Biodiesel can be used in any unmodified diesel engine. Hemp Car will be using hemp oil converted into biodiesel. This is a monumental task, as hemp is illegal to grow in the U.S. and the oil is extremely expensive. The Hemp Car crew say they chose to use hemp because of it's potential to replace petrol fuels. Pyrolysis is the technology which makes this possible.
Pyrolysis is a method that heats plant matter in an oxygen-free environment.
All of these constituents can be used as fuel. Lynn Osburn wrote an excellent paper on biomass fuels entitled, Energy Farming in America. The hemp plant has no psychoactive properties. Cultivating hemp can help replenish spent soil. Hemp can grow almost anywhere, and requires far less pesticides than many other cash crops, such as cotton.