Cooling by Fuel Vaporization

Function

The internal cooling should achieve, next to the external air cooling or liquid cooling, a special cooling inside the cylinder.

How it works

Fuel absorbs a lot of heat during evaporation. It cools the engine from the inside when it reaches, in the form of a fine liquid spray, the combustion chamber where it evaporates before combustion. A fine example of the effectivity of the internal cooling, is motor-racing sport. In this field one has almost always had the problem of overheating with tuned engines, this was often solved efficiently and simply by enriching the fuel mixture. Dragsters, e.g., generally have neither cooling fins nor a cooling system circuit. They lose a great deal of their excess heat through fuel evaporation.

This example shows even more clearly the enormous significance of the internal cooling:
To vaporise, petrol needs 380-500 kJ/kg. This means, to convert 1 kg of petrol into a gaseous state, 380-500 kJ of energy are needed. If we use aluminium, with a linear, specific caloric capacity of 0.9 J/kg*K as a base. To cool 1 kg of aluminium down by 1°C , 0.9kJ are necessary, that makes, with a difference in temperature of 100 °C, 90 kJ. So the vaporisation of 1 kg of petrol is sufficient to cool about 5 kg of aluminium down by 100°C. 10/09