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Post by smithy1 on Dec 15, 2015 2:10:40 GMT -5
If you end up with leftover combustion chamber bits I'd gladly attach them to my 6041 to speed up the process a bit Pretty sure I've got a spare C20B combustion chamber "Top Hat" if you need one Andrew. Smithy.
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Post by enginewhisperer on Dec 15, 2015 6:40:48 GMT -5
I still have the Dart combustor which I was going to mount up to it but it's slightly on the small side - and I have another turbo that might be more suitable for it. As usual there are a few projects in the way of it
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Post by smithy1 on Dec 15, 2015 17:05:07 GMT -5
Hi Smithy You'll be needing ~4.1 sq ins for Primary , 2.7 sq ins for Secondary and 6.8 sq ins for the Tertiary areas. Hi John, I did some number crunching last night and this morning, seems I may have to open up the C20B flame tube, it's total area is substantially smaller than the required ~8824 sq-mm's I require for the 6041.... I must mention that the C20B engine has a much higher pressure ratio and uses a lot of it's mass flow for cooling air flow which the 6041 doesn't. At best the 6041 has a pressure ratio of ~3.8-4.0 while the C20B has a pressure ratio of close to 7:1..! Using the 6041's 106mm inducer I get, 3.1416 x (53x53) which equals an area of 8824sq-mm ....and using the 30-20-50 rule I'll possibly need the following: Primary ~2938sq-mm Secondary ~ 1764sq-mm Tertiary ~ 4421sq-mm For a total of ~8824sq-mm The C20B flame tube is as follows: Primary ~1640sq-mm Secondary ~1698sq-mm Tertiary ~2560sq-mm So for my pressure ratio I'll probably need to open up the C20B flame tube area somewhat to accommodate the 6041's mass flow with the lower pressure ratio. Your thoughts.?? Smithy.
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Post by racket on Dec 16, 2015 0:46:21 GMT -5
Hi Smithy
The 7:1 PR will produce a T2 ~100 C degrees hotter than the 6041's , but you're running ~100 C degrees cooler T I T , so you'll need roughly the same temp rise in the combustor , so the same F/A ratio , just at ~75% of the C20 flows due to the lower mass flow .
The C20 could be running a higher PR across the flametube wall to enhance combustion in the "small" combustor , the 6041's combustor is generously proportioned and can therefore run a lower PR across the wall holes .
What is the ID of the C20 FT in the primary zone??
It could be "undersized" when running the lower 6041 PR , the C20 has got roughly twice the PR , but only 33% more flow , I like 3 times inducer area for the flametube cross sectional area , so ~41 sq inches , or 7.22 inch diameter , which I think I made the FT about that size :-)
The cross sectional area is probably more important than the hole areas as a "skinny" flametube can run into high axial airflow rates which can make burning kero difficult .
Cheers John
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Post by racket on Dec 16, 2015 15:39:47 GMT -5
Hi Smithy
Assuming the C20's 3.6 lbs/sec flow was at our "normal" 3.8 PR , this would require an inducer of ~17 sq ins area , therefore we'd need a FT with ~51 sq ins of cross sectional area ( like my 12/118 engine) or ~8 inch diameter for a can , but if we multiply that 51 sq ins by 3.8 PR then divide by 7 PR we get ~28 sq ins , or a cross section of 5.9 ins - 151 mm dia at the primary zone ................. is this roughly what the C20 has ??
Hope this helps :-)
Cheers John
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Post by smithy1 on Dec 16, 2015 17:35:19 GMT -5
Hi John, The C20B Flame tube "Primary" zone diameter is ~145mm, so still a tad small but may be do-able. We've seen some silly sized flame tubes on a lot of machines and they still run. I might see if I can get look at a C30 flame tube, don't have one handy at the moment but I think we have a "US" one in quarantine....might be worth a look.
Cheers, Smithy.
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Post by racket on Dec 16, 2015 19:14:25 GMT -5
Hi Smithy
Yep , there have been some silly sized FTs used with varying degrees of success, they just get a bit "touchy" as they get smaller than desirable , ..........a generous flametube covers up a lot of other "sins", and is the reason I prefer to go that route .
It still might be easier for you to just fit a C20 fuel nozzle into the existing 6041 FT .
Cheers John
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Post by smithy1 on Dec 17, 2015 2:28:55 GMT -5
Hi Smithy Yep , there have been some silly sized FTs used with varying degrees of success, they just get a bit "touchy" as they get smaller than desirable , ..........a generous flametube covers up a lot of other "sins", and is the reason I prefer to go that route . It still might be easier for you to just fit a C20 fuel nozzle into the existing 6041 FT . Cheers John I think I will take your advice and just fit the C20B fuel nozzle to the existing flame tube...2 of the 6 existing vaporizer tubes are quite badly burnt and I don't fancy making up some new ones either... I might just cut the vaporizer section out and replace it with a C20B flame tube cap and this will accommodate the C20B fuel nozzle and igniter...hopefully for a "Propane Free" start....that'd be cool to see....then I just have to get the electric start sorted..I've made the drive socket, need to get a suitable mounting system for the brushless motor. Smithy.
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Post by racket on Dec 17, 2015 15:55:52 GMT -5
Hi Smithy
Have you any thoughts on why only 2 of the evaps are burnt ??
Could it be due to the preheat LPG ??
I'll look forward to a pic of the evaps when you cut out the section.
Is it possible to use the existing sparkplug position for ignition of the fuel spray ??
Good to see you've made the decision to modify :-)
Cheers John
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Post by smithy1 on Dec 17, 2015 19:02:32 GMT -5
Hi Smithy Have you any thoughts on why only 2 of the evaps are burnt ?? Could it be due to the preheat LPG ?? I'll look forward to a pic of the evaps when you cut out the section. Is it possible to use the existing sparkplug position for ignition of the fuel spray ?? Good to see you've made the decision to modify :-) Cheers John Hi John, I suspect the evaps were burnt during a hot or failed start or two at some point in it's life, I did have a couple of 800C+ starts when learning the process, not enough blower..! LOL....the two burnt ones are next to each other so one has LPG and fuel and the other only fuel. I found these when I first removed the flame tube many moons ago during my first round of modifications. No matter, I can always repair/replace things if needed I guess. It should be possible to maintain the spark plug position, the fuel nozzle spray cone will go right to it...however, I'm not sure if the "spark" will be strong enough for a good ignition, I might fit the C20B igniter and have the spark plug for a back-up if required....I guess I can just leave it there, it's not hurting anything...will save me making a blanking plug. With the igniter, I can run it off a pair of small 3 cell Lipo's connected in series to give me ~24v, this will give me a nice quick/strong spark....when using the normal 12v system the spark is a bit weak and slow. I'll obviously need to test both systems to see if they work or not....If not I can run start propane into the fuel nozzle via a "T" piece with a check valve in the propane line to prevent fuel going back down the line. Will set about cutting the top "round-house" from the flame tube in the next few days...I don't have any car shows etc until early Feb so that will give me some time to get things modded and maybe a test run or two and make any required adjustments etc... Cheers, Smithy.
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Post by racket on Dec 17, 2015 19:22:43 GMT -5
Hi Smithy
So theres no rational reason behind the evap burning, bummer ..............LOL, I was hoping it might have just been the LPG fueled ones , maybe some "aberration" causing it , the spray nozzle will soon fix that :-)
After making the evaporator system on the 6041 I felt it was more work than if I'd simply fitted a spray nozzle and spent the extra time making up a high pressure pump , we live and learn .
Can you use the C20 ignition unit with the existing spark plug or perhaps a " different" plug ?? .............just thinking of trying to save you an extra job.
How will you hold/position the flametube in the combustor once the existing bits are removed??
Cheers John
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Post by smithy1 on Dec 17, 2015 20:23:35 GMT -5
Hi Smithy So theres no rational reason behind the evap burning, bummer ..............LOL, I was hoping it might have just been the LPG fueled ones , maybe some "aberration" causing it , the spray nozzle will soon fix that :-) After making the evaporator system on the 6041 I felt it was more work than if I'd simply fitted a spray nozzle and spent the extra time making up a high pressure pump , we live and learn . Can you use the C20 ignition unit with the existing spark plug or perhaps a " different" plug ?? .............just thinking of trying to save you an extra job. How will you hold/position the flametube in the combustor once the existing bits are removed?? Cheers John Hi John, Yes, I can probably use the ignition unit with the spark plug, however, the C20B high tension igniter line has the positive and earth in the same cable, if I use the spark plug I'll obviously need to separate the cable to suit, easily enough done I suspect. Ideally the igniter should be close to the fuel nozzle as per the C20 setup, I can quite easily drill and tap the outer case to accept the C20 igniter and poke it through the so designed hole in the C20 flame tube cap. In the C20B the flame tube is normally held in position by the fuel nozzle and igniter poking through holes at the top.... and the No:1 NGV/No:8 bearing shield at the bottom....with the 6041 I'll again use the fuel nozzle as an anchor at the top and the end of the tapered part of the flame tube where it enters the turbine housing at the bottom. In the "real C20B engine" the flame tube is actually quite "loose" fitting.... and sometimes they rattle a bit when you tip them upside down etc...I guess they make them a little bit loose to allow for a bit of heat expansion etc... I'll allow for ~1.5-2mm expansion when I fit it to the old flame tube. The fuel nozzle pokes though into the flame tube at the top by ~10mm or so, plenty to play with, it has a "sliding fit", so no dramas in that respect. To act as "flame-out" protection, I might still use your original spark plug and ignition system, I have noticed on some quick "throttle-off" situations from higher P2 settings, the 6041 will sometimes flame-out for a few seconds as the fuel pressure quickly drops off, I suspect the P2 is higher than the fuel pressure at this point causing the fuel flow to stop until the RPM and hence the P2 drops off enough for the "idle fuel flow" to eventually override it, luckily you had the spark plug running all the time while the fuel pump is running....good thing you did too... otherwise I might have had a CC full of fuel.... ...and with all the heat and fuel vapour inside...it might have caused a few "explosive issues"... ....I've since learned to let off the throttle slowly to help avoid such things, I might see about fitting a throttle pedal damper to slow it's travel back to the idle stop. Always plenty of things to do..... Cheers, Smithy.
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Post by racket on Dec 17, 2015 21:25:34 GMT -5
Hi Smithy
You might need to "empty" the fuel accumulator to prevent flameout on those throttle chops , it should have enough high pressure air inside at high fuel flow rates so that when the check valve in the bottom closes on the chop, the high pressure air will still force fuel into the still "pressurised" combustor .
If it still flamesout you might need a slightly higher volume accumulator , I think Bosch make a proper inline accumulator to keep their EFI systems "charged" .
With such a long FT as in the 6041 theres probably up to 8 millimeters of expansion if theres a bad start with lotsa flames inside the can .
Yep , plenty to keep you busy over the holidays :-)
Cheers John
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Post by smithy1 on Dec 21, 2015 13:36:00 GMT -5
Hi All, John, I've been able to "acquire" a nice C30 flame tube, I might do a little math on it to see if it's usable. It's considerably larger in area compared to the C20 item. Just need to find a C30 fuel nozzle to go with it....Although I could make the C20 item fit. Smithy.
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Post by racket on Dec 21, 2015 17:53:53 GMT -5
Hi Smithy
Now thats an interesting "pre combustor" mixing pot .
Cheers John
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