Biodiesel runs in any unmodified diesel engine. There is no "engine conversion" typical of other alternative fuels. The diesel engine can run on biodiesel because it operates on the principle of compression ignition whereby air is compressed and then fuel is sprayed into the ultra-hot, ultra-pressured combustion chamber. Unlike gasoline engines, which use a spark to ignite the fuel/air mixture, diesel engines actually use fuel to ignite hot air. This simple process allows the diesel engine to run on thick fuels. Since biodiesel is chemically similar to petroleum diesel fuel, you can pour biodiesel right into the fuel tank of any diesel vehicle. Biodiesel has many advantages as a transport fuel. Biodiesel has lower emissions, it is made domestically (which increases national security), it does not affect engine performance and biodiesel is produced from plants. Since plants are a product of solar energy, biodiesel is "liquid solar fuel."