Both gasoline and diesel fuel consist of hundreds of different hydrocarbon molecules. In addition, several bio-origin components, such as ethanol in gasoline blending, are common.
Gasoline contains mainly alkanes (paraffins), alkenes (olefins), and aromatics. Diesel fuel consists mainly of paraffins, aromatics and naphthenes. The hydrocarbons of gasoline contain typically 4-12 carbon atoms with boiling range between 30 and 210 °C, whereas diesel fuel contains hydrocarbons with approximately 12–20 carbon atoms and the boiling range is between 170 and 360 °C. Gasoline and diesel fuel contain approximately 86 wt-% of carbon and 14 wt-% of hydrogen but the hydrogen to carbon ratio changes somewhat depending on composition.
Paraffinic hydrocarbons, especially normal paraffins, improve ignition quality of diesel fuel, but low-temperature properties of these paraffins tend to be poor. Aromatics in gasoline have high octane numbers. However, aromatics and olefins may worsen engine cleanliness, and also increase engine deposits, which is an important factor for new sophisticated engines and after-treatment devices. Aromatics may lead to carcinogenic compounds in exhaust gases, such as benzene and polyaromatic compounds. Olefins in gasoline may lead to an increase in the concentration of reactive olefins in exhaust gases, some of which are carcinogenic, toxic or may increase ozone forming potential. Additives may be needed to ensure adequate properties of gasoline and diesel fuel.
Traditional gasoline and diesel fuel are not covered extensively in the “AMF Fuel Information System”. Instead, focus is given to alternative blending or replacement options of gasoline and diesel. However, engine technology together with legislation and standards for gasoline and diesel are discussed briefly.