Why is an engine harder to start on ethanol?
Vapor Pressure – The first difference in these fuels is that ethanol has a lower vapor pressure than gasoline. This means that while the cylinder head is below the boiling point of ethanol, gasoline will more readily vaporize. Since there is very little time from when the injector squirts the fuel to when the spark plug will attempt to ignite it, this can make for significantly less of the ethanol to have turned into a vapor than would have happened for the same amount of gasoline. Liquid fuels do not burn. To compensate for this, all engines will add extra fuel when starting as it is the fuel to air mixture OF THE VAPOR that matters. Carbon-Carbon Double Bonds – Gasoline ignites more easily than ethanol. There are fundamental differences in the physical chemistry of these fuels. In order to start and then maintain a combustion chain reaction, you must have fuel as a vapor well mixed with oxygen and have sufficient kinetic energy (heat) in the molecules to destroy the existing molecula
