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Gasoline , also known as petrol outside of North America, is a transparent, petroleum-derived liquid that is used primarily as a fuel in internal combustion engines. It consists mostly of organic compounds obtained by the fractional distillation of petroleum, enhanced with a variety of additives. A 42-gallon barrel of crude oil yields about 19 gallons of gasoline, when processed in an oil refinery. The characteristic of a particular gasoline blend to resist igniting too early (which causes knocking and reduces efficiency in reciprocating engines) is measured by its octane rating. Gasoline is produced in several grades of octane rating. Tetraethyllead and other lead compounds are no longer used in most areas to regulate and increase octane-rating, but many other additives are put into gasoline to improve its chemical stability, control corrosiveness and provide fuel system 'cleaning,' and determine performance characteristics under intended use. Sometimes, gasoline also contains ethanol as an alternative fuel, for economic or environmental reasons. Gasoline, as used worldwide in the vast number of internal combustion engines used in transport and industry, has a significant impact on the environment, both in local effects (e.g., smog) and in global effects (e.g., effect on the climate). Gasoline may also enter the environment uncombusted, as liquid and as vapors, from leakage and handling during production, transport and delivery, from storage tanks, from spills, etc. As an example of efforts to control such leakage, many (underground) storage tanks are required to have extensive measures in place to detect and prevent such leaks. Gasoline contains benzene and other known carcinogens.〔(【引用サイトリンク】title=Evaluation of the Carcinogenicity of Unleaded Gasoline )〕 ==Octane rating== (詳細はdeflagration. However, the unburned mixture may autoignite by detonating from pressure and heat alone, rather than ignite from the spark plug at exactly the right time. This causes a rapid pressure rise which can damage the engine. This is often referred to as engine knocking or end-gas knock. Knocking can be reduced by increasing the gasoline's resistance to autoignition, which is expressed by its octane rating. Octane rating is measured relative to a mixture of 2,2,4-trimethylpentane (an isomer of octane) and n-heptane. There are different conventions for expressing octane ratings, so the same physical fuel may have several different octane ratings based on the measure used. One of the best known is the research octane number (RON). The octane rating of typical commercially available gasoline varies by country. In Finland, Sweden, and Norway, 95 RON is the standard for regular unleaded gasoline and 98 RON is also available as a more expensive option. In the UK, ordinary regular unleaded gasoline is 95 RON (commonly available), premium unleaded gasoline is always 97 RON, and super unleaded is usually 97-98 RON. However, both Shell and BP produce fuel at 102 RON for cars with high-performance engines and in 2006 the supermarket chain Tesco began to sell super unleaded gasoline rated at 99 RON. In the US, octane ratings in unleaded fuels can vary between 85〔(【引用サイトリンク】title=85-octane warning labels not posted at many gas stations )〕 and 87 AKI (91-92 RON) for regular, through 89-90 AKI (94-95 RON) for mid-grade (equivalent to European regular), up to 90-94 AKI (95-99 RON) for premium (European premium). South Africa's largest city, Johannesburg, is located on the Highveld at above sea level. So the South African AA recommends 95 octane gasoline (petrol) at low altitude and 93 octane for use in Johannesburg because "The higher the altitude the lower the air pressure, and the lower the need for a high octane fuel as there is no real performance gain".〔(【引用サイトリンク】title=95/93 – What is the Difference, Really? )〕 The octane rating became important as the military sought higher output for aircraft engines in the late 1930s and the 1940s. A higher octane rating allows a higher compression ratio or supercharger boost, and thus higher temperatures and pressures, which translate to higher power output. Some scientists even predicted that a nation with a good supply of high octane gasoline would have the advantage in air power. In 1943, the Rolls Royce Merlin aero engine produced 1320 horsepower (984 kW) using 100 RON fuel from a modest 27 liter displacement. Towards the end of the second world war, experiments were conducted using 150 RON fuel (100/150 avgas), obtained by adding 2.5% aniline to 100 octane avgas.〔("Best Gasoline Will Win War of the Future" ''Popular Mechanics'', April 1935 ) article at bottom of page 524〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「gasoline」の詳細全文を読む スポンサード リンク
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