Vegetable Oil Heating Revisited Part 3

Here is the continuation of my vegetable oil heating system. Check out part one and two here.

Oil Burner

The heart of my burner is the preheater block and the nozzle; these two parts haven't changed from my original design. What I did add, is a pressure regulator type valve inside the nozzle. This consists of just a spring and a ball bearing, and it helps keep the nozzle from dripping when the system is off. I didn't come up with this design, but it does help eliminate any drip. I also experimented with having the stepper run backward a few turns when the system shut off, but in the end it wasn't necessary, although may be something I incorporate in the end just to be sure I don't drip any oil.

Temperature Control

The oil/air heater block is just an aluminum block about six inches long, with three holes in the back, and one in the front. In the back, one hole is for air, one is for oil, and the third is for the cartridge heater with the hole in the front for the nozzle.

The temperature of this block is regulated with a temperature controller, which is set at 180deg (although I have found the system will fire fine even at 160deg). As an extra safety I connected a thermal snap switch, which will trip at about 300deg. This switch is wired in series, with the flame eye so it will trip the system if the preheater ever gets this hot. The temperature controller is set to warm the block when there is a call for heat. When the temperature hits 180deg, the burner will fire. If the temperature of the block ever goes above 195 or below 165, it will shut the system down.

Retention Head

The last part of the system is the retention head. The standard retention head appears to be made from a stamped piece of metal. I found that although this retention head works, the flame it produces is very long and narrow. The standard flame from an oil burner is usually shorter and bushier, and this is what I was going for based on the size of my flame chamber. To duplicate this type of flame I made a retention head based on a companies design, which looks more like a turbine. The retention head is made from a piece of stainless steel with a bunch of cuts in it, which are then bent into the turbine shape and inserted in the flame tube. This produced a nice flame that was very similar to a standard oil burner flame that was less than a foot long, which is the depth of my flame chamber.

Boiler

When my burner was all set, I decided to make a slight modification to my boiler. The change was to replace the chamber liner with fire bricks like the kind used in a kiln. The advantage of these bricks is that they protect well, but once they get hot, the surface glows red and will burn up any residual oil.

That completes my rebuild. It's a good thing for me that I have two boilers, both a gas and an oil one, which can heat my house. My system is wired so that I can choose my boiler with a switch; but if the temperature ever drops below 45, it will switch to the other boiler. Now my only problem is how to collect and filter over 1000 gallons of used vegetable oil to 5 microns or better, but that's a topic for another post.