I've been experimenting with burning waste oil in my garage. Most commercial waste oil heaters use a pump fed nozzle and compressed air. I wanted try something much simpler.
Waste oil contains about the same BTU's as heating oil and when burned correctly it burns just as clean. I've been reading about drip-fed waste oil burners over the years and decided to give it a try.
There's a popular drip-fed design on youtube by ozzirt that has been widely copied by many others with varying degrees of success. His design uses a frying pan and a brake rotor for the combustion area and two tractor/trailer brake drums which basically act as a heat exchanger. It seems to work fine but there's not enough heat output for what i need.
I've seen people using old hot water heaters and propane bottles and such to make their waste oil stoves. I have a small potbelly stove that i've been experimenting with. I drilled a 1/4" hole in the lid for the drip tube that has a small valve to regulate oil flow and is gravity fed from 1/4" soft copper tubing that makes a few wraps around the flue pipe to pre-heat the oil. Pre-heating is key. I placed a 6" cast iron pan with the handle cut off in the center of the grate.
Since the grate is about 8" in diameter, this gave a 1" gap around the pan for air flow. I sat a large socket in the center of the pan that stands about 2" tall and placed a heavy gauge 5" steel lid on top of the socket making sure to get it perfectly level. The oil drips on to the center of the lid and quickly disperses to the entire surface of the lid with a bit of overflow into the pan below, forming two seperate rings of fire.
Starting it is done with a few ounces of kerosene and a piece of paper, then opening the oil to a slow drip. After 10-15 minutes there is enough heat in it to then open the oil to a fine steady stream. At this point, the velocity of the air being pulled in the bottom of the stove sounds very similar to a air fed commercial unit, resulting in a massive amount of fire and heat. But sadly without a heat exchanger, the majority of heat was going straight up the pipe.
I'm currently using a 4" pvc end cap as my supply tank that i've been filling with a cup of oil at a time that i place near the stove to pre-heat it before pouring it into the tank, mainly to aid in flow from the "supply tank" to the stove. Flow sucks when it's 10 degrees outside.
A cup of oil lasts about 10 minutes at full burn.I've got an old crock pot that i need to place i fitting in the bottom to use it as a heated tank that'll hold about 2 gallons.
This setup burned great, but after several hours of burning, deposits would build up on the edges of the lid and would wick the oil and drip off, missing the cast iron pan below and end up in the ash pan.
There's a down-draft version that i think would cure many of the ills of a waste oil burner but would require too much modification to my potbelly that i'd rather not do to it, so...
I've gone hybrid. I removed everything from inside the stove, start a regular small coal fire, and turn the oil on. TA-DA...Perfection. I add a small shovel of coal about every 30 minutes to keep the coals going. This thing kicks big ass now.
Now i've got the heat in the stove instead of the pipe. Because of the pre-heat wraps around the pipe, the oil actually exits the drip tube like a gas, squirting fire. Any oil that does actually drip into the hot coals is instantly vaporized into highly flammable gas. It's that intense that when i open the door, i can only hold my phone at it for a few seconds to take a picture before my hands are burning :)
First pic is straight coal.
Second pic is straight waste oil
Last pic is both together.