Back again..!... The GT6041 powered "Green Beast"..!

[smithy1]

Hi John,
I did the "Retro Speed Fest" car racing meet at Eastern Creek over the weekend...unfortunately the "mods" to the flame tube we had discussed actually made the engine flame-out worse than when we ran it at Port Mac....so on Saturday evening I did another quick mod to block up the holes and it came back to how it was...I'm tempted to open up the upper holes in the flame tube head around the fuel nozzle and test it to see if it helps penetrate the fuel spray a tad better, I just need to get this low rpm flame-out issue sorted and she'll be a monster....Your thought's??

Other than that the engine is running as it was when yourself and Chris were present at Port Mac.

Cheers,
Smithy.

[racket]

Hi Smithy

So a definite lean flameout scenario , now we can work from there :-)

Could you measure all of the Primary Zone hole areas for me please , ............swirler, small FT cap holes and all the Primary wall holes ............time to go back to basics to see whats required

Otherwise , it sounds like you had a good time .

Cheers
John

[smithy1]

Jun 13, 2016 19:46:47 GMT -5 racket said:

Hi Smithy

So a definite lean flameout scenario , now we can work from there :-)

Could you measure all of the Primary Zone hole areas for me please , ............swirler, small FT cap holes and all the Primary wall holes ............time to go back to basics to see whats required

Otherwise , it sounds like you had a good time .

Cheers
John

Will do champion...I'll get the outer case off in the next day or so..

Cheers,
Smithy.

[smithy1]

Hi John,
Did a little number crunching this morning....:

The GT6041 comp inducer is 106mm which equates to ~8825mm^... I think you normally use ~10-12% for the vaporizer system and the rest of the 30% for the remaining primary holes, is this correct? This is where I'm a tad confused...

Your original vaporizer "round-house" has 6x18mm holes and 6x15mm holes feeding the 6 vaporizer tubes...I make that ~2585mm^. However, the actual area of your original 6 x 17mm vaporizer tubes adds up to ~1362mm^ or ~15% of the inducer area... which is still substantially more than my C20B cap area, ~30% more.  

My "new" C20B flame tube cap has 54x5mm holes which only equates to ~1060mm^...as mentioned, considerably less area than your original setup...I suspect this may be my issue?? But it's a bit "counter intuitive" considering my test results over the weekend where opening up the "lower down" primary zone hole area had made things worse. I suspect I may actually be having a rich issue at the top of the flame tube around the fuel nozzle rather than a lean issue....not enough air right up high where it's needed...? The "primary zone" lower down may well be OK as is.
 
The engine, as you've seen, runs well at the higher rpm/P2 settings....it's just the poor/fluffy idle and random flame-outs which is giving me grief.

Before the vaporizer tube "burn-out", the engine ran superbly and without issue at any rpm, very efficient indeed...it's only since I fitted the C20B cap and injector that I have had combustion issues at lower rpm/P2's.

Now...taking into account opening up the primary holes lower down the flame tube has actually made the lower rpm/P2 condition worse...and... all else being equal, it seems I should actually open up the holes in the new C20B cap to replicate your original vaporizer tube area and restore the correct total area...??

Your thoughts??

Cheers,
Smithy.

PS...: Come to think of it...I did notice some black-ish smoke during running on the weekend, I thought nothing of it at the time but now it seems to make a little sense considering the lack of hole area at the top of the flame tube. I know the C20B engine has a much higher pressure ratio across the flame tube, which may account for the smaller holes at the top...but for our low P/R we may need to open things up a tad in that "injector" area to allow better air penetration?? Just thinking out loud again..!

[racket]

Hi Smithy

Yep , the evaps had a bit bigger cross sectional area than my "ideal??" , caused by availability of suitable material .

I think you'll have to fit a muff around the Primary zone and drill new holes , a single row around the can rather than the couple of rows that are currently there which work OK for evaporators but not a single spray nozzle which requires that recirculation of flame into the centre .

My TV84 flametube cap had a multitude of small holes ( 36 X 3mm) as well as a swirler ( 9mm X 5mm X 12 of passageways) surrounding the high pressure fuel injector and a single row of holes in the side wall .

The 6041 flametube is ~190 mm in dia , you need a row of Primary holes centered at ~90-95 mm downstream of the fuel injection point .

As we have ~1060 sq mms in the cap , we need ~1,600 sq mms for that row of holes , so perhaps 12 X 13 mm dia , I used 12 X 8 mm dia in the 140 mm dia TV84 flametube which flowed only ~65% of the 6041's airflow .

The row of holes needs to be at ~0.5 flametube diameters downstream of the injection point for a spray nozzle fueled engine , the C20 flametube appears to roughly adhere to that guideline.

What I've normally recommended in the past for guys making engines using spray nozzles is to have that row of wall holes at roughly the position that the fuel spray cone impacts the wall so as to cover all the variables of different fuel nozzles/angles/pressures etc .

Hope this helps

Cheers
John

[smithy1]

Thanks for the info John,

I'll set about getting it sorted as soon as I can....I might even have some suitable 304 SS floating around....an off-cut of the remains of my 8" A/B pipe should work well..

Once again...thanks for your help.

Cheers,
Smithy.

[racket]

Hi Smithy

LOL.....thank my "friend" Lefebvre , the godfather of gas turbine combustion ;-)

Cheers
John

[smithy1]

Hi John,
I had a quick look last night and the 8" 304SS pipe I used for the A/B will be near perfect, (I still have a ~70cm length of it). I'll cut a short section off and split/trim it to suit so I can slightly reduce the 8"/200mm dia to fit the 190mm dia flame tube nice and snug. Need to allow room for the original spark plug...but apart from that it should fit and work fine. I might pre-drill some pilot holes for the 12x13mm holes to help after it's tack welded into place.

I have a car show on the 26th so I'll endeavor to have it ready for that.

On a side note....I might have a shot at the new rpm sensor setup in the next few days too, the proximity sensor I have is similar to the one Anders is using for his front sprocket rpm on his bike, just need to pop the comp housing off and decide where to properly mount the sensor to pick up all 12 blades...or the 6 primary blades if I can mount it accordingly....then set the divider in the readout software to suit...the sensor has an 8mm thread and is ~50mm long (NPN normally open), hopefully it'll be a nice match. If it works OK I'll shoot a setup to you.

Cheers,
Smithy.

[racket]

Hi Smithy

Thats sounds like it'll work for the flametube

Probably better to "count" the 6 main blades , it'll provide a bit more "time" between counts as well as give the rest of the electronics an easier time in case they need it, I'm interested :-)

Cheers
John

[smithy1]

Jun 17, 2016 6:16:05 GMT -5 racket said:

Hi Smithy

Thats sounds like it'll work for the flametube

Probably better to "count" the 6 main blades , it'll provide a bit more "time" between counts as well as give the rest of the electronics an easier time in case they need it, I'm interested :-)

Cheers
John

Indeed, I hope the flame-tube mods work for us.

Yep...was looking at doing that...mind you, the sensor should be working at close to the speed of light so going from 6 to 12 blades shouldn't bother it too much I doubt the blades would be going that quick ...well I hope not anyway.
The "anti surge" port in the inlet may be a bit of an issue so it may also determine where the sensor ends up...When I get a chance I'll pop the entire inlet housing off and do some "proper good engineering" and see if I can point the sensor in the right direction, I'll take some pics for us to ponder over. We have a nice 3 axis angle head mill at my work so I should be able to do a fair job of it.

I have the existing reflective rpm sensor poking through the forward surge port at the moment, as you know they don't like sunlight much...works fine in the dark or when the blower nozzle is over the inlet though.

Cheers,
Smithy.

[smithy1]

Hi John,
I've cobbled a "muff" as per your dimensions etc for the flame tube, as mentioned, I used a section of the 8" 304 pipe...it seemed to come up OK, I'll give it a run this coming Sunday. I only bolted it into place at this stage using some "hot section" T-bolts & nuts from a PT6 engine, they're nice and secure and won't come undone. The reason for bolting is to allow for easy removal if required....if it works as hoped, I'll then Tig it into place and we should be good to go.

Cheers and thanks once again for your help,
Smithy.

[racket]

Hi Smithy

Good idea to have it removable at this stage , hopefully you'll be able to just TIG it in place after it works perfectly ;-)..............I'll have my fingers crossed.

Cheers
John

[smithy1]

Hi John,

After you mentioned the holes had to be radius of the flame tube down from the fuel nozzle spray point, I had a quick look at one I had at work and the C20B setup does indeed seem to mirror this...so it "should" work.

I'll let you know how she goes on Sunday....fingers crossed..!

Cheers,
Smithy.

[smithy1]

Hi John,
I didn't get a chance to run the "Beast" at yesterdays car show, just wasn't safe to do so....too many show cars & little kiddies closeby..! Better safe than sorry! I'm hoping to get an engine run in during the week..

Cheers,
Smithy.

[racket]

Hi Smithy

Bummer ...........heh heh ,she'd bowl little kids over in the blast from the exhaust

Yep , better to be safe , especially firing her up after mods , often best done in private in case they don't workout as planned .

Cheers
John