Diesel is one of the many hydrocarbons/combustibles which can be extracted from crude oil. The most effective means of making diesel fuel combust is to compress it. Diesel is the fuel of choice when designing a high torque output engine for heavy work loads, and this type of fuel requires specifically a diesel engine to use the fuel. The measure of diesel fuel quality is its cetane number, which is a measure of the chemical delay of its ignition.
In many countries, diesel fuel is given standards for chemical properties and quality. For example, in the European Union, the standard for diesel fuel is EN 590.
ULSD: Ultra-Low Sulfur Diesel
In countries with strict emissions controls, sulfur level allowance is reduced to only a handful of parts per millions. The following chart provides some examples, but they may be inaccurate/out-of-date if they haven't been checked in a while.
|Public Road PPM
Unlike lead in gasoline, where the lead was added in to serve a purpose, the sulfur in diesel is from the crude oil source and provides no benefits to the engine. It has to be removed from the fuel in order to meet standards, rather than not be put in there in the first place. However, the process used to remove the sulfur may have unintended consequences for other fuel qualities.