Real Fuel for Real Life!

[YNM]

Cold gas thrusters

[Kryten]

 Boeing's ALASA used a monoprop mixture of nitrous and ethylene. It ended up being cancelled because they basically couldn't get it to not explode in ground tests.

[DerekL1963]

2 hours ago, Kryten said:

 Boeing's ALASA used a monoprop mixture of nitrous and ethylene. It ended up being cancelled because they basically couldn't get it to not explode in ground tests.

The key here is "monoprop mixture", a more conventional bi-prop may or may not suffer the same problem.

[Laie]

On 7/28/2017 at 0:47 PM, Shadow Wolf56 said:

What are some ideas for rocket fuel in real life?

If you're just curios, I suggest you get a copy of Ignition! An informal History of Liquid Rocket Propellants by Jon Drury Clark. It's an interesting and often fun read, and will tell you a lot about all kinds of rocket propellants that have been tried, and why most have been given up.

Samples:

Quote

A monopropellant is a liquid which contains in itself both the fuel and the oxidizer [...]. On paper, the idea looks attractive. You have only one fluid to inject into the chamber, which simplifies your plumbing, your mixture ratio is built in and stays where you want it, you don't have to worry about building an injector which will mix the fuel and the oxidizer properly, and things are simpler all around. But! Any intimate mixture of a fuel and an oxidizer is a potential explosive, and a molecule with one reducing (fuel) end and one oxidizing end, separated by a pair of firmly crossed fingers, is an invitation to disaster.

Quote

But trying to burn [Kerosene] in a rocket motor with nitric acid was a harrowing experience. In the first place, the specifications being what they were, no two barrels of it were alike. (A jet engine doesn't care about the shape of the molecules it burns as long as they give up the right number of BTU's per pound, but a nitric acid rocket is fussier.) [...] Sometimes everything went well, but usually not. It was acid-gasoline all over again —a coughing, choking, screaming motor, that usually managed to reduce itself to fragments, and the engineers to frustrated blasphemy.

 

[DerekL1963]

21 minutes ago, Laie said:

If you're just curios, I suggest you get a copy of Ignition! An informal History of Liquid Rocket Propellants by Jon Drury Clark. It's an interesting and often fun read, and will tell you a lot about all kinds of rocket propellants that have been tried, and why most have been given up.

But keep in mind it's one guy's informal viewpoint and it's now four decades old...  Emphasis on the "informal" and "one guy" - take the second quote above, the Soviets managed to build a number of missiles based on that combination.  In particular, both a tactical missile and a SLBM.

[Kryten]

Given there've been thousands of scud combat launches, nitric acid/kerosene is quite possibly the most used liquid prop combination ever. It's either that or ethanol/lox from V-2 launches.

[Laie]

7 hours ago, DerekL1963 said:

But keep in mind it's one guy's informal viewpoint and it's now four decades old...  Emphasis on the "informal" and "one guy" - take the second quote above, the Soviets managed to build a number of missiles based on that combination.  In particular, both a tactical missile and a SLBM.

Hold on a second. It says "the specifications being what they were, no two barrels of it were alike". In your mind that seems to have become "the author believes that acid-kerosene cannot possibly work, ever". I cannot figure out how you got there.

[DerekL1963]

4 minutes ago, Laie said:

Hold on a second. It says "the specifications being what they were, no two barrels of it were alike". In your mind that seems to have become "the author believes that acid-kerosene cannot possibly work, ever". I cannot figure out how you got there.

Hold on a second yourself.  I can't figure out how you could reach such a conclusion yourself.  All I did was supplement your quote (which indicated that the the author found said engines to be problematic) with other information (which shows that they can be made to work).

[wumpus]

19 hours ago, Kryten said:

Given there've been thousands of scud combat launches, nitric acid/kerosene is quite possibly the most used liquid prop combination ever. It's either that or ethanol/lox from V-2 launches.

Given the rest of what is listed in Ignition!, I'm pretty sure that LOX is preferred to any form of nitric acid in rockets.  Since missiles are typically stored until needed, cryogenics simply are avoided and such evils as nitric acid are tolerated.  I have no idea if RP1 would work better with nitric acid than whatever they were trying at the time, nor what specification "kerosene" has in a scud.

While the V2 did use cryogenic LOX, as far as I know they were launched pretty much after construction (of course, plenty were captured.  Presumably they were still manufacturing them after the launch pads were captured).  LOX/Alcohol still has a higher Isp than nictric acid/kerosene, 

Of course, Redstone (LOX/Alcohol), Jupiter (LOX/RP1), and Atlas (LOX/RP1) missiles were all cryogenic.  They basically built with what the german team understood until development of SRBs advanced enough to replace cryogenics in american ICBMs.

[Shadow Wolf56]

So if I was to make a fuel out of LOX/Ethanol (Liquid Oxygen/Alcohol) What would the fuel mixture be?

[Xemina]

LOX or even, because the gas pressure, and why not, LN2.

[Streetwind]

On 8.8.2017 at 11:25 PM, Shadow Wolf56 said:

So if I was to make a fuel out of LOX/Ethanol (Liquid Oxygen/Alcohol) What would the fuel mixture be?

Not an easy answer. First, it depends on the quality of your alcohol. 100% ethanol is physically impossible to produce, since it is extremely hygroscopic (water-loving), but you could get 99%. However, no ethanol-fuelled rocket has ever used this (...successfully, anyway). Most of them - from the V2 to Copenhagen Suborbitals' test rockets - run on a 75% alcohol/25% water mixture, chiefly to keep combustion temperatures in check.

Next: do you want to run stoichiometric - in other words, do you want a one-to-one combustion, where you have exactly as much oxygen input as the given amount of fuel needs? Stoichiometric uses fuel most efficiently, but also burns the hottest, so again, it's a matter of how much heat your engine can handle.

Running hotter and converting fuel more efficiently improves your Isp, but that's not the only way to do so. Sometimes, running off the stoichiometric ratio actually improves your performance, because the exhaust is comprised of a different mixture of different combustion products. Lighter exhaust has a higher vacuum Isp, but performs less well inside an atmosphere. So, you additionally need to ask yourself what purpose your engine should fulfill.

I could go on.  

I recommend you look up Copenhagen Suborbitals and the data they make available for their engine tests. They do text different fuel/oxidizer ratios as well as chamber pressures, and record graphs of actual engine performance in those situations.

[wumpus]

3 hours ago, Streetwind said:

Not an easy answer. First, it depends on the quality of your alcohol. 100% ethanol is physically impossible to produce, since it is extremely hygroscopic (water-loving), but you could get 99%. However, no ethanol-fuelled rocket has ever used this (...successfully, anyway). Most of them - from the V2 to Copenhagen Suborbitals' test rockets - run on a 75% alcohol/25% water mixture, chiefly to keep combustion temperatures in check.

I understand that even 50% alcohol is fairly popular (and doesn't reduce Isp all that much.  There was a comment in Ignition! that similar products have "evaporation" issues, mainly into technicians*).  95%+ is unlikely to have any advantages over RP1 as the diluted alcohol has tremendous temperature advantages.  LH-LOX mixtures do a similar thing being fuel rich.  This  not only reduces exhaust temperatures down to levels that don't melt every conceivable substance (which is still cooled by pumping cryogenic fuel/oxidizer through it) but hydrogen is the ideal exhaust product, so having extra hydrogen heated passively by the other exhaust can still increase efficiency.

* In the US, it is typically vastly easier to source (or more accurately avoid paying high taxes on) ethyl alcohol with added bittering agents.  I'd suspect this is true for any country where distilled alcohol is taxed.  I'm guessing that chemical labs typically source their alcohol in pure form (for obvious reasons) and didn't realize the issue with the much larger buys needed for rocket testing.

[Shadow Wolf56]

I have been reading this extremely old book http://www.cientificosaficionados.com/libros/cohetes.pdf about liquid fuels because I am kinda interested about it, it says GOX and Gasoline can be used quite efficiently, but what place would GOX be readily available?

Edited August 11, 2017 by Shadow Wolf56

[Shadow Wolf56]

Hey I'm going to post weekly about building a little space program in this thread.

 

Edited August 13, 2017 by Shadow Wolf56

[sevenperforce]

On 8/11/2017 at 10:25 AM, Shadow Wolf56 said:

I have been reading this extremely old book http://www.cientificosaficionados.com/libros/cohetes.pdf about liquid fuels because I am kinda interested about it, it says GOX and Gasoline can be used quite efficiently, but what place would GOX be readily available?

Hospital supply.

[Xemina]

Well really anything, I mean, for example;

S1 RP-1 LOX

S2 LH2 LOX

S3 (RCS) N2H2

Edited August 16, 2017 by Xemina