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Heat energy is needed to vaporise the fuel. Fluids don't burn you know, gases do. So if we want a combustion to occur in the cylinder we must have an mixture of vaporised fuel and oxygen there. To get the fuel to vaporise heat from tha intake air is used, how much heat neccesary depends of which fuel is used and of course the amount of fuel injected.
The vaporisation will cause a drop in intake air temperature and if the fuel used have a high "heat of vaporisation" you will need less or maybe no intercooling (like the CART engines which run on methanol).
"Vapour pressure" is a measure of how much the fuel will vaporise at a mentioned temperature.
If the vaporisation is poor you can inject more fuel to solve the problem (like when the engine is cold), but this is not a good idea since we want high effiecy and much power from our engine. So if a intercooler is used a simple bypass valve controled by intake air temperature can be used to let uncooled air by the intercooler and on that way increase the intake temperature.
But to get too low, really large and effective intercoolers must be used.
On Hondas old turbocharged F1 engine it's intercoolers could reduce the intake temperature to 36 C but the ic bypass increased it to 40 C. In a later more efficient but less powerful engine a intake temperature of 70 C was used (also increased CR, less boost and heated fuel), this engine is still today the most efficient F1 racing engine in history with it's 32% effiency.
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