Diesel or diesel fuel (IPA: [ˈdiː.zəl]; voiced “s” because of its eponym) 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. 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. Rudolph Diesel was not first to invent the diesel engine. His patent was filed in 1893. However Herbert Akroyd Stuart, built the first compression-ignition oil engine in Bletchley, England in 1891. He leased the rights to Richard Hornsby & Sons in July 1892, five years before Diesel's prototype was built.
Petroleum diesel
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 and throughout the the whole of the UK, 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 infrastructural complications.[2]
Diesel-powered cars generally have a better fuel economy than equivalent gasoline engines and produce only about 69% as much greenhouse gas pollution. 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.
The U.S. annual consumption of diesel fuel in 2006 was about 190 billion liters (50 billion gallons).[1]
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).[6] The average chemical formula for common diesel fuel is C12H26, ranging from approx. C10H22 to C15H32
Algae, microbes, and water
There has been much discussion and misinformation about algae in diesel fuel[citation needed]. Algae require 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, and 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 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 has abated.
Given the right conditions microbes will repopulate the tanks and re-treatment with biocides will then be necessary. With repetitive biocide treatments microbes can then form resistance to a particular brand. Trying another brand may resolve this.
Synthetic diesel
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.[7] 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% less particulate emissions than conventional diesel (US- California).[8]
Biodiesel
Main article: Biodiesel
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. 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.[citation needed] 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.
Biodiesel can be produced using kits. Certain kits allow for processing of used vegetable oil that can be run through any conventional diesel motor with little modifications (kit available at [2]). The minor modification needed is the replacement of fuel lines from the intake and motor. The modified fuel lines allow more flow for the new fuel.
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.[9] However, the cetane rating and lubricity of the fuel are both reduced and must be corrected with additives.
ASTM International has developed D6751 as the specification standard for 100% biodiesel, which is used for blending with petroleum diesel. For example, B20 is 20% biodiesel (ASTM D6751) and 80% petroleum diesel (ASTM D975).
Biodiesel refers to a diesel-equivalent processed fuel derived from biological sources (such as vegetable oils) which can be used in unmodified diesel-engine vehicles. It is thus distinguished from the straight vegetable oils (SVO) or waste vegetable oils (WVO) used as fuels in some diesel vehicles.
In this article's context, biodiesel refers to alkyl esters made from the transesterification of vegetable oils or animal fats.
On August 31, 1937, G. Chavanne of the University of Brussels (Belgium) was granted a patent for a 'Procedure for the transformation of vegetable oils for their uses as fuels' (fr. 'Procédé de Transformation d’Huiles Végétales en Vue de Leur Utilisation comme Carburants') Belgian Patent 422,877. This patent described the alcoholysis (often referred to as transesterification) of vegetable oils using ethanol (and mentions methanol) in order to separate the fatty acids from the glycerol by replacing the glycerol with short linear alcohols. This appears to be the first account of the production of what is known as 'biodiesel' today.[1]
Biodiesel is biodegradable and non-toxic, and typically produces about 60% less net carbon dioxide emissions than petroleum-based diesel,[2] as it is itself produced from atmospheric carbon dioxide via photosynthesis in plants. Though this figure can actually differ widely between fuels depending upon production and processing methods employed in their creation. Pure biodiesel is available at many gas stations in Germany.[3]
Some vehicle manufacturers are positive about the use of biodiesel, citing lower engine wear as one of the fuel's benefits. Biodiesel is a better solvent than standard diesel, as it 'cleans' the engine, removing deposits in the fuel lines. However, this may cause blockages in the fuel injectors. For this reason, car manufacturers recommend that the fuel filter be changed a few months after switching to biodiesel (the fuel filter, as part of a routine maintenance plan, is generally replaced anyway). Most manufacturers release lists of the cars that will run on 100% biodiesel.[4]
Other vehicle manufacturers remain cautious over use of biodiesel. In the UK many only maintain their engine warranties for use with maximum 5% biodiesel — blended in with 95% conventional diesel — although this position is generally considered to be overly cautious.[citation needed] Scania[citation needed] and Volkswagen[5] are exceptions, allowing most of their engines to operate on 100% biodiesel. Peugeot and Citroën are also exceptions in that they have both recently announced that their PSA HDi engine can run on 30% biodiesel. The Ford Focus has recently been converted to run on Biodiesel.
Branson's Virgin Voyager, number 220007 Thames Voyager [citation needed] was converted to run on Biodiesel, although an adverse effect occurred when it was proven to reduce reliability significantly, and to raise costs of maintenance also, significantly.
Biodiesel can also be used as a heating fuel in domestic and commercial boilers. Existing oil boilers may require conversion to run on biodiesel, but the conversion process is believed to be relatively simple.
Biodiesel can be distributed using today's infrastructure, and its use and production are increasing rapidly. Fuel stations are beginning to make biodiesel available to consumers, and a growing number of transport fleets use it as an additive in their fuel. Biodiesel is generally more expensive to purchase than petroleum diesel but this differential may diminish due to economies of scale, the rising cost of petroleum and government tax subsidies. In Germany, biodiesel is generally cheaper than normal diesel at gas stations that sell both products.
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