What is the octane number of gasoline


When a driver enters a gas station, he parks his car at a specific terminal, which indicates which fuel can be refueled at this place. In addition to the fact that the car owner must clearly distinguish between the type of fuel (gasoline, gas or diesel), gasoline has several brands, in the designation of which a specific number is indicated.

These numbers represent the octane rating of the fuel. To understand how dangerous the use of gasoline unsuitable for a car can be, you need to figure out what is the difference between these brands, what factors are affected by the RH and whether it can be measured independently.

What is octane number

Before you understand the terminology, you should remember on what principle a gasoline engine works (in detail about the internal combustion engine read here). The air-fuel mixture from the fuel system is fed into the cylinder, where it is subsequently compressed by the piston several times (in models with direct injection, air is compressed, and gasoline is sprayed immediately before the spark is supplied).

At the end of the compression stroke, the BTC is ignited by a powerful spark generated by the ignition system, namely the spark plugs. The combustion of a mixture of air and gasoline occurs abruptly, as a result of which decent energy is released, pushing the piston in the direction opposite to the valves.

What is the octane number of gasoline

We know from physics lessons that when compressed strongly, air heats up. If the BTC is compressed in the cylinders more than it should be, the mixture will ignite spontaneously. And often this does not happen when the piston is performing the appropriate stroke. This is called engine detonation.

If this process often appears during the operation of the engine, it will quickly fail, since often the explosion of the VTS occurs at the moment when the piston begins to compress the mixture or has not yet completed the stroke. At this moment, the KShM is experiencing a special load.

To fix this problem, modern car manufacturers are equipping the engine with sensors that detect knock. The electronic control unit adjusts the operation of the fuel system to eliminate this effect. If it cannot be eliminated, the ECU simply turns off the engine and prevents it from starting.

But often the problem is solved simply by selecting the appropriate fuel - namely, with an octane rating suitable for a given type of internal combustion engine. The number in the name of the brand of gasoline indicates the pressure limit at which the mixture ignites on its own. The higher the number, the more compression the gasoline will withstand before self-igniting.

The practical value of the octane number

There are different modifications of motors. They create different pressure or compression in the cylinders. The harder the BTC is squeezed, the more power the motor will give out. Low octane fuel is used in vehicles with lower compression.

What is the octane number of gasoline

Most often these are old cars. In modern models, more efficient engines are installed, the efficiency of which is also due to high compression. They use high-octane fuel. The need to fill the tank not with the 92nd, but the 95th or 98th gasoline is reported in the technical documentation for the car.

What indicators affect the octane number

When gasoline or diesel fuel is made, the oil is divided into fractions. During processing (filtration and fractionation), pure gasoline appears. His RH corresponds to 60.

In order for the fuel to be used in internal combustion engines without detonation in the cylinders, various additives are added to the liquid during the distillation process.

The RON of gasoline is influenced by the amount of hydrocarbon compounds that act as an antiknock agent (as in the RON additives sold in auto dealerships).

Methods for determining the octane number

To determine which grade of gasoline drivers should use in their vehicle equipped with a specific engine, the manufacturer tests it with a reference gasoline. A specific internal combustion engine is installed on the stand. There is no need to completely mount the entire engine, a single-cylinder analogue with identical parameters is sufficient.

What is the octane number of gasoline

Engineers use different conditional situations to determine the moment at which detonation occurs. The parameters of the VTS temperature, the compression force and other parameters at which a particular fuel ignites independently change. Based on this, it is determined on what fuel the unit should operate.

Octane measurement process

It is impossible to make such a measurement at home. There is a device that determines the unit of the octane number of gasoline. But this method is rarely used by professional laboratories that check the quality of the fuel sold in the country, since it has a large error.

To accurately determine the RON of gasoline, petroleum product manufacturers use two methods in laboratory conditions:

  1. The air-fuel mixture is heated to 150 degrees. It is fed into the motor, the speed of which is fixed at 900 rpm. This method is used to test low octane gasoline;
  2. The second method does not provide for preheating the HTS. It is fed to the motor, the speed of which is set at 600 rpm. This method is used to check for compliance with gasoline, the octane number of which exceeds 92.

Measuring instruments

Of course, such methods of checking gasoline are not available to an ordinary motorist, so he has to be content with a special device - an octane meter. Most often, it is used by those car owners who choose which gas station to give preference to, but so as not to experiment on an expensive power unit of the car.

The reason for this mistrust is the dishonesty of suppliers who use low-quality or diluted gasoline for the sake of enrichment.

What is the octane number of gasoline

The device operates on the principle of the dielectric properties of gasoline. The higher it is, the higher the octane number will be shown by the device. To determine the parameters, you will need a control portion of pure gasoline with a known octane number. First, the device is calibrated, and then the fuel taken from a particular filling is compared with the sample.

However, this method has a significant drawback. The device needs to be calibrated. For this, either n-heptane is used (RON is zero), or gasoline with an already known octane number. Other factors also affect measurement accuracy.

Among the well-known devices for this procedure is the Russian OKTIS. More reliable and accurate in measurements - foreign analogue of Digatron.

How to increase the octane number of gasoline

You can increase the octane number of gasoline on your own if you purchase a specially designed additive for this. An example of such a tool is Lavr Next Octane Plus. The substance is poured into the gas tank after refueling. It dissolves quickly in gasoline. According to some measurements, the agent increases the octane number to six units. According to the manufacturer, if the car must run on 98th gasoline, then the driver can freely fill in the 92nd and pour this additive into the tank.

What is the octane number of gasoline

Among the analogs that are slightly smaller, but also increase the frequency range:

  • Astrohim Octane + (3-5 units);
  • Octane + by Octane Plus (increase by two units);
  • Liqui Moly Octane + (up to five units).

The reason why many car owners use 92nd gasoline with additives instead of the prescribed 95th or 98th is the popular belief (sometimes not groundless) that the owners of gas stations themselves use this method.

Often, substances that reduce the likelihood of premature detonation are used to increase the resistance to premature detonation. An example of this is solutions containing alcohol or tetraethyl lead. If you use the second substance, then carbon deposits accumulate on the pistons and valves.

What is the octane number of gasoline

The use of alcohol (ethyl or methyl) has fewer negative consequences. It is diluted from the ratio of one portion of the substance to 10 portions of gasoline. As those who used this method assure, the exhaust gases of the car become cleaner and no detonation was observed. However, it should be borne in mind that alcohol also has a "dark side" - it is hygroscopic, that is, it is able to absorb moisture. Because of this, both in the tank and in the fuel system, gasoline will have a higher percentage of moisture, which will adversely affect the operation of the engine.

For more information on additives of this kind, see the following video:

Additives in gasoline (fuel) - DO YOU NEED? MY VERSION

How to lower the octane number

Although modern cars are designed to run on high-octane gasoline, there are still many vehicles whose engines use 80 and sometimes even 76 brands of gasoline. And this applies not only to ancient cars, but also to some modern vehicles, for example, walk-behind tractors or special equipment (electric generators).

Such fuel has not been sold at ordinary gas stations for a long time, because it is not profitable. In order not to change the technique, the owners use the method of lowering the octane number, due to which the operation of the engines is adapted to the characteristics of the 92nd gasoline. Here are some ways:

  1. Some people leave the can of gasoline open for a while. While it is open, additives evaporate from the fuel. It is generally accepted that HR decreases by half a unit every day. Calculations show that it will take about two weeks to convert from the 92nd mark to the 80th mark. Of course, in this case, you need to be prepared that the volume of fuel is significantly reduced;
  2. Mixing gasoline with kerosene. Previously, motorists used this method, since there is no need to waste the volume for which the money was paid. The only drawback is that it is difficult to choose the right proportion.
What is the octane number of gasoline

What a dangerous detonation

The use of low-octane gasoline in an engine, the technical documentation of which indicates a different brand of fuel, can lead to detonation. Since the piston and crank mechanism are faced with a large load, unnatural for a particular stroke, the following problems may appear with the motor:

  • Burnout valves;
  • Burnout and deformation of pistons;
  • Deformation of the connecting rods;
  • Overheating of the motor and associated unpleasant consequences.

These are just some of the reasons why the engine should not be allowed to run on low octane gasoline.

In conclusion - another video dedicated to detonation:



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