2. How aggressive these are When tractors were first developed, they used enormous steam engines that were notoriously unreliable and hard to maintain. These were phased out around the turn with the twentieth century and substituted for internal combustion engines which were smaller though powerful and ran on a number of fuels including kerosene, ethanol and gasoline. By the 1960s several of these engines were phased out and only more effective internal combustion engines that ran on diesel and after this, biodiesel. The UK glass industry is pursuing an active programme on energy efficiency and decarbonisation. But building the business case to secure funds remains a barrier. Capital costs can be very high and paybacks periods are often in excess of two years; traditional loans are usually unattractive for this work.