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Chemical analysis and productionGasoline Gasoline, or petrol, is a petroleum-derived liquid mixture which is primarily used as a fuel in internal combustion engines. It is also used as a solvent, mainly known for its ability to dilute paints. It consists mostly of aliphatic hydrocarbons obtained by the fractional distillation of petroleum, enhanced with iso-octane or the aromatic hydrocarbons toluene and benzene to increase its octane rating. Small quantities of various additives are common, for purposes such as tuning engine performance or reducing harmful exhaust emissions. Some mixtures also contain significant quantities of ethanol as a partial alternative fuel. Most current or former Commonwealth countries use the term petrol, abbreviated from petroleum spirit. In North America, the substance is called gasoline, a term often shortened in colloquial usage to gas. It is not a genuinely gaseous fuel (unlike, for example, liquefied petroleum gas, which is stored under pressure as a liquid, but returned to a gaseous state before combustion). The term petrogasoline is also used.[where?][citation needed] The term mogas, short for motor gasoline, is used[citation needed] to distinguish automobile fuel from aviation gasoline, or avgas. In British English, gasoline can refer to a different petroleum derivative historically used in lamps, but this usage is relatively uncommon. Early uses In the United States, gasoline was also sold as a cleaning fluid to remove grease stains from clothing.[citation needed] Before dedicated filling stations were established, early motorists bought gasoline in cans to fill their tanks. Gasoline was also used in kitchen ranges and for lighting, and is still available in a purified form, known as camping fuel, white gas or Coleman fuel, for use in lanterns and portable stoves. During the Franco-Prussian War (1870–71), pétrole was stockpiled in Paris for use against a possible German-Prussian attack on the city.[citation needed] Later in 1871, during the revolutionary Paris Commune, rumours spread around the city of pétroleuses (women using bottles of petrol to commit arson against city buildings). Etymology The name gasoline is similar to that of other petroleum products of the day, most notably petroleum jelly, a highly purified heavy distillate, which was branded Vaseline. The trademark Gasoline was never registered, and eventually became generic in North America and the Philippines. The word "petrol" was first used in reference to the refined substance in 1892 (it was previously used to refer to unrefined petroleum), and was registered as a trade name by British wholesaler Carless, Capel & Leonard at the suggestion of Frederick Richard Simms.[1] Carless's competitors used the term "motor spirit" until the 1930s.[2][3] In many countries, gasoline has a colloquial name derived from that of the chemical benzene (e.g., German Benzin). In other countries, especially in those portions of Latin America where Spanish predominates (i.e., most of the region except Brazil), it has a colloquial name derived from that of the chemical naphtha (e.g., Argentine/Uruguaian/Paraguaian nafta).[4] Chemical analysis and production Gasoline is produced in oil refineries. Material that is separated from crude oil via distillation, called virgin or straight-run gasoline, does not meet the required specifications for modern engines (in particular octane rating; see below), but will form part of the blend. The bulk of a typical gasoline consists of hydrocarbons with between 4 and 12 carbon atoms per molecule (commonly referred to as C4-C12).[5] Many of the hydrocarbons are considered hazardous substances and are regulated in the United States by the Occupational Safety and Health Administration. The material safety data sheet for unleaded gasoline shows at least fifteen hazardous chemicals occurring in various amounts, including benzene (up to 5% by volume), toluene (up to 35% by volume), naphthalene (up to 1% by volume), trimethylbenzene (up to 7% by volume), Methyl tert-butyl ether (MTBE) (up to 18% by volume, in some states) and about ten others.[6] The various refinery streams blended together to make gasoline all have different characteristics. Some important streams are:
The terms above are the jargons used in the oil industry. The exact terminology for these streams varies by refinery and by country. Overall, a typical gasoline is predominantly a mixture of paraffins (alkanes), naphthenes (cycloalkanes), and olefins (alkenes). The actual ratio depends on: the oil refinery that makes the gasoline, as not all refineries have the same set of processing units; crude oil feed used by the refinery; the grade of gasoline, in particular, the octane rating. Currently, many countries set limits on gasoline aromatics in general, benzene in particular, and olefin (alkene) content. Such regulations led to increasing preference for high octane pure paraffin (alkane) components, such as alkylate, and is forcing refineries to add processing units to reduce benzene content. Gasoline can also contain other organic compounds such as organic ethers (deliberately added), plus small levels of contaminants, in particular sulfur compounds such as disulfides and thiophenes. Some contaminants, in particular thiols and hydrogen sulfide, must be removed because they cause corrosion in engines. Sulfur compounds are usually removed by hydrotreating, yielding hydrogen sulfide, which can then be transformed into elemental sulfur via the Claus process. Volatility Gasoline is more volatile than diesel oil, Jet-A or kerosene, not only because of the base constituents, but because of the additives that are put into it. The final control of volatility is often achieved by blending with butane. The Reid vapor pressure (RVP) test is used to measure the volatility of gasoline. The desired volatility depends on the ambient temperature. In hot weather, gasoline components of higher molecular weight and thus lower volatility are used. In cold weather, too little volatility results in cars failing to start. In hot weather, excessive volatility results in what is known as "vapor lock", where combustion fails to occur, because the liquid fuel has changed to a gaseous fuel in the fuel lines, rendering the fuel pump ineffective and starving the engine of fuel. This effect mainly applies to camshaft-driven (engine mounted) fuel pumps which lack a fuel return line. Vehicles with fuel injection require the fuel to be pressurized, to within a set range. Because camshaft speed is nearly zero before the engine is started, an electric pump is used. It is located in the fuel tank so that the fuel may also cool the high-pressure pump. Pressure regulation is achieved by returning unused fuel to the tank. Therefore, vapor lock is almost never a problem in a vehicle with fuel injection. In the United States, volatility is regulated in large cities to reduce the emission of unburned hydrocarbons. In large cities, so-called reformulated gasoline that is less prone to evaporation, among other properties, is required. In Australia, summer petrol volatility limits are set by state governments and vary among states. Most countries simply have a summer, winter, and perhaps intermediate limit. Volatility standards may be relaxed (allowing more gasoline components into the atmosphere) during gasoline shortages. For example, on 31 August 2005, in response to Hurricane Katrina, the United States permitted the sale of non-reformulated gasoline in some urban areas, effectively permitting an early switch from summer to winter-grade gasoline. As mandated by EPA administrator Stephen L. Johnson, this "fuel waiver" was made effective until 15 September 2005.[8] Other means of controlling emission of unburned hydrocarbons are also used. All vehicles which were sold in the United States since in the 1980s, and probably the 1970s or earlier are required to have a fuel evaporative control system (called an EVAP system in automotive jargon), which collects expanding fuel vapor from the fuel tank in a charcoal-lined canister while the engine is stopped and then releases the collected vapors (through a "purge valve") into the engine intake for burning when the engine is running (usually only after it has reached normal operating temperature.) The fuel evaporative control system is also required to include a gasket filling cap which seals the fueling inlet to prevent vapors from escaping directly from the tank through it. Modern vehicles with OBD-II emissions control systems will turn on the malfunction indicator light, or "check engine" light, if it is detected that the gas cap is missing or loose, and not sealing. This light indicates whether any of the emissions controls are not working properly.
Date: 2016-01-03; view: 1089
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