ap0r

KSP inspired me to design a liquid-fueled rocket engine

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Yes, it's designed already. This was just a sketch to show the new geometry (hence the flat plate at the end). An update may take a few more days to come along because real life is kinda of in the way. But I wanted to show that because it looked way cooler than the original one. It's just that it takes a lot of time to convert from my design notes to something that flows along, includes explanations for stuff I barely understand myself and still makes sense somehow... Time wich I don't happen to have in spades right now.

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A commercial oil furnace spray nozzle for the fuel and two impinging holes for the oxidizer.

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This is a fantastic thread.

Over 20 years ago, when I was in high school, we got to visit NASA Ames Research Center. When we were viewing one of the wind tunnels, they explained that the scale models they use don't adequately reflect fluid dynamics. Dynamics don't scale linearly with size. (https://en.wikipedia.org/wiki/Square-cube_law). They had figured out how to compensate for this, but it was still an issue.

My concern is that your source materials assume you're designing a rocket nozzle that's 10-100 times larger than the one you've proposed. All the constants and "rules of thumb" will reflect this. The circumference of your cross-section vs the area is going to be proportionally much higher than your literature expects. (I know that "wetted-perimeter" controls velocity in hydraulics calcs). Therefore your back-pressure/friction will be much higher than you expect.

Those are just my initial thoughts; I'm looking forward to seeing how this progresses.

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7 minutes ago, FleshJeb said:

This is a fantastic thread.

Over 20 years ago, when I was in high school, we got to visit NASA Ames Research Center. When we were viewing one of the wind tunnels, they explained that the scale models they use don't adequately reflect fluid dynamics. Dynamics don't scale linearly with size. (https://en.wikipedia.org/wiki/Square-cube_law). They had figured out how to compensate for this, but it was still an issue.

My concern is that your source materials assume you're designing a rocket nozzle that's 10-100 times larger than the one you've proposed. All the constants and "rules of thumb" will reflect this. The circumference of your cross-section vs the area is going to be proportionally much higher than your literature expects. (I know that "wetted-perimeter" controls velocity in hydraulics calcs). Therefore your back-pressure/friction will be much higher than you expect.

Those are just my initial thoughts; I'm looking forward to seeing how this progresses.

Thanks @FleshJeb. That must have been a cool experience, and you certainly have a valid concern. However, my primary reference material is specifically oriented towards the design of small engines. I of course cross check with other books, and yes, I have found a few differences attributable to scale issues. Thanks for your feedback, and if you think you have any ideas or even better, have found a mistake in my calculations, please, do let me know.

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Oh, duh. How did I miss that?!? :D

Blowback issues: Someone mentioned one-way valves, but a blowoff valve might be better. I saw some 300psi ones for $16. I don't know if they'll handle fluids or just air.

Ignition: I don't know if it's typical to light these from outside the nozzle or not, but you could always ground the body and run an insulated wire up the nozzle to spark in the chamber. It'll fly out when it lights, and it's a cheap solution that doesn't require you to machine another hole. I've been assuming you're going to use some sort of https://en.wikipedia.org/wiki/Piezo_ignition

Fuel-oil nozzle: This looks like a good resource: http://www.delavaninc.com/pdf/total_look.pdf Although the alcohol is going to have much less viscosity, so the numbers will be different.

Anyway, I'm sure you know much more about the mechanical end of this than I do, I'm just having fun playing along. :D

I'll double-check your calcs eventually, no energy tonight.

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13 hours ago, FleshJeb said:

[...]

Ignition: I don't know if it's typical to light these from outside the nozzle or not, but you could always ground the body and run an insulated wire up the nozzle to spark in the chamber. It'll fly out when it lights, and it's a cheap solution that doesn't require you to machine another hole. I've been assuming you're going to use some sort of https://en.wikipedia.org/wiki/Piezo_ignition

[....]

I think you might want to use what copenhagen suborbitals used for an igniter, which is a pyrotechnic device.  I think it was something that makes showers of sparks that's just stuck in the nozzle.  Doesn't require as much fiddling and setup as a spark, and is more reliable.

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5 hours ago, Mad Rocket Scientist said:

I think you might want to use what copenhagen suborbitals used for an igniter, which is a pyrotechnic device.  I think it was something that makes showers of sparks that's just stuck in the nozzle.  Doesn't require as much fiddling and setup as a spark, and is more reliable.

Actually I had tought abouth both methods and I'm undecided between electric ignition, or just sticking one of those kid's fireworks that make lots of sparks up the nozzle. The firework should be much more effective than a piezo sparker, but it might also leave residues... not fun at all! I will have to make tests in order to determine wether the residue is something I can tolerate.

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44 minutes ago, ap0r said:

Actually I had tought abouth both methods and I'm undecided between electric ignition, or just sticking one of those kid's fireworks that make lots of sparks up the nozzle. The firework should be much more effective than a piezo sparker, but it might also leave residues... not fun at all! I will have to make tests in order to determine wether the residue is something I can tolerate.

Only problem is you'd be lucky to get a 3mm spark out of a piezo lighter, depending on what it came out of.

Why not use a torch? You could mount it below the nozzle so it shoots flame up into the plume of unlit fuel. You'd have to shut it off remotely, but it may be useful for preventing build up of unburned gas. (Like the "sparklers" did on the shuttle)

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14 hours ago, ap0r said:

Actually I had tought abouth both methods and I'm undecided between electric ignition, or just sticking one of those kid's fireworks that make lots of sparks up the nozzle. The firework should be much more effective than a piezo sparker, but it might also leave residues... not fun at all! I will have to make tests in order to determine wether the residue is something I can tolerate.

Ooh, good point.  

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Hello! I have a short update today, on cooling.
As always, start on today's date in the first post of the thread, or, if you're new, start from the beginning of the first post of the thread.
If you have any sort of suggestions, ideas, doubts, or even better, think you've found an error, please, do let me know! Thanks

You guys rock.


Also, would you rather have smaller updates more often, or larger updates with more time in between?

  @KerbonautInTraining Yes, I first tougth of that, but the radiant heat of the plume would probably be enough to destroy my plastic mini-torch lighter, that's why I've yet to come up with a decision on ignition method.
Also, the main post got updated :)

Edited by ap0r

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If I made a setup, I would base it on Redstone and Aggregat 4.

I'd use a fuel mixture of 25% water, 75% Ethyl Alcohol. I would pump said mixture into a sprayer at the top of the combustion chamber, and I will also pump Ethyl Alcohol to the bottom of the engine nozzle and ignite it there. I will do that with a Redstone turbopump, consisting of two short water screws that are rotated by a turbine in the center of the turbopump. To rotate the turbine itself, I will have to channel high-pressure steam through it, which will in turn be created by mixing hydrogen peroxide with potassium permanganate (a steam generator).

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Hello,

So currently I am attempting to do essentially the same thing for a research project in school. Only differences that I currently have compared to your design is that I am attempting to use gaseous oxygen and liquid kerosine as my propellants and that I may be looking into a different material other than copper to manufacture the rocket engine. I was wondering what people thought about using titanium for the fabrication of the rocket engine. I am most concerned by the thermal conductivity value of titanium which is much smaller than that of copper. Would it be feasible to build a beginner rocket from titanium or would it be best to stick with copper? Thanks for any help and I am excited for the next post.

 

Edited by views1995

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Well first of all I'm no expert, I'm learning myself so take my advice with a lot of salt. That said, kerosene should give you higher pressures, wich are no problem with a thicker copper wall, and higher temps, wich might make cooling challenging. Titanium is usually not used in rocket chambers, Inconel is a more common material. So I'd definitely recommend you stick to copper for a hobby engine. You'll have to make thicker walls, of course, but titanium seems like it'd be much more expensive, harder to machine, and also cooling would be a more complicated.

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Yeah copper definitely will make life a lot easier. Thank you for the response. I also have another question about your ideas for the cooling jacket. I was wondering essentially how you were planning on designing your cooling jacket. Wether you'd mill in a solid liner through your chamber walls or attach a liner of various tubes to the outside of chamber walls or if you had some other idea. I feel that milling a solid liner through the chamber walls will be out reach for my machining capabilities so I thought of some other designs for the jacket. I drew a picture but it seems I am unable to upload it so I will just describe it. It would be a design of two half cylinders as long as the entire rocket engine. These two half cylinders would be bolted together to house the entire rocket engine inside. Then, water would flow in between the inner walls of these half cylinders and the outer wall of the rocket engine. I would figure a way to ensure that the seal between the two half cylinders would not leak water but I may be overlooking complications of having bolts and nuts in a rocket engine design that is experience such high temperatures. I know it may be a little hard to understand what I'm describe so don't worry about if you cant visualize it. Thanks again.

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16 hours ago, Matuchkin said:

If I made a setup, I would base it on Redstone and Aggregat 4.

I'd use a fuel mixture of 25% water, 75% Ethyl Alcohol. I would pump said mixture into a sprayer at the top of the combustion chamber, and I will also pump Ethyl Alcohol to the bottom of the engine nozzle and ignite it there. I will do that with a Redstone turbopump, consisting of two short water screws that are rotated by a turbine in the center of the turbopump. To rotate the turbine itself, I will have to channel high-pressure steam through it, which will in turn be created by mixing hydrogen peroxide with potassium permanganate (a steam generator).

Are you actually building that or just thinking out loud? That'd be insanely cool!

Also @views1995 if you don't mind waiting a bit, detailed design of the cooling system should come along soon, but this might be a good reference meanwhile.

ZkKrZfV.png?1

Edited by ap0r

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5 hours ago, ap0r said:

Are you actually building that or just thinking out loud? That'd be insanely cool!

I am thinking out loud. I was, in fact, thinking out loud for nearly a year. Then I found someone (you) who can help. I'm thinking of a water/ethanol mixture because they seem extremely easy to get, if you can get a licence to create drinking alcohol. By the way, please consider my turbopump idea, as it is quite simple, and already proven to work on the redstone missile.

5 hours ago, ap0r said:

Also @views1995 if you don't mind waiting a bit, detailed design of the cooling system should come along soon, but this might be a good reference meanwhile.

I planned that too. A sufficient cooling system will be achieved by pumping fuel through tubes inside the combustion chamber and engine nozzle. We can also use nitrogen. The inside of the combustion chamber can be lined with carbon, tungsten, or other such high-melting-point materials.

Edited by Matuchkin

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1 hour ago, totalitor said:

How about using volfram? Melting point 3683 K. Does it need cooling at all?

   

Wolfram  (AKA tungsten for the IUPAC, even skipping their own rules to put the english name instead of the name of the first ones that separate the element, this kind of things shouldn't happen in science) is very difficult to obtain, very expensive, and even more difficult to make a thing with it, IIRC a wolfram part usually needs to be sintered, with isn't cheap at all.

Also you can add a little thorium and the melting point goes up to 4000ºC, but the important is not where it melts, is how it maintains it's strength when the temperature goes up. Example: steel have a melting point far above 1000ºC but it loses lots of his strength only heating it to 300ºC.

Also is very heavy so no use for non-stationary rocket engines.

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First of all sorry for the delay. Work has been hectic. Now, @Matuchkin your project seems to go way beyond my extremely low expertise at this moment. If there's anything I can help with, sure, do contact me, but you are planing on using a gas generator, a turbopump, a combined regenerative/ablative cooling system, all of wich I've deemed too complex/expensive to tackle right now... So I'm not realy sure how I could be of any help.

And @kunok, you're spot on.

Edited by ap0r

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1 hour ago, ap0r said:

you are planing on using a gas generator, a turbopump, a combined regenerative/ablative cooling system, all of wich I've deemed too complex/expensive to tackle right now

Believe me, you only need four chemicals, two of which are easy to get, and two of which you can get at a superstore. Given explanation, you will understand everything. I'm gonna message you later to show how its done.

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1 hour ago, ap0r said:

And @kunok, you're spot on.

Oh, that will be hard to achieve. Rocket engines have to use something like tungsten. If not, you can take a titanium-______ alloy, or something like that. Otherwise, use an insane cooling system. Like, run liquid nitrogen through it, or something- actually a viable, used idea.

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16 hours ago, Matuchkin said:

Oh, that will be hard to achieve. Rocket engines have to use something like tungsten. If not, you can take a titanium-______ alloy, or something like that. Otherwise, use an insane cooling system. Like, run liquid nitrogen through it, or something- actually a viable, used idea.

Inconel 718 is the thing. Is a nickel-iron and more alloy. Nickel based alloys are the most used in the worst parts of jet engines, as far I know.

But this project will be actively cooled no? If not, use an ablative material, because high temperature alloys are very expensive and very hard to machine.

@ap0rif you need manufacturing advices I'm totally in, that's my field, just mention me. Hell if I had a milling machine I will machine myself the nozzle, with the proper geometry.

Edited by kunok

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2 hours ago, kunok said:

Inconel 718 is the thing. Is a nickel-iron and more alloy. Nickel based alloys are the most used in the worst parts of jet engines, as far I know.

But this project will be actively cooled no? If not, use an ablative material, because high temperature alloys are very expensive and very hard to machine.

@ap0rif you need manufacturing advices I'm totally in, that's my field, just mention me. Hell if I had a milling machine I will machine myself the nozzle, with the proper geometry.

A thin layer of nickel-iron should do then, just lining the nozzle and combustion chamber. Then, pump fuel through the combustion chamber and nozzle walls to cool them down. I know that method is used.

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