Depends on the octane number of gasoline different characteristics vehicle, for example, dynamic or performance properties. This is a measure of the resistance of a particular type of fuel to fire (detonation). Separate standards have been developed for different types of fuel, and they are taken into account when selecting the octane number for a specific type of automobile engine. Let's take a closer look at what the octane number of gasoline is, how to measure this parameter, and how it affects the characteristics of gasoline.

The concept of octane number

Octane number is presented as a measure that determines the chemical resistance of the fuel to automatic ignition. Detonation resistance is directly proportional to the OC value. The fuel-air mixture is compressed by the piston during the compression stroke. High pressure can cause the mixture to ignite spontaneously, and this is a problem if detonation occurs before the spark plug produces a spark.

This process is accompanied by a noise effect, reminiscent of the clinking of coins in a ceramic piggy bank. Such sounds can be explained by the formation of high-pressure waves between which a collision occurs.

The consequences of spontaneous combustion can be represented by serious damage to the internal elements of the engine, the piston holes can straighten out, and the connecting rods can bend. The engine fails.

With modern engines, such troubles practically do not occur due to the presence of special computer control units. The corresponding knock sensors are mounted on the engine block and promptly detect frequencies indicating the risk of detonation.

After fixing such frequencies, the gearbox control module returns control of the air-fuel mixture. The moment the spark appears in the spark plugs is delayed, the boost level in the engine is reduced, or the composition of the fuel mixture is adjusted to prevent breakdown.

Developments at automobile concerts are focused on preventing spontaneous combustion in engine components, which is why engines are produced with a high compression ratio. In this context, it is the octane number that is of paramount importance, since high octane fuel is required for engines with high compression ratios. They are used mainly in executive or sports cars. The compression ratio in modern cars can be 10 to 1, but higher rates are also found.

A specific OC is developed by the manufacturer separately for each model and brand of machine. Characteristics of this kind are indicated in the operating instructions, but what will be the consequences of ignoring the recommendations?

Using fuel fluid with a lower RH than required leads to the following consequences:

• detonation;
• failure of piston group elements;
• motor overheating;
• valve burnout;
• reduction in engine power (read about);
• increase in consumption.

If the octane number in the fuel, on the contrary, is higher than necessary, the consequences will not be so dire. We are talking about a slight decrease in dynamics, since the combustible mixture will burn longer.

Octane number measurement (RON and RON)

Determination of the octane number of gasoline is possible by two methods - research and motor. Since the results obtained as a result of these manipulations are different, they are designated as OCH and OCH, respectively. Compliance special conditions for the implementation of both methods is a mandatory measure. It is primarily necessary to select mixtures of high quality reference hydrocarbons with a number of 100 (isooctane) and normal n-heptane with a number of 0.

At the next stage, the octane number is determined using a special installation.

1. ROC – research octane number, determined using a single-cylinder unit with a variable compression ratio (UIT-85 or 65). The crankshaft speed should be 60 rpm, the ignition timing should be 13 degrees, and the intake air temperature should be 52 degrees Celsius. In this case, the resulting indicator determines the behavior of gasoline in medium and low load modes.
2. ROM is the engine octane number, to determine which it is also customary to use a single-cylinder unit, however, the temperature of the intake mixture should be 149 degrees Celsius, and the crankshaft speed should be 900 rpm with a variable ignition timing. The value of the NMO is lower than the OCHI. In this case we are talking about the behavior of fuel under high load conditions. The parameter under consideration affects detonation and high speed when driving uphill, operating the engine under load and partial throttle acceleration.

Separately, it is worth considering the third way to determine the octane number - the use of special instruments, but in this case you should immediately focus on the presence of errors, since the accuracy of such measurements is often questionable.

Use of devices

Absolutely all instruments used to measure the value of octane have a single operating principle - determining the dielectric constant of gasoline, since this parameter depends proportionally on the value of octane. A mandatory measure is to draw up a special calibration relationship in order to obtain the most accurate value. This dependence is constructed taking into account n-heptane and fuel with a known octane number.

Among the most common devices of imported and domestic production are the following.

1. OKTIS– a Russian-made device worth 3,500 rubles is considered the most famous and in demand.
2. Digatron Positioned as a more reliable and accurate device, the cost reaches 700 euros. The device has found application in karting and other sports.
3. OKTAN-IM features 10 calibrations and a built-in internal memory. Demonstrates the highest possible accuracy of readings.
4. OCTANOMETER PE-7300 M It will cost approximately 50 - 60 thousand rubles. Features a built-in software and the ability to connect to a PC. It is allowed to take into account the temperature indicator.
5. SHATOX SX-100M– an imported analogue, the cost of which reaches $1,800. There is a built-in temperature sensor. This indicator is determined using a software method.

It is worth noting that the OR according to instrument measurements may differ significantly depending on the fuel manufacturer due to different calibration dependences. The construction of individual calibrations for each case is a mandatory measure. Gasoline from a specific manufacturer is usually used as a standard.

Among the disadvantages of the considered method for determining OC, one can highlight the difficulty of determining various external factors that can influence the measurement process. Another disadvantage is the impossibility of analyzing unidentified fuel, since the analysis is initially based on comparison.

Increase in HP

Drivers are often interested in how to increase the octane number of gasoline or lower this figure. Increasing the OP is considered a simpler process than decreasing it. This may be the addition of a special anti-knock agent or the use of a complex technological process. It is the first option that is usually preferred.

The following substances can be used as anti-knock agents.

1. Alcohol additives make it possible to achieve an increase in fuel rating by about 3 units, if we are talking about adding 1/10 of ethyl alcohol to 92 gasoline. As a result, we will get 95 fuel. Exhaust toxicity will also be reduced accordingly, but vapor pressure will quickly increase, which can cause vapor locks to form in the fuel line system. Also, do not forget about the hygroscopicity of alcohol. The fuel obtained in this way must be stored appropriately and the amount of water in the mixture must be controlled. If water gets into the engine, the consequences may require expensive repairs.
2. Tetraethyl lead was previously used by manufacturers to increase knock resistance (since 1921). The substance has increased anti-knock properties, but is classified as super toxic and contributes to the failure of oxygen sensors in the exhaust system and catalysts. The chemical formula of the substance is Pb(C2H5)4, it boils at a temperature of 2,000 degrees Celsius, and is distinguished by high viscosity. The octane number increases by 17 units with the help of this additive. Since combustion of the substance leads to the formation of lead oxide and it settles on the internal elements of the engine, causing carbon deposits on pistons and valves, it was not used in its pure form. As an additive to tetraethyl lead, products were used that promote the removal of lead oxide - dibromoethane, dibromopropane or ethyl bromide.
3. It is safer to use special additives in the form of paraffin and aromatic hydrocarbons. In most cases, their use requires sealed storage of gasoline due to the high degree of volatility of such components. You can increase the OC yourself using additives. You just need to buy one of them and add it to gasoline. As an option, you can use ASTROhim Octane Plus, which increases the OR by 3 - 5 units, Lavr Next Octane Plus, which increases the OR up to 6 units, "Octane Plus" Octane Plus, which helps increase the OR by 2 - 2.5 units, as well as methyl tert-butyl ether .

Decrease in score

Since the sale of 76 and 80 gasoline at gas stations has recently ceased, it has become necessary to lower the octane number of the fuel, since equipment running on gasoline with a low octane number is still in use. As an example, we can cite models of walk-behind tractors that were released 10 years ago or earlier.

We have lawyers, we have computer scientists, we also need engineers and other chemists.

The octane number of gasoline determines its resistance to detonation. The higher the octane number, the longer the gasoline does not explode when compressed, the more it can be compressed. That is, if the engine wants to squeeze more energy out of the fuel, it must compress the fuel more, and this can cause gasoline to explode (not in the tank, but in the engine cylinder). Therefore, for such engines they come up with gasolines that can withstand greater compression without exploding. The higher the compression ratio of the fuel in the engine, the higher the octane number of gasoline should be.

How does this affect consumption? Under cat.

Let's take the abstract engine of one abstract modern passenger car. The degree of fuel compression in this engine does not depend on the type of fuel; it is a characteristic associated exclusively with geometric parameters: (Vc+Vh)/Vc, see the picture to the topic. Consumption can only be affected by the energy released during fuel combustion. Is the combustion energy of 95 gasoline different from the combustion energy of 92 gasoline? According to Wikipedia, specific heat gasoline combustion 42-44 MJ. Even if we assume that 42 is for the 92nd, and 44 is for the 95th (this assumption is initially false, since there are also 80th and 98th), then we still cannot talk about a 15% increase in power at all no way.

For our abstract engine, the difference between gasolines is as follows: if the engine has a compression ratio of 6-8, then it is enough for it to have an octane number of 76/80 - gasoline will no longer detonate in the cylinders, but if 80th gasoline is poured into our abstract engine, which has a compression ratio of 8-9, then 80-grade gasoline will begin to explode (detonate) before the spark from the spark plug ignites it, and this will be of little benefit to the engine: gasoline should not explode inside the cylinder in normal mode, it should burn. If you pour 98 into this engine, then it will definitely not detonate ahead of time, but it will burn too slowly after ignition (because it is designed for greater compression) and therefore will flow unburned into the exhaust pipe (from this, by the way, the valve and burned out earlier).

Fortunately, modern engines have “brains” that allow him to decide at what point to ignite the fuel in the cylinder, so in both cases the fuel is ignited earlier than if the original 92/95 had been filled. In the case of a low octane number, this leads to the fact that the fuel burns too early, consumption increases, and the engine noticeably “does not pull.” In the case of an increased octane number, the efficiency simply decreases (due to the extended combustion time of the fuel), consumption increases uncritically, and it may feel like it’s “not working” (this will happen with early ignition, even with native gasoline).

So, the correct answer to the question “does the octane number affect consumption”: if you pour gasoline with an octane number lower than the calculated one, then the consumption will increase, if it is higher, then at least it will not decrease, it may also increase.

If the engine is designed for 95th, the consumption will increase at 92nd. If the engine is designed for the 92nd, then the 95th will not have any advantages.

There are clarifications.

1. If gasoline is diluted with donkey urine, its combustion energy will decrease, and accordingly, consumption will increase. So the consumption depends on the gas station. If only 95 or only 92 is pumped at the gas station, then the consumption may change when switching from one to the other (contrary to the above theory), but in this case this is due to donkey urine, and not due to the octane number of gasoline .

2. A car manufacturer may set a lower octane rating in fuel requirements to attract more poor buyers. It's worth checking your engine's compression ratio to know if it makes sense to try more expensive gasoline without risking the placebo effect. Lowering the minimum octane number can lead to all sorts of special effects, for example, I noticed that after each refueling (I refuel with 95), my car “doesn’t last” for the first few kilometers. This is because the brains have not yet determined what is in the tank, and tuned in to the default 92nd, that is, they turned on the early ignition.

3. 95-ecto, 95-G-drive, etc. - you need to understand that even if they work, that is, even if they add power, it’s definitely not due to a change in the octane number. The octane number is 95, this is indicated on the receipt. Respectively:
1 as I noted above, this fuel can have an increased heat of combustion (due to additives),
2 it may have additives that enhance other characteristics that affect overall efficiency(viscosity, amount and type of gases formed, combustion rate, etc),
3 it may not have donkey urine in its composition (this gives an effect compared to fuel that has this component),
4 or it may have additives that cause a placebo effect.
What is noteworthy is that the oil industry is hiding this point, that is, finding out which option is used for the G-drive and which for the 95-ecto is quite problematic. I am inclined to believe that this is a combination of 3 and 4, but people claim that some types of such gasoline wash away sediment in the gas tank, which hints at elements of option 2 (obviously, they wash sediment directly into the engine, so you need to be more careful with this) .

4. “95 is made from 92 by adding additives.” In fact, it doesn’t matter, even from the 80th, if it has an octane number of 95, then it is 95th, if it burns like gasoline, then it is gasoline, if it releases the required amount of energy, the car will drive on it like on the 95th. As long as there is no donkey urine in the composition and these additives do not corrode what is not necessary (for example, they can kill the catalyst - but this will not affect consumption) - this gasoline is normal 95. If it precipitates in flakes on the second day, then again the problem here is not the octane number.

5. Yes different ways determination of the octane number of gasoline, which are used in different countries by default. The American method of determining the octane number will show approximately 90-92 of its parrots on our 95th. If the manual for an American car says “use 92,” then when you switch to 95, you will receive an improvement in all characteristics in strict accordance with the theory outlined above: the rated gasoline for such a car is an analogue of our 95. You can focus on the compression ratio to check whether the manufacturer is underestimating the requirements and whether he has copied the octane number from the docs for American spare parts. True, I was unable to find the source of this information: Anyone who wants to object is welcome.

P.S. Don’t try to pour 80-octane gasoline into the tank of your car - you’ll get screwed, and I’ll be at fault. Ignition correction "helps" if the octane number differs by 2-3 units, and is intended for small adjustments when the octane number fluctuates, and not for driving at 80. But in principle, people travel in critical situations.

Gasoline - it’s hard to remember something more familiar to a motorist. Every day, cars burn hundreds of thousands of liters of this fuel, but few car owners have seriously thought about how it is produced, the characteristics of the fuel composition and other aspects.

Some terminology

1. Aromatic;
2. Olefinic;
3. Paraffin and others.

These hydrocarbons have flammable properties. The boiling point of the mixture varies from 33 to 250 °C, which depends on the additives used.

What is gasoline made from?

Gasoline production scheme

Fuel is produced at oil refineries. The production process itself is very complex and is divided into several cycles.

Crude oil first enters the plant through pipelines, is pumped into huge tanks, and then settles. Next, oil washing begins - water is added to it, and then electric current is passed through. As a result, salts settle to the bottom and walls of the tanks.

During subsequent atmospheric-vacuum distillation, the oil is heated and divided into several types. There are 2 stages of processing:

1. Vacuum;
2. Thermal.

Upon completion of the primary refining process, catalytic reforming begins, during which gasoline is further purified and fractions of 92-grade, 95-grade and 98-grade gasoline are extracted.

Photo: aif.ru

This process, also called recycling, includes 2 main stages:

1. Cracking – purification of oil from sulfur impurities;
2. Reforming is giving a substance an octane number.

Video: How gasoline is made from oil. Just something complicated

At the end of these stages, fuel quality control is carried out, which takes several hours.

It is noteworthy that domestic factories (in the majority) produce 240 liters of gasoline from 1 ton of oil. The rest comes from gas, fuel oil and aviation fuel.

What is octane number

This phrase is known to many people, but not everyone knows what exactly this term means and why it is so important.

Octane number is the ability of a fuel (including gasoline) to resist spontaneous combustion under pressure. In other words, its detonation resistance.

During engine operation, the piston compresses the fuel-air mixture (compression stroke). At this moment, when the finished mixture is under pressure, it may spontaneously ignite even before the spark plug has given a spark. People call this phenomenon in one word - . A characteristic feature detonation is noise in the engine - a metallic ringing.

Therefore, the higher the octane number, the higher the ability of the fuel to resist detonation.

Gasoline labeling

At gas stations you can find a variety of names, not excluding those that are most familiar to most motorists. Typically, gasoline is marked with the letters “A” and “AI”. Their decoding:

1. “A” - this designation indicates that;
2. “AI” - the letter “I” means the method by which the octane number was determined.

There are 2 ways to determine the octane number - research (AI) and motor (AM).

Research method - it is determined by testing the fuel on a single-cylinder power plant, subject to a variable compression ratio, crankshaft speed of 600 rpm, ignition timing of 13° and air (intake) temperature of 52 ° C. These conditions are similar to light and medium loads.

Motor method - its determination is carried out on a similar installation, but other conditions are different. The air (intake) temperature is 149 °C, the crankshaft speed is 900 rpm, and the ignition timing is variable. This mode is similar to high loads - driving uphill, running the engine under load, etc.

Consequently, the number of AM is always lower than AI, and the difference in readings indicates the sensitivity of the fuel to the operation of the power unit in different modes. It is noteworthy that in some countries in the West, the octane number is defined as the average between the “AM” and “AI” values. In the Russian Federation it is designated only more high value“AI”, which can be seen at all gas stations.

Gasoline brands

The following designations are most often found at domestic gas stations:

• Gasoline AI-98. Different Unlike AI-95, which is produced in accordance with GOST, the 98th is produced in accordance with TU 38.401-58-122-95, as well as TU 38.401-58-127-95. In the production of this brand of gasoline, the use of alkyl lead antiknock agents is prohibited. This high-octane gasoline is produced using a number of components - toluene, isopentane, isooctane and alkyl gasoline.
• Extra AI-95 is gasoline of improved quality, which is achieved through the use of anti-knock additives. Produced from distillate raw materials, catalytic cracking gasoline, with the addition of isoparaffin elements (aromatic) and gas gasoline. There is no lead in the composition, which ensures high quality gasoline.
• AI-95 - the main difference from Extra AI-95 is the concentration of lead, which is 30% higher;
• AI-93 - divided into 2 categories: leaded and unleaded. Leaded fuel is produced on the basis of catalytic reformed gasoline (mild mode) with the addition of toluene and alkyl gasoline, as well as a butane-butylene fraction. Unleaded is produced from the same catalytic reforming gasoline (hard mode), with the addition of butane-butylene fraction, alkyl gasoline and isopentane;
• AI-92 is the most common medium-quality gasoline on the market, containing anti-knock additives. Maximum density – 0.77 g/cmA-923. Can be either leaded or unleaded;
• AI-91 – differs in the content of anti-knock additives. This is unleaded gasoline with an unstandardized density and a certain percentage of lead in the composition;
• A-80 - the composition of this gasoline is similar to that of AI-92. Maximum density – 0.755g/cmA-803;
• A-76 - usually used in agriculture. Leaded and unleaded A-76 with non-standardized density is produced. It contains additives of various types (anti-oxidation and anti-knock), straight-run gasoline, as well as final, pyrolysis and cracking (thermal and catalytic).

Video: AI-92 or AI-95? Acceleration to 100 km and fuel consumption on Mazda Demio (Ford Festiva Mini Wagon)

What kind of gasoline should I use?

Many people are looking for the answer to this question so as not to inadvertently harm the engine. In this case, everything is simple - the fuel requirements are indicated in the operating instructions for a particular vehicle, and are also duplicated on back side gas tank flap. If the manufacturer indicated AI-95 as the recommended fuel, then refuel with 92 only at your own peril and risk. However, it is worth remembering that both the octane number and the brand of fuel may be indicated in the manual and on the label.

Also in the manual can be written different types gasoline. For example:

1. AI-92 – acceptable;
2. AI-95 – recommended;
3. AI-98 - to improve performance.

As you can see, you only need to fill the tank with fuel recommended by the car manufacturer. However, using gasoline with a higher octane number will not cause any harm to the engine. After all, the higher the octane number, the slower the combustion rate and the greater the efficiency of the fuel, which has a beneficial effect on engine performance, efficiency and other aspects. As a rule, the increase in power and efficiency reaches 7%. In addition, modern cars are equipped with ECUs that take into account the quality of the fuel and its octane number, adjusting the settings.

This means that AI-95 must be filled into the tank of a modern car with an atmospheric engine at a high-quality gas station. As a last resort, AI-92 is allowed. You can also focus on the compression ratio - if it is below 10 units, you can fill in AI-92. If higher - only 95th.

As for turbocharged engines, the recommended fuel for them is AI-98 or Extra AI-95, but not AI-92.

Is it possible to mix gasoline?

Many people ask this question. In general, nothing catastrophic will happen from mixing fuel with different octane numbers, but only if you mix the recommended gasoline with a higher octane number. For example, the 92 recommended for a car should be mixed with 95. However, there is no need to downgrade. It is also worth remembering that the density of gasoline with different octane numbers differs, so its mixing may not occur at all - fuel with a higher octane number will simply end up at the top of the tank, and with a lower one at the bottom.

To understand whether a particular brand of fuel is suitable for a car, car enthusiasts look at its octane number (OC). But not everyone understands what octane number is, what it affects and why it is important to fill the car with exactly the fuel for which it is designed.

During operation of a car engine, a mixture of air and gasoline vapor is compressed to a certain value by the cylinder pistons, after which it is ignited by an electric spark. The combustion energy of gasoline vapors, in fact, is the force that rotates the wheels of the car.

However, if you compress the air-fuel mixture too much, it can ignite spontaneously without waiting for the spark to ignite. This process is called detonation and leads to increased wear and engine failure. In modern cars, they try to combat this with the help of special sensors that detect detonation and send a signal to the on-board computer, which either adjusts the fuel cycle, or, if the risk of detonation cannot be eliminated, simply blocks the operation of the engine.

But, modern technologies is not enough, for the correct operation of the engine you definitely need suitable fuel. The indicator of gasoline's resistance to self-ignition during compression is called the octane number of the fuel. The higher the octane number, the more high pressure can withstand gasoline when compressed in the engine chamber.

Why is detonation dangerous?

As mentioned above, during the operation of a car engine, a mixture of gasoline and air is compressed by a piston, ignited by an electric spark and burned, releasing energy that is used to rotate the wheels. The more the air-gasoline mixture can be compressed, the higher the engine efficiency will be. But an increase in compression force leads to spontaneous detonation of gasoline.

Detonation leads to deformation of the pistons and connecting rods. The engine elements, coming into contact with each other, emit clanging sounds and after a short time become completely unusable. If the engine runs on low-octane fuel for some time, then due to detonation:

• valves burn out;
• pistons melt and become deformed;
• connecting rods bend;
• the engine overheats.

All this inevitably leads to rapid breakdown. The damage to engine components may be so serious that a complete replacement of the power unit will be required.

How to increase the octane number of gasoline

In the second half of the twentieth century, the most popular way to increase the octane number of gasoline was to add tetraethyl lead to its composition. This substance effectively reduces the ability of fuel to detonate. Industrial way It is not difficult to produce tetraethyl lead, and its cost has virtually no effect on the final price of the fuel.

Currently, tetraethyl lead is banned for production in almost all countries of the world. Instead, hydrocarbons of the aromatic and paraffin groups are used as additives that increase the octane number. Unfortunately, many of these substances evaporate extremely easily, so the octane number of the fuel drops during long-term storage. If you pour 95 octane gasoline into a regular can and leave it in the garage for several weeks, during this time it will spontaneously turn into 92 octane or even 80 octane. Therefore, it makes no sense to keep a supply of gasoline for a modern car.

How to lower the octane number

It is still used in our country a large number of equipment designed for the use of low-octane gasoline - 80 and even 76. We are talking not only about old brands of cars, but also about walk-behind tractors, gasoline generators and other devices. Purchasing new units will cost the owners too much, so methods of lowering the octane number are quite relevant for our car owners.

Most in a simple way, used by folk craftsmen, is the evaporation of additives. It is believed that if you leave a can of gasoline open, the octane number will decrease by 0.5 every day. Thus, it will take two weeks to turn 92 gasoline into 80 gasoline.

In some cases, a similar effect is achieved by mixing gasoline in a certain proportion with kerosene. At one time, this method was widely used by owners of old cars. But the method did not catch on, since the dilution proportion must be determined empirically each time.

Octane number measurement

Unfortunately, even purchasing fuel at a gas station does not always guarantee compliance with the declared octane number. However, it is extremely difficult to measure it at home; this requires special equipment and reference chemical substances. In laboratories, measurements are performed in two ways - motor and research. Both are based on comparing gasoline with a reference hydrocarbon, which has an octane rating of 100, and n-heptane, which has an octane rating of zero.

• Motor method. The fuel mixture, heated to 150 degrees, is fed into the engine, which is accelerated to 900 rpm. The motor method is best suited for low-octane fuels.
• Research method. The fuel mixture is supplied to the engine without preheating, the rotation speed is 600 rpm. This method is effective for measuring gasoline with an octane number above 92.

In addition, special instruments are used to measure the octane number. However, they are not very popular because they give too much scatter in the measurement results.

What is octane number and does it depend on it? This is the question any motorist asked when refueling his car at a gas station with the thought of choosing a filling hose with some conventional numbers above it.
Octane number is actually the detonation level at which gasoline will ignite and explode in your car's combustion chamber. If gasoline ignites earlier than necessary, at a time when the intake valves are not yet completely closed and the cylinder is not at the top point, then naturally the engine may not only not work at full power, but work incorrectly, and what’s even worse, we will actually get detonation but more on that later.

With such a low octane number, during long-term operation we will get a bunch of problems with engine parts - wear of valves, valve seats, additional carbon deposits, etc. In addition, a mismatch in the octane number for the engine entails the same additional detonation, which is often confused with valve knocking.

The octane number is obtained by shifting the components of gasoline. Isooctane is a substance that is almost non-explosive when pressure increases, and its detonation resistance was taken to be 100 units. At the same time, n-heptane is absolutely resistant to detonation with increasing pressure (one might say self-detonating), therefore its detonation resistance is taken as 0. It is the mixture of these substances that allows you to regulate the octane number in gasoline. In addition, it is added to gasoline trimethylpentane, on which the octane number depends little. There are gasolines with an octane number of more than 100 units, for which they use isooctane with the addition of various amounts of additives.

Additives for increasing the octane number of gasoline

To increase the octane number, aromatic hydrocarbons and branched paraffinic hydrocarbons (alkanes) are added. It is with the use of these components that the octane number increases. But as you noticed, the substances used are called aromatic (aromatic hydrocarbons), i.e. In layman's terms, high-octane gasoline smells stronger than low-octane gasoline. There are also certain disadvantages to this, since high-octane gasoline, after adding aromatic components, is more volatile. That when stored for a long time in an open container or in a certain combination of containers with external environment leads to a decrease in the octane number of gasoline. Therefore, we can say that high octane gasoline must be “fresh”.

Previously in the USSR, to increase the octane number, it was used tetraethyl lead- a toxic mixture containing lead. Unfortunately, tetraethyl lead is not only toxic in itself, but also quickly damages catalytic converters and lambda probes, which have become used in the design of modern cars, as a result of which this additive had to be abandoned. Manganese-based additives have also been used, but these are now also prohibited for environmental reasons. In addition, an additive is sometimes used to increase the octane number - ferrocene. This additive (ferrocene) contains iron and creates a hard-to-remove conductive deposit on the spark plugs (shades of red), which impairs the performance characteristics and accordingly reduces the service life of the spark plugs. Gasolines also contain other additives and impurities. Additives in gasoline perform different tasks. They reduce the amount of harmful impurities in gasoline - sulfur, water, clean engine parts or the fuel system, increase the octane number of gasoline (this was mentioned above). A relatively harmless anti-knock additive for the engine is methyl tert-butyl ether. Now it is widely used in Ukraine, Russia and Europe.

It is quite possible to obtain gasoline with an octane number of more than 110 (and this is aviation fuel). In addition, everyone knows the scheme with mixing gas condensate, because the octane number natural gas usually above 100.

Combustion of gasoline at different octane numbers.

The rate of combustion of gasoline, that is, in fact, an explosion, depends on the octane number. At high octane numbers, gasoline burns for a long time, smoothly. At the same time, the gases in the chamber do not put stress on the pistons with the phenomenon of impact and excessive resonant detonation. The engine runs more evenly, smoothly and clearly. Therefore, in the automotive industry there is a tendency to produce engines of modern cars running on high-octane gasoline.

Determining the octane number of gasoline

You can roughly determine the octane number using a specialized device - Octane meters; it gives an error in octane numbers of 5-10 units. Therefore, simply put, there is no way to check the quality of gasoline without laboratory research.
In the laboratory, the octane number is determined in two ways:
— Motor (MON)
— Research (RON).

In the USA, the octane number is replaced by the so-called octane index, which is the arithmetic average of the octane numbers obtained by the motor and research method for this fuel. But in Japan, only the research method is used to designate gasoline brands. At our gas stations, the octane number obtained using the research method is also declared.

Using gasoline with an inappropriate octane number for the engine.

Use of low octane gasoline.
If it turns out that you filled your car with low-octane fuel, then listen to the engine. If the engine runs stably but pulls poorly, there is nothing to worry about, just burn all the low-octane gasoline and then refill with gasoline with a standard octane number. At the same time, try to avoid dynamic driving to avoid engine detonation.
But if ringing sounds are heard from the engine, which are often confused with the knocking of valves, then this means that the mixture detonates before the valves close. In fact, this blast wave spreads through the engine block and into the exhaust system. In this case, this can lead to burnout of the pistons and exhaust valves, a fact negative impact will be in stock. “Natural” detonation can sometimes be observed in cases of excessive engine load, when climbing a hill, or when driving in high gear. Long-term engine operation, even with “natural” detonation, is unacceptable, as this can lead to engine overheating and, as a result, damage to the cylinder head gasket, burnout of pistons and valves.

Use of high octane gasoline

There is no need to try to use high-octane gasoline for cars whose engines are not designed for it. The disadvantages of this application are also obvious: if the design was originally designed for low-octane gasoline and you used high-octane gasoline, this will entail a complete reconfiguration of the intake and exhaust gases and possibly the replacement of some engine components. The burning time of gasoline in this case is longer and in fact it will be necessary to adjust the piston group and inflammation in such a way that the expansion of the volume of the cylinder - piston is equal to the burning time, while the valves are closed. In fact, on a tuned engine, gasoline burns out late, and there will also be a loss of power.