Octane number - what does it mean?

Gasoline in various volumes is consumed in all countries of the world. There are a lot of varieties, but we, as always, want to get a better product. To assess different types of fuel use a special indicator - the octane number, which can characterize the properties of gasoline. First of all, this concerns its detonation properties and the possibility of using different grades of gasoline in modern engines

To understand what an octane number is, you need to consider the processes that occur when the engine is running. At first glance, everything is very simple - when the piston moves upwards, the volume of the cylinder decreases, the fuel mixture in it (the mixture in a certain proportion of air and gasoline vapor) is compressed. The candle gives a spark, the mixture lights up, and the resulting burning vapor, greatly increasing in volume, moves the piston down.

The described looks good in the form of a scheme, but in fact in this process there are many nuances that can significantly change the picture. Without touching the subtleties of the engine, let's look at the combustion of fuel in more detail. Usually a smooth, smooth burning occurs. 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 speed of flame propagation during ordinary combustion is tens of meters per second, and with explosive combustion up to 2500 m / s. In this case, excessive load is applied to the motor parts, noise and knocking are unusual for the engine. Such sharp, ringing sounds experienced drivers characterize simply - "fingers tapping", which is the first sign of detonation and adversely affects the performance of the motor.

The antiknock properties of gasoline just characterize 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 simplest way is to increase the compression ratio of the engine.

With an increase in the degree of compression of the fuel mixture during its combustion, more energy is released, respectively, the power of the motor increases. Here is the octane number and characterizes the different grades of gasoline for their propensity to detonation. The larger it is, the lower the probability of detonation. Its possibility is determined by the content of various hydrocarbons in the fuel. To establish the anti-detonation resistance, two methods are usually used: motor and research.

The procedure for 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 marking of the brand of gasoline. Petrol, checked by motor method is designated, for example, A-92, and for research - AI-92. The higher the octane number, the higher the detonation resistance of the fuel, and its quality is considered to be the best.

To increase the resistance to detonation in low-grade gasoline add substances that reduce the propensity to detonate - antiknock additives, resulting in gasoline can be used as high-octane. One of them is tetraethyl lead. Thanks to it and other additives used together with it, the detonation capacity of the combustible mixture decreases and the octane number increases. The gasoline to which these additives are added is called leaded. In order to distinguish from the usual, it is painted. The detonation resistance of the fuel is increased, but such gasoline is considered toxic, and in many countries it is not recommended for use.

As a fuel, gas is also used. When using it, there are no problems with detonation, since the octane number of gas is higher: on average, it is 105 units.

The presented material gives an idea of the different grades of gasoline, its quality and characteristics. The explanation of the cause of the detonation and the influence of the octane number on the properties of gasoline is given.