Joe Fedullo has now produced a batch of new style Jets for Stanley type vapourising burners, which he describes below:
I have been playing with Jet designs and think I came up with something that might be better than what is currently available commercially. Take a look and let me know what you think.
Changes to the exit tip:
On the outside, the simple 3/8" hex is replaced with a smaller 5/16" hex that has a smooth taper down to the nozzle exit. The idea of the transition is to smooth flow of the entrained. Herb de la Porte has observed eddy currents around standard jets at the nozzle and this seems like a way to help rectify that. He also has a set of old jets he found somewhere that have a similar design. He lent me one I used to copy the head.
On the inside, I added a 5 degree taper at the exit of the inner hole to create a diverging nozzle. Since the flow is sonic and therefore choked, the diverging nozzle should allow further acceleration of the fuel flow and hopefully more air entrainment. I used about a 2:1 area ratio for the diverging nozzle assuming a #56 jet. With smaller jets, it will be a expanded a little more. I then added a 1/8" radius right at the exit after the taper to help the "pricker" find the hole, but hopefully these don't need to be pricked very often due to the changes in the backside of the jet
Even though I use the multi port jets from Vintage Steam, I have noticed when the rearward centre hole clogs, the flow goes way down even though there are 12 other holes for it to go through. A simple prick usually opens things right back up and I have never seen the radial holes clog when I remove the jets. I took some measurements and the diameter of the holy section of the current multiport jets is 0.196" and the drill for a 1/4-28 hole is 0.213 so there is only 0.0085" radial clearance for fuel flow. That gives about 0.0055 sq inch of area which is almost 4 times my # 57 jet area, (# 57 = 0.0015 sq inch) but empirically it doesn't flow when the back hole gets plugged. Maybe there is a boundary layer issue with such small clearances, or maybe carbon dust plugs up the circumference.
To help, I made several changes to the backside of the jet. First I reduced the minor diameter to 0.175". This should allow much more flow to get to the radial holes perpendicular to the main flow axis. The other big change was the addition of 6 holes on the tapered surface around the main rear hole. These holes are perpendicular to the chamfer pass through the axial hole and also open to the cylindrical surface. I would think these holes eliminate the need for the radial holes, but I started thinking they all converge at a single point which was a potential area for a blockage so I added a dozen radial holes as well. The back of this jet is now Swiss cheese...
It looks like a pretty tricky part to make, but my first preliminary quote came back at $10.06 each in a quantity of 100. Before I get deeper into the quoting process, I wanted to get feedback / see if you guys have any design change ideas. Also if anyone is interested in splitting up the order I can keep you posted as I work through the quote process.
I've made a couple of changes based on some great feedback, which I really appreciate. I will wait a couple more days for further feedback then send them out for production:
1) I've increased the length of the bullet shaped outer tip per feedback from Howard.
2) Changed the spacing of the holes perpendicular to the chamber at the fuel inlet, such that they all do not intersect at the same point giving a potential clog point. They are now in 2 arrays of 3 giving 2 intersection points.
3) All holes are now #66 which was the smallest size anyone I know uses. They can easily be drilled out to any larger size needed.
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