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Post by lukelubinskyj on Nov 13, 2016 11:18:09 GMT -5
Finally finished my build yesterday got the engine started a dozen times first couple times it started there was a nice pop during ignition but I was worried too much heat was getting into the turbine I drilled a couple extra bypass holes in the bottom of my flame tube much easier to start now but I don't have that distinctive pop... I do have the tips of my turbine glowing on idle... Are those extra bypass holes too much? My fuel nozzle is a single 1/16 hole should I change fuel nozzle? I fear my combustion is too far down the flame tube... Here is a short video... youtu.be/x3CM6Awcnko
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Post by finiteparts on Nov 13, 2016 11:48:00 GMT -5
Do you have a compressor discharge pressure gauge or anything to estimate engine speed?
It looks and sounds like you are idling at to low of an RPM...do the tips glow as you go up in speed?
~ Chris
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Post by finiteparts on Nov 13, 2016 11:53:08 GMT -5
Also, if you are using a gaseous fuel and you are only using a single 1/16 inch orifice, you can have combustion issues...of course I am assuming that you have the single orifice directed stright down the combustor centerline...Usually you want to have the fuel holes in a radial orientation to help the fuel mix with the air in the primary zone. In my first engine, I used a 1/4-20 bolt that I drilled 4 holes in the flats of the bolt head and then drilled down the center of the bolt to be the fuel supply.
Can you tell us more about your combustor design?
~ Chris
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Post by lukelubinskyj on Nov 13, 2016 12:05:41 GMT -5
My combust er is a 5 inch housing , the flame tube is 4 inch.. it is built according to jet specs.com with the addition of extra 3 , 3/8 hokes I added in tge bypass zone thinking tgat would help but after I added those holes I don't get the pop sound during startup. I'm using propane, and yes a single hole pointing verticlefor the nozzle... if I start adding fuel after its self sustaining a slight blue flame will protrude the turbine as it starts to spool higher... then the blue flame dissappears then the turbine will start to glow... I don't have a boost guage... I will add one tomorrow...
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Post by lukelubinskyj on Nov 13, 2016 12:16:43 GMT -5
Other thing is on the first couple attempts of starting after that pop sound I would have that sound that you hear from the space shuttle taking off hard to describe after I added those extra bypass holes it sounds more like a fan
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Post by finiteparts on Nov 13, 2016 13:18:56 GMT -5
Yeah...try changing that injector and I bet you will have better results.
Is the sound you are trying to describe a pulsing kind of sound? Maybe surging the compressor on start up...it is easy to compressor surge at startup.
~ Chris
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Post by lukelubinskyj on Nov 13, 2016 13:29:25 GMT -5
The sound I had before I added bypass holes was like a bass deep throated rumble... and self sustaining rpm seemed to be a lot higher and harder to start
Now it sounds like a fan and will self sustain at much lower rpm with less fuel. But the turbine seems to get much hotter and turbine glow...
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Post by finiteparts on Nov 13, 2016 13:45:22 GMT -5
Yep...sounds like the compressor was surging somewhat. When you added more bypass in the combustor, you reduce the total engine flow restriction downstream of the compressor. This allowed the compressor to push more mass flow through the engine with less effort (PR) and so you moved the engine operating line away from the compressor surge line. So this should help explain it a bit better... if you look at the orange line, it is sitting right up by the surge line (the left edge of the map). If you ran your engine here, you would experience mild surge and that is likely the noise that you heard. When you drilled some more dilution holes, you relieved the back pressure on the compressor and for the same pressure ratio, the operation moved to the right towards the green line. The danger on randomly drilling holes is that you can readjust the flow splits in the combustor such that you get the primary zone to lean (because the air sees an easier path through the other dilution holes) and you get combustor instability. That will definitely make your injector situation worse since it delays the fuel jet mixing with the proper amount of air till further down the combustor. But, it sounds like your extra holes made your engine work better, so I would say that if you fix your fuel nozzle to have multiple orifices blowing into the primary zone, you should be pretty happy. Good luck! Chris
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Post by lukelubinskyj on Nov 13, 2016 14:20:54 GMT -5
Thanks for your help... I will change nozzle tomorrow, add a boost guage, and shoot another video!
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Post by racket on Nov 14, 2016 2:43:31 GMT -5
Yep , that 1/16" hole will be shooting 6 inches down the flametube before starting to do much mixing with the air , by that time its getting to the Tertiary holes , keep the several new radial injections holes at 1/16" or less so that the fuel is given a decent squirt .
Try and idle at ~5 psi P2 , temperatures will be lower than at lesser P2s , 5 psi gives a safe reliable idle from which good acceleration rates can be achieved.
Cheers John
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Post by lukelubinskyj on Nov 14, 2016 20:49:18 GMT -5
Thanks for the help... I changed the nozzle today, it accelerates much faster now... no more glow of the turbine... sounds different now... seems to start fine... and the heat is way higher up on my combuster, I can tell because tge lid of by combuster is discoloured now... I never got a video I'm sorry...
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Post by racket on Nov 14, 2016 21:59:44 GMT -5
Excellent news :-)
Now you can start to enjoy your creation
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Post by Johansson on Nov 15, 2016 5:53:53 GMT -5
Great work!
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Post by smithy1 on Nov 15, 2016 13:25:43 GMT -5
Would love to see a vid of it in latest config.
Next up for you...."Afterburner"...we love the A/B's here..!
Cheers, Smithy.
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Post by lukelubinskyj on Nov 15, 2016 13:33:33 GMT -5
I was just trying to research afterburners I have one week till I hafta present my turbojet at a party, everyone has to bring a project...I think I'll have the best one!
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