Gasoline - flammable liquid that has no color, or with a slight yellowish tint (if there are no special additives).In order to improve the working properties of the motor fuel used in internal combustion engines, manufacturers are trying to increase the octane number of gasoline.For this purpose, the respective components added thereto.If the combustion characteristic audible sound of metal produced by the detonation wave during its multiple reflections from the walls of the cylinder, the efficiency of the engine is reduced, moreover, it is accelerated wear.
In this case we say that the fuel quality is poor, as the octane number is low.Antiknock motor fuel, that is, the ability to resist self-ignition due to compression in the cylinders of the engine running and characterizes the figure.Numerically it is the volume fraction of isooctane (its other name: 2,2,4-trimethylpentane) in a two-component mixture containing also n-heptane.Such a mixture with regard to its antiknock under standard test conditions, produces an effect equivalent investigated fuel.
Isooctane - branched chain saturated hydrocarbon C8H18.He is due to its properties, it is difficult to oxidize even at high compression ratio, so its resistance to knock conventionally taken to be 100 units.N-heptane in the engine behaves differently: even at low degrees of compression process of combustion is accompanied by a detonation effect, so the value of this indicator for it is taken as 0 units.In those cases where the gasoline octane number above 100, for quality assessment scale used conventional mixtures, where the main component - isooctane - tetraethyl added various dosages.
Therefore, it can be argued that this figure is the most important characteristic of the motor fuel.It shows how much petrol is resistant to detonation, that is, arbitrary fire into the engine cylinders.The probability of an explosion of fuel in internal combustion engines will be dropped if the rate is high.If the octane number of gasoline correspondence units 95, it detonates the mixture consisting of 95% 2,2,4-trimethylpentane and 5% normal heptane.After initial processing of oil for a product called naphtha, this characteristic value rarely exceeds 70 units.Therefore, to improve the quality of low-grade gasoline is used not only for compounding (mixing with high-octane products), but also antidetonators administered in an amount of up to 0.3%.
Fuel quality depends largely on the composition of the natural resources from which it is obtained by fractionation or distillation, - oil.For it are important indicators such as viscosity, fractional composition, the presence of sulfur compounds and waxes, as well as the water content and the dissolved salts.However, these factors probably affect the processing characteristics and the choice of technology.The quality of gasoline, that is, the value of its octane number, determines the composition of the hydrocarbon oil, and then its processing method, which also depends on how much gasoline is octane, n-heptane, aromatic compounds, and so forth.
anti-knock properties of gasoline increases contained therein aromatic hydrocarbons.High concentrations of benzene primarily affects the state of the environment as a source of benzopyrene (a carcinogen).Elevated levels of high-boiling aromatic compounds contributes to soot formation in the combustion chamber and on the valves of the engine.All this degrades performance indicators such as engine power, efficiency, environmental and economic aspects of its work.Soot formed in the combustion chamber causes the car owners to choose the engine fuel so that the octane number was high.Otherwise, power is significantly reduced or the motor operates with a detonation.
