's 70C hotter (40K vs 90K). What I'm afraid of is to make a ridiculous assumption of mass fraction.
The other fact, is that if you look at the weights of those rockets, you'll see that all should fit within current F9 tooling (3.65m diameter). But the methane version is kind of pushing it. I guess it would be something like 70m tall (like the Falcon Heavy). If you keep the OD, the hydrogen version should be above 100m. And it would be something like 30 times taller than wide. I just don't see it viable with current tooling.
« Last Edit: 10/06/2011 07:31 PM by baldusi »

Offline Kaputnik

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Re: New methane SC engine.
« Reply #10 on: 10/06/2011 07:38 PM »
Would one of these engines be suitable to getting a manned vehicle off the mars surface and back to Orbit?  If you're doing in-situ Methane/Lox production of course.   Elon's far reaching goals would seemingly be better served by al Methane over combinations of other fuels.

Would be rather over-sized for any near-term sort of Mars vehicle. Unless you made a CH4 version of Kestrel.

Not sure I'm sold on the 400s claim for vac isp- don't believe I've seen such a high number before.
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Offline baldusi

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Re: New methane SC engine.
« Reply #11 on: 10/06/2011 07:50 PM »
Not sure I'm sold on the 400s claim for vac isp- don't believe I've seen such a high number before.
The true question is, do you believe the 360s vac for an RD-191 chamber? If so, how much could you add with an extension bell?

Offline strangequark

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Re: New methane SC engine.
« Reply #12 on: 10/06/2011 08:00 PM »

Would be rather over-sized for any near-term sort of Mars vehicle. Unless you made a CH4 version of Kestrel.

Not sure I'm sold on the 400s claim for vac isp- don't believe I've seen such a high number before.

You shouldn't be. Zubrin's 380s was overzealous. 400s would need an expansion ratio over 1000.

Offline cambrianera

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Re: New methane SC engine.
« Reply #13 on: 10/06/2011 08:19 PM »
From Encyclopedia Astronautica

"RD 160
Glushko Lox/LCH4 rocket engine. 19.6 kN. Upper stage. Developed 1993-1996. Isp=380s. Methane version of lox / kerosene upper stage engine RD-161. Gimbaling +/- 6 degree in two planes.

In 1996 the RD-161 prototype had been completed, development of a methane version was estimated to take four years. Nozzle expansion ratio is 120/0.05=2400.

Application: Upper stage."

This is one of higher ISP I've seen for LCH4.

400 seems too much.
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Offline baldusi

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Re: New methane SC engine.
« Reply #14 on: 10/06/2011 08:25 PM »

Would be rather over-sized for any near-term sort of Mars vehicle. Unless you made a CH4 version of Kestrel.

Not sure I'm sold on the 400s claim for vac isp- don't believe I've seen such a high number before.

You shouldn't be. Zubrin's 380s was overzealous. 400s would need an expansion ratio over 1000.

In the Energomash paper the expansion ratio of the RD-191 is 29 (is area/area, like (1430/262.4), right?). Let's not forget that this thing has something like 262Bar of chamber pressure. So the expansion ratio is normally very high.
The Merlin 1C has an expansion ratio of 14.5, and the vacuum has an expansion of 117. If we scaled the 29.6 of the RD-191, that would mean an expansion ratio of 240 for the vacuum version. How much extra isp would it get, if the "stock" vacuum isp was 360?

Offline cambrianera

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Re: New methane SC engine.
« Reply #15 on: 10/06/2011 08:38 PM »
Again from Encyclopedia Astronautica.

"RD 161 2
Glushko Lox/Kerosene rocket engine. 19.9 kN. Design concept 1990's. Proposed for use on Soyuz M-3. Version with uncooled nozzle extension. Engine Cycle: closed gas generator. Feed Method: turbopump. Isp=365s.

Engine: 141 kg (310 lb). Chamber Pressure: 117.70 bar. Area Ratio: 370.6. Thrust to Weight Ratio: 14.39. Oxidizer to Fuel Ratio: 2.6.

Status: Design concept 1990's.
Unfuelled mass: 141 kg (310 lb).
Height: 2.21 m (7.25 ft).
Diameter: 1.02 m (3.34 ft).
Thrust: 19.90 kN (4,474 lbf).
Specific impulse: 365 s.
Burn time: 900 s."

This is the LOX/RP1 version of RD 160.

You can't gain so much ISP switching to LCH4
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Offline baldusi

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Re: New methane SC engine.
« Reply #16 on: 10/06/2011 08:59 PM »
You can't gain so much ISP switching to LCH4
You are not reading what I'm writing. The 360 vacuum is for fuel rich methane variation of an RD-191. The switch is not from going to methane from RG-1. The Switch is from an expansion of 29.6 to 240.
BTW, RD-160/1 both had expansion ratios of 355. I'm not guessing the switch from RP-1 to methane, I'm talking about the change in expansion ratio and how much can it add.

Offline strangequark

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Re: New methane SC engine.
« Reply #17 on: 10/06/2011 09:14 PM »

In the Energomash paper the expansion ratio of the RD-191 is 29 (is area/area, like (1430/262.4), right?). Let's not forget that this thing has something like 262Bar of chamber pressure. So the expansion ratio is normally very high.
The Merlin 1C has an expansion ratio of 14.5, and the vacuum has an expansion of 117. If we scaled the 29.6 of the RD-191, that would mean an expansion ratio of 240 for the vacuum version. How much extra isp would it get, if the "stock" vacuum isp was 360?


I'd have to run the numbers, but the thing is that your thrust coefficient (which is what you increase with higher expansion ratio) flattens out asymptotically. 400s is just way too high for CH4. I can post some plots later tonight maybe.

Offline baldusi

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Re: New methane SC engine.
« Reply #18 on: 10/06/2011 09:32 PM »

In the Energomash paper the expansion ratio of the RD-191 is 29 (is area/area, like (1430/262.4), right?). Let's not forget that this thing has something like 262Bar of chamber pressure. So the expansion ratio is normally very high.
The Merlin 1C has an expansion ratio of 14.5, and the vacuum has an expansion of 117. If we scaled the 29.6 of the RD-191, that would mean an expansion ratio of 240 for the vacuum version. How much extra isp would it get, if the "stock" vacuum isp was 360?


I'd have to run the numbers, but the thing is that your thrust coefficient (which is what you increase with higher expansion ratio) flattens out asymptotically. 400s is just way too high for CH4. I can post some plots later tonight maybe.
Which was exactly the sort of answer that I was looking for. If you see how I derived my numbers, I supposed that if the Merlin 1C gained 40s of is by increasing it's expansion from 14.5 to 117, then I supposed doing the same 8 times expansion to whatever the Methane engine did, it would get those same extra 40 seconds. Now, if isp converges exponentially to the infinite case, my question is if the fact that you already need high "stock" expansion due to the huge chamber pressures, mean that you gain exponentially (or inverse power law) less isp for a alpha multiplication of the expansion ratio. If this would be the case, the higher the chamber pressure for a given thrust, the closer the gap of isp from SL a SL optimal nozzle to vacuum optimized one.
It seemed counter intuitive to me.

Offline cambrianera

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Re: New methane SC engine.
« Reply #19 on: 10/06/2011 10:22 PM »
You can't gain so much ISP switching to LCH4
You are not reading what I'm writing. The 360 vacuum is for fuel rich methane variation of an RD-191. The switch is not from going to methane from RG-1. The Switch is from an expansion of 29.6 to 240.
BTW, RD-160/1 both had expansion ratios of 355. I'm not guessing the switch from RP-1 to methane, I'm talking about the change in expansion ratio and how much can it add.

From my earlier post:
"RD 160
Glushko Lox/LCH4 rocket engine. 19.6 kN. Upper stage. Developed 1993-1996. Isp=380s. Methane version of lox / kerosene upper stage engine RD-161. Gimbaling +/- 6 degree in two planes.

In 1996 the RD-161 prototype had been completed, development of a methane version was estimated to take four years. Nozzle expansion ratio is 120/0.05=2400."

Expansion ratio=2400!!!!
Seems I'm not the only one not reading!
Oh to be young again. . .

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