A couple first timer questions

[ckliever]

Hello all,

It’s been a couple years since I started my build (T46 based). I got quite a bit of the fabrication of the combuster done before the project was set aside. I am back at it now and have a couple questions.

Is compressed air viable for use as startup or will it not generate enough velocity? I was imagining a nozzle mounted into the turbo inlet. What kind of psi would be needed?

For the oil system I plan to use a shureflo pump like others have. What type of pressure regulator can I use? Am I right that a simple T fitting with a ball valve and return line will not work?

Thanks for the info!!

Chris

[enginewhisperer]

depending on the pump you may find you don't need a regulator, but it can be harder to start the engine with high oil pressure when cold.
A ball valve and return will work but you'll have to keep an eye on the pressure.

I have used an adjustable fuel pressure regulator for this purpose in the past and it worked fine. You can also set it up to increase pressure with "boost" to let you run a lower pressure for starting.


If you're using compressed air you need it to impinge on the compressor wheel and spin it to generate enough flow.
Usually the easiest method is a large leaf blower, but it may need modification to get enough pressure.

[ckliever]

Thanks for the help! I may try the ball valve setup. My concern was the hard starting with cold oil. I plan to have an oil pressure gauge so I should be able to monitor and adjust pressure as the oil heats up.

When you say “impinge” I assume you mean the air needs to strike the inducer blades at an angle that produces maximum energy. My idea was to mount the nozzle in the intake hub at an angle to the inducer blades so the air would strike them at a 90 degree angle. If I could supply 100psi or so do you think a setup like that would work?

Do you or anyone else happen to know the thread pitch of the delavan variflo nozzles? I can’t seem to find the info online. Next step will be trial and error at the hardware store!

[racket]

Delavan oil burner fuel nozzles have thread measuring 9/16” - 24 UNEF.

Large leaf blower for starting , radial wheel on the leafblower NOT the newer axial fans as they don't like to produce pressure , pressure we need to force the air through the flametube holes

[ckliever]

Thanks for the nozzle thread info! Ok, I’ll scrap the compressed air start idea. Dang, I’m building a go kart for the motor and I hoped I could make it self sustaining but I didn’t want to try to make an electric starter.

[ckliever]

One more question: what are the options for gaskets/seals for the combustor end caps? Do people use high temp rtv sealant or will that not hold up under the heat?

[racket]

Its preferable to have flat surfaces that don't need anything , but some silicone sealant will do the job , just make sure your end cap is relatively thick so that it doesn't warp under the air pressure produced , so fairly close spaced fasteners

[ckliever]

Gotcha. I have my combuster built so I guess we’ll see if it is airtight or not and then go from there. I think I’ve got 20 bolts holding the end cap to the flange.

[racket]

That should do the job :-)

[ckliever]

Another question: what kind of fittings and oil line material are people using? My turbo has an outlet fitting that is 3/4 or 1” npt with what was probably a compression fitting on it. There’s a bit of rubber hose still inside but no compression sleeve or anything. Can I just use a barbed rubber hose fitting and an automotive hose back to the oil tank? The pressure is quite low from what I understand. Or do I need to use steel or copper hard lines?

Thanks!

[racket]

Be careful about rubber close to the turbine scroll as the radiant heat will degrade it , a bit of metal at that position and then some hose , there shouldn't be any pressure in the return, but still use large bore plumbing .

Full metal on the pressure delivery though

[ckliever]

Got it John, thanks.

I don’t want to use an oil cooler. How much oil would I need in my tank to keep temps down without running an oil cooler?

[racket]

Depending on the length of your run times and the size of the turbo ,the amount of lube required will change.

But considering our fuel burn rates, run times might only be 5 minutes , so 5 liters might be sufficient , though double that for a big turbo would be better especially with high ambient temps .

[ckliever]

My turbo is a T46 with a roughly 70mm inducer. Run times of 5 minutes sound reasonable so I’ll go with your 5 litre figure unless you think otherwise. Thanks!

[ckliever]

What type of thermocouple are people using and how should it be mounted in the jet pipe?