N2O/Ethanol bipropellant rocket engine

[Johansson]

That is the problem with engines this small, one single injector like this flows all the engine need and making three smaller ones instead would require such small drills that they probably would snap instantly.

Yup, regenerative cooling by methanol. I will also follow your advice and run it with more methanol than needed to keep the combustion temp down during the initial testing.

That is another problem with these small engines, I cannot drill any film cooling holes around the edge of the chamber since one single 1mm hole extra would litterally flood the engine...

[mator]

It is pleased, that I am useful with my council for somebody)))
I find in shop with electronics 0.8 mm drill. And also in my univercity told that all holes in engine mustnt be less than 0.8mm. Maybe it is possible to decrease flow with some additional hydrodynamic resistance? But it can be difficult.
As I understand you want to make a special cooling layer from fuel steam? With injectors that placed nearly chamber sides?

And another thing, that I learned recently, and I cant keep silent, is that engine start must be smoothly. Because injectors calculated on chamber pressure impact. During the start there no pressure in chamber so liquid flow through injectors will be much bigger. So in chamber enters much more propellant and when it ignits, we have a sharp jump of pressure and probability of engine explode much higher that usually.

[Johansson]

I don´t know if film cooling is needed, perhaps running the engine a bit rich is enough to keep the nozzle throat from melting.

You are correct about the extra flow from the injectors during starting, without the chamber pressure the pressure drop over the injectors will be more than twice as high as when the engine is running.

I don´t know how to regulate down the N2O pressure safely though, guess I have to try and see if the engine blows up or not.

[mator]

I think that engine won't melt. I think that there more hazard that component-coolant boil to steam and change processess in engine. But maybe...

To safe engine during start (with displacement fuel by gases ingection systems, not with turbopumps) in real rockets there are some special devices, that limit component flow by hydraulic resistance. I think that you can find with some information about them in your books. But do they really necesary?

[mator]

Feb 19, 2012 9:46:19 GMT -5 Johansson said:

I don´t know how to regulate down the N2O pressure safely though, guess I have to try and see if the engine blows up or not.

Maybe by gas reductor?

[Johansson]

I think I will try to run it without any flow restrictions first, I rather build a new core than fit some restriction that I don´t know if I need.

Something I have been thinking about lately is cheramic coating inside the CC and nozzle to reduce heat transferto the aluminum, I use it with great success in my JU-01 gas turbine where it endures 900°C in the NGV without any visible signs of damage to it.

I don´t know how well the coating sticks to aluminum but I will coat a test piece and put it under the torch to see how well it shields the metal from the heat and if the coating stays in place.

I have an IR termometer that I can use to see how much slower the back of the test piece heats up compared to an uncoated one.

[wolfdragon]

Johansson,

Best recipe for making things stick to aluminum (not acid etch):

While wearing latex/polyethylene gloves to prevent oils from your hands transferring to the parts...

1: Degrease with acetone
2: Wet sand 600 grit, use deionized water (distilled is OK, no tap water)
3: Once everything is nice and dull, clean again with acetone
4: Wipe dry with clean towels (paper towels that are absorbent are OK)
5: Within 15 minutes of step 4, coat the aluminum with whatever you are using

If you happen to have aluminum acid etch primer about, then use that as it's easier and faster.


If it doesn't stick after that, it will never stick to it...

[Johansson]

Thanks for the walkthrough Wolfdragon!

[Johansson]

I spent a couple of hours today cutting cooling fins around the nozzle throat section with a 2mm thick mill saw.



I left 5mm of wall thickness so that the nozzle would survive the pressure during engine operation.



Here are the engine parts piled up, not much left to do now before I can weld the aluminum parts together.



I think I will only coat the nozzle, the CC tube is so long that it would be difficult to put a fine layer of cheramic coating inside it and besides it is the nozzle throat that is most in need of the extra heat shield.

[mator]

Gut!

[Johansson]

Yesterday I made the fuel line connecting the regenerative cooling housing to the fuel injector.



The more plumbing a rocket engine has the more advanced it is, ask any 10 year old you like.



Cheers!

[Richard OConnell]

It looks absolutely terrifying. Congratulations.

[Johansson]

A guy from Norway told me it looked cute, terrifying sounds better though. ;D

[mator]

I think that it is looking fantastisch!!!!

[ernie wrenn]

I can produce some bianary explosives and have a NICE bottle rocket!! Once the theory is proven, lets up scale it and apply for some of that free Oboma money. We can offer it as a inexpensive areal bird repellant for airports to keep the runways clear.

ernie