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number (a measurement of ignition quality), viscosity, and flash point. Additives might also be present in small quantities to improve combustibility (alkyl nitrates), reduce corrosion of storage vessels (surfactant), or reduce gum formation (antioxidants such as aromatic amides or phenols).

Diesel fuels are categorized as the middle distillates from crude oil and are more dense than gasoline. As defined in the U.S. Chemical Substances Inventory under the Toxic Substances Control Act, diesel fuels consist of hydrocarbons with carbon numbers predominantly in the range of C9 to C20 and boils in the range of 163 to 357°C (IARC 1989). That definition encompasses both diesel fuels No. 1 (DF1) and No. 2 (DF2). DF1 is essentially kerosene and consists of hydrocarbons with numbers predominantly in the range of C9 to C16 and boiling in the range of 150 to 300°C. DF1 contains little benzene (e.g., less than 0.02%) or polycyclic aromatic hydrocarbons (Millner et al. 1991). DF2 is essentially equivalent to fuel oil No. 2 used for automobiles and boils between 160 and 360°C (IARC 1989). DF2 is more viscous than DF1 and spans a carbon number range of C11 to C20 (IARC 1989). DF2 also contains a greater variety of compounds and includes olefins and mixed aromatic olefin-type compounds, such as styrenes. More information on the composition of diesel fuels can be found in IARC (1989) and Millner et al. (1992).

The characteristics of DF2 (Jenkins et al. 1983a) are the following:




Saturated hydrocarbons



Substituted benzenes



2-Ring aromatics



3-Ring aromatics



Polar aromatics


Refractive index


Density at 25°C (grams per milliliter)


Viscosity at 25°C (centistokes)


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