Quote from: baldusi on 10/06/2011 08:59 pmQuote from: cambrianera on 10/06/2011 08:38 pmYou can't gain so much ISP switching to LCH4You 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 160Glushko 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!
Quote from: cambrianera on 10/06/2011 08:38 pmYou can't gain so much ISP switching to LCH4You 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.
You can't gain so much ISP switching to LCH4
Engine: 129 kg (284 lb). Chamber Pressure: 118.00 bar. Area Ratio: 352. Thrust to Weight Ratio: 15.5. Oxidizer to Fuel Ratio: 3.69.
Which seems in line with the RG-1 version. Unless you can produce some more credible documentation, I'll go with 355 for the RD-160 expansion. In particular, I couldn't even find a reference in the Energomash Russian page.
Elon's remarks about a light hydrocarbon fuel which is mostly methane sounds a lot like LNG to me. I was looking over some of the physical properties of LNG versus 100% methane and in terms of density and boiling point they are very similar. I would imagine that there would be a slight ISP reduction by using LNG instead of methane. I am scratching my head a little over why he said it that way instead of just saying methane.
Given Musk's comment on an 80 percent methane fuel the other 20 percent could be hydrogen meaning Spacex is working on a Hythane fueled engine, and Hythane should improve the combustion efficiency of a Methane powered pintel injection system much like it improves the amount of fuel combusted in a cylinder. Perhaps enough to reach and ISP of 400. Some blenders have gone so far as to produce tri-mix fuels consisting of hydrogen, methane and gasoline so there certainly could be an opportunity to produce a fuel superior to either RP-1 or hydrogen.
Hmmmm, I was plain wrong.Doing some search I found this patent:http://patents.com/us-7547385.htmlThey say"There is no significant solubility of hydrogen in liquid methane."Well, I'm curious what really means"a very high efficiency light hydrocarbon that uses predominantly methane"
I think the T/W objections from last time this was discussed still apply.To the best of my knowledge, both staged combustion and methane will reduce T/W, making it a fairly iffy design decision using SpaceX's usual preferences.
If their presence is accounted for, other contaminants are removed and the mixture is uniform and doesn't vary
why are ethane butane, propane, hydrogen etc are not acceptable in rocket grade mixture? they are all rocket fuels. If their presence is accounted for, other contaminants are removed and the mixture is uniform and doesn't vary why would you go to the extra trouble of refining it to almost 100% methane?
that "can be refined to near 100%" is what worries me. Look at this page I found, that's super expensive. If you search the site for even higher grade methane, it become even more ridiculous. (700$ for a 14L container).http://www.sigmaaldrich.com/catalog/ProductDetail.do?lang=en&N4=22562|SUPELCO&N5=SEARCH_CONCAT_PNO|BRAND_KEY&F=SPECI'm hoping they can design an engine that can run with "regular" LNG while being unaffected by the associated impurities.
This is what I get with reasonable assumptions on combustion chemistry. A 100 lbf engine with an expansion ratio of 400 is pretty darn big (granted, much lower chamber pressure, but still). An epsilon=3000 engine just isn't worth the increase.
To the best of my knowledge, both staged combustion and methane will reduce T/W, making it a fairly iffy design decision using SpaceX's usual preferences.The T/W of Merlin 1D makes it to the best of my knowledge the best liquid fueled engine around. The Russians can't match it, it would be even harder using methane, and SpaceX probably can't match the Russians at SC.
Perfect, intersects at about 365 in 29, and goes to 385 in 240 expansion.So, I redid the numbers with isp of 355 for the first stage version, and 380 for the second stage version.
Quote from: baldusi on 10/07/2011 03:37 pmPerfect, intersects at about 365 in 29, and goes to 385 in 240 expansion.So, I redid the numbers with isp of 355 for the first stage version, and 380 for the second stage version.Very nice. And I agree that an all-CH4-blend vehicle would be very much in SpaceX's usual modus of operations.Could you try running the same numbers for Falcon Heavy? Eyeballing it, it should be around 65-70 tonnes...