Post by racket on Apr 23, 2016 18:28:18 GMT -5
Hi Fredrik
Classic case of tangential air delivery tube at the Primary Zone causing the necessity to have vastly oversized hole areas in the FT to get air through the wall holes .
Your current setup has air at maybe 100m/s being swirled past the Primary Zone holes , there is simply no way that high speed air can suddenly turn 90 degrees and go through the holes , some small quantity will but the majority can't until too far down the flametube wall, your increased hole area flametube is simply "two wrongs making a right"
LOL......Why guys persist in mounting the delivery tube at the Primary Zone I have no idea , I've been telling them for a decade its a bad idea
If its positioned at/below the dilution Tertiary Zone , half of the air goes through those big Tertiary holes reducing the remaining air velocity by 50%, with further reduction at the Secondary Holes , so by the time the air reaches the Primary Zone it is nice and slow and is evenly distributed around the flametube providing an even flow into the flametube for combustion to take place where it should .
If you checkout my GT6041 build you can see where I mounted my air delivery tube jetandturbineowners.proboards.com/thread/78/garrett-gt6041-powered-kart?page=6 , it has a diffusing funnel at the outer can wall to spread the air flow , it then dumps into a plenum area around the flametube funnel where it can spread out further and slow down even more before moving up the side of the flametube past the Tertiary Holes where half the air is removed and it eventually makes its way to the Primary Holes at lowish speeds without swirl , swirl around the outside of the flametube increases the length of travel which in turn increases frictional losses .
As you are using Propane for fuel , it should all be combusted well before the Secondary holes due to its excellent burning characteristics , delayed combustion is a sure sign that theres something wrong with the combustor design .
Your current flametube diameter is sufficiently big enough for propane.
I'd suggest you have have a mixture of hole sizes at the Primary Zone , with maybe 3 larger holes spaced around the FT at 120 degree intervals to produce some deeper penetrating air jets , a multitude of smaller holes simply won't produce the required turbulence for good combustion , all they'll do is cool the wall .
Try 12 X 6mm plus 3 X 10mm dia holes for the Primary Zone , 5 X 8 mm for Secondary and 5 X 10 mm for Tertiary , with air delivery near the bottom/outlet end of the combustor feeding into the plenum surrounding the funnel thats guiding the gases from the circular flametube into the smaller rectangular scroll port .
Hope this helps explain whats going on
Cheers
John
Classic case of tangential air delivery tube at the Primary Zone causing the necessity to have vastly oversized hole areas in the FT to get air through the wall holes .
Your current setup has air at maybe 100m/s being swirled past the Primary Zone holes , there is simply no way that high speed air can suddenly turn 90 degrees and go through the holes , some small quantity will but the majority can't until too far down the flametube wall, your increased hole area flametube is simply "two wrongs making a right"
LOL......Why guys persist in mounting the delivery tube at the Primary Zone I have no idea , I've been telling them for a decade its a bad idea
If its positioned at/below the dilution Tertiary Zone , half of the air goes through those big Tertiary holes reducing the remaining air velocity by 50%, with further reduction at the Secondary Holes , so by the time the air reaches the Primary Zone it is nice and slow and is evenly distributed around the flametube providing an even flow into the flametube for combustion to take place where it should .
If you checkout my GT6041 build you can see where I mounted my air delivery tube jetandturbineowners.proboards.com/thread/78/garrett-gt6041-powered-kart?page=6 , it has a diffusing funnel at the outer can wall to spread the air flow , it then dumps into a plenum area around the flametube funnel where it can spread out further and slow down even more before moving up the side of the flametube past the Tertiary Holes where half the air is removed and it eventually makes its way to the Primary Holes at lowish speeds without swirl , swirl around the outside of the flametube increases the length of travel which in turn increases frictional losses .
As you are using Propane for fuel , it should all be combusted well before the Secondary holes due to its excellent burning characteristics , delayed combustion is a sure sign that theres something wrong with the combustor design .
Your current flametube diameter is sufficiently big enough for propane.
I'd suggest you have have a mixture of hole sizes at the Primary Zone , with maybe 3 larger holes spaced around the FT at 120 degree intervals to produce some deeper penetrating air jets , a multitude of smaller holes simply won't produce the required turbulence for good combustion , all they'll do is cool the wall .
Try 12 X 6mm plus 3 X 10mm dia holes for the Primary Zone , 5 X 8 mm for Secondary and 5 X 10 mm for Tertiary , with air delivery near the bottom/outlet end of the combustor feeding into the plenum surrounding the funnel thats guiding the gases from the circular flametube into the smaller rectangular scroll port .
Hope this helps explain whats going on
Cheers
John
