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Post by racket on Dec 4, 2013 3:34:32 GMT -5
Hi Anders
Some of that good high nickel material should do the job .
Heh heh , Anna will tell you 8 inches is still too big , you'll need to make it smaller ;-)
Cheers John
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Post by Johansson on Dec 4, 2013 23:51:18 GMT -5
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Post by racket on Dec 5, 2013 2:24:52 GMT -5
Hi Anders
This is turning into a well thought out machine ...............heh heh , maybe a laser "gun sight" on the top of those combustors, ..... for aiming at the finish line ;-)
Cheers John
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Post by Johansson on Dec 6, 2013 0:12:26 GMT -5
That would look interesting for sure. =)
Our "competitors" in the Rocket Launchers Team who used a modified APU engine in their kick didn´t have more power than this and they ran almost 170km/h with the throttle far from pinned the entire run, no fairings on their kick either so the drag should be somewhat equal to what our kick will have.
I sure hope the track will be good this year, if the engine and suspension performs as planned we have a shot at the standing class record! =)
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Post by Johansson on Dec 8, 2013 16:52:57 GMT -5
I started making the afterburner today, a 30 cm wide body with a 13.5cm jet nozzle. I will use two spray nozzles to get fuel into it and have an inconel flame holder that should last longer than the stainless one in our old kick. It´s one damn big hole for sure, I wonder in what tune it will sing? Cheers! /Anders
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Post by racket on Dec 8, 2013 19:10:11 GMT -5
Hi Anders
LOL.....bigger and better :-)
How are you going to position the two spray nozzles so as to provide a uniform spread of fuel ??
Cheers John
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metiz
Senior Member
Joined: April 2011
Posts: 297
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Post by metiz on Dec 8, 2013 20:16:53 GMT -5
Is "loud" considerd a tune?
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Post by Johansson on Dec 8, 2013 23:57:02 GMT -5
Hi Anders LOL.....bigger and better :-) How are you going to position the two spray nozzles so as to provide a uniform spread of fuel ?? Cheers John Hi John, Do you suggest more nozzles? We used two simple injectors with drilled 1mm holes on the old kick and that worked like a charm, so I figured two spray nozzles pointing at each others would work. /Anders
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Post by racket on Dec 9, 2013 0:42:58 GMT -5
Hi Anders Ideally you want an even spread of fuel so that it forms a combustible mix across the entire cross section of the A/B , otherwise there will be rich and lean areas where the temperature rise won't be at a maximum, which will lower potential thrust. The ring of holes design pointing roughly towards the turbine wheel seems to do the job, I found that if the holes were drilled alternately a bit to both sides of axial that the atomisation was improved due to the fact that the spray droplets weren't blown back onto the spray ring but to each side of it with no large droplets coming off the spray ring tubing . When I did the GT6041 spray ring jetandturbineowners.proboards.com/attachment/download/236 there were the same number of holes directed slightly to the "smaller" area inside the spray ring as to the "larger" area outside it as I wanted less heat along the A/B wall to try and keep it a bit cooler ..............LOL, I don't know if I succeeded or not but it was the intention. With such a large cross section you may need two concentric spray rings to adequately cover the entire A/B area . It would be possible to experiment with spray ring designs by using a leaf blower to simulate gas flow from the turb wheel ,..... the better the coverage, the better your power output potential ..............she's gunna burn some fuel :-) Cheers John
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Post by Johansson on Dec 9, 2013 5:45:18 GMT -5
Hi John,
I think I´ll fit a number of spray nozzles around the entry cone into the AB duct so everything can be removed from the outside, we won´t have any flanges on the AB since a leak in the old AB flange caused a severe burn on Olovs leg.
A very good idea to use the leaf blower to test the AB initially, it should help finding the right spot for the spark plug as well.
Cheers! /Anders
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Post by racket on Dec 9, 2013 17:29:18 GMT -5
Hi Anders
Where are you mounting your TOT thermocouple/s ??
I had problems fitting the thermocouples into the A/B without being impacted by the fuel spray , I needed to displace the spray ring a lot further down the tube that I'd liked to have so that the thermocouples weren't going to produce incorrect readouts, ..............I was tempted to fit the thermocouples to read T I T but decided to play it safe and leave them as TOT pickups and live with the consequences of increased "wasted" space ............I guess with the twin turbos there'll be plenty of ducting between the turbos and the A/B entry for fitting the thermocouples , ........I'd be inclined to get the fuel into the connected ducting as early as possible, right at the Y junction where there'll be the most turbulance, to buy as much time/distance as you can for combustion , its all gotta happen within a couple of milliseconds , a lot quicker than in the flametube, also the higher gas velocity in that smaller diameter section prior to the inlet cone will sheer/atomise/evaporate the fuel droplets quicker..............the only potential problem I see is getting an even coverage compared to a spray ring within the AB, but having seen how some DIY ABs are fueled , they ain't fussy , just dump it in and they'll burn it :-)
At one time I considered using a single large "solid cone" spray nozzle centered in the AB , with the spray towards the turb wheel , but couldn't find a large enough spray nozzle , I think I was considering a >50 GPH nozzle , it needed to be a stainless nozzle which was the hard part to find , plenty of plastic agricultural ones though .
Cheers John
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Post by Johansson on Dec 10, 2013 5:35:53 GMT -5
Hi John,
I´ll post some pics from last nights build session where you can see the Y-tube, the temp probes will be placed in the legs just before they join upstream the cone to the afterburner.
If our old A/B with two straight fuel holes worked as good as it did a ring of 5-6 spray nozzles should work even better, it will be very interesting to see how the new A/B will work with the better fuelling arrangement and high temp flame holder.
Where do you place the spark plug on your afterburners? Just downstream the flame holder or close to the jet nozzle? We have considered a hot streak ignition to get rid of the spark plug and ignition system but it would take some time to get it right and we have none to spare right now this close to the race.
Cheers! /Anders
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Post by turbochris on Dec 10, 2013 11:34:39 GMT -5
if you need a quick hot streak just put a brake master cyl somewhere, fill it w diesel, and put a lever on it.
I like to fill the Ab w fuel wide but try to keep the walls cool.
the above makes using a sparkplug harder no fuel near the plug it wont work have to extend the electrodes.
Spraying the fuel into the middle of the wheel works but forget trying to measure TOT
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Post by Johansson on Dec 10, 2013 15:35:11 GMT -5
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Post by racket on Dec 10, 2013 16:26:54 GMT -5
Hi Anders
I notice you've got a propane cylinder on the kick , does it have propane in it, or is it for something else ??
If you do have propane onboard , why not plumb some of it to your AB ignition point , its vastly superior ignition qualities should make light off much easier ............ignitor needs to be just downstream of the flameholder , preferably in an eddy behind the flameholder where the gas velocity is lower and theres some hope of ignition , also the flame can then travel behind the rest of the flameholder to fire off the AB, I fitted the GT6041 ignitor electrodes ~50mm downstream of the flameholder, I still wasn't happy with its performance as it required low gas producer power for ignition , it wouldn't ignite at higher powers , probably due to the relatively high gas speeds in the minimally sized AB compared to the dump style ABs .
You guys are doing a very professional build :-)
Cheers John
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