Turbojet heat issues

[sharky]

Hey all, I’m in high school and am new to this forum but for the past few months I’ve been working on building a turbojet with an eBay turbo (76mm) and have finally got it running! The only problem though is that when it is running the turbine is getting far past the dull red color I’ve been told is safe. My only thoughts of what could be happening is that the oil is getting far too hot and isn’t having as great of a cooling effect that is could be. Can anyone here tell me if this is the case and what else I could possibly do to fix it?
Here’s a YouTube video of it running:

youtu.be/4vAObWd09ug?si=jXADbPr2RPJmOHOk

Thanks in advance

[enginewhisperer]

Do you have the specs of the turbo?
Chances are the compressor to turbine sizes are a bit mismatched for turbine use.

[sharky]

Yeah sure, this is straight off the eBay page:
Compressor:
A/R 0.80
Inducer 76.6mm
Exducer 102.3mm
Inlet 4"
Outlet 2.5"

Turbine:
A/R 0.96
Inducer 73.5mm
Exducer 64.3mm
Turbine flange T4
Outlet V band

Cooled type: Oil cold Only
Bearing: Floating Bearing
Power : Up to 600-1000HP

[racket]

Fuel injector ............design specs please

Also the turbine stage is too small , though without a jet nozzle it should still not need to get that hot

[racket]

And please , do not go anywhere near the exhaust with a wheel running at anymore than dull red , that wheel of yours is ready to turn into shrapnel and when it does you'll end up with a face full of metal :-(

[sharky]

Yeah, that’s probably a good idea. As far as the injector goes, I have a fuel rail with 10 holes 5 on each side, extending about 7” into the flame tube. What size ratio of the compressor to turbine would be best?

[sharky]

The holes are 1mm in diameter

[racket]

Hi

Have you read through here jetandturbineowners.proboards.com/thread/680/diy-turbines , just click on the icons for the info .

"Fuel rail " could you please explain what you mean by " 5 holes each side ".

Your propane needs to be injected radially within the flametube at the level of the Primary holes , NO axial injection .

The fuel needs to be injected across the entire cross section of the flametube , so generally a tube with its end blanked off with a couple of rows of 6 X 1mm holes equally spaced around the tube is all thats required .

Your 76 mm inducer is getting a tad large for propane unless a very large cylinder is used to allow sufficient flow for full power runs .

Generally high temps, when no jet nozzle fitted, when using propane is caused by poor fuel injection causing late combustion .

Ideally the turbine exducer area needs to be ~20% larger in area than the comp inducer area , currently your exducer at 3247 sq mms vs your inducer at 4536 sq mms is only ~72% rather than 120% , this will put excessive backpressure on the engine causing the comp to run possibly into the surge region of the map at poor efficiency which will require more power from the turbine, being generated by higher temperatures .


Though as I mentioned in my earlier email , without a jet nozzle and any extra backpressure theres a chance the engine will operate without those excessive temps , it'll depend on just how wide the comp map is .

But I'd be looking at the fuel injection first :-)

Cheers
John

[sharky]

Ok, thanks! I’ll fix the injector and get back to you

[sharky]

Oh, and by “fuel rail” just mean the pipe that has the injector holes. I read on the documents you linked that you need at least 50 psi of oil pressure. My 12v pump puts out around 20psi at full speed, should I just get a different pump or is it more about flow rate. The pump is rated for 3.2 gallons per minute although I find it hard to believe it’s getting up to that.

Thanks

[racket]

We need that 50 psi measured at the turbo inlet , the actual flow rate through the turbo will be dependent on how hot the oil is and its ability to flow through the turbo , so we don't want too thick an oil used in cold weather .

Theres no way your pump is flowing 3.2 GPM - 12 lpm , there would be barely a quarter of that going through your turbo when cold, my pump only flows ~10 lpm and I have 70 psi delivery pressure through much larger bearings etc

Disconnect your turbo drain from the tank and do a measurement test of what is actually passing through the turbo to determine what your pump is producing

Cheers
John

[sharky]

Ok thanks, I’ll do that

[sharky]

I tried it with the new injector just as described and to me it seems to be doing worse? I’m not entirely sure(especially since I’ve found some more leaks in the weld) what could be wrong but all that seems to have changed is 1. I can no longer get it to sustain, and 2. When I turn up the gas way higher to try to get it going, flames start to exit the turbine. This was happening before too but far after I got it sustaining. I’m pretty sure the leaks are old because I don’t know what could have made them, which means it was running before despite the leaks. I’m not entirely sure what’s happening but would appreciate any help.
Thanks

[sharky]

Also I fixed the oil pressure:)

[racket]

Hi

OK , next lets look at the combustion chamber.

From your video it appears to be more than large enough , but the first thing that could be wrong is the air delivery tube positioning at the Primary end , not a good idea as it tends to cause combustion issues as the flame gets blown to one side .

Also , how is your flametube designed ??

Is all air going through the wall holes of the flametube ??

What is the inlet to the comp housing like ??

More pics and video would be appreciated, as they make diagnosis easier :-)

Cheers
John