The hydrogen in the fuel combines with the oxygen and burns to form water. Normally this is in the form of steam, but if it is cooled it will condense on the liner surface and wash away the lube oil film. Fuels also contain sulphur. This burns in the oxygen and the products combine with the water to form sulphuric acid. If this condenses on the liner surface, then corrosion can take place. Once the oil film has been destroyed then wear will take place at an alarming rate. One solution is to insulate the outside of the liner so that there was a reduction in the cooling effect. On the latest engines, the liner is only cooled by water at the very top, relying on the air in the scavenge space to cool the lower part of the liner.