Making fuel from wood. The photograph, taken in 1951, shows a Russian automobile fitted with a 'wood gasifier' (arrow). Similar vehicles were relatively widespread in Europe in the 1940s and 50s, and achieved conversion efficiencies of roughly 3 kg of wood consumed per power-output equivalent to 1 liter of gasoline. Modern biotechnological approaches, using enzymes like the ones found in termite guts, are still struggling to surpass that efficiency . But they do offer a much more convenient and clean fuel product, ethanol.
Chaffron and von Mering Genome Biology 2007 8:229 doi:10.1186/gb-2007-8-11-229