"Fat Boy" 12/118 thrust engine

[racket]

Hi Smithy

Yep , she'll be a tight fit , probably with some compromises that will undoubtedly have some negatives with regards power output .

I'll most likely make a "scroll" setup like I did for Andrews 10/98 freepower postimg.org/image/n1vv298xd/ , and by having the scroll inlet at the top where theres more room for it , by the time the gases get to the bottom the scroll can be reduced in width , the actual gearcase protrusion at the input is the same size as the root diameter of the wheel , I'm thinking of skimming a few millimetres off the diameter of the casing to provide that tad of clearance I need .

Its early days so lots more thinking to be done , but having gone through the process of making the last gearbox this is going to be a lot easier .

On a different note , I picked up another early 1954 copy of my Cohen and Rogers "bible" off aussie Ebay the other day for $11 , a steal .

Cheers
John

[madpatty]

Hi Racket,

Your threads are interesting as always.

Will this power turbine scroll setup be acting in reverse mode?

Gases entering axially and leaving radially from top.

Or else how this scroll can be used for axial power turbine?

Cheers.

[racket]

Hi Patty

The "scroll" is similar to a turbo scroll but its to the side of the axial wheel , it allows us to use an axial wheel whilst having the gases pass from the gearbox side of the wheel and exit cleanly into the atmosphere thru a diffusing exhaust

Cheers
John

[madpatty]

Hi Racket,

If i have interpreted it right, its like having the axial turbine wheel in the exducer portion of the otherwise radial turbine scroll..

As if there is the radial turbine wheel with only exducer portion.

Can you share some more pics of that scroll if you can.

Thanks.

[racket]

Hi Patty

Heres one other postimg.org/image/7taj284mp/ , there aren't many pics unfortunately .

All I try to do is gradually reduce the cross section of the "scroll" as it wraps around the side of the axial wheel blades , the reduction in area "forces" the gases through the wheel .

Cheers
John

[racket]

A couple of pics from inside the gearbox



And the pinion shaft and gear

[racket]

The original snout on the gearbox input was a bit too big in diameter for the hub diameter of the 4th stage C30 wheel after allowing for ducting wall thickness as well as an insulating blanket , so it needed turning down a bit from agricultural industrial to "aerospace"



Now I've got to find a way to get some pressure lube spray jets into the snout to lube the pinion bearings and gear mesh

[racket]

Finally , the teststand and engine are on the trailer ready to be hooked up to the car , hopefully if the weather is OK , just a couple of days now until I get some decent numbers .

[smithy1]

Where are you thinking of taking it John?? The "test area" near the kart track??

Be sure to use that nice Jet-A1....the 20L should last at least 30 secs.. ;-)

Cheers,
Smithy.

[racket]

Hi Smithy

Yep , the "test track" just outside the motocross track ..............I had mixed results , I'm still checking out video to try and understand why one thermocouple was measuring 920 C whilst the other only had mid 600 C , resulting in a quick shutdown from ~25 P2 .

At 25 psi P2 the fuel pump was "out of breath" on 12 Volts , the dump valve was fully closed and I was winding on PWM power , she's thirsty, but certainly making power with 4 psi of total pressure measured at the pitot, from the blast coming out of the turbine wheel into that open diffuser pipe. .

I'll write up my thoughts tomorrow ..............thankfully the turbine wheel looks OK, and the rotor was still spinning freely afterwards .

Cheers
John

[smithy1]

Hmmm, 920C is a bit high, 600C is a lot better...but I think your high reading T/C is possibly not reading correctly, loose connection or localized hot spot somewhere maybe??.... you'd certainly know if it was actually that hot, she'd be really glowing....besides, when we had it running at the kart track a couple of months ago, everything was spot on, no silly temps, all pressures were good and it was running very nicely as well as making a lovely noise, albeit at a reasonably low P2.

I remember checking all the gauges several times while you were fiddling with the controls, she was purring away beautifully and I didn't see anything untoward or abnormal.

If you did indeed have 920C egt, the TIT would have been close to 1100C..!!! There would be evidence of that for sure, turbine inducer tips would at least be a bit "coloured" one would think.

Cheers,
Smithy.

[racket]

Hi Smithy

I started checking things , thermocouples are OK , held both together in a gas flame and both registered similar temps up to the ~850 C max I took them to , the colouration of both tips went through the same spectrum range as would be expected of their relevant temps , both cooled down at the same temp reading rate once removed from the flame so I can discount that as a potential candidate .

Next I checked the two P2 gauges against each other when connected to a tee piece , both within a psi or so of each other , so OK there.

Decided to check fuel pressure gauge as well as flow , everything OK .

Time to pull the engine and have a look inside, thankfully nothing appears damaged , though very dirty inside outer can , lotsa black soot with witness marks of "fluid" being "spun" through it .

Thought I'd better check the orientation of that "fluid" flow , just ordinary residual comp outflow swirl , but there was the appearance of overheating in the "top" of the flametube , which if was the case of an extra hot flame would after going through the NGV and turb , exit at the 920 deg C thermocouple .

Now all I had to find is the cause .

Cheers
John

[madpatty]

Hi Racket,

Very similar to what i was encountering sometime ago with my flametube..

A hotspot both in the flametube and NGV exactly at the same position everytime.

Interesting to find out what the cause is in your case.

Cheers.

[racket]

Hi Patty

I think I've found the problem during the test run .

Initially during the test at 0.5 bar P2 , TOT temps were 639 and 570 C with rpm of ~33,000 and a T2-T1 of 65 C degrees during compression , this gives a very poor 55% effic , but this could be different if the P2 g/g was a mere 1 psi under reading , something that a cheap non calibrated g/g could do .

At a 1.0 bar P2 TOT of 611 and 537 C at ~44,000 rpm with a 100 deg C rise during compression for an efficiency of ~65% .....getting better.

But once extra fuel was added to get to a 1.5 bar P2 , that TOT spiked to 927 C on one thermocouple but only 600 odd degrees on the other , fuel pressure at 68 psi , so a pressure drop of a bit over 40 psi on the injectors .

Today I did a water flow test of the injectors at 40 psi


Measured flow rate was 2,200 ml/minute .

With the engine level/horizontal , there was water dribbling back out of the mouths on 6 of the lower evaporators , this is partly explained by the fact that all of the evaporators are positioned with their outlets on a smaller radius from the shaft than their inlets so that the outlets are positioned towards the center of the flametube annulus, this downward slope towards the inlet on the lower evaps would aid in the flow reversing, but this isn't the complete story , the waist that I fitted into my evaporators was acting as a bit of a dam wall preventing the water from being forced along the evaporator by its velocity out of the injector .

The witness marks in the soot covering the outer cans inner wall indicate a fluid being swirled around it , this is probably the fuel dribbling out of the evaporator , another indicator is a difference in colour of the rear wall of the flametube where that dribbling has occurred compared to the rest of the wall.

Normally the air velocity into the evaporator aids in forcing the fuel along the evaporator inside wall , but because of the ~9.5mm dia waist in my 11.5 mm ID evaporator , nearly 50% greater area , there isn't such a high velocity at the mouth to prevent dribbling .

Theres a case to be made for a modification to my fuel manifold with longer injection syringe segments so that their outlets are beyond the waist , this will mean the waist/dam wall will prevent outflow not only from the wall but also the higher air speed through the waist "throat" .

Considering the high water flow at 40 psi "fuel pressure"drop at a mere 1.5 bar - 22 psi P2 , full throttle flow will be in excess of 100 psi and closer to 3 litres/min than the projected 2.5 lpm , so maybe I need to go to the next larger gauge syringe needle for the injectors to both lower pressure but also give more strength to the longer injector length .

A few more pics of the flametube








And the "hot" segment at the top of the FT



Cheers
John

[racket]

Some video of the run, ............LOL, taken by my assistant from a "safe" distance youtu.be/EGG4OpEUFYM

Best part is that 4 psi of P4t coming out of the engine .