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Post by racket on Sept 11, 2016 23:13:23 GMT -5
Hi Smithy
I'd go with the 16 mm X 14 of , the couple of big holes will take care of producing turbulence for good mixing , you just need to get the air in there .
On the original 6041 flametube I had the dilution holes plunged for best flow , but you might get away with just plain holes as the rest of the C20 holes appear to be plain as well , this will increase the pressure drop across the flametube but we don't want to "unbalance" the rest of the holes in the FT .
The original C20 flametube must have been setup for a "lean burn" Primary Zone and a fairly large pressure drop across the wall , possibly to mitigate some sort of combustion problems.
Cheers John
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Post by smithy1 on Sept 12, 2016 3:20:20 GMT -5
Hi Smithy I'd go with the 16 mm X 14 of , the couple of big holes will take care of producing turbulence for good mixing , you just need to get the air in there . On the original 6041 flametube I had the dilution holes plunged for best flow , but you might get away with just plain holes as the rest of the C20 holes appear to be plain as well , this will increase the pressure drop across the flametube but we don't want to "unbalance" the rest of the holes in the FT . The original C20 flametube must have been setup for a "lean burn" Primary Zone and a fairly large pressure drop across the wall , possibly to mitigate some sort of combustion problems. Cheers John Will do John....thanks again for the tips. Cheers, Smithy.
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ripcrow
Veteran Member
Joined: December 2015
Posts: 114
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Post by ripcrow on Sept 24, 2016 5:17:38 GMT -5
Had the pleasure of meeting smithy at Pambula motorfest today. The green beast fired up and attracted a nice crowd. Loved the jet dragster.
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Post by racket on Sept 24, 2016 19:25:49 GMT -5
Hi Rodney
He's a gentleman :-)
Hope you found the experience inspiring , yep , that little dragster performs beautifully.
Cheers John
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Post by smithy1 on Sept 25, 2016 18:52:23 GMT -5
Yep, met Rod at Pambula...The Beast was running fairly well on the weekend, had a few runs of ~40psi P2 with lots of A/B hits & pops.... so she's working nicely up in the higher rpm range. EGT's at idle are still good @ ~500C. At full noise I was seeing ~690-710C....so she's nearly optimal.
Was really good to actually meet up with a fellow member and have a nice chat about turbines in general.....we just need Rod to get a machine running..!
On a side note...have finished drilling and cleaning up all the new holes in the C20B flame tube....the lower extension cone is all rolled & welded together, just need to trim/adjust to fit the turbine inlet and make it a nice sliding fit in the bottom of the C20 flame tube....and we should be ready to do some further testing.
Cheers, Smithy.
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Post by racket on Sept 26, 2016 0:28:59 GMT -5
Hi Smithy
It'll be interesting to see if the reduced cross sectional area of the C20 flametube causes any combustion issues , its those unknowns of R and D that makes it "fun??" ;-)
Cheers John
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Post by smithy1 on Sept 26, 2016 20:43:18 GMT -5
Hi Smithy It'll be interesting to see if the reduced cross sectional area of the C20 flametube causes any combustion issues , its those unknowns of R and D that makes it "fun??" ;-) Cheers John Fun..?? Surely you jest..! It works in a C20, but at a much higher pressure ratio....so after opening up the dilution zone.... we should know soon enough....! Cheers, Smithy.
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Post by smithy1 on Oct 9, 2016 19:04:51 GMT -5
Hi John, Hope your new 12/118 mods work well for you....I'm sure it will be fine. Have a good breather and a cup of tea before and after firing her up and you'll be fine. I look forward to hearing the results. On a side note....I did a car show at Bargo on Saturday...the "Beast" is running really, really well, had her up to ~41-42 psi P2 and over 500psi fuel pressure at the fuel nozzle, temp at full noise & full A/B is 680-690C.....she's sounding fantastic too at full noise with a nice A/B "crackle" to her. There's no "squealing" as Andy and some of the others get with their A/B's....not sure if that's a good thing or not..? When you, Chris and I were at the Port Mac kart track I think we only had her up to ~38psi P2 IIRC...So I think I can happily say she's pretty close to her potential. I doubt taking her any higher will be of much use and would possibly start to hurt things...As she is, she's happy. Combustion sounds a lot better now than at the kart track...she was a bit "fluttery" back then...I've since cleaned up the primary zone holes, added some small boundary layer holes to the top plate and had a play with the secondary's, basically just making the air flow as easily as I possibly could going into the flame-hold zone...seems to have worked a treat. I haven't touched your original dilution holes as I feel they're doing a fine job and there's no indication of excess heat down there. I'm very happy with the way she starts and runs now with the single C20 fuel nozzle, I've had her light off on the jet fuel several times but it can be a bit hit 'n miss sometimes, I suspect the fuel spray is a tad heavy to be easy to light.... so I'm keeping my propane start system in place...just in case. I have some new ideas for this issue and will let you know in due course. I think/hope you'd be very happy to see your baby working so well. I wish you were there to see it in person. Just a matter of keeping up the maintenance to help keep her running the way I like.. She's a very thirsty girl though... I've also found a nice slow return of the throttle from max to min has all but eliminated the flame-outs... I'll be fitting a throttle damper to it soon.. I haven't fitted the "modded" C20 flame tube yet, still nutting out the total length, slip joints and "clocking" of the injector and igniter ports so it can be pretty much plug 'n play fitment, I've allowed for 2.5-3mm length expansion, do you think this will be enough or should I give it a little more?? Then I'll give it a few test runs...but the existing flame tube will suffice for the time being. Cheers, Smithy.
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Post by racket on Oct 9, 2016 20:46:36 GMT -5
Hi Smithy LOL, at 42 psi P2 - 3.86 PR the 6041 comp will be having a tip speed of ~1,800 ft/sec - 73,000 rpm , thats getting pretty high , no wonder she's "crackling" .............yep , thats all she'll give, the mass flow won't be increasing much as the inducer tips have well and truly gone supersonic, both actual and relative , and probably causing problems . I'm very happy to see how you've got her performing , you were the man for the job Cheers John
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Post by smithy1 on Oct 10, 2016 2:12:39 GMT -5
Hi Smithy LOL, at 42 psi P2 - 3.86 PR the 6041 comp will be having a tip speed of ~1,800 ft/sec - 73,000 rpm , thats getting pretty high , no wonder she's "crackling" .............yep , thats all she'll give, the mass flow won't be increasing much as the inducer tips have well and truly gone supersonic, both actual and relative , and probably causing problems . I'm very happy to see how you've got her performing , you were the man for the job Cheers John Yeah....at that 42psi P2 and ~27c ambient, my rpm gauge was telling me she was doing ~74,500..! I wonder what effect the lower density 27C air has at that P2.?? I was starting to feel some reverb/flutter from the inlet at those P2's...so not ideal...I've backed the max throttle stop off a tad so she can stay in the happy zone at ~40psi max. In the "cooler morning air" she was quite happy, but as the density dropped off with the ambient temp increase...she didn't sound real happy at all....beating the air to death indeed.. I think we're now finally getting the best out of the "Beast"...she's certainly got plenty of mumbo....I had the nose up against a steel fuel drum which in turn was up against the a small concrete gutter....she pushed the side of the drum in ~2"... ...At 20c ambient I'm guessing ~200-210lbs thrust wet..! I'll have to hook up a strain gauge of some sort one day.....I can certainly feel she wants to be let loose and go..! Cheers, Smithy.
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Post by racket on Oct 10, 2016 4:32:19 GMT -5
Hi Smithy
74,500 rpm and 3.86 PR are right on the map where they should be , so she's flowing "ballpark"
Your inducer tip speed would be ~1.3 Mach relative to the incoming air , so right up there , the fact that the wheel is only a 12 blader makes it hard to get the higher pressures due to the gap between blades , she efficiently flows 160 lbs/min at 3:1 PR at 78% effic , but only 165 lbs/min at 3.86 PR at a poor 70% , yep , keep her to 40 psi especially on anything but a cold day , 70,000 rpm is probably fast enough, you'll get a bit more pressure at those rpm on a cold day vs a hot one .
It'd be interesting to know the actual thrust as it will indicate/validate the theory , your temps and pressure should be producing that sorta thrust level .
I think you've reached her limits .
Cheers John
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Post by smithy1 on Oct 11, 2016 1:09:30 GMT -5
Thanks for the "validation" John. I guess there's not much else to do to her now....just keep her running at her best....status-quo.
Cheers, Smithy.
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Post by racket on Oct 11, 2016 22:24:16 GMT -5
Hi Smithy
LOL, if you're looking for something to do , you could do some tests to see what your jetpipe total pressures are using a pitot tube , then see if the maths are correct , you should have 10.7 psi total pressure exiting the 6041. ;-)
Cheers John
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Post by smithy1 on Oct 12, 2016 16:34:04 GMT -5
Hi Smithy LOL, if you're looking for something to do , you could do some tests to see what your jetpipe total pressures are using a pitot tube , then see if the maths are correct , you should have 10.7 psi total pressure exiting the 6041. ;-) Cheers John I'd be really happy with 10-11psi in there... Where would you place the pitot tube?...I'm guessing the "straight" section of the pipe...not the divergent or convergent sections.?? Cheers, Smithy.
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Post by racket on Oct 12, 2016 18:27:39 GMT -5
Hi Smithy
Probably just before the fuel spray ring in the A/B , its the pressure thats available after the diffusion and its associated losses , so more static and less dynamic which should make it easier to get an accurate reading .
Once you have the total pressure and a thrust reading the maths can be fiddled back and forth to find mass flow and some other rough parameters , can't have too much data .
I don't know of many accurate thrust readings being done for our engines , but its invaluable in working out if the engine is performing as it should , LOL, noise alone doesn't give an accurate indication.
When I was doing the TV84 development it was only because I had good thrust, T2 and jetpipe total pressures that I was able to finally understand the maths and accept the fact that the thrust I was achieving was all that could be expected from the engine , there just wasn't any more to give without excessive temperatures
Cheers John
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