I used to work for MAN Diesel (Engineering) in Research and Development, and they tried running engines on everything from unrefined heavy oil (looked like thick black sludge that was the left overs from the crude after petrol quality was removed). You had to heat it up before starting the engine, and engine really didn't like it. Con rods 8 inch thick was mangled all the time.
They had one running on abattoir waste. It was ground up fat, gristle, skin, small bones, you name it (I often debated disposing of my boss this way). It was ground into a hard paste, almost like soap or lard, and felt like sandpaper. That you had to melt too before the engine would start and when it did start, jesus the emissions was nasty, it smelled bad before it burned too.
Another running on food waste, vegetable waste, you name it it was tried. Its surprising, its more a case of what CAN'T you run an engine on. Its more down to is it effective, some of them the output was barely enough to operate a kids toy, others was powering 100s of lights.
Augsburg where the main development was done, I was told they had a water powered engine, as I recall it used precious metals in the reaction to charge the battery which in-turn powered a standard electrical engine. They was looking at other materials which could be used to save on the metals. Really even though they say its Water Powered it was Hydrogen which produced the power, and it used massive amounts of copper and some amount of gold/platinum. I left the company before I got any where near that so don't know alot about it.