Many automobiles and boats, as well as almost all eighteen-wheelers, are powered by diesel fuel, a petroleum-based fuel which is similar to gasoline. While a gasoline and oxygen mixture is ignited in the engine cylinder by a spark from the spark plug, diesel fuel is ignited by compression. The piston in a diesel engine travels up the cylinder, compressing the air. At the top of the stroke, atomized diesel fuel is injected into the cylinder, and ignites in the heat created from the friction of this compression.

Diesel fuel is about 18% heavier than gasoline and consists mainly of hydrocarbons that range from C10 to C24, meaning 10 to 24 carbon atoms with various configurations of hydrogen atoms attached to the carbon atoms. Gasoline, on the other hand, is usually in the C7 to C11 range, while kerosene, used for jet engine fuel, is weighted just between diesel and gasoline in the C12 to C15 range. The higher the number of carbon atoms, the heavier the product.

Before shipment from the petroleum distillery, the composition of diesel fuel may be varied by the distilling facility, depending on the latitude of the distillation facility and weather; specifically, the temperature at the time of distillation. The heavier diesel fuel will tend to thicken, or solidify, in cold weather, unlike gasoline which is basically unaffected by colder temperatures.

Though diesel fuel is heavier than gas, it is lighter than other petroleum-based products such as crankcase oil and lubricating oil. With a flash point of 120-degrees to 160-degrees, depending on the method of distillation, diesel is not as volatile as either kerosene or gasoline. Gas, however, burns considerably cleaner than petroleum-based diesel fuel.

Biodiesel, a diesel fuel produced from transesterification of vegetable oil or animal fat, is touted as the fuel for the 21st century. Biodiesel is essentially the reaction of alcohol with fatty-acids to produce a mono-alkyl ester. Because biodiesel is still in its infancy, at present, it is used in a blend with petroleum-based diesel fuel, even though it is classified as a fuel on its own. Until diesel engine modification catches up with biodiesel technology, a biodiesel/petro-diesel blend is used in today’s conventional diesel engines with no changes necessary to the engine.

Biodiesel fuel burns far cleaner than petroleum-based diesel oil for the simple reason that it leaves fewer hydrocarbons. Biodiesel also emits less carbon dioxide and is biodegradable, non-toxic, and essentially free of sulfides and aromatics. Because of its cleaner, less toxic properties, biodiesel fuel is more environmentally friendly than petro-diesel, and even gasoline.