First turbojet almost complete! What fuel?

[noshell]

Hi everyone, my first post/engine so be kind!
Ive built myself a fairly small turbojet and am nearing startup.

Its pretty small, the inducer is 29mm. I used jetspecs for the calculations.

What kindof gas is best to use? I have aquired a 10kg butane bottle, but i understand butane is fairly low pressure. Can this work? If not what gas is best to use.

[racket]

Hi

Welcome :-)

It'll be good enough to get it fired up , if you want more pressure keep the cylinder warmed.

All the best with the spoolup , you'll be needing a lot of rpm, >50,000 , so strong starting setup .

Cheers
John

[noshell]

Thanks for the reply.To be honest my leaf blower barely spins it over its only a cheap one.
Maybe like 1000rpm.The turbocharger seems in good condition, i mean its a journal bearing turbo so there is a fair amount of resistance. Is there no chance it will just gradually get itself going?

Oh, also. I am i correct in assuming a regulator wont flow enough gas? They all say 1.5kg per hour. This must be only a few psi. I imagine an unregulated valve will be better.

[smithy1]

Jul 28, 2021 0:29:09 GMT -5 noshell said:

Thanks for the reply.
To be honest my leaf blower barely spins it over its only a cheap one.
Maybe like 1000rpm.
The turbocharger seems in good condition, i mean its a journal bearing turbo so there is a fair amount of resistance.

Is there no chance it will just gradually get itself going?

No, 1000rpm is nowhere near enough on an engine that size...it will also have a bit more resistance with oil pressure too, the faster you can spin it the easier it is to get running and "over the hump". If you try to start with the rpm too low, it will just get hot.

My 106mm inducered engine needs ~10,000rpm even before I think about lighting it up...it will self sustain at ~20,000 and idles nicely at ~25,000-28,000.

Smithy.

[noshell]

Got it started
Add the td025 to the list of working turbos. Haha
Got it started on butane, runs lovley. Goes mad if you turn the bottle upside down but does sometimes cut out.

Managed to get it going with the leaf blower, i reckon it gets itself going from a few thousand rpm tbh, it gets a big BOOF out the back and thats enough to get her going.

Super happy 😊

[racket]

Congratulations :-)

LOL.......you might be getting a flame alight at a few thousand rpm but selfsustain will be ~70,000 and idle will be closer to 100,000 rpm , keep the starter on her until you see >5psi P2

Do you have a P2 gauge on the engine to know what pressure the comp is turning out , probably best not to go past ~15-18 psi

Cheers
John

[noshell]

Thanks
Ill stick a gauge on and have a look.

It does not suck very hard from the compressor opening. But it runs nice and smooth. Im not sure if it needs more or less holes in the flame tube.

I plan on having the oil pump powered by the boost itself. I notice nobody else has done this so im keen to do that.

Ive built several steam/compressed air engines so making one shouldnt be too much trouble.

[racket]

Its a very small turbo , so not a huge mass flow , you may find that any bleed air to power a pump may send your temperatures too high , be careful .

As for flametube holes , as long as you followed Jetspecs you should be OK

[smithy1]

Aug 8, 2021 0:52:47 GMT -5 noshell said:

Thanks

I plan on having the oil pump powered by the boost itself. I notice nobody else has done this so im keen to do that.

If you wish to use boost pressure to pressurize an oil tank to feed the bearings, you may want to think twice. Max boost pressure will be quite small if you keep it to 15-18 psi as John suggestes I'd imagine which would be marginal..... and only ~4-5psi @ idle....you'll need more oil pressure than that methinks.

Smithy.

[noshell]

So, my bright idea is to have two air cylinders per oil cylinder, so in theory 4psi boost would produce 8psi of oil pressure, and i could just have a restrictor or bleed off so pressure cant exceed 14psi or so.

Its all a tad ambitious but itl be interesting.

I ran it the other day with a boost line going to my mamod steam engine hahaa. Just to see if it produces enough boost and flow to run it. Safe to say it runs it easily so j should be able to make an air powered oil pump.

[wannabebuilderuk]

Aug 12, 2021 10:29:32 GMT -5 noshell said:

So, my bright idea is to have two air cylinders per oil cylinder, so in theory 4psi boost would produce 8psi of oil pressure, and i could just have a restrictor or bleed off so pressure cant exceed 14psi or so.

Its all a tad ambitious but itl be interesting.

I ran it the other day with a boost line going to my mamod steam engine hahaa. Just to see if it produces enough boost and flow to run it. Safe to say it runs it easily so j should be able to make an air powered oil pump.

Turbos need at least 40psi to function properly and not get destroyed if they're not ball-bearing style cores.