First post, first attempt at building a turbo jet.

[sputnik]

Hi all,

I figured I'd start a thread given I've only just found this forum and A, thought I'd share my project and B, ask for some wisdom from the experts on here!

Long story short I've been learning TIG welding and decided to scratch an itch I've had for ages and use my newly learned (and by no means perfected) welding skills to build a turbo jet.

Here's my progress so far:



The turbo is a 76mm journal bearing Borg-Warner unit from a Mercedes truck.






I made the combustion chamber by rolling 1.5mm 304 stainless sheet to give me a tube of just under 7" diameter and seam welded it.






The flame tube has been made from a 5" 304 stainless tube, I followed the maths from Colin Furzes website for the hole sizes, they are as follows:
Primary holes - 24 holes at ~7.5mm
Secondary holes - 8 holes at ~10mm
Tertiary holes - 8 holes at ~17mm

The fuel rail (designed for BBQ gas at the moment) is 20mm diameter with 18x 3mm holes drilled in it.




That's everything currently "built".  Other bits I have are:
 - Oil pump* - this will be made up of a power steering pump from an MX5 (Miata for all you guys from across the pond ) and will be driven by a 12v electric motor of which I am yet to acquire.
 - Ignition - I have an igniter from a gas BBQ that will be mounted into the end of the flame tube.
 - Gauges - I have oil temp and pressure gauges
 - Trusty leaf blower for starting

Bits I'm yet to make are:
 - Exhaust section - I plan on making this later once the jet runs, I will be going down the afterburner route provided all works well.
 - *Oil pump - I may change plans if I can find a budget 12v or 240v oil pump.
 - Thermocouple for EGTs
 - Oil reservoir and pipework

Now onto some questions I hope you guys can help me with:

1. Firstly have I made any glaring mistakes, anything I'll need to change in order for the jet to run eventually?
2. Oil supply, this has been my biggest hurdle so far as I know very little about the turbo I have.  Its an old journal bearing turbo and all the literature I can find is for the updated ball bearing equivalent.  So I don't really know how much pressure and flow it will require, if I need a restrictor fitted or not etc...  So any help in that regard would be really appreciated.
3. I've seen most people use spark plugs for ignition, I managed to pick up a BBQ igniter cheap so bought that as it came with wiring and a button etc...  Is this a bad idea?
4. Is my fuel rail design appropriate?  I kind of winged that bit from looking at photos of other peoples builds online before finding this forum.
5. If anyone can recommend a budget alternative to my oil pump, and / or any links to thermocouples with gauges or how to plumb one in with a gauge please let me know.
6. As I said at the start this has been a good excuse for me to practise my TIG welding.  As such whilst welding captive nuts onto the inside of the combustion chamber (to allow the flame tube to be bolted in) I had some warping of the flange due to me putting to much heat in to the metal.  Does this mating surface need to be a perfect seal?


Finally if you've made it this far thanks for reading, I'm new to the forum so apologies if I've asked questions that are covered elsewhere (I have read several other informative posts and had a search round but could do with some input for my particular set up).  Also feel free to critique my design, build and welds, I'm here to learn so constructive criticism is welcomed.

Cheers, Rob 

[racket]

Hi Rob

Welcome to the Forum :-)

Maybe have a read here jetandturbineowners.proboards.com/thread/680/diy-turbines and I'll get back to you on your questions

Cheers
John

[racket]

Hi Rob

LOL.....your first mistake was following Colins suggestions :-(

Use Jetspecs www.nuclearprojects.com/jetspecs/

Oil supply .............at least 45 psi and lots of it so NO restrictors/restrictions , with pressure pickup at the turbo lube inlet .

Ignition , high voltage generator units off ebay

Your fuel injector is too long , it only needs small holes 12X1/16" dia and all pointing radially at the Primary holes

Turbine outlet temp gauge , ...............K type sheathed thermocouples and Digital thermometer off Ebay , not expensive .

Cheers
John

[sputnik]

Hi John,

Thanks for the feedback those links are really helpful! I'll take a look at jetspecs this afternoon and see how far off I am

As for the fuel rail I should have added I haven't cut it to length yet as I need to drill the hole and mount a collar for it still. (Assuming you ment the overall length and not just the length of the perforated section).

Probably a daft question but is the idea with those high voltage generators to use them to power a spark plug?

Thanks again,

Rob

[racket]

Hi Rob

Jetspecs will produce a working combustor .

The fuel injector perforated section is a tad long , you can use just 2 closely spaced rows of 6 holes each with holes 30 degrees apart so that theres good coverage of the flametube cross sectional area , discharging between your two rows of Primary holes , you need small discharge holes so that the fuel will travel across the flametube , too many large holes produce a fuel rich core within the flametube and potential combustion issues.

Yep , those high voltage generators throw a decent spark , but they have limited duty cycle so turn off as soon as ignite happens .

Your endcap is a bit too thin , I'd suggest increasing the number of bolts to try and flatten it out , a good seal is imperative if you want the engine to perform , any leakage of compressed air means your turbine stage has to work much harder , reducing thrust potential from the engine , and increasing turbine temperatures .

Cheers
John

[sputnik]

Hi John,

Yes you're spot on about it being thin. I ended up using some sheet steel I already had. But in hindsight it wasnt the best idea, I may just remake the flame tube and end cap, I'll see how the results from jetspecs go and determine if mine is salvagable. Fortunately I bought a decent length of pipe for the fuel rail so I can just re-do that with what's left.

Thanks for all your help thus far John, I'll let you know how I get on.

Cheers,

Rob

[sputnik]

Hi guys, little update.

So good news is that I checked all my maths and hole sizes against Jetspecs and fortunately my flame tube is near enough spot on.

Also I realised I'd made an error when cutting the flame tube I left it a couple of mil too long as opposed to too short for the expansion gap.  This lead to the gapping between the flame tube and housing that I thought was caused by warping from the welding.  ie the bottom of the flame tube was fouling the bottom of the combustion chamber leading to a gap at the top.  Now that been fettled it sits flush as pictured below.





Since my last post I've knocked up a test bench from some box section and got hold of:
- Oil feed and return pipework
- A thermocouple
- A power steering pump and electric wiper motor for the oil system
- A 12v battery

All of this is yet to be set up, below is how the set up is so far.





Going forward I could do with some more help please.
- Can anyone recommend gasket material that will handle the temperatures between the combustion chamber and turbo exhaust housing.  (As I've used thin material I cant guarantee a good seal.)
- Also has anyone else used a wiper motor and power steering pump to power their oil system?  If so did you have to step it up or down or can I link the the shafts to each other 1:1?  If that makes sense.
Failing that is there a way to calculate RPM?

Thanks for looking and any help, Rob

[racket]

Your wiper motor might be a tad underpowered , there are 24V 500W scooter motors that if run on 12V produce reasonable rpm for 1 : 1 connections to oil pumps , thats what I like to use .

As for the turb scroll seal , its unknown just what sort of expansionary distortions there will be with your thin flange , but you could try some muffler putty

[sputnik]

Hi guys,

Bit of an update after a while away (kids, house etc slows this stuff down  ).

As far as things go since my last post I have remade and fitted the fuel rail as per Rackets tips above.  I've also fitted the spark plug, got my hands on some stove gasket material to add a layer between the cap and combustion chamber and bit the bullet and upgraded my oil pump set up to a scooter motor.  I also mounted up an oil cooler and filter, which may be overkill but I've got a small reservoir so went for it anyway.  As it sits now it looks like this:








The next jobs to go through are to finish the reservoir and start the wiring.  2 questions I have at the moment are:

 - Does the reservoir need to be sealed or vented?
 - As this will be run on BBQ gas what's the procedure for hoking this up to the fuel rail safely?  Do I need a non-return valve etc?

TIA

[racket]

Hi Rob

Oil tank needs to be vented as theres always some air/gases being dumped into it with the returning oil , the return line MUST be positioned ABOVE the oil level, the oil level will rise somewhat when running due to there being some entrapped air, so allow some buffer .

You shouldn't need a non return valve in the propane line as the gas pressure will always need to be above combustor pressure otherwise the engine won't work .

Cheers
John

[sputnik]

Thanks John,

On a side note I'm loosing access to the machine shop I used to roll the flame tube. For this reason I'm going to roll the cones for the exhaust / afterburner now (even though the jet doesnt run yet).
I got the maths for that off Andy Morris' video, my question is that the exhaust outlet of the turbo measures 80mm, I've got some 73mm tubing spare so I could use that for the first section (pre cone) if that makes sense, will stepping down with this restriction cause running issues?

Cheers
Rob

[racket]

Hi Rob

Its better if you don't reduce the flow area as losses will be the result , having said that , if you can do it smoothly , you might reduce them

Cheers
John

[sputnik]

Hi all,



Finally got everything together and outside for its first test.  This is how the set up currently looks:









Unfortunately that's where the good news ends annoyingly the high voltage generator for the spark plug died almost immediately so I'll have to replace that.

But more crucially I'm having real trouble with my oil system  .  Below is a diagram of the oil system routing and an image of the system itself.  When I run the pump the oil doesn't flow smoothly, there's air gaps and bubbles in the oil, as i tried closing the valve to direct oil up to the turbo the pressure at the turbo is still showed 0psi but the pipes throughout the system repeatedly blew apart (showering the house with oil, which my wife is thrilled about  ).
I've checked and the turbo is getting oil to it (only a trickle) and the oil is returning to the reservoir however I'm still stuck as to what's causing the flow/pressure issues around the system?






Any help is greatly appreciated, thanks,

Rob

[racket]

Hi Rob

I think you need to plumb things differently .............oil tank direct to pump with large diameter tubing to prevent cavitation , out of pump to oil cooler , oil cooler to filter , out of filter to tee piece with one side to turbo and the other back to oiltank via bleed valve to maintain pressure measured at turbo oil inlet.

Your current setup where your oilpump is sucking through the cooler is most likely the cause of your problems

Cheers
John

[sputnik]

Thanks John,

I did try by-passing the oil cooler altogether but it made no difference. I will replumb the system as you've suggested though and give it another go.

Thanks for the help!