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Post by racket on Aug 17, 2011 16:42:21 GMT -5
LOL.....nearly , .................still got to fit the seat and figure out a way to get the start air into the compressor with the seat in place ...............I'm workin' on it :-)
Cheers
John
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Post by stoffe64 on Aug 17, 2011 16:43:39 GMT -5
nice work john...i sure would love to see a film with it running  |
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Post by racket on Aug 17, 2011 22:05:17 GMT -5
Hi Stephan
LOL....so would I :-) ....................yesterdays video would have been both informative and entertaining as it had flames , bangs , pops and me stuffing up by not removing the starter early enough , it was reducing the airflow and stopping the spoolup , this engine is flowing a huge amount of air at idling conditions .
Cheers
John
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Post by racket on Sept 7, 2011 20:39:46 GMT -5
A/B inlet diffuser Attachments:
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Post by racket on Sept 7, 2011 20:50:36 GMT -5
A/B inlet diffuser , from 120mm ID at turbine wheel exducer out to the 150 mm ID for the A/B tube Attachments:
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Post by racket on Sept 7, 2011 20:57:02 GMT -5
Mounted on the turbine scroll housing with the Vband clamp A/B tube slides into the slip joint and seats against flange and is held in place by 3 2" X 5/16" UNF screws thru "saddles" welded to A/B body and into threaded bosses on mounting flange . Attachments:
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Post by Johansson on Sept 7, 2011 23:20:06 GMT -5
Sweet! I imagine forming that stainless cone was a bit tricky. |
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Post by racket on Sept 8, 2011 0:56:06 GMT -5
Hi Anders
Not too bad a job , made the usual card board template first to make sure it fitted then cut the stainless , ........................because the mounting flange had a bore with a 7.5 degree taper in it , the 15 degree included angle cone was able to be "forced" into the heavy flange to true it up by using a piece of plywood and long screws through the 3 boss holes , it was nicely "pressed" in place prior to TIG'ing ........................LOL, still a days work though :-)
Cheers
John
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Post by racket on Sept 10, 2011 23:07:27 GMT -5
I'm currently up to the stage of constructing the fuel injection system for the karts A/B , .................. due to the design of the A/B my thermocouples for TOT measurement are displaced to the outlet of the diffuser , and to prevent fuel spray from contacting the thermocouples I needed to determine the axial distance between the spray ring and thermocouples to minimise "wasted" A/B length .
The engine will require ~4 litres/min of fuel to the A/B ,................... with 20 spray orifii , thats ~200 cc/hole/min .
A test rig was manufactured using a short "blind ended" length of the same 3/8" OD stainless tubing as the fuel ring is constructed from and a single 0.7mm hole was drilled in its side , the tubing was then pressed into a fitting that was screwed onto a garden tap .
When water pressure was applied to the test rig it squirted horizontally ~10 feet at the required 200ml/min flow through the 0.7mm oriface , this was much further than expected :-(( ........................but upon application of the leafblower to simulate the gases exiting the turb exducer , the jet of water was reduced to ~2 - 3 inches before it disintergrated into a spray going "backwards .
This was still a considerable axial distance so I opened up the hole to 1.0mm diameter , this increases flow area by about 2 times , so a decision to reduce the number of holes in the A/B sprayer to 16 was made , this would now require a flow of ~250ml/hole/minute , ....................this produced a horizontal jet of ~6 feet when the test rig was fitted to the garden tap .
The leafblower reduced the axial squirt to between 1 and 2 inches ................getting more like it :-)
There was one unfortunate side effect of having a squirt of fuel going axially towards the imaginary turb wheel exducer's gas flow and that was that some of the "fuel/water" was blown straight back onto the spray ring where it flowed around to the downstream side of the tubing and was blown off in large droplets , not the best thing for fast combustion :-(
I then tried "offsetting" the fuel to gas flow ,.......... this dramatically affected the outcome by not only shortening the fuel squirt length ( to<1 inch ) compared to a "head on " approach but also blew the fuel spray to the side of the tubing in a well broken up spray without any large droplets .
It only required an "offset" of ~15 degrees between fuel squirt and gas flow for this to occur , this should easily be accomplished by drilling the 16 X 1.0mm dia holes in a staggered pattern slightly to each side of the centreline of the spray ring , the centreline of my spray ring is ~90 mm diameter , the A/B crossectional area "outside" the sprayring should be roughly equal to that inside the ring, allowing for a cooling airflow along the inside of the A/B wall , I want more fuel in the "centre" than near the "outside" to keep wall temps down .
Time to start drilling holes :-)
Cheers
John
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Post by turbochris on Sept 11, 2011 8:28:45 GMT -5
John, why don't you spray the fuel into the center of the turbine wheel like I do? it works really well and CDP can be used to pressurize a fuel tank as it needs little fuel pressure. When the fuel hits the wheel it's instant vapor. Wait, don't do that, I'm doing it to kick all your asses!
as for the dynamics, I imagine the fuel hitting the center of the wheel, getting spread radially and then hitting the hot gas flow at a 90 degree angle. At this point I wonder what the fuel density is in the center of the tailpipe and near the walls. The distribution probably isn't that good but it will keep most of the burn in the center away from the walls. never thought of a good place to put the TOT probe, I was thinking of going by TIT instead.
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Post by racket on Sept 11, 2011 17:04:43 GMT -5
Hi Chris
Yeh , I don't like wasting ~6 inches of A/B length between turb and spray ring but its just one of those tradeoffs we sometimes have to make , I couldn't find any other way of mounting the thermocouples with any safety :-(
Hopefully the remaining 18 inches, plus several inches of nozzle, will be sufficient length to produce reasonable combustion within the relative small diameter A/B , its right on the 400 ft/sec gas speed limit at the flameholder .
Cheers
John
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Post by racket on Sept 24, 2011 18:59:02 GMT -5
Up the A/B , with 3/8" dia stainless tube spray ring containing 16 X 1mm ( 0.040") dia holes positioned ~75mm - 3 " forward of the flame holder , and ~50mm - 2" downstream of the thermocouples and the exducer diffuser The "Y" flame holder is welded to 3 pieces of flat stainless that are pop riveted to the A/B at their forward ends allowing expansion both axially and radially of the flame holder as there is a 3mm gap under each stainless flat at the flame holder Y section . Attachments:
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Post by racket on Sept 24, 2011 19:13:03 GMT -5
Readjusted the A/B activation pressure switch to 28psi P2 , the A/B can be armed at any time but won't activate until there is 28psi in the combustor , once this pressure is reached, both the A/B fuel pump and the ignitor are switched on .
As soon as P2 drops below 28psi the A/B will deactivate , even though it remains armed and ready for further use until the dashboard mounted toggle switch is flicked off .
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Post by turbochris on Sept 25, 2011 8:06:05 GMT -5
Considering everyone here uses way too many parts in their builds (including you John) that's pretty cool. What's next? Turkey feathers?
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wolfdragon
Senior Member
Joined: April 2011
Posts: 287
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Post by wolfdragon on Sept 25, 2011 8:47:22 GMT -5
a variable nozzle would be awesome... being surrounded by jets with turkey feathers all day does make me wonder "how hard could it be... i really..."
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