There are much better ways of generating petrol-like fuel substitutions.
One such method is to use heat to break down a feedstock into what chemists call Syngas - a mix of CO and H. This will run a stationary engine directly, but could be combined into hydrocarbons by using the Fischer–Tropsch process. The resulting hydrocarbon mix can then be spilt by fractional distillation. The Fischer-Tropsch can be tuned to produce the bulk of the hydrocarbons of a specific length.
The beauty is with this method, is doesn't matter what your feedstock is as long as it's organic. Tyres, plastic, newspapers, grass clippings, doesn't matter. Although moisture tends to screw with it a bit.
It's something I'd very much like to play with at some point.