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Diesel or Diesel fuel is a specific fractional distillate of fuel oil (mostly petroleum) that is used as fuel in a diesel engine invented by German engineer Rudolf Diesel. Although diesel generally refers to a fossil based fuel, Rudolf's first engines ran on peanut oil, which today might be referred to as biodiesel. The term typically refers to fuel that has been processed from petroleum, but increasingly, alternatives such as biodiesel or biomass to liquid (BTL) or gas to liquid (GTL) diesel that are not derived from petroleum are being developed and adopted.

Petroleum diesel

Diesel is produced from petroleum, and is sometimes called petrodiesel (or, less seriously, dinodiesel) when there is a need to distinguish it from diesel obtained from other sources such as vegidiesel (biodiesel) derived from pure (SVO) or recycled waste (WVO) vegetable oil. As a hydrocarbon mixture, it is obtained in the fractional distillation of crude oil between 250 °C and 350 °C at atmospheric pressure.

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. 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. 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) adsorbers (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).

Chemical composition

Petroleum derived diesel is composed of about 75% saturated hydrocarbons (primarily paraffins including n, iso, and cycloparaffins), and 25% aromatic hydrocarbons (including naphthalenes and alkylbenzenes). The average chemical formula for common diesel fuel is C12H26, ranging from approx. C10H22 to C15H32.

Algae, microbes and water

There has been a lot of discussion and misinformation about algae in diesel fuel. An alga is a plant, and it requires sunlight to live and grow. As there is no sunlight in a closed fuel tank, no algae can survive there. However, some microbes can survive there. They can feed on the diesel fuel.

These microbes form a slimy colony that lives at the fuel/water interface. They grow quite rapidly in warmer temperatures. They can even grow in cold weather when fuel tank heaters are installed. Parts of the colony can break off and clog the fuel lines and fuel filters.

It is possible to either kill this growth with a biocide treatment, or eliminate the water, a necessary component of microbial life. There are a number of biocides on the market, which must be handled very carefully. If a biocide is used, it must be added every time a tank is refilled until the problem is fully resolved.

Biocides attack the cell wall of microbes resulting in lysis, the death of a cell by bursting. The risk of filter clogging may continue for a short period after biocide treatment until cellular residues break down and are absorbed into the fuel.

Synthetic diesel

Wood, straw, corn, garbage, and sewage-sludge may be dried and gasified. After purification the so called Fischer Tropsch process is used to produce synthetic diesel. Other attempts use enzymatic processes and are also economic in case of high oil prices. Synthetic diesel may also be produced out of natural gas in the GTL process or out of coal in the CTL process. Such synthetic diesel has 30% less particulate emissions than conventional diesel (US- California)


Biodiesel can be obtained from vegetable oil (vegidiesel / vegifuel), or animal fats (bio-lipids, using transesterification). Biodiesel is a non-fossil fuel alternative to petrodiesel. It can also be mixed with petrodiesel in any amount in modern engines, though when first using it, the solvent properties of the fuel tend to dissolve accumulated deposits and can clog fuel filters. Biodiesel has a higher gel point than petrodiesel, but is comparable to diesel #2. This can be overcome by using a biodiesel/petrodiesel blend, or by installing a fuel heater, but this is only necessary during the colder months. There have been reports that a diesel-biodiesel mix results in lower emissions than either can achieve alone. A small percentage of biodiesel can be used as an additive in low-sulfur formulations of diesel to increase the lubricity lost when the sulfur is removed.

Chemically, most biodiesel consists of alkyl (usually methyl) esters instead of the alkanes and aromatic hydrocarbons of petroleum derived diesel. However, biodiesel has combustion properties very similar to petrodiesel, including combustion energy and cetane ratings. Paraffin biodiesel also exists. Due to the purity of the source, it has a higher quality than petrodiesel.

Ethanol can be added to petroleum diesel fuel in amounts up to 15% along with additives to keep the ethanol emulsified. [1]


Internal Combustion Engines

Diesel is used in diesel engines, a type of internal combustion engine. Rudolf Diesel originally designed the diesel engine to use coal dust as a fuel, but oil proved more effective. Diesel engines are used in cars, trucks, motorcycles, boats and locomotives.

Packard diesel motors were used in aircraft as early as 1927, and Charles Lindbergh flew a Stinson SM1B with a Packard Diesel in 1928. A Packard diesel motor designed by L.M. Woolson was fitted to a Stinson X7654, and in 1929 it was flown 1000 km non-stop from Detroit to Langley, Virginia (near Washington, D.C.). In 1931, Walter Lees and Fredrick Brossy set the nonstop flight record flying a Bellanca powered by a Packard Diesel for 84h 32m. The Hindenburg was powered by four 16 cylinder diesel engines, each with approximately 1200 horsepower available in bursts, and 850 horsepower available for cruising.

The very first diesel-engine automobile trip was completed on January 6, 1930. The trip was from |Indianapolis to New York City, a distance of nearly 800 miles (1300 km). This feat helped to prove the usefulness of the internal combustion engine.

A new generation of diesel combustion uses a rail that keeps the fuel pressurised until it reaches the combustion chamber at Mach 2 (2350 km/h). The injection of diesel is more finer with particles 4 nanometres apart and droplets are smaller that they could fit on a pin head. As the result, the fuel is burned more efficiently and equally whilst producing more power, torque and better fuel economy and reduced emissions. With a more complete combustion, there is a reduction of soot and evaporative pollutants and the diesel engine is more silent as an equivalent petrol car.

Automobile racing

In 1931, Dave Evans drove his Cummins Diesel Special to a nonstop finish in the Indianapolis 500, the first time a car had completed the race without a pit stop. That car and a later Cummins Diesel Special are on display at the Indianapolis Motor Speedway Hall of Fame Museum.

With turbocharged Diesel-cars getting stronger in the 1990s, they were entered in touring car racing, and BMW even won the 24 Hours Nürburgring in 1998 with a 320d. After winning the [2 Hours of Sebring in 2006 with their Diesel-powered R10 LMP, Audi won the 24 Hours of Le Mans, too. This is the first time a Diesel-fueled vehicle has won at Le Mans against cars powered with regular fuel or other alternative fuel like methanol or bio-ethanol. Competitors like Porsche predicted this victory for Audi as the regulation is pro-diesel. French automaker Peugeot is also planning to enter a diesel powered LMP in 2007.


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, and should a person be found to be using this untaxed diesel fuel for a typically taxed purpose (such as "over-the-road", or driving use), the user can be fined US$10,000. In the United Kingdom it is known as red diesel, and is also used by agricultural vehicles. Diesel fuel, or Marked Gas Oil is dyed green in the Republic of Ireland. The term DERV (short for "diesel engined road vehicle") is also used in the UK as a synonym for diesel fuel. In India, taxes on diesel fuel are lower than on gasoline as majority of the transportation, that transports grains and other essential commodities across the country, runs on diesel.


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