Chicken John converted his 1975 pickup truck to run on coffee grounds or walnut
shells or pretty much any other trash you can burn. And not only does it run on
trash, but it's a carbon-negative vehicle. Seriously. The truck itself is
completely unmodified. Chicken just added a gasifier to it. It can run on gasoline with the flip of a switch. Gasification isn't some new-fangled technology. In Europe during World War II, over a million vehicles ran using wood burning gasifiers when gasoline and diesel were unavailable. The Cafe Racer: the car of yesteryear . . . today!

How does it work? Watch the video . . .

http://www.chickenjohn.com/mayor/innovation.html

Gasification Overview
Basically it works like this: you burn stuff in a low-oxygen environment to extract hydrogen gas. You cool the hydrogen gas, filter it, and feed it into a regular gasoline engine. The engine doesn't know the difference, and it runs the same as if it was running on gasoline. There are several types of gasifiers. The Cafe Racer uses a stratified downdraft gasifier.
Gasifier Mileage
15 pounds of organic material is roughly equivalent to a gallon of gas. Chicken gets a ton of walnut shells (that's 2000 pounds) for 40 bucks. That's equivalent to 133.33 gallons of gas (or GGEs (gasoline gallon equivalents) in the alternative fuel lingo). That works out to 30 cents a gallon. The truck gets the same mileage on a GGE of walnut shells as it wood on a gallon of gas.

Emissions
The gasifier does emit some carbon dioxide--the same CO2 that would be released if the organic material decomposed in the dump. But gasification doesn't emit the methane that would be released during decomposition. Gasification also produces some carbon monoxide, water, tar, and charcoal.
But there's a way to make gasification carbon negative. The charcoal that is created during gasification is special. It's called bio-char. Because the low-oxygen fire in the gasifier doesn't burn up all of the wood, the bio-char retains a bunch of nutritious minerals that plants love, and it makes for a unique kind of fertilizer. The bio-char itself contains a lot of carbon that is kept out of the atmosphere, and using it as fertilizer helps plants and trees gather more carbon dioxide out of the air.