Waste motor oil is a good source of energy for a Lister. The only drawback is the abrasive wear that this fuel causes and the premature ring and cylinder end of life. There may be a good solution to this though and that is Vacuum Distillation. This process is a lot easier to set up than imagined, requires low temperatures and could likely be conducted using only engine coolant and/or exhaust heat. Refineries use this process a lot and old motor oil is often recycled using this method. Since the abrasive character of burning used oil comes from the "ash" produced mostly from the additives, it is likely that vacuum distillation would easily remove most of these. Only additives that form "Azeotropes" would remain but reduced if the operation uses a "reflux" bubble chamber between the boiler and the condenser.
The higher the vacuum, the lower the temperature required. Since the system is sealed, theoretically once the vacuum is pulled, it stays as long as an equal amount of distilled oil is removed for the waste oil that is added to the boiler. However, if any oil breaks down, or any molecular changes occur, additional vacuum or evacuation flow will likely be needed to maintain the correct vacuum. The product must be pumped out to keep the seal. The feed can be orifice and needle valve regulated since the vacuum will suck it into the retort, just keep the feed and pump out balanced. A fluid level glass, float, or indicator will also be needed in both ends.
Also, playing the higher vacuum lower temperature option will result in more water coming over the still if there is any in the oil. Other more volatile materials will also come over. As long as they are fuels it doesn't matter, but if destructive additives start coming over, the purpose of the whole operation becomes defeated. The key will be finding the vacuum that gives the best balance.
The vacuum process might be useful with waste veg. oil too, but probably in reverse. I.E. Using vacuum distillation to remove water and taking the purified product from the retort side of the operation using a staged retort.
Assuming most Lister users likely have welders, and since low cost flux core migs are so common now days, construction should not be an issue. Silver solder, Phos/copper and other techniques used in HVAC work would also work. It is also possible to assemble such as system without any welding or soldering, but perhaps not as efficient. Old 20 pound propane tanks for instance that may no longer be safe at 110-120 PSI in the summer would be OK in a vacuum system as long as they are not in really bad condition. Use one for the retort and one for the distillate collector. Set the retort tank in the top of that barrel you use in that thermo-syphon cooling system. You might even use two smaller barrels, one smaller top barrel that just fits around the propane tank retort, then the coolant flows into a lower barrel for more cooling. Insulate the top barrel to keep more heat for the vacuum distilling input.
Another more efficient method would be to weld or braze a DIY heat exchange coil or loop into the inside of the tank used for the retort, and circulate engine coolant through it. If designed correctly thermo-syphon would also work for the coolant flow, I.E. larger tubing and fewer coils and bends inside the retort tank. Input the coolant into the top coil and exit from the bottom coil to a radiator or barrel.
Most electric vacuum pumps sold pretty much everywhere for automotive AC work will give the proper vacuum, and there are dozens of ways to rig a mechanical vane type vacuum pump to a Lister, preferably using a clutch of some type. If you are running a generator, the electric method is easiest to set up and control. Whatever method, just rig a regulator so the vacuum pump only comes on when the vacuum is not high enough, and use a tank to "store" some vacuum between vacuum pump cycles so the system stays balanced better. If you just leave the pump running you will needlessly wear it out soon, and burn a lot more extra energy than you would like.
In summary, the idea is to set up a self distilling waste motor oil fuel feed for the Lister, not sacrifice engine life, and take advantage of a high energy fuel source that is widely available. Waste motor oil usually has more energy than diesel per gallon.
Also bear in mind that there is a close cousin to this process called Steam Distillation. While this would also likely work, it would be more complex requiring a boiler, and/or system steam circulation pumps and so forth, slightly higher temperatures, and may waste more energy. The steam serves to reduce the "partial pressure" and creates a type of "artificial" vacuum. Then you have to add a water separation stage.
I will eventually get on of those round tooits and do this myself like I eventually do with everything else. In the mean time, why withhold this from the rest of the Lister folks? Since most folks here are pretty smart and creative, here is something to experiment with!
