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Diesel fuel

Diesel fuel in general is any liquid fuel used in diesel engines, whose fuel ignition takes place, without spark, as a result of compression of the inlet air mixture and then injection of fuel. (Glow plugs, grid heaters and heater blocks help achieve high temperatures for combustion during engine startup in cold weather.) Diesel engines have found broad use as a result of higher thermodynamic and thus fuel efficiencies. This is particularly noted where diesel engines are run at part-load; as their air supply is not throttled as in a petrol engine, their efficiency still remains high.

The most common type of diesel fuel is a specific fractional distillate of petroleum fuel oil, but alternatives that are not derived from petroleum, such as biodiesel, biomass to liquid (BTL) or gas to liquid (GTL) diesel, are increasingly being developed and adopted. To distinguish these types, petroleum-derived diesel is increasingly called petrodiesel.[1] Ultra-low-sulfur diesel (ULSD) is a standard for defining diesel fuel with substantially lowered sulfur contents. As of 2006, almost all of the petroleum-based diesel fuel available in UK, Europe and North America is of a ULSD type. In the UK, diesel fuel for on-road use is commonly abbreviated DERV, standing for diesel-engined road vehicle, which carries a tax premium over equivalent fuel for non-road use (see Taxation).[2] In Australia diesel fuel is also known as 'distillate'.[3]


  • Origins 1
  • Types 2
    • Petroleum diesel 2.1
    • Synthetic diesel 2.2
    • Biodiesel 2.3
    • Hydrogenated oils and fats 2.4
    • DME 2.5
  • Storage 3
  • Measurements and pricing 4
    • Cetane number 4.1
    • Fuel value and price 4.2
    • Taxation 4.3
  • Uses 5
    • Railway 5.1
    • Aircraft 5.2
    • Military vehicles 5.3
    • Cars 5.4
    • Other uses 5.5
  • Chemical analysis 6
    • Chemical composition 6.1
    • Chemical properties 6.2
    • Hazards 6.3
      • Reduction of sulphur emissions 6.3.1
      • Environment hazards of sulphur 6.3.2
      • Algae, microbes, and water contamination 6.3.3
      • Road hazard 6.3.4
  • Further reading 7
  • See also 8
  • References 9
  • External links 10


Diesel fuel originated from experiments conducted by German scientist and inventor Rudolf Diesel for his compression-ignition engine he invented in 1892. Diesel originally designed his engine to use coal dust as fuel,[4] and experimented with other fuels including vegetable oils[5] such as peanut oil, which was used to power the engines which he exhibited at the 1900 Paris Exposition and the 1911 World's Fair in Paris.[6]



Petroleum diesel

A modern diesel dispenser

Petroleum diesel, also called petrodiesel,[7] or fossil diesel is the most common type of diesel fuel. It is produced from the fractional distillation of crude oil between 200 °C (392 °F) and 350 °C (662 °F) at atmospheric pressure, resulting in a mixture of carbon chains that typically contain between 8 and 21 carbon atoms per molecule.[8]

Synthetic diesel



Paraffinic synthetic diesel generally has a near-zero content of sulphur and very low aromatics content, reducing unregulated emissions of toxic hydrocarbons, nitrous oxides and particulate matter (PM).[10]


Biodiesel made from soybean oil


FAME as a fuel is regulated under DIN EN 14214[13] and ASTM D6751.[14]

FAME has a lower energy content than diesel due to its oxygen content, and as a result, performance and fuel consumption can be affected. It also can have higher levels of NOx emissions, possibly even exceeding the legal limit. FAME also has lower oxidation stability than diesel, and it offers favourable conditions for bacterial growth, so applications which have a low fuel turnover should not use FAME.[15] The loss in power when using pure biodiesel is 5 to 7%.[12]

Fuel equipment manufacturers (FIE) have raised several concerns regarding FAME fuels: free methanol, dissolved and free water, free glycerin, mono and diglycerides, free fatty acids, total solid impurity levels, alkaline metal compounds in solution and oxidation and thermal stability. They have also identified FAME as being the cause of the following problems: corrosion of fuel injection components, low-pressure fuel system blockage, increased dilution and polymerisation of engine sump oil, pump seizures due to high fuel viscosity at low temperature, increased injection pressure, elastomeric seal failures and fuel injector spray blockage.[16]


As FAME contains low levels of sulphur, the emissions of sulphur oxides and sulphates, major components of acid rain, are low. Use of biodiesel also results in reductions of unburned hydrocarbons, carbon monoxide (CO), and particulate matter. CO emissions using biodiesel are substantially reduced, on the order of 50% compared to most petrodiesel fuels. The exhaust emissions of particulate matter from biodiesel have been found to be 30 percent lower than overall particulate matter emissions from petrodiesel. The exhaust emissions of total hydrocarbons (a contributing factor in the localised formation of smog and ozone) are up to 93 percent lower for biodiesel than diesel fuel.

Biodiesel also may reduce health risks associated with petroleum diesel. Biodiesel emissions showed decreased levels of polycyclic aromatic hydrocarbon (PAH) and nitrited PAH compounds, which have been identified as potential cancer-causing compounds. In recent testing, PAH compounds were reduced by 75 to 85 percent, except for benz(a)anthracene, which was reduced by roughly 50 percent. Targeted nPAH compounds were also reduced dramatically with biodiesel fuel, with 2-nitrofluorene and 1-nitropyrene reduced by 90 percent, and the rest of the nPAH compounds reduced to only trace levels.[18]

Hydrogenated oils and fats





In the US, diesel is recommended to be stored in a yellow container to differentiate it from kerosene and gasoline, which are typically kept in blue and red containers, respectively.[20] In the UK, diesel is normally stored in a black container, to differentiate it from unleaded petrol (which is commonly stored in a green container) and leaded petrol (which is stored in a red container).[21]

Measurements and pricing

Cetane number

The principal measure of diesel fuel quality is its cetane number. A cetane number is a measure of the delay of ignition of a diesel fuel.[22] A higher cetane number indicates that the fuel ignites more readily when sprayed into hot compressed air.[22] European (EN 590 standard) road diesel has a minimum cetane number of 51. Fuels with higher cetane numbers, normally "premium" diesel fuels with additional cleaning agents and some synthetic content, are available in some markets.

Fuel value and price

As of 2010, the density of petroleum diesel is about 0.832 kg/L (6.943 lb/US gal), about 11.6% more than ethanol-free petrol (gasoline), which has a density of about 0.745 kg/L (6.217 lb/US gal). About 86.1% of the fuel mass is carbon, and when burned, it offers a net heating value of 43.1 MJ/kg as opposed to 43.2 MJ/kg for gasoline. However, due to the higher density, diesel offers a higher volumetric energy density at 35.86 MJ/L (128,700 BTU/US gal) vs. 32.18 MJ/L (115,500 BTU/US gal) for gasoline, some 11% higher, which should be considered when comparing the fuel efficiency by volume. The CO2 emissions from diesel are 73.25 g/MJ, just slightly lower than for gasoline at 73.38 g/MJ.[23] Diesel is generally simpler to refine from petroleum than gasoline, and contains hydrocarbons having a boiling point in the range of 180–360 °C (360–680 °F). The price of diesel traditionally rises during colder months as demand for heating oil rises, which is refined in much the same way. Because of recent changes in fuel quality regulations, additional refining is required to remove sulphur, which contributes to a sometimes higher cost. In many parts of the United States and throughout the United Kingdom and Australia,[24] diesel may be priced higher than petrol.[25] Reasons for higher-priced diesel include the shutdown of some refineries in the Gulf of Mexico, diversion of mass refining capacity to petrol production, and a recent transfer to ultra-low-sulphur diesel (ULSD), which causes infrastructural complications.[26] In Sweden, a diesel fuel designated as MK-1 (class 1 environmental diesel) is also being sold; this is a ULSD that also has a lower aromatics content, with a limit of 5%.[27] This fuel is slightly more expensive to produce than regular ULSD.


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. "Untaxed" diesel (sometimes called "off-road diesel") is available in some countries for use primarily in agricultural applications, such as fuel for tractors, recreational and utility vehicles or other noncommercial vehicles that do not use public roads. This fuel may have sulphur levels that exceed the limits for road use in some countries (e.g. US).

This untaxed diesel is dyed red for identification,[28] and using this untaxed diesel fuel for a typically taxed purpose (such as driving use), the user can be fined (e.g. US$10,000 in the US). In the United Kingdom, Belgium and the Netherlands, it is known as red diesel (or gas oil), and is also used in agricultural vehicles, home heating tanks, refrigeration units on vans/trucks which contain perishable items such as food and medicine and for marine craft. Diesel fuel, or marked gas oil is dyed green in the Republic of Ireland and Norway. The term "diesel-engined road vehicle" (DERV) is used in the UK as a synonym for unmarked road diesel fuel. In India, taxes on diesel fuel are lower than on petrol, as the majority of the transport for grain and other essential commodities across the country runs on diesel.

Taxes on biodiesel in the U.S. vary between states; some states (Texas, for example) have no tax on biodiesel and a reduced tax on biodiesel blends equivalent to the amount of biodiesel in the blend, so that B20 fuel is taxed 20% less than pure petrodiesel.[29] Other states, such as North Carolina, tax biodiesel (in any blended configuration) the same as petrodiesel, although they have introduced new incentives to producers and users of all biofuels.[30]


Diesel fuel is widely used in most types of transport. The petrol-powered passenger car is the major exception.

Unlike petrol and liquefied petroleum gas engines, diesel engines do not use high-voltage spark ignition (spark plugs). An engine running on diesel compresses the air inside the cylinder to high pressures and temperatures (compression ratios from 14:1 to 18:1 are common in current diesel engines); the engine generally injects the diesel fuel directly into the cylinder, starting a few degrees before top dead centre (TDC) and continuing during the combustion event. The high temperatures inside the cylinder cause the diesel fuel to react with the oxygen in the mix (burn or oxidise), heating and expanding the burning mixture to convert the thermal/pressure difference into mechanical work, i.e., to move the piston. Engines have glow plugs and grid heaters to help start the engine by preheating the cylinders to a minimum operating temperature. Diesel engines are lean burn engines,[31] burning the fuel in more air than is needed for the chemical reaction. They thus use less fuel than rich burn spark ignition engines which use a stoichiometric air-fuel ratio (just enough air to react with the fuel). As Professor Harvey of the University of Toronto notes, "due to the absence of throttling [constant amount of air admitted, per unit fuel, with no user-determined variation], and the high compression ratio and lean fuel mixture, diesel engines are substantially more efficient than spark-ignited engines", generally; Harvey cites the side-by-side comparisons of Schipper et al. and the estimates of >20% lower fuel use and (given difference in differences in energy content between fuel types) >15% lower energy use.[32] Gas turbine and some other types of internal combustion engines, and external combustion engine, both can also be designed to take diesel fuel.












Military vehicles

Armoured fighting vehicles use diesel because of its lower flammability risks and the engines' higher provision of torque and lower likelihood of stalling.[39][40]


Diesel-powered cars generally have a better fuel economy than equivalent petrol engines and produce less greenhouse gas emissions.[41] Their greater economy is due to the higher energy per-litre content of diesel fuel and the intrinsic efficiency of the diesel engine.[42] While petrodiesel's higher density results in higher greenhouse gas emissions per litre compared to petrol,[43] the 20–40% better fuel economy achieved by modern diesel-engined cars offsets the higher per-litre emissions of greenhouse gases, and a diesel-powered vehicle emits 10–20 percent less greenhouse gas than comparable petrol vehicles.[44][45][46] Biodiesel-powered diesel engines offer substantially improved emission reductions compared to petrodiesel or petrol-powered engines, while retaining most of the fuel economy advantages over conventional gasoline-powered automobiles.[44] However, the increased compression ratios mean there are increased emissions of oxides of nitrogen (NOx) from diesel engines.[47] This is compounded by biological nitrogen in biodiesel to make NOx emissions the main drawback of diesel versus petrol engines.[47]

Other uses

Poor quality diesel fuel has been used as an extraction agent for liquid–liquid extraction of palladium from nitric acid mixtures.[48] Such use has been proposed as a means of separating the fission product palladium from PUREX raffinate which comes from used nuclear fuel.[48] In this system of solvent extraction, the hydrocarbons of the diesel act as the diluent while the dialkyl sulphides act as the extractant.[48] This extraction operates by a solvation mechanism.[48] So far, neither a pilot plant nor full scale plant has been constructed to recover palladium, rhodium or ruthenium from nuclear wastes created by the use of nuclear fuel.[49]

Diesel fuel is also often used as the main ingredient in oil-base mud drilling fluid.[50] The advantage of using diesel is its low cost and that it delivers excellent results when drilling a wide variety of difficult strata including shale, salt and gypsum formations.[50] Diesel-oil mud is typically mixed with up to 40% brine water.[51] Due to health, safety and environmental concerns, Diesel-oil mud is often replaced with vegetable, mineral, or synthetic food-grade oil-base drilling fluids, although diesel-oil mud is still in widespread use in certain regions.[52]

During development of Rocket engines in Germany during World War II J-2 Diesel fuel was used as the fuel component in several engines including the BMW 109-718.[53] J-2 diesel fuel was also used as a fuel for gas turbine engines.[53]

Chemical analysis

Chemical composition

Diesel does not mix with water.

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).[54] The average chemical formula for common diesel fuel is C12H23, ranging approximately from C10H20 to C15H28.[55]

Chemical properties

Most diesel fuels freeze at common winter temperatures, while the temperatures greatly vary.[56] Petrodiesel typically freezes around temperatures of −8.1 °C (17.5 °F), whereas biodiesel freezes between temperatures of 2° to 15 °C (35° to 60 °F).[56] The viscosity of diesel noticeably increases as the temperature decreases, changing it into a gel at temperatures of −19 °C (−2.2 °F) to −15 °C (5 °F), that cannot flow in fuel systems. Conventional diesel fuels vaporise at temperatures between 149 °C and 371 °C.[22]

Conventional diesel flash points vary between 52 and 96 °C, which makes it safer than petrol and unsuitable for spark-ignition engines.[57] Unlike petrol, the flash point of a diesel fuel has no relation to its performance in an engine nor to its auto ignition qualities.[22]


Reduction of sulphur emissions

In the past, diesel fuel contained higher quantities of sulphur. European emission standards and preferential taxation have forced oil refineries to dramatically reduce the level of sulphur in diesel fuels. In the European Union, the sulphur content has dramatically reduced during the last 20 years. Automotive diesel fuel is covered in the European Union by standard EN 590. In the 1990s specifications allowed a content of 2000 ppm max of sulphur, reduced to a limit of 350 ppm by the beginning of the 21st century with the introduction of Euro 3 specifications. The limit was lowered with the introduction of Euro 4 by 2006 to 50 ppm (ULSD, Ultra Low Sulphur Diesel). The standard currently in force in European Europe for Diesel Fuel is the Euro 5, with a maximum content of 10 ppm.

Emission standard At latest Sulphur content Cetane number
Euro 1 1. January 1993 max. 2000 ppm min. 49
Euro 2 1. January 1996 max. 500 ppm min. 49
Euro 3 1. January 2001 max. 350 ppm min. 51
Euro 4 1. January 2006 max. 50 ppm min. 51
Euro 5 1. January 2009 max. 10 ppm min. 51

In the United States, more stringent emission standards have been adopted with the transition to 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.[58]

Environment hazards of sulphur

High levels of sulphur 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. Moreover, sulphur in the fuel is oxidised during combustion, producing sulphur dioxide and sulphur trioxide, that in presence of water rapidly convert to sulphuric acid, one of the chemical processes that results in acid rain. However, the process for lowering sulphur also reduces the lubricity of the fuel, meaning that additives must be put into the fuel to help lubricate engines. Biodiesel and biodiesel/petrodiesel blends, with their higher lubricity levels, are increasingly being utilised as an alternative. The U.S. annual consumption of diesel fuel in 2006 was about 190 billion litres (42 billion imperial gallons or 50 billion US gallons).[59]

Algae, microbes, and water contamination

There has been much discussion and misunderstanding of algae in diesel fuel. Algae need light to live and grow. As there is no sunlight in a closed fuel tank, no algae can survive, but some microbes can survive and feed on the diesel fuel.[60]

These microbes form a colony that lives at the interface of fuel and water. They grow quite fast 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.[61]

Water in fuel can damage a fuel injection pump; some diesel fuel filters also trap water. Water contamination in diesel fuel can lead to freezing while in the fuel tank. The freezing water that saturates the fuel will sometimes clog the fuel injector pump.[62] Once the water inside the fuel tank has started to freeze, gelling is more likely to occur. When the fuel is gelled it is not effective until the temperature is raised and the fuel returns to a liquid state.

Road hazard

Petrodiesel spilled on a roadway poses a hazard to vehicles, due to its high evaporation temperature. After the light fractions have evaporated, a greasy slick is left on the road which can destabilise moving vehicles, causing them to skid. Diesel spills severely reduce tyre grip and traction, and have been implicated in many accidents. The loss of traction is similar to that encountered on black ice. Diesel slicks are especially dangerous for two-wheeled vehicles such as motorcycles and other two wheeled vehicles.

Further reading

  • L. D. Danny Harvey, 2010, "Energy and the New Reality 1: Energy Efficiency and the Demand for Energy Services," London:Routledge-Earthscan, ISBN 1-84407-912-0, 672 pp.; see [1], accessed 28 September 2014.

See also


  1. ^ Traders and importers now use the term, as well as academic journals for example ACS publications (See 2006 article on comparing Petrodiesel emissions with other types of fuel). The term is common in blogs and informal wiki sites, and is used several times in this article itself.
  2. ^
  3. ^ The Macquarie Dictionary 3rd ed, The Macquarie Library 1997
  4. ^ DE 67207  Rudolf Diesel: "Arbeitsverfahren und Ausführungsart für Verbrennungskraftmaschinen" pg 4.
  5. ^
  6. ^
  7. ^ macCompanion Magazine
  8. ^ Chris Collins (2007), “Implementing Phytoremediation of Petroleum Hydrocarbons, Methods in Biotechnology 23:99–108. Humana Press. ISBN 1-58829-541-9.
  9. ^
  10. ^
  11. ^ Bosch Automotive Handbook, 6th edition, p327-328
  12. ^ a b
  13. ^
  14. ^
  15. ^
  16. ^
  17. ^
  18. ^ Petrol vs Hemp
  19. ^ Bosch Automotive Handbook, 6th edition, p328
  20. ^
  21. ^
  22. ^ a b c d e
  23. ^ Table 2.1
  24. ^ Australian Institute of Petroleum – Facts about Diesel Prices
  25. ^ Gasoline and Diesel Fuel Update
  26. ^
  27. ^
  28. ^ Cited as 26 CFR 48.4082-1. This regulation implements 26 U.S.C. § 4082-1.
  29. ^ Texas Biodiesel Laws and Incentives
  30. ^
  31. ^ See How Stuff Works [2] for an excellent explanation
  32. ^ L. D. Danny Harvey, 2010, "Energy and the New Reality 1: Energy Efficiency and the Demand for Energy Services," London:Routledge-Earthscan, ISBN 1-84407-912-0, p. 264, 267; see [3], accessed 28 September 2014.
  33. ^
  34. ^
  35. ^
  36. ^
  37. ^
  38. ^
  39. ^
  40. ^ Tillotson 1981, pp. 63
  41. ^
  42. ^
  43. ^
  44. ^ a b
  45. ^
  46. ^
  47. ^ a b
  48. ^ a b c d
  49. ^ Torgov, V.G.; Tatarchuk, V.V.; Druzhinina, I.A.; Korda, T.M. et al., Atomic Energy, 1994, 76(6), 442–448. (Translated from Atomnaya Energiya; 76: No. 6, 478–485 (June 1994))
  50. ^ a b
  51. ^
  52. ^ Slumberger Oil Field Glossary, diesel-oil mud,
  53. ^ a b
  55. ^
  56. ^ a b
  57. ^
  58. ^ "Idle Hour," Feature Article, January 2005
  59. ^ U.S. Energy Information
  60. ^
  61. ^
  62. ^

External links

  • U.S. Department of Labor Occupational Safety & Health Administration: Safety and Health Topics: Diesel Exhaust
