GT3788VA Variable nozzle turbojet build

[mitch]

First post here, and pretty much my first real turbojet build. I had made one previously using a small garrett t25. Please ignore the mediocre welds haha, I am slowly getting better and most of the combustion chamber was done when I still didn't have much practice. I have lots of plans for this build, and will keep this updated with pics of the build and the components that are going into it. The unique thing about this build is that the VNT feature of the turbo will be used. 

[mitch]

[racket]

Hi Mitch

Welcome to the Group :-)

A coat of paint will soon fix those welds ..............what are your plans for the engine ?/

Cheers
John

[mitch]

Haha, a very thick coat of paint maybe. I have lots of plans for the engine. I plan to get it running and have figured out the VNT system, so I want to figure out how to run it and use the VNT to make more thrust and boost. It is a hybrid at the moment, as it has gaseous and liquid fuel systems, the liquid uses an evaporation tube system to atomize the fuel properly. After having it run reliably I will create a "ECU" for it that will make it so I can run it from a few feet away, and that will also log run information and have safeties built into it to kill the fuel should boost get too high, EGT get too high, or oil pressure drop too low. After that, it will be put onto a tricycle. ( the ECU will make controlling the jet from the handlebars of a bike much easier)

[racket]

Hi Mitch

The VNT will enable you to fine tune the turbine stage "stator" , but you won't get any more P2 (boost) or thrust than a normal scroll housing of the right size, thrust is a function of turbine inlet temperatures ( T I Ts) and component efficiencies , none of these can be "improved upon" by having the VNT .

A VNT can be a dangerous addition to an engine unless operated with extreme care, I'd normally recommend that once the best power position is determined , the vanes are fixed in that position and not moved .

I'll be looking forward to seeing the build progress :-)

Cheers
John

[mitch]

Thanks for clarifying that racket, that makes sense. What makes the VNT dangerous? Haha, so far, it has actually saved me. Before using an evaporator system, I had a liquid fuel nozzle just sitting open in the flame tube. It came loose as I forgot to tighten it down before a test run. The nozzle and compression fitting blew off and the VNT stators caught the 2 items before they could make it into the turbine wheel!
I'll upload pics of the aftermath.

[racket]

Hi Mitch

Potential disasters for a DIY turbine with VNT operated carelessly can include over speed , over temperature, surge and a bent shaft, please be careful.

Probably best to fix the vanes at around half movement , then adjust a little each way to find best operating condition .

That was a lucky escape :-)

Cheers
John

[mitch]

Oh, okay I see what you mean now. What I had in mind for the VNT system on this turbojet was to use voltage modulation to control the vane position. It uses oil pressure and a 0-12v signal to move the vanes around. 6-9 volts seems to place the vanes in a "middle" position, which should work well. Only think I am worried about is burning out the VNT solenoid, as in the large diesel truck it came off of, it would be constantly changing due to variance in engine speed. I thought about welding the vanes to the unison ring

[racket]

Hi Mitch

Is there any way you can make a manual vane adjuster ??

Voltage modulation sounds "good" , but things can go wrong and you don't see it happening unlike a manual control where theres a visual indication of vane positioning.

Cheers
John

[mitch]

I have thought about trying to make a manual vane adjuster, but my turbo uses a 3 phase electric actuator, which controls how the oil Tees off in the turbo, where the Teed oil is used to change the vane position. Would be much easier to make it manual if the turbo used vacuum, that way I could just remove the diaphragm and replace it with a lever of some sort.

[mitch]

Ordered a new oil pump this weekend, as my previous pump ( a 12v, 2.8 gpm 45 psi capable shurflo) wasn't able to supply the larger turbo with enough enough to make me happy. New pump comes in at flowing 5 gpm, 60 psi capable, and has better self priming capabilities.

[mitch]

Got the oil filter relocated, and got the engine up onto the stand

[racket]

Hi Mitch

Nicely mounted up ................plenty of umbilical and wires to hook up :-)

Cheers
John

[mitch]

[mitch]

Okay, need some help with this one. I tried to run my turbojet for the first time in about a month today, last time I ran it it ran fine. Today I go to start it- using a leaf blower and propane- and I could not hold combustion. When I do get ignition, the flame sputters bad, and ends up blowing small flames out the compressor side... I am stumped. When I push air through the turbojet assembly, hardly any comes out through the turbine side, almost like it is clogged. I even took the compressor housing and turbine housing off, inspected them, inspected the guide vanes, and nothing was out of the ordinary. The inlet tubing going from the compressor housing to the combustion chamber was hotter than I have ever felt it before, like flame was being routed into their instead of the exhaust pipe into the turbine housing. Anyone have any ideas?