Distillation of crude oil into different fuel categories
In the distillation processing (boiling off) of crude oil, four broad product fractions or categories are generated:
Each of these fuel categories boils at higher temperature ranges, until the oil will not boil without thermal decomposition. The nonboiling fraction is called residuum or residual oil.
- refinery gas (primarily methane, ethane and hydrogen),
- liquefied petroleum gas (primarily propane and butane),
- and distillate fuels.
Distillate fuels are further subdivided into several categories for specific uses.
The "lightest," or lowest temperature boiling fraction (all distillate fuels broadly overlap in boiling range) is called kerosene, and is used for commercial jet turbine engines fuels, for small heaters and for wick-fed illuminating lamps.
The next fraction, used during cold weather conditions for automotive or truck fuels in "compression ignition" engines, is called "diesel" fuel.
The next higher boiling fraction is used for residential heating furnaces, called "home heating oil". This same boiling range oil is also used in warmer conditions as diesel fuel for larger land-based, on- and off-road engines, such as trucks, busses, earth moving and material lifting and moving equipment, farm equipment and railroad diesel locomotives.
The next heavier fraction supplies fuel for industrial heaters and boilers.
Finally, the "heaviest," or highest boiling distillate fractions are often blended with residual oil to make fuels for large steam boilers and, with fuel preheating, for very large compression ignition engines, such as ocean-going ships (e.g. IFO 180 and 380). Small and medium sized marine vessels use distillate fuels in several of these land-based categories (e.g. MDO and MGO).
(EPA, August 1999)