Petroleum diesel

Petroleum diesel
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A vintage diesel pump
Diesel is produced from petroleum, and is sometimes called petrodiesel when there is a need to distinguish it from diesel obtained from other sources such as biodiesel. It is a hydrocarbon mixture, obtained in the fractional distillation of crude oil between 200 °C and 350 °C at atmospheric pressure.
The density of diesel is about 850 grams per liter whereas gasoline (British English: petrol) has a density of about 720 g/L, about 15% less. When burnt, diesel typically releases about 40.9 megajoules (MJ) per liter, whereas gasoline releases 34.8 MJ/L, about 15% less. Diesel is generally simpler to refine than gasoline and often costs less (although price fluctuations sometimes 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). Also, due to its high level of pollutants, diesel fuel must undergo additional filtration which contributes to a sometimes higher cost. In many parts of the United States, diesel is higher priced than gasoline.[1] Reasons for higher priced diesel include the shutdown of some refineries in the Gulf of Mexico, and the switch to ULSD, which causes infrastructure complications.[2]
Diesel-powered cars generally have a better fuel economy than equivalent gasoline engines and produce only about 69% of the greenhouse gases. This greater fuel economy is due to the higher energy per-liter content of diesel fuel and also to the intrinsic efficiency of the diesel engine. While diesel's 15% higher volumetric energy density results in 15% higher greenhouse gas emissions per liter compared to gasoline[3], the 20-40% better fuel economy achieved by modern diesel-engined automobiles offsets the higher-per-liter emissions of greenhouse gases, resulting in significantly lower carbon dioxide emissions per kilometer.[4][5]
On the other hand, diesel fuel often contains higher quantities of sulfur. European emission standards and preferential taxation have 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) starting in 2006 and becoming mandatory on June 1, 2010 (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 because they prevent the use of catalytic diesel particulate filters to control diesel particulate emissions, as well as more advanced technologies, such as nitrogen oxide (NOx) adsorbers (still under development), to reduce emissions. However, the process for 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.