"Fat Boy" 12/118 thrust engine

[racket]

Hi Anders

Looks like the batteries "settled" overnight as they cooled off , voltage down to ~13.1 V by morning , recharged them again to 14 V , and had a tad more in the morning than the previous day , I think they're "full" ...............just gotta wait till the rain goes away before taking it back out for another test .

Cheers
John

[racket]

Hi Guys

Did a test run this morning , still only getting a "hung start" at ~22,000 rpm , need another 8,000 + rpm .

a bit of video youtu.be/i9XAYR3Zui4

At least this time theres was enough battery power that the oilpump kept enough pressure to keep the fuel pump activated ...........gotta think on this , I must be missing something .

The P2 gauge in the vid is registering the start propane pressure going to the multiple injection points .

Cheers
John

[dieselguy86]

John

What does the electric motor spin the rotor up to "dry"? Im curious if your starter just isnt spinning it fast enough?

My wren 44 turboshaft engine will spin the engine up to ~20,000rpms dry, and struggles to get it to 30,000 rpms during startup. If the o-ring in the bendix is wore too much ill have hung starts around 28k and rising egt's. Has to hit 30k to disengage the starter.

Joe

[racket]

Hi Joe

"Dry" she should spin her up to ~12,000 rpm , thats what I was getting with the old exhaust/turbine shroud , all I changed was the "pipe" , so I intend doing some comparison testing of the two , it'll only take a couple of minute to swap them around , I'm thinking the new pipe might be allowing more flow so maybe the rpm will be lower due to a greater load.

The starter can easily spin >30,000 rpm now that its equipped with the step up gearbox.

If there are differences in rpm I might try doing a start with the old pipe installed just to discount any of the "electrics"

Cheers
John

[racket]

Hi Joe

Just did a rough test of the two "pipes", even with the batteries discharged a bit from this mornings couple of start attempts , they both produced ~11,000 rpm .

I'll recharge batteries and repeat the testing, but at this stage theres not much in it ...........bummer :-(

Cheers
John

[Johansson]

Is there any chance you can use the leaf blower to give the rotor some extra spin during startup?

[Johansson]

Or add an impingement pipe in the turbine scroll and use scuba air as a boost starter?

[jetjeff]

Hi John,

Don't feel too bad about Fat Boy, I've been at turbine building off and on since 2008 and have yet to build a self sustaining engine. Hey, even the guys at Rolls Royce, G.E. and Pratt and Whitney have problems with their engines as you see on the news, from time to time.

Regards

Jeff

[racket]

Hi Anders

I think impingement is probably where I'll be going , I've been trying to fathom out a way of having the "old" exducer shroud for starting and then removing it once started , but can't seem to find a way to do it .

I'll do some fuel flow vs pressure checks just to make sure nothings blocked .

Hi Jeff

Yeh , none of us are immune from unforeseen problems , when I first contemplated this build I knew I was stretching my luck a bit as the parts weren't the most compatible , but I like a challenge to keep the grey cells alive, its certainly doing that :-((( .............ideally I need some "variable" devices to get "over the hump" ...........or a massive amount of starter power to get rpm high enough that the turb efficiency improves ............still a few things more to try :-)

Cheers
John

[enginewhisperer]

massive starter power sounds like a good plan to push the engine up to speed

I keep looking out for a big high pressure centrifugal blower that could be converted to a DC motor or petrol engine to work as a turbine start cart.

Otherwise what about putting together a quick turbo based bleed air starter?

[racket]

Hi Andrew

LOL...........Bleed air starter .........I think thats what this engine might be eventually .

Before I do anything I'll explore IGVs ...........heres my "logic??" ..........with preswirl the compressor gets "weakened" making the turbine more "powerful??" relatively speaking .

One of the problems I have is the inbalance of tip speeds , the comp is a lot bigger than the turb and as horsepower produced is a function of gas deflection and blade speed , if I can increase the turb blade speed, relatively speaking, then it might have the necessary power to spin the comp , I've got plenty of RPM reserves on both the comp and turb at my design ~60,000 rpm limit .

Cheers
John

[enginewhisperer]

What about a leaf blower starter setup with an additional electric ducted fan right in front of the comp inlet - to add some pressure / flow but also to induce swirl into the compressor?

There are a lot of cordless leaf blowers now using an axial fan, and some of them are pretty cheap (Bunnings had 240v ones for $25 the other week) but an RC EDF unit can probably be found in the right size with more power.

[racket]

Hi Andrew

Yep , lotsa of options , just been doing some research on preswirl vanes upstream of the comp inducer and its sounding good .

Maybe also some impingement from high pressure gases.

But first a start attempt with the old "pipe" ,.............batteries being recharged :-)

Cheers
John

[enginewhisperer]

good luck

[turboron]

John, 15 degrees with rotation will reduce mass flow and pressure ratio at a speed. Of course, the turbine also loses mass flow and pressure. Since you will be on the starter for part of the spin up I have no idea what the transient effect will be on the road to idle. The turbine scuba tank injection sounds more straight forward.

Thanks, Ron