I decided to throw this up here, maybe someone with more time than I have will get intrigued and make some headway.
I played around a few years ago, and some really interesting things were learned, tested etc, but like I said, I don't have time, and likely won't any time soon.

Gasification, where you heat a fuel beyond it's ignition point, without the presence of oxygen, so you are left with a gas / vapor fuel.
There are lots of videos on youtube, and articles scattered around the internet. Almost everything you come across involves "woodgas", where wood is burned with reduced air flow, and the smoke is so rich in fuel, that it can be burned in an engine.

I decided to experiment with oil, and the result was good.
Basically, I found a long long piece of 1/4" steel tubing, and one end waste oil was poured in, then it was coiled up in a wood stove for heat, then the other end had a small coil through a pail of water, and the open end laying out in the yard.

The fire made the coil red hot, and the open end in the yard, would bellow out a white/yellow colored gas, depending on the coil temp.
The gas/vapor that came out, flowed along the blades of grass, and when you lit it with a lighter, burned off like propane or something.
I got an old lawn mower to run on it, not very well though, as all I did was take the carb off, and leave the oilgas tube hanging in the intake elbow, so it would rev a bit, burn to lean, slow down, then rev again. lol.

Anyways, after much reading, oilgas apparently has a very high octane rating, so it should be possible to run it in diesels or gasoline engines. Diesels would need to use it as a supplement, as the compression alone won't ignite it.
I wanted to try it, but can't find the time. Only a few people have the time and money to fool around with stuff like this, and it seems I only have either; never both.

Basically, the way I was going to try it, was to put insulation on the exhaust headers, to keep heat in, and then build a 4" exhaust tube with steel coiled tubing inside, so the exhaust would heat the waste oil in the coils. The coils would heat the waste oil, and then there would be an old propane tank or other steel tank, with a removable bottom to remove any crud once in a while. From there, the tubing would run close to the fan behind the rad, to cool off. From there, it would enter the air intake of the engine. It MUST be cooled off before it is exposed to fresh air, otherwise it just ignites on it's own.

But the basic operation is very simple; push waste oil through pipe, heat pipe to really high temperatures, oil turns to gassy vapor, cool off, now you have a gaseous fuel.

I know of one other person, that I helped slightly, that is playing with systems using electric heat and playing around with small mower engines, but is planning on getting his bronco with a 460 converted to run it.

A couple neat parts of this process:
-Use settling tanks to collect garbage from oil; no filters. Even engine oil with heavy metal particles, once it's gassified, they should settle on the bottom of crud tanks, I doubt any heavy metals will stay floating in a gas that is close to the weight of air.

-Leave the stock fuel system alone! since the fuel enters the air intake, you don't have to pump garbage through the fuel system.

-Use fuel that is absolute garbage... Even if oil has water in it, the water just turns to steam and steam goes into the intake.... not desirable, but certainly less trouble than getting water into the fuel system of a gas or diesel vehicle. Even waxy junk oils will work, they will either break down into the gas, or settle in a crud settling tank.

-Clean burning.... Once the oil is vaporised, it burns REALLY clean, like natural gas clean. I don't have any idea about emissions, but as far as watching the gas ignite, it looks like a natural gas flame. I'm not sure, but it might even be possible that one day someone could make this work even with a DPF on the truck. Someone with a lot of money to burn lol.

Now the bad things: (cause theres no free lunch. )

-Heat required... if the oil isn't heated enough, it's more of a vapor, and less of a gas. I still had good results using it, but I think you'd eventually get the intake gummed up with oily residue. I filled a few containers, and it can settle out after a few minutes. This is what happens when the heat is too low, it creates an oily vapor instead of an actual break down to gas.

Keeping the heat hot enough is basically the main problem. I think that you need about 800* to crack it, and that isn't feasible all the time from the engine.
BUT, if the oil is preheated from exhuast, then brought up to full temp afterwards, the energy used should be small.

Anyways, if your into this kind of thing, next time you have a junk old lawnmower engine, you'll see that a gas engine can actually burn oil. I'll let you guys draw your own conclusions, but if nothing else, I thought this was very very cool. lol.