Turbojet heat issues

[sharky]

Ight thanks

[sharky]

That worked a treat, thanks for the help!

Test 3:
youtu.be/j6hYaEX-X9s?si=p8sbgcuGYjib8DCW

[racket]

What sort of numbers do you have now ??

[sharky]

Around 8 psi but at that point there was no color to the turbine what so ever so I probably could’ve turned it up higher.

Here’s a vid with a different camera where you can see the p2 gauge at around one minute in.

youtu.be/Sxv8AH6tfIg?si=Lj1RH_GjQGsk5HiA

[racket]

8 PSI is a healthy and safe idling speed , as long as the turbine wheel doesn't colour, its safe to take it up to higher rpm , try for 15 psi and then 20 psi , but don't go higher without more instrumentation

[sharky]

Alright, and as far as jet tubes go, is there any formula I can plug in to the turbo sizes to get an efficient one?

[racket]

With your jetpipe and nozzle , the jetpipe needs to ideally have an ID the same size as the scroll casting bore for the turbine wheel exducer so that theres a smooth transition , a tad larger is OK if it means a ready made size tubing .

As for the jet nozzle size , this is where things get difficult to "calculate" , it needs to be small enough to fully expand the gases , but not so small as to increase jetpipe gas temps past ~1200deg F- 650 C , or a dull red on the wheel .

You could start with a nozzle dia similar to your compressor wheel's inducer diameter to be on the safe side , actual required size will depend on a number of engine component variables, efficiencies etc etc , trial and error is the only way unless you have both compressor and turbine Maps for your turbo , if you do then it is possible to calculate a ballpark size , but the final sizing needs to be done on the running engine performance numbers .

[sharky]

Ok, just to check, the jet pipe is supposed to converge at the end right? My compressor inducer’s bigger than the turbine exducer so I just wanted to triple check before I buy pipe

[stoffe64]

As i have understood it ,the jetpipe outlet should be around the same diameter as the compressor wheel inducer

On my HX60 that would be 76mm,my comp wheel is 76mm inducer
My turbine wheel exducer is 86mm
When you put on the jetpipe on the outlet you gain more velocity and thrust

The engine becomes a turbojet, othervise without the jetpipe it is just a turbine engine!
I hope you understand what i tried to explain

[racket]

Hi

Could you please provide your comp and turb wheel dimensions please ..............it could be contributing to your heat problems if I read your comments correctly about the "hole in" is bigger than the "hole out " of the turbo rotor

Cheers
John

[stoffe64]

WOW...you have a big mismatch here my friend, your compressor wheel inducer is bigger than your turbine exducer!!
THAT is bad

Feb 27, 2024 17:56:47 GMT -5 sharky said:

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]

Hi Stephan

Thanks for that , yep , its a bad matching of parts ................I certainly wouldn't be fitting a jetnozzle on it until I'd explored higher P2s with an open pipe , if its temps are reasonable then maybe a slight reduction at the nozzle , but I doubt it'll accept much backpressure before temp get excessive :-(

Cheers
John

[stoffe64]

Hello John!
If it would be the other way around, to have a too big turbine wheel you can use water injection or water/methanol injektion to compensate for the small compressor wheel.

BUT on this engine....bleed off some compressor air? But then it overtemp Again....hmmm
Difficult one...it runs to some limitations but i consider this engine a achievment anyway...Good work there!
Hell....my project has been on for 10 years now,still NOT built...DUUUHHH!!
Cheers/Stephan

[sharky]

Ok, thanks everyone for this, I think I’ll probably just put a straight pipe on the end with some sort of v-band connection so I can try different converging pipe sections on the end easily until I find one that doesn’t heat the turbine up too much. Does this mean that an after burner’s out of the equation?

And also, what is the best way to find the turbine’s heat other than color? I was thinking of putting a temp probe in the sheet metal connection between the turbo and combustion chamber. Would that be accurate with back pressure?

Thanks a lot everyone,
Sharky

[richardm]

Make bacon shaped jet pipe that fits your turbo with a V band and an outlet diameter the same as your compressor inlet
Then you could experiment by increasing your jet pipe outlet area a little bit at a time by cutting a thin slice and see what you get .

Température can be monitored with a type K thermocouple positioned just after the turbine Could be installed in the jet pipe. Never install any device upstream in the flow to the turbine. A failing probe would damage the turbine.