I’ve read this group with interest for some time, but until just recently, have not had the resources available to pursue WVO burning in earnest. I’ve paid particular attention to those who’ve struggled with short chambers, as my primary appliance is a Weil McLain boiler, WGO-2, with an 8.5” chamber depth. It seems that the primary problems around this style chamber are that WVO burns slower, and as such the flame tends to be longer for a given firing rate. Efforts to shorten the flame with a Kagi style head have been only moderately successful, since it also appears to induce enough additional combustion air to cool the flame enough that output is quite low.
So, in an effort to move the “science” of short chambers further, I have acquired a Beckett AF along with a siphon nozzle and adapter (thanks Jesse). My theory is that if you have a short chamber, you must use a Kagi style head with significant combustion air, but that the cooling effect must be compensated for. I am in the middle of constructing a AIR/OIL copper tube exchange preheater using 1” OD copper, and 1/2” ID copper for air w/BB exchanger. What I’m going to add however, is a secondary air-only preheater with a separate PID control that will be elevated somewhere north of 400F degrees, in an attempt to aid with combustion by helping offset the added swirl air. So the system will look like this: Indoor tank (275 gallon) with a small pump that will feed a copper gravity tube, excess will runoff back into tank fill. (approximately 35” of column will gravity feed the siphon nozzle) The oil, and air will feed through solenoids, through the air/oil heater, to approx 275-300F, then air will feed the secondary heater to 400-500F (TBD) and through the siphon nozzle.
The burner tube will have a Kagi head or perhaps a fabbed high swirl head, and significant air to shorten the flame. Steady state will be achieved, and the secondary heater will be dialed until best burn is achieved. If I can get the air hot enough to accelerate vaporization and combustion, the goal should be achieved. Look for photos of the two preheaters tonight. I’m working on the air/oil, and the air only is done. Kudos to Eric for his elegant preheater design. Still to be determined: A good method of insulating a 500F device from little fingers and heat loss, which in a 50F shop, could be fairly significant. And controls. I’m figuring two PID controllers will be needed, along with a fairly robust air source since I am running through two restrictions instead of one. I’m looking mostly at removing the oil pump and retrofitting a Thomas or gast type pump. I have a shop compressor, but don’t wish to run a large compressor at all times.
In my experience (9.25” chamber depth) the only way to shorten the flame (even with kagi head) is AL OT of blower air.even this is still too long of a flame. The problem with this is the blower air cools the oil spray before it has time to burn and then it won’t burn. This results in a wet gooey chamber. The flash point of veggie oil is well over 450*.(can’t remember the exact temp at the moment. I’ve thought about heating the combustion air too but that will take a lot of electric and i’m still not sure it will do the trick. Even if it does, it would be considered excess air and would waste a lot of heat up the chimney. Interested to see your outcome though. What burner came on this boiler, i’m assuming and afII.
The stock burner is an AFG. Not sure what head. The original nozzle is a 0.75 / 70B. The chamber has a refractory lining. The stock flame does hit the back wall with refractory. The way I see it, the small amount of electricity burned would be paid for by free fuel, so it’s worth trying I guess.