Finally...started building

[adibrook]

Umm...hello. I'm back again.

I can't remember when i last posted here, but i know that getting a turbocharger took me ALOT longer than expected. But still...the end result was alot better than i expected.

I was just going to go to a scrap yard, where i had to pay £25 to get a turbo off some cheap modern car. Knowing modern manufacturing techniques, i bet that turbo would have been tiny, and made of pressed tin foin about .5mm thick which is made from recycled coke cans (ok, ok...that is abit exagerated, but you get the idea). Anyway, i went down to the harbour on my way to the scrap yard, and i noticed some bloke changing turbos on his boat. So i asked if he wouldn't mind selling his old turbo. So he gladly gave it to me for nothing, since i saved him the effort of throwing it overbord!

I got REALLY lucky. This is a proper "british" turbo, which weighs about a tonne and is all made up of outragiously thick cast iron. That is ALOT better than the one i was gonna get from the scrappy...and i got it for nothing!!!

Now i have my lump of britishness sitting on my workbench...and looking very good. I stripped it down, and got all the oil/muck/fish guts/other sea stuff out of it, and it turns great! Now it just needs to be turned into a jet :-) (easy, right?)

I have two questions. First, i'v attached a very crappy MS Paint version of my design. Do yuo think it's an ok design? Anyone see any major bad things about it? Any advice welcomed.

Secondly: How do you build a flame holder? I know it's a cylindrical pipe with holes in it, but i don't know the exact detiels. Do you just get a pipe that roughly the right size, and just randomly drill holes in it? Or is there some pattern for making holes, and/or some way of finding out the exact size and shape of the flame holder.

Once again...any advice welcomed. i really want to get this "off the ground". Please help...
Thanks

[larry cottrill]

I have two questions. First, i'v attached a very crappy MS Paint version of my design. Do yuo think it's an ok design? Anyone see any major bad things about it? Any advice welcomed.

Secondly: How do you build a flame holder? I know it's a cylindrical pipe with holes in it, but i don't know the exact detiels. Do you just get a pipe that roughly the right size, and just randomly drill holes in it? Or is there some pattern for making holes, and/or some way of finding out the exact size and shape of the flame holder.

adibrook -

I've never, ever thought of building one of these things, so naturally, I'll be happy to give you lots of great advice!

First, there's not much wrong with your drawing, except where the exhaust comes out of the combustion tube [flameholder] -- ideally, the holes in the rear of the flameholder are still forward of the boundary between the chamber and the 'nozzle' leading to the turbine. Basically, and ideally, here's what you want to happen:

The air leaves the compressor volute [the outer shell] with a heck of a velocity, but you need to convert this into static pressure. You do this by providing a 'diffuser' section -- a gradually expanding tube that leads to the chamber entrance. The air enters the chamber at fairly high pressure and only moderate velocity.

The air has to be made to take a pressure drop through the holes in the combustion tube -- that way, you know that all the flame stays captured inside the tube. The way you make sure you have that is that the total area of the holes should be somewhat smaller than the area of the chamber entrance. Usually, you'll have a slug of small holes uniformly scattered all over the front end of the tube, and a small number of somewhat larger holes at the tail end, just before the flame gets out into the exhaust nozzle. This final set of holes is called the 'dilution zone' and essentially acts as a kind of 'augmentor', leaning out the combusted mixture, slowing the exhaust flow somewhat, but also significantly increasing the combustion flow mass density while cooling it at the same time. The idea is to maximize the gas flow momentum that hits the turbine, while reducing the temperature significantly. Good news for your new turbine!

Just as the diffuser pipe traded off velocity in favor of pressure, your nozzle pipe must do the opposite -- increase velocity significantly while allowing static pressure to decrease practically to atmospheric. So, this should be a long cone that narrows to the inlet size of the turbine housing [volute].

Of course, you ought to hear from some guys who've done this. An interesting site that you've probably seen is the Kiwi Jet Powered Beer Cooler site:
http://www.asciimation.co.nz/beer
although it doesn't seem to me that he gives a lot of technical calculations and such truck. However, you can kind of see how he did things and get a feel for how the thing should be rigged. You may be clever enough with Google or some such to ferret out some other guys that have successfully built these.

It would be fun to know what kind of basic dimensions you have in the guts of your turbine and compressor. And useful, too, for some others out there who might actually know what they're talking about from experience.

And yes, you certainly did get lucky to get your hands on that piece of gear, in good condition, for zero outlay!

I hope what I've said here is basically correct; all I know about these engines is what I've read in very old engineering textbooks. But maybe this will kick some others who are more experienced into correcting whatever I got wrong and into giving you some more concrete advice!

Best of luck!

L Cottrill

[adibrook]

Ok...thanks. That was quiet alot of help.

So te hole pattern should be abit like this?

[larry cottrill]

Well, I think you could start with holes a lot closer to the front end than that -- you want to start getting some good mixing right away, and I'd think you'd want just enough 'dead space' in the front end to let your fuel spray fan out well into the space.

When you get down to these kinds of details, others would be much better than I to tell you what is actually known to work. As I said, I've never done it.

L Cottrill

[adibrook]

Oh...right. thanks. So, i reckon i'll start with the small holes, say, 25mm away from the front end?

[NanoSoft]

adibrook hello i have recently built a turbine engine that works! So i can give you advice.

to calculate the dims of your flame tube there is a cool program that you can use at this site http://www.ivcity.com/turbosoft

other then that its all pretty easy. But it depends on what fuel you are going to use. I used kero and it worked fine as long as you have a good fuel vaporizer and a good ignition source. One thing that suprised me when i tried to start mine was the amount of fuel it required to run. For more and better info join this yahoo group and goto the files section and there is all kinds of files and pictures to help you through your building experience. the link http://groups.yahoo.com/group/DIYGasTurbines/

hope this helps

[adibrook]

Ok...Thanks. that program is great! Now i know how many holes i need and what size!

Umm...this is going REALLY well. i have all the piping, the ignition system, and even the oil pump! All i need now is a motor to power the oil pump, a few metal bits (i can get them on monday) and a leafblower.

Will the engine still work with nothing on the exhaust? i know that it needs an exhaust cone to generate decent thrust, but for my first test ca i run it without an exhaust cone?

Also, what sort of fuel amount will it eat? Will i get away with starting it on the gas from a small propane blowtorch regualtor, or will i need a proper big camping stove bottle and regulator?

[NanoSoft]

Glad to here its coming along well. Yes you can start it without a jet pipe. Infact i suggest it, untill you work the bugs out. the exact amount of fuel my jet consumes is i don't know but i do know its close to 14 USg/hr without exhaust nozzle which increases fuel consumption even more and if you put a after burner on the fuel consumption goes way up.

to roughly figure out the fuel consumption. Join that yahoo group http://groups.yahoo.com/group/DIYGasTurbines/ goto files section and there is a document .txt file named Rule of Thumb number 9-1 to help. Its next a series of very useful documents i would look at them all. If you don't yahoo then i would recommend you join even if thats all you use it for because it is a very useful sight full of pictures of other peoples projects. Or i can post them if need be.

[adibrook]

This is getting "funny".

Basically, my mig suddenly started going wrong for no reason. the gas valve is leaking, and the wire control is not working. It allways feeds out wire at full speed, even if you tyrun the dial to low....bugger! Still, an engeneer from the welders maker company sent me his phone number, and i'll contact him on monday to see if that can be sorted out.

also, i need to find a way to attach the oil pump to the turbo...and i still need to find a motor to drive the pump. appart from that it's going well. the oil pump is a nissan power steering pump with it's own oil tank.

And...i also found an old oil pressure guage in my shed. It's off our old boat. It says methly chloride on it...that puzzles me abit, but still...i can remember it being a functioning oil pressure meter.

[Al Belli]

Your gage might have formerly lived as a temperature gage. The older British cars used a pencil shaped bulb filled with ethyl ether; a capillary tube ran to a pressure gage, which was calibrated in temperature units equivalent to the vapor pressure of the ether at various temperatures. Yours may have had methyl(ene) chloride in it as the working medium.

Al Belli

[adibrook]

Thats possible. However, the markings are in lb/inch^2 and in some other mesurement.

Either way...it should work ok