by definition , biofuels are fuels that are comprised of biological ingredients like plant material. in order to be used in an automotive engine, plant material has to go through a refining process. this process turns raw plant material into ethanol. both corn ethanol and switch grass fuels come from plants that are replenishable . that means they can be grown over and over again. just like regular gassoline powered cars, biofuels emit carbon dioxide, but up to 94 precent less.