Cooking oil, reverse flow combustor, radial turbine engine

[sundaypilot97]

Greetings everyone!

After many years, since junior high actually, of thinking about embarking on a project to build my own working turbojet engine, I may finally be able to give it a try.

My early interest were model planes, I was fascinated by jet powered models back in the early 2010s, and there were basically none in my country. And with our buying power, almost impossible to acquire.

Fast forward to today, my hobby is flying sailplanes/motorgliders, so I actually never steered away from aviation related stuff, just decided to put myself into the cockpit  .


Anyway, to the topic. I am mainly interested in building a standard turbojet, using a complete rotor assembly out of a turbocharger. Hence, the radial turbine wheel. I figure, those turbines are probably made out of Inconel, and likely better than anything I could make following Schreckling's and Kamps instructions out of stainless.

Reverse combustor would be imho preferable, as it would allow the use of existing short shaft out of turbocharger unit, and that short of a shaft should allow higher rpm, also the resonant frequency would be lower than that of a longer shaft.

Now onto the fuel. I am really interested in trying to make this run on cooking oil. Properly filtered, of course, preheated if necessary. The engine could be a gas start, i am not shying away from propane. I have experience using cooking oil in furnaces, and always wondered hey why not try to run a turbjne on it, after all, the energy density isnt that far off from diesel, and if preheated a bit, it flows extremely well.

All this means I will probably have to do some engineering myself, but I am still wondering, are there any plans out there, at least for an engine with a reverse combustor and radial turbine wheel? 

Old Phoenix comes to mind, but i dont think it uses a reverse combustor.

Tools I have available for the build are: 10x20 toolmakers lathe, diy 1600w spot welder, diy sheet metal roller, pillar drill, fluxcore welder, various hand and measuring tools

I would like to keep any milling to a minimum, if not completely out, hence the Kamps style diffuser, instead of a kj66 radial-axial type, is my preferred.


Lots of talking, so I bolded my main question,so that you dont have to go through a lengthy post.


Talk to you next time,
Adrian

[racket]

Hi Adrian

Welcome to the Group , that quite an ambitious project :-)

Firstly , I'm not aware of any plans for a reverse flow combustor , I really can remember one even being built , though could be wrong on that point , but agree it would be better for your fueling ( and all of us ) as it could be made considerably longer .

Standard turbo shafting still has rotor "gyrations" but the thick oil film/s controls it, simply sticking a turbo shaft on some ball bearings isn't going to work, high speeds create all sorts of problems.

As for your choice of fuels , yep , preheating will let just about any type of fuel work , but I think I'd be doing some experimenting with a normal turbo based engine with a sore thumb combustor first, to find out whats required to get efficient combustion before attempting to fit it to a micro style engine where other issues could be creating problems and confusing the situation.

The GTBA www.gtba.co.uk/ have been working on producing a radial turb engine but haven't got plans out yet .

Cheers
John

[sundaypilot97]

Hello racket,

I will first say that I saw your 200lb thrust turbojet project on yt, quite imoressive, I was the one who commented it would be a great self-launch/sustainer propulsion platform for a sailplane.

Well, aren't all the traditional turbocharger based engines radial turbine based, aas they simply use an existing unit?

So I guess the main issue is adapting the annular combustor to feed the radial turbine?

The main reason of using the radial turbine would be to avoid making an axial turbine wheel, which, if made out of stainless, would be the limiting factor as far as RPM's go.


PS: My original idea was to keep a separate oil tank and original turbo bushings and tunnel, and just do away with the heavy casing. 

[CMDR_Boom]

By reverse flow, I suspect you mean something like of which is employed on the PT6. Reverse flow isn't actually reverse flow, it's just another packaging technique to get more into less space. Air can go any direction you want with more or less efficiency in doing so. 

[sundaypilot97]

Jul 12, 2024 11:21:32 GMT -5 CMDR_Boom said:

By reverse flow, I suspect you mean something like of which is employed on the PT6. Reverse flow isn't actually reverse flow, it's just another packaging technique to get more into less space. Air can go any direction you want with more or less efficiency in doing so. 

Like this


ibb.co/DVW4YNp

[racket]

Now thats a nice engine :-)

Whats its specs ??

With reverse combustors theres always a problem getting sufficient flametube cross sectional area whilst having it around the jetpipe , invariably a larger diameter engine is required unless some compromises are made .

That engine has done a nice job of having the Primary Zone around the nozzle so as to increase area , along with a "curved" comp diffuser to keep overall diameter as small as possible.

As long as you use "original" turbo specs for the bearings you won't have problems , making the shaft tunnel isn't a bit job .

The reverse combustor mounting etc won't be any different than what we do , other than its reversed .

In hindsight it would have been easier if I'd used reverse combustors in my engines as the combustion process has always been a bit "fragile" and fraught with problems due to the short lengths used, I'll be interested to see how you go with the build :-)

Cheers
John

[racket]

www.turbinetechnologies.com/Portals/0/pdfs/gas_turbine_tech_sheets/UnivofMinnesota.pdf

An interesting Paper :-)

[sundaypilot97]

Ok this is a really noob quesrion but is there a description somewhere for NGV for a radial turbine? Obviously turbi based engines dont seem to use any.


Even Kamps book describes that the radial wheel could be used, and that the biggest drawback is its higher mass, hence slower throttle response.

[racket]

imgbb.com/gjMLXfN

Theres info and pics in my build threads of the NGV stator . jetandturbineowners.proboards.com/thread/1459/11-127-manned-flight-engine?page=10

Don't worry about acceleration times , the RC aircraft guys need to have extremely low idle speeds to reduce thrust for landing , its only from those very low rpm that the extra mass is a problem , if you idle a 0.5 Bar P2 it'll accelerate away like piston engine .

Cheers
John

[finiteparts]

"PS: My original idea was to keep a separate oil tank and original turbo bushings and tunnel, and just do away with the heavy casing."

Just an FYI.

The bearing sump needs to be large enough to keep the oil away from the dynamic seals when the centerline pitch angle changes.   Turbocharger manufacturers recommend that the mounted angle be less than 15 degrees,



as this keeps the flooded oil level below the bottom of the dynamic seal.   Once the seal is flooded, it can pump oil out of the sump into the compressor or turbine backface cavities by viscous action. So one of the concerns on an aircraft application of a turbo based engine is that certain angles of pitch, if not accompanied with sufficient g-loads (i.e. during climb or descent) could put the engine in a condition were the sump pumps significant oil through the seals.

You may help the situation by adding a sump scavenge pump, but this will increase the battery power demand, overall system weight and compressor/turbine air "contamination" into the sump.   The increased leakage of compressor/turbine gas across the dynamic seals, due to the lowered sump static pressure (which is how the scavange pump works, i.e. constant volume), will increase the oil temps somewhat (so you will just need to up-size the oil cooler), but this also reinforces the importance of a good air/oil separator in the oil return system as there will be more air entrained in the oil froth.  It may also play into the selection of a oil tank sizing, such that you have a larger volume of oil than needed in case there is any overboard loss through the seals.

Just some thoughts to mull over when you are designing your engine for an aircraft based application.

Good luck,

Chris

[sundaypilot97]

Well it is pretty far fetched to say i am designing a turbine for aircraft application at this point. Just getting it to run would be a success.



Right now I am also looking into a sore thumb type of engine as well as into the annular chamber style, as racketmotorman suggested. However I really want to do away with the extra weight, the idea then would be to try to rebuild the turbo casing out of thinner and lighter material.

[racket]

Hi Adrian

What sized engine do you actually want to build ??

Cheers
John