Diesel engines have higher thermodynamic and therefore high fuel efficiencies. Diesel engines are usually run at part-load; as the air supply is not throttled as in a petrol engine, their efficiency is very high.
The most common type of diesel fuel is a particular fractional distillate of petroleum l, but alternatives, such as biodiesel, biomass to liquid (BTL) or gas to liquid (GTL) diesel, are also being developed and adopted increasingly.
Petroleum-derived diesel is usually referred to as petrodiesel. Ultra-low-sulfur diesel (ULSD) is a specific standard for diesel fuel that has substantially low sulfur contents.
The most common measure of diesel fuel quality is the cetane number. It is a measure of the delay of ignition of a diesel fuel.