75mm inducer jet engine won’t start.

[apm04]

I’m quite new to this forum and have never posted, but I’m a high schooler who is trying to build one of these engines.

No matter what I do I cannot get it to ignite in the flame tube. I’m almost 90% sure that’s the problem. I tried it with a torch at the back originally and had no luck, so I tapped a spark plug attached to a grill igniter into the top of the combustion chamber.

I run the igniter constantly and even after flushing the thing with air and only slightly cracking the propane, it won’t ignite. It makes me think I have a problem getting air into my flame tube. I am currently figuring out how to post photos to help pinpoint the problem. The propane is probably burning post-turbine because it just won’t light where the spark plug is.
The AR ratio is ≈0.73 and the exducer diameter is 70mm.

It’s a GT35R from ebay.

[apm04]

Uploaded an IMGUR album with relevant photos and can take as many as needed.

imgur.com/a/XFMO0kP

There is soot on the flame tube but I’m not sure why because the fuel is burning post turbine when lit.

[racket]

Hi

Stick with your torch at the turbine exducer , and with your leafblower , you'll be needing a leafblower for this size turbo , held a little way from the comp inlet but close enough for it to be gently rotating the compressor wheel , start feeding in your propane until you get it to ignite at the torch , the flame should then retreat back inside , increase the propane at the same time you engage the leafblower firmly against the comp housing inlet and give it more throttle to increase airflow through the engine .

If your propane flow is too great for the amount of air you'll have flames exiting the turb wheel , simply increase blower power if not already at full throttle , or gently retard propane supply .

I'm assuming you have already checkouty the relevant info here jetandturbineowners.proboards.com/thread/680/diy-turbines , just click on the icons for the info .

We all have problems getting that first spoolup to work so don't be hard on yourself :-)

To add pics to your Post you need to hit "Reply" not "Quick Reply ".

Cheers
John

[apm04]

Thank you for your advice. I’ll keep trying but I’m struggling to get the flames back into the combustion chamber even with the propane only slightly cracked.

Another notable detail is that after attempting to start it and even after thorough flushing of the air with a leafblower the flame tube reeks of propane when removed.

It’s possible I’m getting air bypassing the primary and maybe even secondary holes just to exit in the tertiary section. If you have any ideas as to if this is happening and or what to do about it I’m all ears. Thank you in advance for your advice.

[racket]

Hi

Thanks for the pics :-)

I'm assuming you don't have any sort of "restriction" between propane cylinder and engine other than the cylinder valve which can be used as a "throttle" .

Be careful your cylinder doesn't have an automatic shutoff if flows become "excessive for a BBQ" , we need a cylinder that gives uninterupted flows as we use many times more fuel than a BBQ .

Your flametube appears to be a tad "skinny" .

Do you have a Link to the Ebay specs for your turbo ??

Cheers
John

[racket]

Hi

Our engine "stink" of fuel when pulled apart , thats normal .

How did you "design" the flametube ??

With only a cracked propane valve and flames exiting the turbine , you need more airflow , you need to seal the blower against the comp housing , INCLUDING those surge slot holes which if left uncovered will simply spill too much pressure from the blower supply .

Cheers
John

[apm04]

Here’s a link to the eBay turbo

www.ebay.com/itm/154601745343?chn=ps&norover=1&mkevt=1&mkrid=711-117182-37290-0&mkcid=2&itemid=154601745343&targetid=1262749490102&device=m&mktype=&googleloc=9011833&poi=&campaignid=15428034462&mkgroupid=133947154481&rlsatarget=pla-1262749490102&abcId=9300763&merchantid=262594499&gclid=EAIaIQobChMIqNSq_bCw9gIVBY6zCh0shwRmEAQYAiABEgKNx_D_BwE

As for propane I have a forge regulator that gives me up to 35 psi as opposed to the 1psi of a grill regulator, however if this restriction is too high I can remove this regulator from the line.

I used jet spec for the hole areas and diameters and found my flame tube diameter(4 inches) by doubling the cross sectional area of my inducer.

[apm04]

I also have an attachment on my blower to completely seal the compressor inlet including the surge holes.

[racket]

Hi

Thanks for the turbo Link :-)

Ditch the regulator , our engines use more fuel than any forge , we need to supply fuel at pressures EXCEEDING the compressor discharge pressure , a 35 psi regulator on an engine running 35 psi of P2 , won't supply any fuel to the engine , you'd be needing a 70psi regulator , easier to simply use the cylinder valve , your engine , even at a high idle will be consuming half a pound of fuel per minute .

We need a minimum of 3 inducer areas for our flametube IDs , your 61.5mm inducer = 2970 sq mms X 3 = 8911 sq mms = 106.5 mm diameter for the ID , though if running propane it is possible to get away with a tad less, its not whats causing your problems at present .

Fuel injector ...................what design ??

Generally with propane usage , its either the fitting of a regulator, or the fuel injector design, that causes them to not fire up , propane MUST only be injected radially within the flametube , there MUST NOT be any axial injection as that only results in the fuel being blown straight down the flametube centre and out the turbine without mixing with the air .

We'll get her fired up , hang in there :-)

Cheers
John

[apm04]

The design I am using for my injector is just a bit of 1/2" pipe with 8 holes drilled radially. (4 on each side) I have it injecting around the middle of the primary stage with all gas exits occurring before the end of the primary holes. I'll also try ditching the regulator but I would have thought the issue was reversed(and that I had too rich a mixture) considering it only burned in open air.

Worst case scenario I imagine is that I have to figure out a way to grind the pipe out of the tube as I have it welded in there. I probably should have made it adjustable until I had startups down but oh well its a lesson learned.

[racket]

Hi

You need your holes to be equally spaced so that the radial spray covers the entire cross section of the flametube at the middle of your Primary holes , probably 2 rows of 6 holes , each row having them 60 degrees apart but the rows staggered so that there'll be 12 sprays at 30 degrees apart , the holes only need to be 1/16" - 1.6mm diameter , if they're much bigger theres not enough "pressure" to squirt the fuel across the flametube and we end up with a super rich mixture going down the centre of the flametube and not burning correctly .

If I understand correctly , you have a line of 4 holes drilled through the tube to produce another line of 4 holes on the other side , this would effectively be like only having 2 holes at 180 degrees , theres a lotta Primary air that hasn't got any fuel mixed with it , understandable why your engine is misbehaving , gotta have good fuel/air mixing :-(

Cheers
John

[apm04]

Thank you so much for this info. I’ll work on grinding the tube out of where it was and replacing it. Hopefully won’t be too hard

[racket]

Hi

One other thing I should mention and that is your fuel plumbing , it really needs to be SAFE , ideally metal tubing between tank and engine , at the least , metal anywhere near the engine , a gaseous propane leak will produce a very dangerous "explosive" situation .

Cheers
John

[apm04]

THANK YOU
I haven't quite gotten the propane regulator-less yet, but I redid my fuel injector exactly as you stated and I was able to produce a rumbling sound in the combustion chamber. I was also able to ramp it up and it boosted the crap out of the leafblower even at just 5PSI propane pressure. I didn't want to run it any higher as to not piss off the neighbors at this hour, but your advice really helped.


One more thing- I ran relatively "low" RPM in the grand scheme of things and my turbine wheel still got hot. Does this resolve itself once it picks up at idle or is there a problem with my flame tube?

[racket]

Hi

Congratulations :-)

Our temperatures generally are at their lowest with ~7-10 psi P2 from the comp , they then increase progressively as we ramp up the power , at low rpm/P2 of less than 5 psi P2 the temps increase the lower we get until a point is reached where the turbine wheel will fail ................meltdown :-(

Initially try for an idle of at least 5 psi P2 , any lower and you're heading towards a "hung start" scenario with potential to kill your engine , once you "understand" your engine you can play with idle settings.

With only 5 psi of propane delivery pressure you still haven't reached idling speed .

Things should get easier from here on :-)

Cheers
John