Newbie that had some problems.

[nsmikle]

Hey all..

I have been reading this site now and then, just checking out the scene.

I have done 3 gas turbine projects before. The first two were crude but somewhat successful.. The last one was a turbo-shaft.. I actually calculated it for it.. I had a proper oil system in place too.. What happened was that i decided to make a vehicle to attach it to and that was my worst mistake..
I got so caught up with making the Go-kart and i didn't realise that i was facing some major problems. The Turbine was extremely difficult to start. I have pics coming up. A sad shame I did not get it to Start fully. And I am unable to amend this project though because i left it in another country. So all of my revisions have to go into another project when i get the money.

This is a picture of the finished Project.. It only looks Decent.. You can see i just slapped on a chain just for proof of concept. i really wanted a gearbox. I did not fabricate an axial 2nd turbine so i just used a large broken KKK K32 with new ball bearings i put in.

Spark circuit, Gas tank and Battery not shown.. Initial test had no oil filter It was loudest non starting turbine i ever had. It's a drag racer so don't mind the terribly wide axel



Looking back on a project i can do nothing about since it is not in my possesion , My main problems/Questions are narrowed down to this,

1. The inlet to the combustion chamber..
2. A proper fuel injection mechanism ( i had the regular propane ball valve )
3. Far reach spark plug and placement ( the spark plug was just too short)
4. A proper on vehicle starting system. (Leaf Blower FTL)
And them i have some questions about the flame tube..(pics later)

I want to post some detailed drawings of the problem areas tomorrow so you guys tell what solutions I can use.

[nsmikle]

Ok.. regarding the Combustor.. this is what i have.. just a regular can shape.



I tried to make it a counter flow.. as in the air enters from the bottom of the combustor makes a U-turn through the flame tube then heads into the primary turbine. The flame did not "start" until halfway down into the flame tube..(the top near the spark plug was colder)..



The combustor inlet is the short tube to the right of the small turbo (Mitsubishi td-05)
I think the combustor inlet was horribly positioned now that i look back on it.. where do you think is the best position/shape for the inlet?

[racketmotorman]

Hi

How did you determine your flametube hole sizes , areas and distribution ??.............it looks like it has too much hole area .

Theres nothing wrong with having the delivery air plumbed to the "bottom" of the combustor , both of my DIY engines have been constructed that way and they've worked OK .

Did you have "radial" holes in your propane injector or "axial " ones ??

Freepower equiped engines shouldn't be any harder to spoolup than one with a jet nozzle if the freepower turbine stage is correctly proportioned , if using a small gas producer such as you are , its generally low component efficiencies necessitate an "oversized" freepower turb stage due to the low gas speeds possible from the available thermodynamic energy exiting the gas producer .

From your pics of your freepower stage it appears to be large enough ............I feel your problems were the flametube ...........what is the diameter of the flametube and your compressor wheels inducer , for a small turbo like yours I'd recommend that the flametube be at least twice the inducer diameter and preferably 3 times the inducer so as to slow the air down for good combustion .

You mention that "burning" is too far down the flametube , this could be caused by both too much hole area as well as too small a flametube diameter .

Cheers
John

[nsmikle]

Thanks for the reply.

I have to go back to my drawings for the dimensions. My memory is a little fuzzy since i made it last year.

The propane injector was one single axial hole. At first it was a 1mm sized hole then i increased to 2.5mm..

Inducer of the compressor is 46mm.. or around 1.8"

The Chamber inlet pipe is 42mm ID or 1.6"

The diameter of the chamber is 114mm OR ~ 4.5"

The diameter of the flame tube is 75mm or 3" ( So it was too small then)

The flametube holes i was not too sure about.. the book mentioned the Primary Zone, Secondary Zone and the the Dilution Zone..So I totally guessed the flame holes, i don't know what i was thinking.. that is the one thing i am sorry did not calculate.
The Flame tube got a Blue-ish tinge at it's middle after the first attempts to start. ( It is new in the pictures).

Afterward, I happened to see a real canister from a Power plant gas turbine.. it was from a Westinghouse. That is when I confirmed something was totally wrong with my Flame tube. But i did not have my camera or a ruler at the time.. and i don't have the book anymore and i had to leave the country..

[nsmikle]

The westinghouse flame tubes looked somewhat like this..but inside had Three circular Swirlers suspended in the middle. They were also coated in a thick rough white material..

Should it be more like these? How would you determine the hole sizes and locations? Is there any books with the appropriate formula or is it more eperimential/experience based?

[racketmotorman]

Hi

Firstly, an axial holed fuel injector will squirt the fuel too far down the "tube before mixing with the air , you need to have radial holes that squirt the fuel towards the flametube wall , 6 radial holes as a minimum spaced 60 degrees apart , NO axial holes as they will complicate combustion .

Secondly ,the total hole area in the flametube should equal your comp inducer area which at 1.8" dia is ~2.5 sq inches .

Thirdly , that 2.5sq ins of flametube hole area needs to be divided up into 30% for the primary zone holes where combustion is taking place ,20% for secondary mid way down the "tube to complete any combustion , and 50% tertiary at the lower outlet end for dilution of the hot gases so that turbine inlet temperatures are within limits .

16 X 0.25" dia holes for primary

5 X 0.375" dia holes or secondary

4 X 0.625" dia holes for tertiary

Fourthly, at 3" dia your flametube would probably be too skinny if using kero/diesel but for propane you'll probably get away with it if fuel delivery is OK and theres good fuel/air mixing promoting fast combustion

Our low pressure flametubes don't always compare with high pressure industrial turbine engine flametubes .

Theres a "Program" for designing flametubes on the Yahoo Groups DIY Gas Turbines group , its called Jetspecs .

Cheers
John

[nsmikle]

Noted, Thanks again..

I really want to switch from propane to diesel/kerosene but i will search around first before i ask any more questions..

[GRIM]

Hi All ,
This may be of interest to the turbine builders, not radial , but it could easily be made that way,
Let me know if anyone would like drawings etc,

G

[nsmikle]

Seems kool... i can see that the gas can help to atomize the liquid as it exit's the nozzle.

I was thinking of just doing liquid alone. One of my major problems was proper metering of the fuel.. Two types of fuel at the same time might make it harder to control.

[racketmotorman]

Hi

I tried start propane and main fuel thru the same manifold , lotsa problems , changedto seperate manifolds , problems gone

Chers
John

[nsmikle]

Ok.. i am ready to ask the next question..

I had an issue with Starting.. I have used a backpack leaf Blower and a compressor before.. just to cumbersome and no fine control.

I noticed that some have used a hand held leaf blower and some people use a Small high rev- electric motor.

On my next build I need something that is a Part of the engine/vehicle and is compact.. so i like the idea of the RC-car electric motor. I just need to know what specs i should look at to get a proper one. (I hope they can spin at a high enough rpm).. the method of control is whole other issue.

Thanks.

Just for those curious for more shots:

By-pass valve.. It's Brass.. but it was just temporary until i got a real waste gate.
Notice, no Exhaust pipe.. some flaws in the design caused this.. Mainly that i did not get the proper sized wheels.. and that space was made for a 20kg Butane tank in the middle of the vehicle.




Oil sump:




Chain drive, I had to Fabricate a thicker Turbine shaft and bearing housing that was strong enough to support the drive sprocket:



Before:




After:



The next project will be done to higher degree of detail now that i have more time and this site for help

[racketmotorman]

RC motors work OK , used on micro turbines

[nsmikle]

Thanks, still here i am looking for job.. need some cash before i can start this again.