Gasoline is a flammable liquid, notIt has a color or with a slight yellowish tinge (if there are no special additives). In order to improve the working properties of motor fuel used in internal combustion engines, manufacturers are trying to increase the octane number of gasoline. To do this, add the appropriate components. If during combustion of fuel a characteristic metallic sound produced by a detonation wave is observed when it is repeatedly reflected from the walls of the cylinder, the efficiency of the engine decreases and, in addition, its wear is accelerated.
В этом случае говорят, что качество топлива unsatisfactory, since the octane number is low. The detonation resistance of motor fuel, that is, the ability to withstand self-ignition due to compression in the cylinders of the operating engine, characterizes this index. It is numerically equal to the volume fraction of isooctane (its other name is 2,2,4-trimethylpentane) in a two-component mixture containing also n-heptane. Such a mixture, when determining its detonation resistance under standard test conditions, creates an effect equivalent to the fuel under study.
Isooctane is the ultimate hydrocarbon of C8H18isostroeniya. Due to its properties, it is difficult to oxidize even at a high compression ratio, so its detonation resistance was conventionally assumed equal to 100 units. H-heptane in the engine behaves differently: even at low compression ratios, its combustion process is accompanied by a detonation effect, so the value of this index for it is taken as 0 units. In cases where the octane number of gasoline is above 100 units, a conditional scale of mixtures is used to assess its quality, where various doses of tetraethyl lead are added to the main component - isooctane.
Therefore, it can be argued that this indicatoris the most significant characteristic of motor fuel. It shows how gasoline is resistant to detonation, that is, to an arbitrary ignition in the cylinders of the motor. The probability of a fuel explosion in the engine will be minimized if this figure is high. If the octane number of gasoline corresponds to 95 units, it detonates as a mixture consisting of 95% of 2,2,4-trimethylpentane and 5% of normal heptane. After primary oil treatment for a product called straight-run gasoline, this characteristic rarely exceeds 70 units. Therefore, in order to improve the quality of low-grade gasoline, not only compounding (mixing with high-octane products) is used, but antiknock agents are introduced in an amount of up to 0.3%.
The quality of fuel depends largely on the compositiona natural fossil from which it is obtained by fractionation or distillation - oil. It is important for such indicators as viscosity, fractional composition, the presence of sulfur compounds and paraffins, as well as the water content and dissolved salt in it. However, the listed factors are more likely to influence the processing features and the choice of technology. The quality of gasoline, that is, the value of its octane number, determines the hydrocarbon composition of the oil, and then the way it is processed, which also determines how much iso-octane, n-heptane, aromatic compounds will be in the gasoline, and so on.
Anti-knock properties of gasoline increasearomatic hydrocarbons contained in it. The high content of benzene primarily affects the state of the environment, as it is a source of benzapyrene (a carcinogen). The high content of high-boiling aromatic compounds contributes to the increase of carbon formation in the combustion chamber and on the engine valves. All this affects such performance indicators as engine power, efficiency, environmental and economic aspects of its work. Nagar formed in the combustion chamber, forcing the owner of the car to choose motor fuel in such a way that the octane number of gasoline was high. Otherwise, the power is significantly reduced or the engine works with a detonation.
