I am learning about bio diesel.

Diesel and gasoline engines perform best with very different types of fuel. Gasoline engines neeed high octane fuels; the standard is isooctane (2,2,4-trimethylpentane) It has an octane rating of 100 by definition. The opposite is n-heptane with a defined octane rating of 0. These measure the tendency of a fuel to knock in a test engine. Diesel fuels are rated by their cetane number. Cetane (n-hexadecane) is given the rating of 100, it is a great diesel fuel, Highly branched molecules are bad diesel fuels. The needs of the two fuels are therefore just about opposites of each other. This is basically the result of the ignition methods - spark plug (gasoline) vs compression (diesel)