### Diesel Fuel

Because of their unique compression-ignition principle, diesel engines run on fuel oil instead of gasoline. The fuel is injected into the cylinder at the end of the compression stroke and the heat of compression ignites the mixture. Diesel fuel used in automotive applications comes in two grades, No. 1 diesel fuel and No. 2 diesel fuel. No. 1 diesel is the more volatile of the two and is designed for engines that will operate under varying load and speed conditions. No. 2 diesel is designed for a relatively uniform speed and high loads.