"Fat Boy" 12/118 thrust engine

[Johansson]

Bohoo, no video...

[racket]

Hi Anders

Nope , no video , it was a bit of a spur of the moment decision to do a test as the weather was turning nasty , nothing really to show , just an engine making lotsa noise , though it was producing some thrust as the test stand started moving backwards, even though on soft grass, until it came up against its tethering rope.

I had a good look up into the turbine wheel and there wasn't any "colour" despite temps well into the 600s C , there was some reflected glow in the NGV but no flames or anything .

This morning I measured up the turb shroud/tube and found it was at 106 mm dia , the usual diameter , but when I measured the shroud at the exducer tips the diameter was 110 mm due to the clipping of the wheel , so I might try to turn out those 4 mm so that the exhaust doesn't have any constriction downstream of the exducer .

While I was fiddling around I also did some heating of the thermocouple sheathing to note colour vs temp reading , and by mid 600s C its was a nice red , but during the test run yesterday at similar temperatures I didn't notice any such colour despite it being an overcast afternoon and in the shade of a thick mango tree, something ain't right , so I've ordered an infrared thermometer
www.ebay.com.au/itm/D-S-30-1-Industrial-Digital-High-Temperature-Infrared-Thermometer-50-1050-C-/181328485392?hash=item2a38051c10:g:1xEAAOSwll1WzDJ0

and will check the running turbine wheel at various radius', after all , its the temperature of the wheel thats important to me not the gas temperature , which if those gases are impacting at high velocity onto the thermocouple could be indicating a temperature much hotter than actual static gas temp , the temp that the turb wheel is experiencing .

LOL, I'll get this engine to sing one way or the other :-)

Cheers
John

[racket]

Hi Guys

Infrared thermometer arrived this morning and I've been having some fun checking all sorts of things for temperatures , even the inner walls of the oven cooking my lunch , oven thermo set on 180 C and new thermometer showing 177 C wall temp , close enough.

So this arvo I've been heating the engines thermocouple and cross checking temps between the two thermometers and they're in reasonable agreement , so unless the turbine tips are glowing fairly brightly, more towards the pinkish red than dull red , there'll be more fuel added .

Time to think about doing a sundown test run so that I can check those colours .

Cheers
John

[Johansson]

Nov 1, 2016 23:00:14 GMT -5 racket said:

Hi Anders

Nope , no video , it was a bit of a spur of the moment decision to do a test as the weather was turning nasty , nothing really to show , just an engine making lotsa noise , though it was producing some thrust as the test stand started moving backwards, even though on soft grass, until it came up against its tethering rope.

I had a good look up into the turbine wheel and there wasn't any "colour" despite temps well into the 600s C , there was some reflected glow in the NGV but no flames or anything .

This morning I measured up the turb shroud/tube and found it was at 106 mm dia , the usual diameter , but when I measured the shroud at the exducer tips the diameter was 110 mm due to the clipping of the wheel , so I might try to turn out those 4 mm so that the exhaust doesn't have any constriction downstream of the exducer .

While I was fiddling around I also did some heating of the thermocouple sheathing to note colour vs temp reading , and by mid 600s C its was a nice red , but during the test run yesterday at similar temperatures I didn't notice any such colour despite it being an overcast afternoon and in the shade of a thick mango tree, something ain't right , so I've ordered an infrared thermometer
www.ebay.com.au/itm/D-S-30-1-Industrial-Digital-High-Temperature-Infrared-Thermometer-50-1050-C-/181328485392?hash=item2a38051c10:g:1xEAAOSwll1WzDJ0

and will check the running turbine wheel at various radius', after all , its the temperature of the wheel thats important to me not the gas temperature , which if those gases are impacting at high velocity onto the thermocouple could be indicating a temperature much hotter than actual static gas temp , the temp that the turb wheel is experiencing .

LOL, I'll get this engine to sing one way or the other :-)

Cheers
John

Hi John,

I see, although I think you underestimate just how many of us who would love to see a 5 minute video of you doing this and that with the test stand and talk a little about the upcoming test.

Good to hear that there weren´t any licking flames or hot spots visible during the run, with the new IR thermometer you should be able to cross reference the temps with those read by the probes.

A 4mm smaller radius than the exducer might upset things for an engine running close to the limits, probably a good idea to open it up a little.

Cheers!
/Anders

[racket]

Hi Anders

LOL , I once tried doing a walk around video of my first kart , it turned out terrible , I couldn't do the commentary as well as video , gave up after that :-(

I'll leave the videos to you younger guys who are much more capable ;-)

The turbine shroud/pipe has been machined with a nice long tapered section from 110mm exducer tip diameter out to the pipes 106mm bore well past the end of the turb wheel boss , this should help to "unblock" the exit from the wheel .

Cheers
John

[racket]

Hi Anders

LOL, after re installing the machined shroud pipe and "looking" at it for a few days , I wasn't happy, so I removed it and machined it parallel at 110 mm dia out to the end of the turb hub boss , then did a 4 degree taper to the 106 mm exit ............heh heh , now it looks "right" ;-)

Hopefully a test run this coming week where if it ain't glowing it gets more fuel , I wanna hear her at full throttle, even if only for a few seconds .

Cheers
John

[Johansson]

Nov 11, 2016 20:22:34 GMT -5 racket said:

Hi Anders

LOL, after re installing the machined shroud pipe and "looking" at it for a few days , I wasn't happy, so I removed it and machined it parallel at 110 mm dia out to the end of the turb hub boss , then did a 4 degree taper to the 106 mm exit ............heh heh , now it looks "right" ;-)

Hopefully a test run this coming week where if it ain't glowing it gets more fuel , I wanna hear her at full throttle, even if only for a few seconds .

Cheers
John

Hi John,

You´d make an excellent youtube-star John, I still remember the pulsejet turbine video with a smile on my face.



I am crossing every finger I have for the new shroud pipe to do the trick, good luck and don´t forget to charge the camera batteries!

Cheers!
/Anders

[racket]

Hi Anders

OH NO , not the PJ turboprop vid, I'd hoped that was long buried in the archives :-)

Cheers
John

[racket]

Hi Guys

Another test run this morning, but still no success :-(

The mods to the pipe/shroud appear to have made a bit of difference as I had an extra psi of P4t at 1.0 bar P2 (2.2 psit vs 1.0 psit) , but TOTs were ~650-680 C , the IR thermometer indicated 675 C on the exducer , so I think we can accept the other thermocouples are indicating the correct temps , the turb wheel was starting to glow a light pink colour as I was testing in the shade of some trees at 7.00 am .

What the test did show up was the big jump in fuel pressures once past that 1.0 bar P2 , it was indicating a fuel pressure of 23 psi at 1 bar , so only a pressure drop of ~8 psi across the injectors .

When I attempted to give her a "gut full" of fuel to try and reach a higher P2 the fuel pressure ended up at 76 psi for only a P2 of 26 psi , a 50 psi fuel pressure drop , this is excessive and probably >50% more fuel than its possible to burn "correctly" with the airflow available, TOTs were >1,000 C for several seconds , P4t was just under 8 psit.

There appears to be a combustion problem , maybe the flametube is simply too short to complete combustion before the Tertiary Zone .

I'll drop the engine out and check the flametube and evaps , I might have to resort to burning liquid LPG gas to obtain the speed of combustion necessary.

Cheers
John

[Johansson]

Sorry to hear that John.

Are you using kerosene or pump diesel as fuel?

The "environment friendly" pump diesel around here is so weak that it hardly burns, a guy at Speed Weekend with a huge RC turbine powering an ice yacht tried to run his engine on diesel but it evaporated so slowly that most of the combustion ended up in the tail pipe. Once back home he switched to kero and it ran like a champ again.

Cheers!
/Anders

[racket]

Hi Anders

Kero and Jet A mix , so should be OK

Cheers
John

[Johansson]

Nov 16, 2016 1:34:36 GMT -5 racket said:

Hi Anders

Kero and Jet A mix , so should be OK

Cheers
John

Bugger, it would have been a quick fix otherwise.

[ripp]

Hi John,

Please do not be angry with me John,

but the following must be said.

The inlet areal is too big for the turbine wheel.

The mass flow is too much
    
     118 * 118/4 * 3,14 = 10930mm² new big Compressor wheel
        98 * 98/4 * 3,14 =   7540mm² orig. Compressor wheel
    129,5* 3,14 *19,56 =   7956mm² Turbine wheel

Which is 45% more inlet area!

You can do the following test.

When the engine is running,( before the turbine wheel is start to glow ) you open the drain fitting and let

the air pressure out with a ball valve. When everything is still in the green area, you can more open the

fuel and check speed, pressure and temp.

Hope that helps!

Ralph

translate.google.at

[racket]

Hi Ralph

LOL.......yep , the comp inducer is too big for the "standard" turbine wheel , but the modifications to the exducer should allow the quantity of gases to pass .

Opening any sort of "bypass/dump" will most likely exacerbate the situation due to the reduction in mass flow passing through the turbine wheel compared to the compressor ...........let me explain a bit more on this ............we've expended energy ( HP or Kw) in compressing the air that we bypass/dump , that energy has to be produced by the turbine wheel , the turbine energy is produced by, mass flow times gas deflection, if we've reduced the mass flow then we need to increase the gas deflection , and the only way to do that with fixed NGV vanes is to increase velocity , and to do that we need a higher temperature , pressure drop being already at maximum.

An increase in temperature reduces gas density which means more bypass required which in turn creates more problems , I'm in a no win situation .

On my Garrett TV84 turbo engine back in October 1998 , I had fitted a bypass between the "sore thumb" combustor and jetpipe which consisted of a 20mm pipe and gate valve , the engine at that time was fitted with an "undersized" turbine stage , at a latter date after some expensive surge inducer failures a larger stage was fitted , the bypass was an attempt to control surge .

When the bypass was opened at a P2 pf 20 psi , TOT increased from 520 C to 760 C , P2 dropped to 12 psi , not a good outcome :-(

There is one more thing to try , and that is LPG/propane fueling , either as an "extra" to add some speed to the kero combustion or to completely replace the kero .

If that fails , then I'll redesign the engine with a large capacity bleed air system in conjunction with fitting a standard turbine wheel and a NGV with "lower" angles to produce more gas deflection from the stage so as to produce the required horsepower to power the comp , there will be full expansion through the turbine stage which will be equipped with a diffusing exhaust to maximise the pressure drop .

The bypassed air at full P2 pressure could then be fed to a separate combustor that supplies hot gases for either thrust or shaft horsepower through a "smallish" freepower wheel .

The engine isn't "dead" just yet, I'm not giving up on all the potential airflow that the 118 mm inducer promises :-)

Cheers
John

[Johansson]

You can´t bleed the compressor somewhere along the way from inducer to exducer to reduce the work load on the compressor at the same time as you dump some excessive air? Something like those ported shroud compressor covers only with the ports further downstream?