As suggested, untreated engine oil is probably not a good idea for automotive diesel engines.

Years ago we were on a cruise ship (back before 9/11 when it was still possible to take tours of the engine room) and the subject of engine oil came up - I think in the context of "how do they change the oil in the ship's diesel engines?" And the answer was - "they don't. The engineer described a closed loop system where a portion of engine oil was removed on a continual basis and mixed with the fuel and burned with an appropriate amount of make-up oil added the crankcase continuously. Seems to make sense...

A recent article in the Seattle PI talked about the cruise ships in Seattle - "A lot of them burn what's called bunker-C , and it's so dirty and it's so black and it's so awful, they have to heat it until they can get it to the point where they can move it around the pipes. It's like tar". If that's the case, diluting the fuel with appropriately filtered crankcase oil seems highly appropriate. If this is true, then the only waste to be disposed of would be the used filters. Seems like a good design. Obviously, the system would have to be designed to handle the quality of fuel being used.

It would be pretty cool, though probably highly impractical, to have a closed loop system on our cars, where an oil change would consist of a filter change and adding motor oil to the make-up tank... and the only other maintenance maybe an oil pan flush every 200k or so.