Diesel fuel is a flammable mixture of hydrocarbons made by the fractional distillation of petroleum, which occurs at between 200 to 360 degrees Celsius, which is 392 to 680 degrees Fahrenheit. The mixture is mainly comprised of alkanes, cycloalkanes and aromatic hydrocarbons possessing between 12 and 20 carbon atoms.
Like most hydrocarbon mixtures, diesel fuel is chemically inert. Its chemical properties make it useful as a fuel or in some cases, as a solvent, making it similar to kerosene. Diesel fuel oxidizes very slowly upon continued exposure to air. Diesel fuel can be described by its cetane number, which is a measure of ignition quality inversely proportional to the octane number for gasoline. Most diesel engines burn diesel fuel with a cetane number of 50 or higher.
Physically, diesel fuel appears as a colorless to light brown liquid with a specific gravity of 0.81 to 0.96, making it less dense than water. Diesel fuel freezes at negative 8.1 degrees Celsius, which is 17.5 Fahrenheit, rendering it less suitable for cold weather applications when compared to gasoline. Diesel fuel has a higher specific gravity, higher viscosity and lower volatility than conventional gasoline, but diesel fuel contains more energy per gallon than gasoline due to its higher density.