KSP inspired me to design a liquid-fueled rocket engine

[Elthy]

The hard part about a turbopump isnt the gas generator i think...

[ap0r]

On 29/6/2016 at 11:21 PM, Matuchkin said:

No, this is important. I'm thinking of a simple gas-generator, to power your fuel pump. It's not as complex as you think. All that you have to do is:

- Dump those aforementioned KMnO₄ (potassium permanganate) pills into a can.

- Pipe pressurized H₂O₂ into it. The reaction will create hot, pressurized steam.

- Steam automatically goes out the other end of the KMnO₄ can and can spin a turbine.

Hi, sorry for the delay. There is no need for a turbopump to achieve the desired mass flow rates. My engine is very small!

9 hours ago, Elthy said:

The hard part about a turbopump isnt the gas generator i think...

Yes, a turbopump + gas generator is a pretty simple concept, but the devil lies in the details, and implementation is a nightmare, and thus it should only be used if no other alternative exists. To quote from Rocket Propulsion Elements:

"Engines with turbopumps are preferred for booster and sustainer stages of space launch vehicles, long-range missiles, and in the past also for aircraft performance augmentation."

 

[SinBad]

I think the issue with gas driven turbo pumps is that they are difficult to throttle accuratly, especially as their throughput doesnt scale linearly with rpm due to funkeyness with fluids at pressure moving at high speeds.

[ap0r]

Yeah, that and they are also subjected to pretty extreme forces, so they demand expensive materials and high precision machining.

[totalitor]

Hi!

Here are some pictures what I have been doing. Well, I don't have a lathe so I have to do parts some other way. I made de Laval nozzle by using only ball pen hammer. I know, it's quite clumsy but I had to try.  Look at the pictures, you get the idea. Give comments please.

 

  http://imgur.com/a/X7HPo

 

 

 

 

 

Edited August 25, 2016 by totalitor

[totalitor]

Hi!

New picture in imgur album. I tried to braze copper tubes together and it went well. I'm reducing chamber diameter to 6,4 mm, cooling gap would be 0,8 mm. Learning new skills, interesting.

[totalitor]

Hi!

I am calculating dimensions but I get weird result in combustion chamber lenght. Becouse of materials I have, combustion chamber diameter would be 6,4 mm, throat diameter 2 mm. I am planning to use gaseous oxygen and 75 % alcohol. Combustion chamber would be between 10-21 cm (including converging section) according a book "How to design small rocket engines".. Sounds a little long. This rocket never flies and it doesn't need to be efficient but am I calculating wrong that chamber lenght?

[Rath]

By the way, warn the cops on paper so they don't think you are a terrorist if it goes kablooie.

[A Fuzzy Velociraptor]

How did you determine your heat flow into the cooling system?

[totalitor]

Me? I'm following instructions of that book " How to design small rocket engines". I study ways to put parts together only by brazing. Exact calculations later. Now I am wondering how to do injector. Combustion chamber has only 6.4 mm diameter and there should go fuel and two oxyxen holes. How to drill  three 1 mm holes to that? I am planning to attach oxygen inlets not to injector plate but to the sides of the engine. Look at the last pictures and say would this work?

http://imgur.com/a/X7HPo

 

[SinBad]

Have you considered sand casting the fiddly copper parts?

[A Fuzzy Velociraptor]

5 hours ago, totalitor said:

Me? I'm following instructions of that book " How to design small rocket engines". I study ways to put parts together only by brazing. Exact calculations later. Now I am wondering how to do injector. Combustion chamber has only 6.4 mm diameter and there should go fuel and two oxyxen holes. How to drill  three 1 mm holes to that? I am planning to attach oxygen inlets not to injector plate but to the sides of the engine. Look at the last pictures and say would this work?

http://imgur.com/a/X7HPo

 

Actually it was directed at ap0r.

Your engine looks very rough that it is difficult for me to tell exactly what is going on there that I can't really give a recommendation.

[ap0r]

On 22/8/2016 at 1:28 AM, A Fuzzy Velociraptor said:

How did you determine your heat flow into the cooling system?

Sorry for the LONG delay, @A Fuzzy Velociraptor, I've been having some seriously hectic days, and on top of it my ISP went poof for a whole week in my town.
With respect to your question, I simply assume the chamber to be perfectly conductive (It's copper so the asumption is not a horrible one), and thus the heat input to the cooling system equals to the heat output from the engine. I further assume that the heat flow is 0.5 Kw/cm2/sec, or 3Btu/sq inch./sec . This is an educated guess based on other's people experience with similar engines.

On 22/8/2016 at 8:13 AM, totalitor said:

Me? I'm following instructions of that book " How to design small rocket engines". I study ways to put parts together only by brazing. Exact calculations later. Now I am wondering how to do injector. Combustion chamber has only 6.4 mm diameter and there should go fuel and two oxyxen holes. How to drill  three 1 mm holes to that? I am planning to attach oxygen inlets not to injector plate but to the sides of the engine. Look at the last pictures and say would this work?

http://imgur.com/a/X7HPo

 

I wouldn't reccomend that you put the oxygen at right angles to the fuel, that might cause a bad mix and if pure oxygen touches the chamber walls they might oxidize quickly and damage the engine.
Looking at the last figure, i've noticed that the chamber/nozzle looks to be assymetrical along the lenght axis. Or is that just due to the angle the picture was taken from?

[totalitor]

 

Nozzle is really like triangle. Bad craftmanship that's all. Should be round.

 

Fuel and oxygen feed - what would you recommend?

Oxygen from side?

Or oxygen from behind parallel to fuel? Or a little angle?

What is the best?

 

 

Edited September 1, 2016 by totalitor

[Mad Rocket Scientist]

18 hours ago, totalitor said:

 

Nozzle is really like triangle. Bad craftmanship that's all. Should be round.

 

Fuel and oxygen feed - what would you recommend?

Oxygen from side?

Or oxygen from behind parallel to fuel? Or a little angle?

What is the best?

[...]

From what I know about full-size engines, they tend to use impinging feed systems.  That should mix the fuel better, but I don't know much about smaller engines.

[A Fuzzy Velociraptor]

On August 24, 2016 at 10:48 PM, ap0r said:

Sorry for the LONG delay, @A Fuzzy Velociraptor, I've been having some seriously hectic days, and on top of it my ISP went poof for a whole week in my town.
With respect to your question, I simply assume the chamber to be perfectly conductive (It's copper so the asumption is not a horrible one), and thus the heat input to the cooling system equals to the heat output from the engine. I further assume that the heat flow is 0.5 Kw/cm2/sec, or 3Btu/sq inch./sec . This is an educated guess based on other's people experience with similar engines.

I wouldn't reccomend that you put the oxygen at right angles to the fuel, that might cause a bad mix and if pure oxygen touches the chamber walls they might oxidize quickly and damage the engine.
Looking at the last figure, i've noticed that the chamber/nozzle looks to be assymetrical along the lenght axis. Or is that just due to the angle the picture was taken from?

You can have the fuel enter at right angles to the oxidiser; it is not uncommon especially with "staged" engines like HTP-RP1 style engines. However the injector systems will not be the shower head style yall are most likely using and will instead use an impinging injector style which will stillpromote adequate mixing. However it will tend to increase the heat flux into the chamber wall especially since those mixures will be hypergolic.

On August 25, 2016 at 3:31 AM, totalitor said:

 

Nozzle is really like triangle. Bad craftmanship that's all. Should be round.

 

Fuel and oxygen feed - what would you recommend?

Oxygen from side?

Or oxygen from behind parallel to fuel? Or a little angle?

What is the best?

 

 

I dont know enough about your system. Given the earlier pictures I imagine performance if not your goal that just a straight showerhead style should be easiest to produce. Also what are the planned size of you injector holes as that will be the main thing that will affect your mixing. I also dont know the size of the diagrams you have whether they represent the entire plate or if they represent a close up on a triplet.

14 hours ago, Mad Rocket Scientist said:

From what I know about full-size engines, they tend to use impinging feed systems.  That should mix the fuel better, but I don't know much about smaller engines.

They tend to use impinging feed systems because it increases performance. The size of the engine doesnt significantly affect the desirable type of injector (splash plates excepted). The size of the injectors are very small generally in the range of three hundreths of an inch with the whole doublet/triplet/pentad less than a quarter inch.

[totalitor]

On page three on this topic there is a picture about small rocket engine (at the end). There is a cooling gap but on the throat area the gap is a lot wider. According the book  "Design of liquid propellant fuelled engines" :  "Abrupt change of flow direction and sudden expansion or contraction of flow areas should be avoided".

In that picture cooling gap is not the same all the way.

How important is to keep cooling gap uniform?

 

[A Fuzzy Velociraptor]

7 hours ago, totalitor said:

On page three on this topic there is a picture about small rocket engine (at the end). There is a cooling gap but on the throat area the gap is a lot wider. According the book  "Design of liquid propellant fuelled engines" :  "Abrupt change of flow direction and sudden expansion or contraction of flow areas should be avoided".

In that picture cooling gap is not the same all the way.

How important is to keep cooling gap uniform?

 

In general you will want to maintain a fairly constant velocity profile for a number of reasons. Since the density and massflux should be constant in order to maintain a contant velocity, a contant area is desired. As the radius decreases, the thickness in the annulus needs to increase. As a rough approximation you can consider the circumference of the annulus to be like the side of the rectangle and the thickness as the other. As the circumference decreases the other side has to increase to maintain area.

[totalitor]

If I keep thickness in the annulus same all the way from nozzle area to injector area, does the velocity of coolant on nozzle throat increase? Have I understood correctly it is a good thing considering cooling?

I am just wondering should I keep outer tube straight or follow inner tube curve. A straight version would be easier to do.

[Rocketthrust]

I want to do the same.

 

[A Fuzzy Velociraptor]

12 hours ago, totalitor said:

If I keep thickness in the annulus same all the way from nozzle area to injector area, does the velocity of coolant on nozzle throat increase? Have I understood correctly it is a good thing considering cooling?

I am just wondering should I keep outer tube straight or follow inner tube curve. A straight version would be easier to do.

The velocity would increase. In theory it should increase the convective coefficient; however you will be more likely to experience cavitation which is very not good. A lot of it depends on your geometries and pressures that it isnt easy to give a definate answer. With just a straight tube you will decrease the velocity significantly at the throat which could cause some material to be trapped which could result in boiling of the flyid which is also very not good. Ideally you will want to maintain a roughly constant velocity such that you would follow the curve somewhat but would fall away a little bit near the throat. Of course your system is a very simple/low performance engine that you are operating so youll have to apply my advice to that where I work on much more exact systems.

[totalitor]

Thank you for advice A Fuzzy Velociraptor.

 

So let me introduce my first rocket engine : RUD-1

 

http://imgur.com/h6KLaIJ

 

Showerhead/ film cooling injector system

Combustion chamber diameter: 6,4 mm

Combustion chamber lenght including nozzle area: 50 mm

Nozzle throat diameter: 2,5 mm

Oxygen hole diameter: 1 mm.

Fuel hole diameter: something (two holes)

Planned propellants: gaseous oxygen and 75 % ethanol

Cooling liquid: water

Cooling gap between tubes: 0,8 mm

100 % copper (excluding brazing material)

Firing day: unknown

 

I don't know will this work.

 

This is how I made it:

http://imgur.com/a/ko9WJ

 

Edited September 1, 2016 by totalitor

[A Fuzzy Velociraptor]

What are you expecting for thrust and chamber pressure? Those are two pretty defining features that you normally start from but they dont seem to be listed.

[totalitor]

I use "How to design small rocket engines" book for insructions. I took there example and made 1/10 size of that (chamber lenght is just guessing).

Example engine thrust is 20 pounds and chamber pressure is 300 psi. I don't know how those scale, maybe thrust in my engine is 2 pounds but I don't know about chamber pressure. Maybe that is the same? Fuel and oxygen flow rates will also be 1/10.

I will make different versions becouse fabrication is so easy, one day for an engine. And it is not expensive.

[kurja]

So when's the festive first test firing?