Jakob Bull Posted October 8, 2017 Share Posted October 8, 2017 Hi all iv built a vanturi burner and it has a problem I think. it lights fine and runs fine (no sputtering) but when I open the air vent(Just a thumb screw to open and close the top)I can't open it any more then 3mm or it will blow out when I lowered the pressure to 2-3psi I could open it slightly more but then same results. Can anyone help me? I can't find anyone with this problem maybe it isn't a problem just a very small window of adjustability thanks for the help in advance. (Iv added a drawing of what all the dimensions are.) Sorry forgot to add my gas orifice was 0.6mm then I swapped it for 0.8mm that worked better. do I just need to increase that again to decrease the pressure difference and slow the air intake or am i over thinking it. Quote Link to comment Share on other sites More sharing options...
bluesman7 Posted October 8, 2017 Share Posted October 8, 2017 I think that you need a bigger orifice. Quote Link to comment Share on other sites More sharing options...
Mikey98118 Posted October 8, 2017 Share Posted October 8, 2017 The first thing I see is that there's no gas assembly OR ANY THREADED HOLE FOR ONE on that burner; this leads me to the a suspicion that you were just aiming a temporary gas jet down through the burner, without any way to ensure it is centered or parallel to the burner's axis. You had scant chances to judge your burner's performance that way. Quote Link to comment Share on other sites More sharing options...
Jakob Bull Posted October 8, 2017 Author Share Posted October 8, 2017 Hi Mikey I do have it all plumbed up properly now those pictures were just to show what type of shape I have Quote Link to comment Share on other sites More sharing options...
Jakob Bull Posted October 9, 2017 Author Share Posted October 9, 2017 But it is still blowing out when I open the air all the way and I have increased the orifice to 1mm Quote Link to comment Share on other sites More sharing options...
Jakob Bull Posted October 9, 2017 Author Share Posted October 9, 2017 This is it running at 2psi then I turned it up to 10psi I can't open the air any more or it will blow out what I want to fix is the turbulent flame or is it running ok? 20171009_203041.mp4 Quote Link to comment Share on other sites More sharing options...
timgunn1962 Posted October 9, 2017 Share Posted October 9, 2017 I don't think there's a problem with that flame, unless you intend to use it as a torch. How does it fare in a forge? That's the only thing that matters with a forge burner. There are certainly things you can do to make a burner work "better" in open air (a flame retention cup, for example), but they tend to adversely affect performance in a forge. Quote Link to comment Share on other sites More sharing options...
Jakob Bull Posted October 9, 2017 Author Share Posted October 9, 2017 56 minutes ago, timgunn1962 said: It dose have a taper at the end if that's what you mean by a ''retention cup''? Quote Link to comment Share on other sites More sharing options...
timgunn1962 Posted October 9, 2017 Share Posted October 9, 2017 It's not really what I had in mind as a flame retention cup. I'm not entirely sure what the "flare" actually does in most of the burner designs I see out there. In the "classic" Venturi design, there is a reduction to a very short "throat", followed by a 1-in-12 tapered diffuser. As I understand it, this diffuser is intended to slow down the fluid flowing through the Venturi while the flow is still primarily laminar. In the designs where the "throat" is extended to become the full length of the burner tube, the laminar-to-turbulent transition occurs within the extended throat and there does not seem to be a mechanism by which the 1-in-12 taper can work as an effective diffuser. That is not to say that it does not provide some benefit, just that I don't understand the mechanism. When a burner discharges into a forge, the relatively fast-moving mixture causes a slight pressure reduction in the forge atmosphere immediately adjacent to the exiting mixture. This draws the surrounding atmosphere in, just like the fast-moving gas exiting the gas jet draws in air at the Venturi, albeit to a lesser extent because the mixture speed at the burner tip is much lower than the gas speed at the jet. Because the forge atmosphere is effectively all flame, this means that flame is being drawn to the emerging mixture and this stabilizes the flame on the burner nozzle. It makes a huge difference to flame stability and is why it is pretty pointless trying to tune a forge burner in open air. A flame retention cup is usually a sizeable step-change in diameter (typically to twice the diameter, 4 times the area) and, as I understand it, works rather like a miniature forge, setting up a toroidal (donut-shaped) ciculating flame on the step of the retention cup and stabilizing the flame. When a flame retention cup seems appropriate, the flame design I tend to use is more-or-less as shown in the Amal atmospheric injector leaflet. http://amalcarb.co.uk/downloadfiles/amal/amal_gas_injectors.pdf Though I don't use a burner port nozzle as shown in the Amal drawing and I tend to weld something up from whatever is to hand. For a 1/2" burner, I'll slip a 1" length of 3/4" pipe over the end and then slip a 2 1/2" length of 1" pipe over that to get a 1" id retention cup about 1 1/2" long. I've not found the dimensions to be critical, but I've always stuck to a cup of twice the burner ID. About the only time I use a retention cup in a forge is when I am aiming for very low temperatures for heat-treating (around 800 degC, 1572 degF or a little less). In this case, the flame is extremely rich and I want to give it all the help I can. For forging or welding temperatures, I don't use a cup. It's the only pic I have that shows the retention cup at all. Quote Link to comment Share on other sites More sharing options...
Jakob Bull Posted October 10, 2017 Author Share Posted October 10, 2017 Ok cheers that was very interesting and helpful, I did think the burner tube length might interfere with the flare and was wondering if it would allow the flame to burn inside slightly but was hoping it would stabilize the flame and stop it oscillating as much. it dose seem to help at lower pressure tho. Also not that I'm going to but if I was to polish the internal bore my hypothesis is that it would help with stability of the flame but might create a mixing problem. What do you think? Quote Link to comment Share on other sites More sharing options...
Frosty Posted October 10, 2017 Share Posted October 10, 2017 Jakob: I can't open the video after almost a 60 mb. download. How about some stills, videos are much less use than stills. I can study details in a still, I can zoom in on some small thing, or put two different angles up on the same screen to compare, etc. Videos are usually shaky, move around too much and only last a few seconds. Frosty The Lucky. Quote Link to comment Share on other sites More sharing options...
Jakob Bull Posted October 10, 2017 Author Share Posted October 10, 2017 Ok. This is running 2psi and 10psi as I open it as much as I can. (photos are not in order) Quote Link to comment Share on other sites More sharing options...
Mikey98118 Posted October 12, 2017 Share Posted October 12, 2017 Actually, your burner is running very well, considering there is no practical flame retention nozzle. So, begin by mounting it in a forge; alternatively, build or buy a working flame retention nozzle. Quote Link to comment Share on other sites More sharing options...
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