ripcrow
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Joined: December 2015
Posts: 114 
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Post by ripcrow on Aug 8, 2016 4:09:14 GMT -5
Primary holes are 4.5 mm. 31 in total. I did start them right at the top of the tube. Not sure if that was smart. My lpg gas inlet is basically two bits of pipe sealed with gas flowing from the top down through the gap between the pipes and exiting towards the combustor walls. My liquid fuel injector sits in the middle section of the internal length of pipe and is protected from the flame. I'll see if I can Mock something up to show how I done it.
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Post by racket on Aug 8, 2016 16:56:41 GMT -5
Hi Rodney
Too many small holes , at 4.5 mm the distance they can "inject" into the flametube is severely limited , all they'll do is cool the wall .
Also because of your tangential delivery tube the air going through those primary holes is "restricted" by the swirling air going past them .
I'd open up 6 of the holes to 8 mm dia and see what happens , then if things haven't improved , I'd get rid of the tangential air delivery tube and fit a straight in one with a diffusing funnel at the combustor wall
Cheers
John
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ripcrow
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Joined: December 2015
Posts: 114
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Post by ripcrow on Aug 9, 2016 2:11:17 GMT -5
Will try that John on the weekend. Thinking today because the gas is injected close to the centre ( within a 1 1/2 inch centre ) could I be getting a fuel rich mixture in the centre of the tube. When I built it I thought the gas would disperse but know I'm thinking the air pressure is keeping it to the centre of the tube.
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Post by racket on Aug 9, 2016 16:37:43 GMT -5
Hi Rodney
Unless the gas is injected radially outwards it can't mix with the incoming air through your multitude of small wall holes .
It generally requires relatively small diameter holes in the injector and at least 6 of them to cover the cross sectional area of the flametube , the small diameter keeps pressure drop and velocity high so that the individual fuel/gas jets carry a reasonable distance, 6 X 1mm diameter holes is a reasonable starting point .
Because you have a tangential air delivery its "difficult" for the swirling air getting through the wall holes to "flow" into the centre of the flametube , think water down a plug hole where theres always a hollow core .
Years ago a guy used a porous metal air silencer as the injector for his propane fuel , the propane simply poured out of the "silencer" at low velocity and travelled down the core of the flametube and didn't start to burn until it encountered the large dilution holes in the tertiary zone , it took us a while to fathom out his problem , a change to the more conventional radial jets of fuel cured his problems .
Cheers
John
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ripcrow
Veteran Member
Joined: December 2015
Posts: 114
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Post by ripcrow on Aug 10, 2016 2:09:13 GMT -5
Ok so I'll rebuild the gas injector and see if I can modify the air inlets.
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Post by racket on Aug 10, 2016 19:52:37 GMT -5
Excellent :-)
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ripcrow
Veteran Member
Joined: December 2015
Posts: 114
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Post by ripcrow on Aug 14, 2016 1:57:58 GMT -5
Altered the gas injectors drilled 4 primary holes larger and altered the air inlet to 90 degrees. Couple of things. My liquid fuel nozzle is glowing red now , I'm still getting flame outside the tube but you can actually see the air penetrating the flame in the tube. I can get the flame to stay in the tube with enough reduced fuel. It's fires straight away when cold but refuses to light up when hot unless coaxed and they lights up with a bang. Lots more pressure in the tube itself as its trying to blow the liquid fuel nozzle out of its holder. It's only held in with a small hammer resting on top of it at the moment.
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ripcrow
Veteran Member
Joined: December 2015
Posts: 114
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Post by ripcrow on Aug 20, 2016 4:27:27 GMT -5
Got the jet to run. Purrs along ok but very slow in throttle response. Can't post the video to YouTube but when I can I'll post a link up. I'm going to try a new gas bottle tomorrow as the one I'm using is nearly empty. Any other suggestions to improve throttle response. No p2 or egt gauge on it yet but starts very easily just seems to not want to rev up very high. Doesn't sound to be sucking very hard either.
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Post by racket on Aug 20, 2016 5:06:59 GMT -5
Sounds like you're idling too low .
Once idling at 5 psi the acceleration should be good
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ripcrow
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Joined: December 2015
Posts: 114
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Post by ripcrow on Aug 20, 2016 6:03:02 GMT -5
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ripcrow
Veteran Member
Joined: December 2015
Posts: 114
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Post by ripcrow on Aug 21, 2016 2:55:25 GMT -5
Got throttle response today. Turns out the gas bottle is low and freezes very quick. Started it this morning and started to rev it up and it responded well up and down the rev range but only for a short time before the bottle froze and it was flat out maintaining an idle.
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Post by racket on Aug 21, 2016 18:32:15 GMT -5
Looks like you'll need to sit the gas bottle in a large container of warm water so as to maintain vapour pressure
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ripcrow
Veteran Member
Joined: December 2015
Posts: 114
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Post by ripcrow on Aug 23, 2016 2:42:57 GMT -5
I'm thinking is there a way to test the pressure drop through the flame tube to ensure the hole area is correct to achieve the 5% drop. Perhaps a gauge with a long tube attached so nothing melts fitted in to the end cap of the combustor. Compare readings to the boost gauge. Just as a way of fine tuning the combustor.
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Post by racket on Aug 23, 2016 3:44:16 GMT -5
Yep , that should work .
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