Why are there different varieties of ethanol for light duty vehicles (E85) and heavy duty vehicles (E95)? Why can't E95 just replace E85?

Response:

E85 (a blend of 85% fuel ethanol and 15% gasoline) is used in spark ignition engines (i.e. gasoline engines). The gasoline is added to provide good cold start and warm up performance due to ethanol's low volatility, which results in more difficulty vaporizing at cold starts.

E95 (a blend of 95% fuel ethanol and 5% gasoline) is used in compression ignition engines (i.e. diesel engines). The addition of gasoline above five percent in diesel applications lowers the flash point to unacceptable levels.

Consequently, E85 cannot be used in diesel applications. Thus, E85 and E95 are not interchangeable because of the two different types of engines.