To build up long chain organic molecules from short chain ones takes net input of energy. 'Cracking' petroleum involves basically breaking down long chain 'lubricating oil length' ones to 'petrol length' ones with a catalyst, pressure and heat.

Diesels (and jet engines) can run on 'longer chain' organic molecules than 'petrol' engines - methanol and ethanol and gases will work in 'petrol' ICE engines, but they need to be adjusted.