He must be a ex Land Rover owner who's no longer got one. I think he's lost the plot. How much energy has to be used (electric/gas) to sustain the 300 deg C for a long enough period to complete the combustion. Dead cats, really! Imagine a pile of those rotting in your backyard awaiting processing.
Another alternative to Biodiesel and Ethanol (both easy to make) is the coal fired/gas burning setups installed on the back of cars, that where used during WW2 when petrol was rationed.