Diesel fuel is very similar to heating oil which is used in central heating. In Europe, the United States and Canada, taxes on diesel fuel are higher than on heating oil due to the fuel tax, and in those areas, heating oil is marked with fuel dyes and trace chemicals to prevent and detect tax fraud.
Similarly, "untaxed" diesel is available in the United States, which is available for use primarily in agricultural applications such as for tractor fuel. This untaxed diesel is also dyed red for identification purposes.
Here is a working animation of how a diesel engine operates:
Diesel is produced from petroleum, and is sometimes called petrodiesel when there is a need to distinguish it from diesel obtained from other sources. As a hydrocarbon mixture, it is obtained in the fractional distillation of crude oil between 250 °C and 350 °C at atmospheric pressure.
Petro Diesel is considered to be a fuel oil and is about 18% denser than gasoline.
The density of diesel is about 850 grams per liter whereas gasoline has a density of about 720 g/l, or about 15% less. When burnt diesel typically releases about 40.9 megajoules (MJ) per liter, whereas gasoline releases 34.8 MJ/l also about 15% less.
Diesel is generally simpler to refine than gasoline and often costs less (although price fluctuations often mean that the inverse is true; for example, the cost of diesel traditionally rises during colder months as demand for heating oil, which is refined much the same way, rises).
Diesel fuel, however, often contains higher quantities of sulfur.
In Europe, emission standards and preferential taxation have both forced oil refineries to dramatically reduce the level of sulfur in diesel fuels.
In contrast, the United States has long had "dirtier" diesel, although more stringent emission standards have been adopted with the transition to ultra-low sulfur diesel (ULSD) occurring in 2006 (see also diesel exhaust). U.S. diesel fuel typically also has a lower cetane number (a measure of ignition quality) than European diesel, resulting in worse cold weather performance and some increase in emissions.
High levels of sulfur in diesel are harmful for the environment. It prevents the use of catalytic diesel particulate filters to control diesel particulate emissions, as well as more advanced technologies, such as nitrogen oxide (NOx) absorbers (still under development), to reduce emissions. However, lowering sulfur also reduces the lubricity of the fuel, meaning that additives must be put into the fuel to help lubricate engines. Biodiesel is an effective lubricant. Diesel contains approximately 18% more energy per unit of volume than gasoline, which, along with the greater efficiency of diesel engines, contributes to fuel economy (distance traveled per volume of fuel consumed).