Diesel fuel (pronounced /ˈdiːzəl/) in general is any liquid fuel used in diesel engines. The most common 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. Ultra-low sulfur diesel (ULSD) is a standard for defining diesel fuel with substantially lowered sulfur contents. As of 2007, almost every diesel fuel available in America and Europe is the ULSD type. In the UK, diesel is commonly abbreviated DERV, standing for Diesel Engined Road Vehicle (fuel).
Diesel engines are a type of internal combustion engine. Rudolf Diesel originally designed the diesel engine to use coal dust as a fuel. He also experimented with various oils, including some vegetable oils, 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.
Diesel fuel is produced from petroleum and from various other sources. The resulting products are interchangeable in most applications.
Petroleum diesel, also called petrodiesel, or fossil diesel 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.
The density of petroleum diesel is about 0.85 kg/l (7.09 lb/US gal), about 18% more than petrol (gasoline), which has a density of about 0.72 kg/l (6.01 lb/US gal). When burnt, diesel typically releases about 38.6 MJ/l (138,700 BTU/US gal), whereas gasoline releases 34.9 MJ/l (125,000 BTU/US gal), 10% less by energy density, but 45.41 MJ/kg and 48.47 MJ/kg, 6.7% more by specific energy. Diesel is generally simpler to refine from petroleum than gasoline. 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 sulfur which contributes to a sometimes higher cost. In many parts of the United States and throughout the United Kingdom and Australia diesel may be higher priced than petrol. Reasons for higher priced diesel include the shutdown of some refineries in the Gulf of Mexico, diversion of mass refining capacity to gasoline production, and a recent transfer to ULSD, which causes infrastructural complications.
Unlike petroleum ether 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 15:1 to 21:1 are common); the diesel is generally injected directly into the cylinder near the end of the compression stroke. The high temperatures inside the cylinder cause the diesel fuel to react with the oxygen in the mix (burn or oxidize), heating and expanding the burning mixture in order to convert the thermal/pressure difference into mechanical work; i.e., to move the piston. (Glow plugs are used to assist starting the engine to preheat cylinders to reach a minimum operating temperature.) High compression ratios and throttleless operation generally result in diesel engines being more efficient than many spark-ignited engines.
This efficiency and its lower flammability and explosivity than gasoline are the main reasons for military use of diesel in armoured fighting vehicles like tanks and trucks. Engines running on diesel also provide more torque and are less likely to stall as they are controlled by a mechanical or electronic governor.
A disadvantage of diesel as a vehicle fuel in some climates, compared to gasoline or other petroleum derived fuels, is that its viscosity increases quickly as the fuel's temperature decreases, turning into a non-flowing gel at temperatures as high as -19 °C (-2.2 °F) or -15 °C (5 °F), which can't be pumped by regular fuel pumps. Special low temperature diesel contains additives that keep it in a more liquid state at lower temperatures, yet starting a diesel engine in very cold weather may still pose considerable difficulties.
Another rare disadvantage of diesel engines compared to petrol/gasoline engines is the possibility of runaway failure. Since diesel engines do not require spark ignition, they can sustain operation as long as diesel fuel is supplied. Fuel is typically supplied via a fuel pump. If the pump breaks down in an "open" position, the supply of fuel will be unrestricted and the engine will runaway and risk terminal failure.
Diesel-powered cars generally have a better fuel economy than equivalent gasoline engines and produce less greenhouse gas emission. Their greater economy is due to the higher energy per-litre content of diesel fuel and the intrinsic efficiency of the diesel engine. While petrodiesel's higher density results in higher greenhouse gas emissions per litre compared to gasoline, the 20–40% better fuel economy achieved by modern diesel-engined automobiles offsets the higher per-litre emissions of greenhouse gases, and a diesel-powered vehicle emits 10-20 percent less greenhouse gas than comparable gasoline vehicles. Biodiesel-powered diesel engines offer substantially improved emission reductions compared to petro-diesel or gasoline-powered engines, while retaining most of the fuel economy advantages over conventional gasoline-powered automobiles. However, the increased compression ratios mean that there are increased emissions of oxides of nitrogen (NOx) from diesel engines. This is compounded by biological nitrogen in biodiesel to make NOx emissions the main drawback of diesel versus gasoline engines.
Diesel engines can operate on a variety of different fuels, depending on configuration, though the eponymous diesel fuel derived from crude oil is most common. The engines can work with the full spectrum of crude oil distillates, from natural gas, alcohols, gasoline, wood gas to the fuel oils from diesel oil to residual fuels. This is implemented by introducing gas with the intake air and using a small amount of diesel fuel for ignition. Conversion to 100% diesel fuel operation can be achieveved instantaneously.
In the past, diesel fuel contained 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 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.
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. Moreover, sulfur in the fuel is oxidized during combustion, producing sulfur dioxide and sulfur trioxide, that in presence of water rapidly convert to sulfuric acid, one of the chemical processes that results in acid rain. 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 and biodiesel/petrodiesel blends, with their higher lubricity levels, are increasingly being utilized 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).
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 C12H23, ranging approximately from C10H20 to C15H28.
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.
These microbes form a colony that lives at the interface of fuel and water. They grow quite fast in warmer temperature. 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 dead cells then gather on the bottom of the fuel tanks and form a sludge; filter clogging will continue after biocide treatment until the sludge abates.
Given the right conditions, microbes will repopulate the tanks, and re-treatment with biocides will be necessary. With repetitive biocide treatments, microbes can form resistance to a particular brand. Trying another brand of biocide with another antibiotic may resolve the problem.
Petrodiesel spilled on a road will stay there until washed away by sufficiently heavy rain, whereas gasoline will quickly evaporate. After the light fractions have evaporated, a greasy slick is left on the road which can destabilize moving vehicles. Diesel spills severely reduce tire 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.
Wood, hemp, straw, corn, garbage, food scraps, and sewage-sludge may be dried and gasified to synthesis gas. After purification the Fischer-Tropsch process is used to produce synthetic diesel. This means that synthetic diesel oil may be one route to biomass based diesel oil. Such processes are often called biomass-to-liquids or BTL.
Synthetic diesel may also be produced out of natural gas in the gas-to-liquid (GTL) process or out of coal in the coal-to-liquid (CTL) process. Such synthetic diesel has 30% lower 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, cleaner burning alternative to petrodiesel. It can also be mixed with petrodiesel in any amount in some modern engines, but some manufacturers strongly recommend against such use. Biodiesel has a higher gel point than petrodiesel, but is comparable to diesel. 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. A small fraction of biodiesel can be used as an additive in low-sulfur formulations of diesel to increase the lubricity lost when the sulfur is removed. In the event of fuel spills, biodiesel is easily washed away with ordinary water and is nontoxic compared to other fuels.
Biodiesel can be produced using kits. Certain kits allow for processing of used vegetable oil that can be run in any conventional diesel motor with modifications. The necessary modification is the replacement of fuel lines from the intake and motor and all affected rubber fittings in injection and feeding pumps a.s.o (in vehicles manufactured before 1993). This is because biodiesel is an effective solvent and will replace softeners within unsuitable rubber with itself over time. Synthetic gaskets for fittings and hoses prevent this.
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 does.
The use of biodiesel blended diesel fuels in fractions up to 99% result in substantial emission reductions. Sulfur oxide and sulfate emissions, major components of acid rain, are essentially eliminated with pure biodiesel and substantially reduced using biodiesel blends with minor quantities of ULSD petrodiesel. Use of biodiesel also results in substantial reductions of unburned hydrocarbons, carbon monoxide, and particulate matter compared to either gasoline or petrodiesel. CO, or carbon monoxide, 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 localized formation of smog and ozone) are up to 93 percent lower for biodiesel than diesel fuel. Biodiesel emission of nitrogen oxides can sometimes increase slightly. However, biodiesel's complete lack of sulfur and sulfate emissions allows the use of NOx control technology, such as AdBlue, that cannot be used with conventional diesel, allowing the management and control of nitrous oxide emissions.
Biodiesel also may reduce health risks associated with petroleum diesel. Biodiesel emissions showed decreased levels of 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 benzo(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.
Diesel displaced coal and fuel oil for steam power vehicles in the latter half of the 20th century, and is now used almost exclusively for combustion engine of self-powered rail vehicles (locomotives and railcars).
The first diesel-powered flight of a fixed wing aircraft took place on the evening of September 18, 1928, at the Packard Motor Company proving grounds at Utica, USA with Captain Lionel M. Woolson and Walter Lees at the controls (the first "official" test flight was taken the next morning). The engine was designed for Packard by Woolson and the aircraft was a Stinson SM1B, X7654. Later that year, Charles Lindbergh flew the same aircraft. In 1929 it was flown 621 miles (999 km) non-stop from Detroit to Langley, Virginia (near Washington, D.C.). This aircraft is now owned by Greg Herrick and is at the Golden Wings Flying Museum nearby Minneapolis, Minnesota. In 1931, Walter Lees and Fredrick Brossy set the non-stop flight record flying a Bellanca powered by a Packard diesel for 84 hours and 32 minutes. The Hindenburg rigid airship was powered by four 16-cylinder diesel engines, each with approximately 1,200 horsepower (890 kW) available in bursts, and 850 horsepower (630 kW) available for cruising. Modern diesel engines for propellor-driven aircraft are manufactured by Thielert Aircraft Engines and SMA. These engines can run on Jet A fuel, which is similar in composition to automotive diesel and cheaper and more plentiful than the 100 octane low-lead gasoline (avgas) used by the majority of the piston-engine aircraft fleet.
The most-produced aviation diesel engine in history has been the Junkers Jumo 205, which, along with its similar developments from the Junkers Motorenwerke, had approximately 1000 examples of the unique opposed piston, two-stroke design power plant built in the 1930s leading into World War II in Germany.
Poor quality (high sulfur) diesel fuel has been used as a palladium extraction agent for the liquid-liquid extraction of this metal from nitric acid mixtures. Such use has been proposed as a means of separating the fission product palladium from PUREX raffinate which comes from used nuclear fuel. In this system of solvent extraction, the hydrocarbons of the diesel act as the diluent while the dialkyl sulfides act as the extractant. This extraction operates by a solvation mechanism. 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.
Diesel combustion exhaust is a major source of atmospheric soot and fine particles, which is a fraction of air pollution implicated in human heart and lung damage. Diesel exhaust also contains nanoparticles.
While the study of nanoparticles and nanotoxicology is still in its infancy, the full health effects from nanoparticles produced by all types of diesel are unknown. At least one study has observed that short term exposure to diesel exhaust does not result in adverse extra-pulmonary effects, effects that are often correlated with an increase in cardiovascular disease. Long term effects still need to be clarified, as well as the effects on susceptible groups of people with cardiopulmonary diseases.
It should be noted that the types and quantities of nanoparticles can vary according to operating temperatures and pressures, presence of an open flame, fundamental fuel type and fuel mixture, and even atmospheric mixtures. As such, the resulting types of nanoparticles from different engine technologies and even different fuels are not necessarily comparable. In general, the usage of biodiesel and biodiesel blends results in decreased pollution. One study has shown that the volatile component of 95% of diesel nanoparticles is unburned lubricating oil.
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 (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 non-commercial vehicles that do not use public roads. Additionally, this fuel may have sulphur levels that exceed the limits for road use in some countries (e.g. USA).
This untaxed diesel is dyed red for identification, 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 (e.g. US$10,000 in the USA). 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 DERV ("diesel engined road vehicle") is used in the UK as a synonym for unmarked road diesel fuel. In India, taxes on diesel fuel are lower than on petroleum, as the majority of the transportation that transports grains and other essential commodities across the country runs on diesel.
In some countries, such as Germany and Belgium, diesel fuel is taxed lower than petrol (gasoline) (typically around 20% lower), but the annual vehicle tax is higher for diesel vehicles than for petrol vehicles. This gives an advantage to vehicles that travel longer distances (which is the case for trucks and utility vehicles) because the annual vehicle tax depends only on engine displacement, not on distance driven. The point at which a diesel vehicle becomes less expensive than a comparable petroleum vehicle is around 20,000 km a year (12,500 miles per year) for an average car. However, due to the recent rise in oil prices, the advantage point is becoming lower, resulting in more people opting to buy a diesel car where they would have opted for a gasoline car a few years ago. Such an increased interest in diesel has resulted in slow but steady "dieseling" of the automobile fleet in the countries affected, sparking concerns in certain authorities about the negative effects of diesel.
Taxes on biodiesel in the U.S. vary among states, and in 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. 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.