locomotive engineer license

When tractors were first developed, they used enormous steam engines which were notoriously unreliable and challenging to maintain. These were phased out round the turn in the 20th century and substituted with internal combustion engines that have been more compact yet still powerful and ran on the variety of fuels including kerosene, ethanol and gasoline. By the 1960s many of these engines were phased out and only more effective internal combustion engines that ran on diesel and after this, biodiesel. Flickr: Jason Bache: