75mm inducer jet engine won’t start.

[apm04]

Propane line without the regulator is still on its way. In the mean time I did another spool up and had a rude awakening in regards to my oil system.
Its always been quite loud but after spooling it up and then back down again the bearing stopped moving a little earlier than normal. I thought I had cooked it. I shut it all off and let the oil pump circulate oil and it eventually solved itself, but I feel like I was incredibly close to losing the turbo. I decided to do a quick tour of my oil system and posted it to youtube here:

youtu.be/gh-c0X4qREs


I have the specs of the pump and turbo in/outlets in the description. Is the pump oversized or is it a different problem?

[racket]

Hi

Yep , a grossly oversized pump .

Theres a good chance you have cavitation problems with the pumps inlet , if it has 1" fittings then you need probably at least a 1" ID suction line between oiltank and pump .

There could also be a problem with your oil tank fittings , the suction pickup looks "undersized" as well .

Solution ................install a 1" nipple and tee piece at the oil pump suction inlet , have your pressure side bypass going to one of the tee sides and your oil tank supply to the other, this way your pump can suck through the large bore of the 1" nipple without restriction , the upstream tee being fed from both the tank and bypass will comfortably reduce any restrictions , you could add an oil cooler in the bypass line .

On the outlet side of your pump there might be some restriction feeding into the 1/2" Tee piece , it might also benefit from increasing in size , but try the suction side mods first

Cheers
John

[apm04]

Thank you for all of the advice. Every time I have followed it my success rate has improved. I made a couple other changes and I also added a needle valve. I can get it to spool every single time now. I'm also able to throttle it up. I am so close to idle, but right as I am about to reach idle speed while increasing fuel flow, I suddenly lose power and it spools back down again. I am linking a video in case that helps for diagnosis of the problem. I also have photos of the flame tube after a bunch of hot runs to see if the heat marks indicate any problems.



www.youtube.com/watch?v=SvcmKH0QrX4


Here's some images of the flame tube:

[racket]

Hi

Your propane cylinder may have a "safety" device to prevent large amounts of discharge , and your sized turbo will need "large amounts" , some countries have these "safety??" devices

Cheers
John

[apm04]

I've done a bit of research on this since you've told me, and I cannot seem to find a safe way around it. My country(USA) only sells tanks with OPD valves. These valves have a built in excess flow check valve that shuts off all flow if it exceeds a certain rate. To get around this, could I just run two tanks in parallel for double the flow rate? I'm getting close to half already.

[racket]

OK , two tanks might do the job getting you to self sustain , but it won't allow you to get to high power settings , maybe time to think about some liquid fuel spray to augment your propane.

Or try and source a forklift truck/ industrial propane tank without the safety shutoff .

As you have already got the engine alight and spooling up , I think I'd be inclined to simply add liquid fuel into your propane flame "pilot light" so that you can explore your engines "envelope" ;-)

Cheers
John

[apm04]

It worked! It ran great and I got it up to speed about twice in a row. It idled without a hitch and pushed past the hung start stage easily. However, today I ran it and had a spectator watching turbine temp. I misread a command and added more gas instead of cutting it and the turbine wheel cooked itself. Currently coping with it. At least I got footage of it idling. Though I would really like to fix it and I am not quite sure what my next step is. I have looked into new turbine wheels(unlikely), buying the same turbo again, or buying a real Garrett gt35 instead of a cheap eBay Chinese turbo. I would have to be convinced that it'd be harder to ruin a higher quality turbo because I especially don't want to dump cash into a more expensive turbo to have the same operating failure. The hot start took mere seconds to destroy my current one and I am not sure if I want to do that to a more expensive one

[racket]

Yep , cooked turbine wheels don't "taste" very nice :-(

But you can cook an expensive wheel as easily as a cheap one , theres only a few hundred degrees of temp difference , probably better at this stage to stick with the cheap versions and correct the operational parameters .

Do you have a P2 gauge on your engine ??

If you do , then an idle speed this early in your development needs to be ~7-10 psi , this should ensure that the comp is operating at reasonable efficiencies , once you are confident with your engines operation , then and only then , start to reduce idle P2s , but don't go below ~4 psi without a jetnozzle attached , or 5 psi with one , your jetpipe temperature gauge is your best friend at low power settings , temps should be below 600deg C -1100 F , several seconds of higher temps during a spoolup are OK , but be careful of extended spoolups with high temps,...... a fast start is a good start :-)

Cheers
John

[apm04]

Alright. It's only $120 for a replacement I might as well order one. In the meantime I do need to fit a P2 gauge and a couple of other doodads other than just a person to see if it "gets hot" lol. Do you have any suggestions for cheap instruments with good enough response times?

[racket]

Ebay is the place to go , you'll need a sheathed K type thermocouple for the jetpipe temps and a compatable thermometer , an oil pressure gauge and a P2 gauge as a minimum

[dieselguy93]

Hello apm04 I too am from the U.S. and had a struggle for a while with the safety valve but finally got a setup to work. If you’re interested just shoot me a pm. Hope you get it all sorted out and don’t have anymore turbines cook.

[apm04]

What's up diesel. This is a VERY late reply as I don't check this forum very often anymore, but I had my engine finished last year and cooked the shit out of it lol. I am in college now so I don't have much time for it but I've considered another project at some point in the future. Let me know if you have any questions. Safety valve was a hidden issue that not many had discussed besides racket here. I likely won't be on this forum very much if at all so if you want to contact me regularly enough you might want to pm me some kind of contact info so I can be in touch.