The refining process also rearranges molecules in other ways, because of the high temperatures, many bonds are broken and reformed. Chains of carbons are broken and remade, sometimes in alternative ways. Moleules which have the same chemical formula, but differ in structural arrangement are called isomers. However octane is more readily combusted, therefore in an engine the octane sometimes pre-ignites. However, because lead is highly toxic and especially so to young children, major efforts were forthcoming to discontinue the addition of lead to gasoline and find new ways of improving engine performance.
Unleaded gases are less efficient than the leaded gases of the past.
Releases less pollutants, but also less efficient. Currently more expensive. The fuels discussed generate heat on combustion - however, we don t necessarily use the energy as heat. The fuel is used as an energy source for the boiling of water. The water turns to steam.