Gasoline in varying volumes is consumed in all countries of the world. There are many varieties of it, but, as always, we want to get a better quality product. To evaluate different grades of fuel, a special indicator is used - the octane number, which can characterize the properties of gasoline. This primarily concerns its detonation properties and the possibility of using different grades of gasoline in modern engines
To understand what octane is, it is necessary to consider the processes that occur when the engine is running. At first glance, everything is very simple - as the piston moves upward, the cylinder volume decreases, the fuel mixture inside it (the mixture in a certain proportion of air and gasoline vapors) is compressed. The candle gives a spark, the mixture lights up, and the resulting combustion fumes, significantly increasing in volume, move the piston down.
The described looks good in the form of a diagram, but in fact in this process there are many nuances that can significantly change the picture. Without touching on the intricacies of the engine, we consider in more detail the combustion of fuel. Usually there is a calm, smooth burning. During this process, several intermediate compounds are formed. They are unstable, and when a certain concentration is reached, explosive combustion can occur.
This will be a completely different process. The flame propagation velocity during normal combustion is tens of meters per second, and during explosive combustion up to 2500 m / s. In this case, an excessive load acts on the motor parts, noise and knocks that are unusual for the engine occur. Experienced drivers simply characterize such sharp, ringing sounds - “knocking fingers”, which is the first sign of detonation and negatively affects the performance of the motor.
The antiknock properties of gasoline just characterizes the octane number. Now you can return to the motor itself. The fact is that designers are always concerned about getting more power from the same engine, all other things being equal. The easiest way is to increase the compression ratio of the engine.
With an increase in the compression ratio of the fuel mixture during its combustion, more energy is released, respectively, the motor power grows. Here is the octane number and characterizes various grades of gasoline by their tendency to detonate. The larger it is, the less likely it is to detonate. Its ability is determined by the content of various hydrocarbons in the fuel. Two methods are usually used to establish antiknock resistance - motor and research.
The method of measuring the octane number in each case is different, and its value will be different for each type of measurement. The result is displayed in the designation of the brand of gasoline. Gasoline tested by the motor method is designated, for example, A-92, and by research - AI-92. The higher the octane number, the higher the fuel detonation resistance, and its quality is considered the best.
To increase the resistance to detonation, low-grade gasoline is added with substances that reduce the tendency to detonation - antiknock, as a result of which gasoline can be used as high-octane. One of them is tetraethyl lead. Thanks to him and other additives used together with him, the detonation ability of the combustible mixture decreases and the octane number increases. The gasoline to which such additives are added is called leaded. In order to distinguish from ordinary, it is painted. The knock resistance of the fuel is increased, but such gasoline is considered poisonous, and in many countries it is not recommended for use.
Gas is also used as fuel. When using it, there are no problems with detonation, since the octane number of the gas is higher: on average it is 105 units.
The material presented gives an idea of the different grades of gasoline, its quality and characteristics. An explanation is given of the cause of detonation and the influence of the octane number on the properties of gasoline.