This means the octane number. Gasoline octane number: what is it?

What is the octane number of gasoline and what depends on it? This question was asked by almost every motorist who refueled 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.

What happens if the octane number of the gasoline being poured is very different from that provided by the design?

If gasoline ignites earlier than necessary, while the intake valves, and the cylinder is not at the top point, it is natural that not much useful power will remain from this explosion. She'll just go down the drain! The engine will run at full power, detonation, “sneezing”, etc. will appear. and so on. With such a low octane number of gasoline, we will get a lot of problems. And it's not just a loss of power. Here there is wear on the valves and seats under them and additional carbon deposits... In addition, the discrepancy octane number for the engine, entails that additional unplanned detonation, which can be confused with valve knocking. But it’s not about them at all!
The same can be said about the case when the octane number is too high. The explosion in the combustion chamber will occur late, that is, when the valves have already opened. Hence all the same problems, but from the mirror side, that is, not before the valves closed, but after they had already opened...

Modern engines have automated systems power management, the so-called ECU. which constantly monitor the ratio of fuel and air in the combustion chamber, detonation, rotation speed, the period of ignition of the mixture with spark plugs, and the time of fuel injection into the chamber. All this allows you to somewhat adjust the “correctness” of the operation, which means using gasoline with a certain spread in octane number. That is, if a car is supplied with 95 gasoline, then it will probably run well on 92, but the use of 80 gasoline will clearly affect the operation of the engine. With such a wide range of adjustments to all engine operating characteristics, the ECU simply cannot cope.

How is the octane number of gasoline determined during production?

The octane number is obtained by shifting the balance of gasoline components. By and large there are two of them. This is isooctane and n-heptane, the rest is not so significant, at least for the octane number of gasoline. Isooctane is a substance that is almost non-explosive. It reacts little to increased pressure and temperature, up to a certain limit. As a result, its detonation resistance was taken to be 100 conventional units. At the same time, n-heptane is not at all resistant to detonation with a slight increase in pressure. We can say that it has self-detonation, so its detonation resistance is taken as 0 conventional units. It is the mixture of these components that allows you to regulate the octane number in gasoline, obtaining gasoline with different octane numbers: 80, 92, 95.98. In fact, there is gasoline with an octane number of more than 100 units. In this case, only isooctane is used, with the addition of various amounts of additives. It is about additives that increase the octane number of gasoline that we will talk about next.

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), that is, in layman’s terms, high-octane gasoline smells stronger than low-octane gasoline. There are also certain disadvantages to this, since high-octane gasoline is more volatile due to the inclusion of aromatic components. Which, if stored for a long time in an open container or with a certain connection between the container and the external environment, will lead to a decrease in the octane number of gasoline. Therefore, we can say that high-octane gasoline must be “fresh”. Previously, in the USSR, tetraethyl lead was used to increase the octane number - a toxic mixture containing lead. Unfortunately, tetraethyl lead is not only poisonous in itself, but also quickly disables catalytic converters and lambda probes, which began to be used in the design of modern cars. As a result, I had to abandon this additive completely. Manganese-based additives were also used, but these are now also prohibited for environmental reasons. In addition, an additive, ferrocene, is sometimes used to increase the octane number. This additive (ferrocene) contains iron and creates a difficult-to-remove conductive coating on the spark plugs (a red tint), which worsens performance characteristics, (you can see about them in the “Spark Plugs” section) and, accordingly, reduces the service life of the spark plugs. Gasolines also contain other additives and impurities. Additives in gasoline perform various tasks. Reduce the amount of harmful impurities in gasoline - sulfur, water. Also clean engine parts or fuel system. A relatively harmless anti-knock additive for the engine is methyl tert-butyl ether. Currently, it is most widely used in Ukraine, Russia and Europe.
It is quite possible to obtain gasoline with an octane number of more than 110 (these are aviation fuels, but again with lead additives, which again is unacceptable for modern systems car engine control). In addition, there is a well-known scheme with mixing gasoline and gas condensate. In this case, it is also possible to “raise” the octane number. After all, the octane number of natural gas is usually above 100 units.

Combustion of gasoline at different octane numbers

The rate of combustion of gasoline, that is, in fact, the time of the explosion, also depends on the octane number. At high octane numbers of gasoline, gasoline burns longer and smoother. At the same time, accordingly, explosive gases do not cause shock loads and unnecessary resonant detonations on the pistons. The engine runs more evenly, smoothly and clearly. Therefore, the automotive industry has a tendency to produce modern car engines running on high-octane gasoline. In this case, with a normally tuned engine and the proper octane number of gasoline, detonation will be minimal.

Determining the octane number of gasoline

The octane number can be determined with a specialized device - an octane meter. 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 tests. In the laboratory, octane number is determined in two ways:

Motor (MON). More information about this method of determining the octane number can be found in the article “Motor method for determining the octane number of gasoline”;
- research (RON).

After research, the following indicators are obtained, summarized in the table below

Research Motor Octane Index Tradename
method method
A-80 A-76 78 Standard
AI-91 A-82.4 86.7 Regular
AI-92 A-83 87.5 Regular
AI-95 A-85 89 Regular
AI-93 A-87 91 Premium
AI-98 A-89 93.5 Super

In the USA, the octane number is replaced by the so-called octane index, which is the arithmetic mean component of the octane numbers obtained using the motor and research method for of 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.

Use of 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 and overloads.
If ringing sounds are heard from the engine, which are often confused with valve knocking, then 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, it can lead to burnout of the pistons and exhaust valves. Of course, maybe not in the case of burning one tank of fuel, but the fact of the negative impact will be obvious. “Natural” detonation can sometimes be observed in cases of excessive engine load, when climbing a hill, or when driving in high gear. Prolonged operation of the engine, 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 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 explosion time for gasoline, in this case, will be slightly delayed, that is, at the wrong time. In fact, the valves and ignition will need to be adjusted. On an untuned engine, high-octane gasoline will burn late, resulting in a loss of power.

Gasoline is a flammable liquid that is colorless or has a slight yellowish tint (unless special additives are present). In order to improve performance properties motor fuel used in manufacturers are trying to increase the octane number of gasoline. To do this, appropriate components are added to it. If, during fuel combustion, a characteristic metallic sound is heard, created by the detonation wave when it is repeatedly reflected from the cylinder walls, then the engine efficiency decreases, in addition, its wear accelerates.

In this case, they say that the quality of the fuel is unsatisfactory, since the octane number is low. The detonation resistance of motor fuel, that is, the ability to resist self-ignition due to compression in the cylinders of a running engine, characterizes this indicator. Numerically, it is equal to the volume fraction of isooctane (its other name: 2,2,4-trimethylpentane) in a two-component mixture also containing 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 a saturated hydrocarbon of C8H18 isostructure. Due to its properties, it is difficult to oxidize even at high temperatures; therefore, its detonation resistance was conventionally taken to be 100 units. N-heptane behaves differently in an engine: even at low compression ratios, its combustion process is accompanied by a detonation effect, so the value of this indicator for it is taken as 0 units. In cases where the octane number of gasoline is above 100 units, a conventional 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 indicator is the most significant characteristic of motor fuel. It shows how resistant gasoline is to detonation, that is, to spontaneous fire in the engine cylinders. The likelihood of a fuel explosion in the internal combustion engine will be minimized if this indicator is high. If gasoline corresponds to 95 units, then it detonates as a mixture consisting of 95% 2,2,4-trimethylpentane and 5% normal heptane. After primary processing of oil 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 is used (mixing with high-octane products), but also anti-knock agents are introduced in amounts of up to 0.3%.

The quality of the fuel depends largely on the composition of the natural resource from which it is obtained by fractionation or distillation - oil. Important indicators for it are viscosity, fractional composition, the presence of sulfur compounds and paraffins, as well as the water content and salts dissolved in it. However, the listed factors rather influence the features of processing and the choice of technology. The quality of gasoline, that is, the value of its octane number, is determined by the hydrocarbon and then by the method of its processing, which also determines how much isooctane, n-heptane, aromatic compounds, and so on will be in gasoline.

The anti-knock properties of gasoline are increased by the content of benzene it contains, primarily affecting the condition environment, as it is a source of benzopyrene (carcinogen). An increased content of high-boiling aromatic compounds contributes to increased carbon formation in the combustion chamber and on engine valves. All this worsens performance indicators such as engine power, efficiency, environmental and economic aspects of its operation. The carbon deposits formed in the combustion chamber forces the car owner to choose motor fuel in such a way that the octane number of gasoline is high. Otherwise, the power is significantly reduced or the engine runs with detonation.

When a driver stops at a gas station, he usually does not think about what the number “92”, “95” or “98” means in the designation of fuel grades. He just buys the fuel he needs and leaves. But the octane number is the most important indicator for gasoline. Therefore, any driver should know what it is.

This is the ability of gasoline to ignite under high pressure (that is, under strong compression). The higher this number, the greater the pressure the fuel will withstand without detonation in the engine.

How is octane number measured?

There are two methods - exploratory and motor. In both cases, the same installation UIT-65 or UIT-86 is used, which is a single-cylinder engine with a variable speed crankshaft in a minute:

• When tested using the research method, the revolutions were set at 600. The resulting figure characterizes engine operation at light loads. It is this that is indicated as a designation of the type of gasoline;
• when testing using the motor method, the same installation already operates at 900 rpm.

The result shows how the engine behaves when driving downhill and when accelerating sharply.

The octane number according to the research method is always higher than that according to the motor method. The maximum research octane number of gasoline available for sale is 102. This fuel is used in racing car engines. At regular gas stations, the maximum is 98-grade gasoline, but this is not found everywhere.

In addition, there is also a compact household device, the octane meter OKTIS-2, priced at about 4,500 rubles. How is the octane number determined using it? There are two ways - put the device on the gun directly at the gas station or immerse it in a container of gasoline. As tests by experts from the magazine “Behind the Wheel” have shown, OKTIS-2 gives a small error relative to laboratory tests, but is too sensitive to the chemical composition of the fuel and the technology for its production.

How to increase octane number

At oil refineries, various additives are added to the feedstock. Tetraethyl lead used to be popular, but now it is banned almost all over the world due to its extreme toxicity (it can quickly lead to disability and even death). Ferrocenes and manganese “kill” the engine and exhaust system. One of the most common additives currently approved is MTBE (methyl tertbulyl ether).

But how do you increase the octane number of fuel in “domestic” conditions? The principle is similar. On car markets and store shelves you can find a huge number of bottles (250-300 ml) with loud names like “super octane corrector”, “octane booster” or “motor fuel booster”. They are produced under many brands, including those well-known in Russia and the near abroad (for example, Astrokhim) or even all over the world (Liqui Moly, Castrol, Hi-Gear, Runway). In fact, the main element in the composition of such liquids is alcohol. It contains up to 90%. There is nothing wrong with this, since alcohol is one of the most popular anti-knock substances and in moderate concentration (up to 15%) does not require engine retuning. The remaining 10% of the composition is, as a rule, various types of hydrocarbons that are safe for the engine.

However, it should be understood that if you pour a “miracle bottle” into the tank (even if you completely follow the instructions), then it is impossible to get, for example, 95 gasoline from 92 gasoline.

An "octane corrector" can be useful in an emergency situation - if the driver refueled with low-quality fuel and heard detonation. Then a bottle of such “chemicals” will help you get to a gas station with good gasoline.

Decrease in octane number

This problem is relevant, first of all, for owners of old cars. There are practically no 76 and even 80 gasoline on sale now (at least at network gas stations), and 92 is no longer suitable.

Some car enthusiasts try to add kerosene or diesel fuel(which can have a detrimental effect on the engine), others put up with it and still use the AI-92. But there is no really effective and safe way to reduce the octane number at home.

If gasoline is “not like that”

If the octane number is too low (for example, if you fill in 80 gasoline instead of 92), detonation will occur.. The normal combustion speed of gasoline for engine operation is from 15 to 60 m/s. When they say that fuel detonates, it means that it does not burn, but explodes, and much faster than expected, namely at a speed of 2000-2500 m/s. This creates a blast wave that is reflected from the walls of the engine cylinders. People around hear loud and unpleasant claps. At the same time, engine wear increases many times over.

If, on the contrary, the driver “overdid it” and poured gasoline with an octane number higher than required, then such gasoline will burn longer than it should, giving off more heat. The engine will overheat. This has a particularly serious effect on valves, which can burn out within 10-20 thousand kilometers. Since the engine will run smoother and quieter, the driver may think that such a replacement of gasoline is even beneficial. Not really.

Conclusion

Not all drivers know what the octane number of gasoline is. The main thing to remember is that you should refuel with gasoline with exactly the octane number specified by the car manufacturer, since the engine is designed for it. And - not a step aside.

It does not ignite when compressed, the more you can compress it. In other words, if more energy needs to be squeezed out of the fuel, then the fuel-air mixture in the combustion chamber needs to be compressed more strongly, and this can cause it to spontaneously ignite explosively.

Therefore, for engines with a high compression ratio, gasoline is used that can withstand high compression without exploding. This is achieved by introducing special additives into gasoline at oil refineries.

How does the octane number of fuel affect its consumption?
For example, let's take a conventional engine of one conventional modern car. The degree of fuel compression in a given engine does not depend on the type of fuel used; it is a characteristic that is associated only with geometric parameters. Fuel consumption can only be affected by the energy of the fuel released during its combustion. Are there any differences in the combustion energy of 95 octane gasoline from the combustion energy of 92 octane gasoline? The accepted specific heat of combustion of gasoline ranges from 42 to 44 mJ/kg. Even if we assume that 42 mJ/kg refers to 92-grade gasoline, and 44 mJ/kg for 95-grade gasoline, then even a 10% increase in power will still not work.

For our conditional engine, the difference between gasolines is as follows: if the compression ratio of the engine is 6 - 8:1, then an octane number of 76-80 will be sufficient for its fuel - there will be no detonation in the cylinders, but if the same gasoline with an octane number 80 is poured into our conditional engine, the compression ratio of which is 8 - 9: 1, then such gasoline will begin to detonate (self-ignite in an explosive manner) before the spark plug ignites it, and the engine will not receive any benefit from this. At normal operation engine, the gasoline inside the cylinder should not explode, it should burn “gently”. If you pour gasoline with an octane rating of 98 into this engine, it will not detonate exactly, but instead, after ignition, it will burn more slowly, because it is designed for a higher compression ratio and therefore will not completely burn in the combustion chamber. By the way, this used to cause valves to burn out on old cars. In modern engines, fortunately, there are “brains” that allow it to decide independently at what moment to ignite the fuel in the cylinder, therefore modern cars in both cases, the fuel will be ignited earlier than if “native” 92-95 gasoline was used as fuel.

If gasoline with a low octane number is used, this causes it to burn too early, consumption increases, and the engine is frankly “stupid.” In the case of using gasoline with a higher octane number, due to the increased combustion time of the fuel, the efficiency of the engine simply decreases with a loss of its power, while consumption does not increase critically.
Answering the question about the influence of the octane number on consumption, we can say this: if the octane number is lower than the calculated one, then the consumption will increase, but if it is higher, then at least it will not decrease. If the engine is designed for 95 gasoline, then when running on 92 gasoline, its consumption will increase. If you pour 95-grade gasoline into an engine designed for 92-grade gasoline, there will be no advantages.
Some automakers resort to marketing ploys to attract buyers by declaring a lower octane number in the requirements for the fuel used. Therefore, in order to have an idea whether it makes sense to fill in more expensive gasoline, you should pay attention to the compression ratio of the engine.

Determination of the octane number of gasoline.
You can determine the approximate octane number of gasoline using a specialized device - an octane meter, which has an error of 5-10 units. Simply put, it is not possible to check the quality of gasoline without laboratory testing.
In laboratory conditions, there are two methods for determining the octane number - research and motor. With the research method, the fuel is examined in relation to the reference one. The motor method uses a special single-cylinder internal combustion engine with a special cylinder head design, which allows the engine to change the compression ratio.

In the USA, the concept of octane number has been replaced by the so-called octane index, which is the arithmetic average component of octane numbers, which were obtained using the research and motor method for a given type of fuel. In Japan, only the research method is used to designate the brand of gasoline. It is the research method that is used when declaring the octane number of gasoline at our gas stations.

Let's start with the basics

Octane number is an important indicator of gasoline quality, characterizing its anti-knock resistance. Detonation is a spontaneous, independent of the spark on the spark plug, ignition of the working mixture in the cylinder under the influence of temperature and pressure, accompanied by abnormally rapid combustion. Insignificant and short-term detonation, which usually occurs with a sharp increase in load, does not pose a particular threat, although it is manifested by unpleasant knocks and a characteristic “clattering” sound, which experienced motorists call “ringing of fingers.”

Under heavy load, detonation can be stronger and more destructive. The resulting knocking noises can be “masked” by the general noise of the engine. Prolonged detonation is extremely dangerous. It can destroy an engine in a matter of hours (or even minutes).

In pursuit of additional power, engine builders throughout the last century followed the simplest path - increasing the compression ratio (i.e., the ratio of cylinder volumes when the piston is at the bottom and top dead centers). More high pressure compressed working mixture provoked detonation. Gasoline with an increasingly higher octane number was required. If in the thirties of the last century greatest achievement They considered gasoline with an octane number of 76, but now it’s not surprising that it’s 100.

The octane number of the fuel is determined on a special single-cylinder engine by comparison with a mixture of isooctane (an isomer of 2, 2, 4-trimethylpeptane octane) and η-heptane. An octane number of gasoline equal to, for example, 92 means that its knock resistance corresponds to the resistance of a mixture of 92 parts isooctane and 8 - η-heptane. Although both substances are usually included in gasoline, the octane number does not mean that gasoline consists only of them. This is a much more complex “cocktail”, the exact recipe of which is often not known even to its manufacturers themselves. When the American Russell Marker of the Ethyl Corporation developed a method for determining octane number in 1926, he chose η-heptane as a zero standard for only one reason: a specific isomer of a high-purity hydrocarbon compound cannot be obtained from petroleum, but η-heptane can be produced from pine resin .

If everything is clear in principle with the octane number, let’s begin to confuse everything. Octane numbers (and there are at least two of them) are not the only units for measuring anti-knock resistance. Even on the same engine stand, two indicators are determined using two different methods.

The ASTM Research Method gives us the Research Octane Number, or more correctly the Research Octane Number (RON). Remember the letter “and” in the labeling of our old gasolines?

During the test, a single-cylinder engine with a forced variable compression ratio is operated under controlled conditions with a minimum load.

To determine the octane number using the motor method (MOC), the working mixture supplied to the same engine is preheated, the crankshaft speed is increased, and the ignition timing adjustments are changed. Thus, gasoline is subjected to a more stringent test that is closer to real use. Typically, the RON of a fuel is 8–10 units higher than its RON. This ratio is worth remembering; it can be useful for practical calculations.

There is no general, standard method for indicating the knock resistance of gasoline in the world. In Europe and Australia, the research method is used. In our country, until recently, both were in use, as evidenced by the mentioned letter “and” (or its absence -
evidence of the use of the motor method). In New Zealand, Australia's neighbor, more urinary tract surgeries are performed. Even a study was conducted about reducing its minimum from 82 to 81 units. But North America is going its own way. They use completely different names, fortunately denoting the same parameter. The anti-knock coefficient used here is AKI - Anti-Knock Index, road octane number RdON - Road Octane Number (not to be confused with RON - Research ON - 0H according to the research method), pump octane number PON - Pump Octane Number or simply (R+M) /2. The last designation explains the essence of all the previous ones. In the USA and Canada, the arithmetic mean of okatn numbers obtained using two different methods is indicated, that is
AKI=IOC+URO/2. AKI is 4–5 units less than IOC
(RON). These numbers may also come in handy.

Little excursion

If all of the above is clear to you, you will have to complicate the situation. Very often, fuel sellers indicate the type of gasoline instead of the octane number. At the same time, in different countries The same words hide different numbers. Moreover, there is no uniformity even in the individual states that make up the United States.

Let's start from the original stove. We already supply A-92 gasoline as Regular, A-95 as Premium and A-98 as Super. The A-76, disguised as an A-80, has not yet disappeared, but a quick ban left the “old man” without a name. Data for some other countries are shown in the summary table. Let's comment on it right away.

The mountain states of the United States are no different from other mountainous regions of the world. The altitude here is higher and the air is thinner. No matter how hard you try, without supercharging, the pressure in the cylinder both at the beginning of the compression stroke and at the end of it will be lower than on the plain. Consequently, gasoline here may also have reduced resistance to detonation. Remember this when planning to descend from the mountains for a long time. The slightly lower requirements for OC in California can be explained simply: it is necessary to push residents of the richest state to buy the “hundredth” that is available in abundance. Ferrari and Porsche will say thank you. And oil traders too. In a number of European countries, the 95 has long been considered “standard” or “regular”. They don't make things worse.

But in some third world countries complications are possible with Regular and Standard: they may be similar to our A-76 (80). In addition to being educational, the information presented here also has practical significance. Knowing the country of origin of the purchased foreign car, its owner will be able to determine what kind of gasoline should be fed to his steel horse. After all, the vast majority of cars, except for sports, executive and tuning ones, as a rule, are content with the Regular/Standard grade without indicating the real octane number in the manual. These numbers are also useful for servicemen, as they help determine how to eliminate, for example, the “dullness” of the machine. Just switch to gasoline with high O4 or change the expensive engine control unit. By the way, especially for mechanics, we note that those who suffer more from severe detonation (and from severe detonation) carburetor engines. Injection engines usually have a detonation sensor in the form of a miniature piezoelectric microphone, based on the signal from which the electronic brains delay ignition, reducing detonation. The engine suffers less, the car owner suffers more. Due to worsening dynamics and rising fuel costs.

Let's get back to the topic

What does all this confusion have to do with our colleague's car? His Mitsubishi came to us from the States. Let's look at the table. Both as a “Japanese” and as an “American” the car should rejoice at our 92nd. And switching to 95 will not add any dynamics or efficiency to it.

Most likely, our colleague was unconsciously wishful thinking. He should install on-board computer or at least refuel at the same pump for a week or two, regularly recording consumption and mileage data. Then repeat the measurements on a different type of fuel. However, taking into account city traffic jams, the result will still be very approximate.

If the savings are confirmed, there are several possible ways for them to occur.

The first and simplest. Due to the summation of tolerances and other technological reasons, a certain part of the machines has characteristics that differ from the passport ones. And this must be taken for granted.

Second, less optimistic. Over the years of operation, soot and other deposits have accumulated in the combustion chamber, its volume has decreased, and the compression ratio has, accordingly, increased. This is what “adapted” the engine for gasoline with a higher octane number. It can be treated by regularly adding anti-carbon additives to gasoline plus prolonged driving at high speed. An alternative to the additive would be to use Shell V-Power “cleaning” gasoline, but you will have to pay for the lack of extra hassle. If “chemistry” does not help, then “mechanics” remains. However, it is better not to disassemble the engine without more compelling reasons. If chemistry helps, most likely the engine will have to be adjusted.

Third, the most difficult. The engine management system, ignition, and exhaust gas recirculation system are faulty. Replacing the control unit is not difficult, but very expensive. It’s worth consulting a good diagnostician if you can find one. As well as a catalytic converter specialist.

A little more theory

Numerous studies from around the world confirm that switching to gasoline with a higher octane number at a constant compression ratio does not provide any benefits, but only increases fuel costs. The calorific value, and therefore the stored energy, of different types of fuel is approximately the same. High-octane gasoline produces the same amount of energy as standard gasoline, but burns more slowly. As a result, the fuel that has not had time to burn can be thrown into the muffler (death to the catalyst) and further into the atmosphere (death to the living).

Moreover, according to the Gas Bank USA website, car manufacturers (BMW, Porsche, Mercedes-Benz, etc.), even when recommending high-octane gasoline, allow the use of standard gasoline without a threat to the engine, but with some deterioration in the vehicle’s parameters.

The magnitude of this deterioration can be judged from the data published by Hyundai Motor. Premium gasoline 4.6-liter V8 engine Genesis sedan produces a maximum power of 375 hp. s., and on the standard one (AKI-87) - 386, i.e. less than 2% less.

The American Smart Fortwo owner's manual contains the same warning as for Mercedes vehicles: "To ensure long-term reliable operation and excellent engine performance, use Premium Unleaded gasoline." And the bottom line: “Regular gasoline will not harm your car.”

We do not advocate switching to low-octane gasoline. But if your car is designed for it, is there any point in paying extra money? With the same chemical composition, equal energy intensity and the use/non-use of additives independent of the octane number, the only difference between types of gasoline is the amount of profit received by the fuel seller.

Useful formulas

When determining what gasoline your car needs, it is useful to know that:
AKI = RON+MON/2;
RON - MON ≈ 8–10;
RON - AKI ≈ 4–5;
AKI 87usa= RON 92eu;
AKI 90 ≈ RON 95;
Where:
AKI - Anti-Knock Index - anti-knock coefficient (USA);
RON - Research Octane Number - research octane number (RON);
MON - Motor Oil Number - motor octane number (MON).