Octane+Rating

 [|Octanes] are a family of hydrocarbon that are typical components of gasoline. They are colourless liquids that boil around 125 °C (260 °F). One member of the octane family, isooctane, is used as a reference standard to benchmark the tendency of [|gasoline, petrol, or benzin] fuels to resist self-igniting. Self-ignition leads to inefficiencies (or even engine damage) if it occurs during compression prior to the desired position of the piston in the cylinder as appropriate for valve and ignition timing. The problem of premature ignition is referred to as pre-ignition and also as [|engine knock], which is a sound that is made when the fuel ignites too early in the compression stroke. Severe knock causes severe engine damage, such as broken connecting rods, melted pistons, melted or broken valves and other components. The **octane rating** is a measure of how likely a gasoline or liquid petroleum fuel is to self ignite. The higher the number, the less likely an engine is to pre-ignite and suffer damage.  [|Isooctane] (upper) has an octane rating of 100 whereas [|n-heptane] has an octane rating of 0. The most typically used engine management systems found in automobiles today monitor the level of knock that is being produced by the fuel being used. In modern computer controlled engines, the timing of the ignition will be automatically altered by the fuel management system to reduce the pre-ignition to an acceptable level. The octane rating of [|gasoline] is measured in a test engine and is defined by comparison with the mixture of [|2,2,4-trimethylpentane] (iso-octane) and [|heptane] that would have the same [|anti-knocking] capacity as the fuel under test: the percentage, by volume, of 2,2,4-trimethylpentane in that mixture is the octane number of the fuel. For example, petrol with the same knocking characteristics as a mixture of 90% iso-octane and 10% heptane would have an octane rating of 90. [|[2]] A rating of 90 does not mean that the petrol contains just iso-octane and heptane in these proportions, but that it has the same detonation resistance properties. Because some fuels are more knock-resistant than iso-octane, the definition has been extended to allow for octane numbers higher than 100. Octane rating does not relate to the energy content of the fuel (see [|heating value] ). It is only a measure of the fuel's tendency to burn in a controlled manner, rather than exploding in an uncontrolled manner. Where the octane number is raised by blending in ethanol, energy content per volume is reduced.  A US gas station pump offering five different (R+M)/2 octane ratings It is possible for a fuel to have a Research Octane Number (RON) greater than 100, because iso-octane is not the most knock-resistant substance available. Racing fuels, [|avgas], [|liquefied petroleum gas] (LPG), and [|alcohol fuels] such as [|methanol] may have octane ratings of 110 or significantly higher. Typical "octane booster" [|gasoline additives] include [|MTBE], [|ETBE] , [|isooctane] and [|toluene]. [|Lead] in the form of [|tetra-ethyl lead] was once a common additive, but has been banned since the 1970s.
 * Octane rating ** or **octane number ** is a standard measure of the performance of a motor or aviation fuel. The higher the octane number, the more compression the fuel can withstand before detonating. In broad terms, fuels with a higher octane rating are used in high-compression engines that generally have higher performance. In contrast, fuels with low octane numbers (but high [|cetane numbers] ) are ideal for diesel engines. Use of gasolines with low octane numbers may lead to the problem of <span style="background-color: #ffffff; color: #0b0080; font-family: sans-serif; font-size: 13px; text-align: start; text-decoration: none;">[|engine knocking].