Today we will talk about such a phenomenon rarely discussed by ordinary people as octane and cetane numbers in fuel. What is it compared to one another? What is the difference? Where is octane used and where is cetane used? And do I need to know this?
Octane number
Let's start with the basics, the simplest and most common indicator, octane number. It is used as a rating scale for gasoline. Octane number, as many have probably heard, is an indicator that characterizes the detonation resistance of gasoline, that is, the ability of the fuel to resist spontaneous ignition during compression .
What does this mean? Gasoline with a higher octane rating can be compressed to higher atmospheres (high pressure) without the air-fuel mixture igniting prematurely. In other words, we can draw this conclusion under one of those numbers that we usually see at gas stations: 92, 95, 98 - this is an indicator of how much you can compress the air-fuel mixture before the gasoline in it ignites.
C₈H₁₈ Octane Layout
If premature ignition of the fuel occurs, before an electric spark passes within a given period of time, we will get so-called detonation, an extremely harmful phenomenon for any engine, which engineers have long learned to deal with. As we can see, including with the help of fuel.
By the way, did you know that the scale of alkanes, which includes octanes, extends from 0, which corresponds to heptane (C₇H₁₆), to 100 units, which corresponds to octane (C₈H₁₈)? Now you know, or at least you remember. Here is a small digression into the chemical jungle of the school curriculum.
What else is high-octane gasoline useful for, besides the absence or minimal presence of the possibility of detonation? With a high compression ratio, the engine is able to develop more torque with the same amount of fuel consumed. That is, the engine becomes efficient. In this case, the engine allows you to set the phases in advance, which will give a time reserve when the piston moves to top dead center and optimally ignite the mixture.
And finally, thanks to the above advantages, high-octane fuel works better in engines with turbines and superchargers.
A few words about low-octane gasoline. All those indicators, only with a minus sign, are observed for fuel with a low octane number. This is due to the use of AI-80, 92 gasoline in relatively low-power naturally aspirated engines.
Cetane number
Cetane is used for a similar rating scale, only for diesel fuel. The flammability characteristic of diesel fuel, which determines the combustion delay period of the working mixture.
What does it mean? This is a measurement of the time interval from the moment when fuel is injected into the cylinder and when that fuel begins to burn. According to science - the period of time that passes from the injection of fuel into the cylinder until it begins to ignite .
The high cetane number of diesel fuel will be a measured indicator of how quickly the fuel ignites once injected into the cylinders. Conversely, a low cetane number means that it will take some time for the fuel to ignite.
C 16 H 34 Cetane layout
The cetane index is also measured on the hydrocarbon scale, the leftmost one of which will be 1-methylnaphthalene, (C 11 H 10) - 0 is displayed, 100 - cetane (C 16 H 34).
The advantage of accelerated combustion of diesel fuel is that the engine running on it can develop more torque, the ignition delay will be minimal, and the speed of acceleration will be higher. The synchronization of the phases by running the engine on high-cetane fuel can be carried out more accurately, igniting the air-fuel mixture at the moment when maximum torque is required.
The final advantage of a high cetane index is low emissions of hydrocarbons into the atmosphere, since such fuel burns more completely. But at the same time, studies show that more particulate matter is emitted from the exhaust pipe than diesel fuel with a low cetane rating.
Be that as it may, the higher the cetane number, the better, this is an indicator of a higher quality diesel engine.
We hope there will be no questions now.
Video taken from YouTube channel: "Engineering Explained"
Most car owners have a vague idea of what octane number is. As a rule, their knowledge is limited to the understanding that the higher this indicator, the. Alas, such an interpretation is far from the truth. And since novice drivers are taught a lot of things, but very little is not included in the training course, a little information on this topic will not hurt anyone.
The purpose of the octane number of gasoline and how to change it.
This obscure term refers to the degree of resistance of liquid fuel to detonation. In other words, what is the ignition threshold of gasoline under pressure, that is, during compression. A mixture of two hydrocarbons is taken as a standard: isooctane and n-heptane. However, methods for determining OC may vary, so there is a classification of this indicator depending on the method of determination:
- OCHI – research OC;
- OChM – motor OCH.
Since the instrumental mechanisms of these methods are not the same, there is a difference between the values of RON and NON, which is called the sensitivity of liquid fuel. Both methods are laboratory. And if we are talking about the real indicator obtained from a working power unit, we talk about the actual octane number. It is determined using a special stand with the engine running. But the closest indicator to reality is the road OC, which is measured on a moving vehicle.
Isooctane is a substance that is practically inflammable under the influence of compression force, therefore a mixture consisting only of it has a maximum possible octane number of 100. On the contrary, a mixture consisting only of n-heptane has a zero octane number. In this case, the combustion of n-heptane as a result of exposure to even minimal pressure is accompanied by characteristic knocks in the CPG, which are called detonation. This is exactly what occurs if you use fuel with an octane rating that is inappropriate for a given power unit. Metallic ringing is formed as a result of the propagation of sound waves resulting from too rapid combustion of fuel assemblies. Repeatedly reflected from the surface of the pistons/cylinders, they become clearly audible and recognizable by experienced drivers. Thus, the octane number shows how quickly the engine cylinders are pumping.
The influence of the engine rating on the characteristics of the power unit
The relationship between the combustion rate of gasoline and the OS is linear. The lower the octane number, the less time it takes to ignite the fuel assembly, which directly affects fuel consumption - if it burns faster than it should, then it enters the combustion chamber at a speed increased by the corresponding value. But this does not mean that by simply increasing the engine speed, we can save: if combustion occurs more slowly than it should, this is also bad, since the engine efficiency decreases, which leads to a loss of engine throttle response and a deterioration in dynamic characteristics. By pouring fuel with an octane rating of 92 into an engine running on 95-octane gasoline, you will get . If the situation is the opposite (instead of the working 92 we fill in the 95), the consumption will remain the same, but the engine power will decrease. So using the wrong gasoline is possible, but not advisable. It is recommended to do this only under force majeure circumstances, but not on a regular basis.
How to determine the octane number of gasoline
The NMC, according to GOST 511/82, is measured using a special installation UIT65M, consisting of the following components:
- a device that measures detonation;
- single-cylinder engine, characterized by a dynamic compression ratio and degree of detonation;
- devices designed to regulate the likelihood of detonation processes.
The measurement algorithm itself is as follows:
- the test fuel is poured into the engine and, by manipulating the compression ratio, detonation phenomena of a specific magnitude are achieved;
- They compose a reference mixture characterized by the same amount of detonation, and the OC of the original fuel is determined from the ratio of n-heptane to isooctane.
GOST 8226/82 describes the procedure for measuring OC using the research method. In this case, the operating mode of the motor is characterized by lower loads, as a result of which the ROM always turns out to be slightly higher at nominal value. If there is a need to independently measure the octane number, this can be done using commercially available instruments. An example is an octane meter, which uses a measurement method based on the dielectric constant of liquid fuel (this value varies proportionally to the octane number).
The peculiarity of the method is the creation of a calibration scale that allows one to determine the OC with acceptable accuracy. To construct such a scale, you will need a certain amount of n-heptane and gasoline with a precisely established octane number. A similar procedure can be used to determine the cetane number for diesel fuel. The possibility of using this method is based on the fact that gasoline is currently produced without using the direct distillation method, but through campauding technology, or mixing components. However, determining the octane number of gasoline using this method also has disadvantages:
- to carry out research it is necessary to have already identified fuel;
- the influence of external factors can greatly distort the measurement results;
- the method is unacceptable for measuring gasoline of different types and produced in different ways;
- each instrument must be calibrated using reference devices;
- measurements must be carried out under careful adherence to the temperature conditions given in the device specification.
All instruments that measure OC use a similar measurement principle, and therefore their advantages and disadvantages are generally identical. Note that the octane number can be greater than 100 due to the inclusion of certain additives in gasoline, but none of these devices are able to work with such liquids.
One of the most affordable octane meters is the domestic development of OKTIS, which can be purchased for approximately 3,500 rubles. The German Digatron device is more accurate and reliable, but it costs several times more, about 600 euros. Nevertheless, it is he who is considered the most in demand on the Russian market. For its operation, a reference fuel is required, which is compared with the test fuel, and on the basis of this, conclusions are drawn about the octane number of the latter. The disadvantage of this octane meter, as well as other analogues, is that for each measured gasoline from different manufacturers, a corresponding reference sample will be required, since in this case the calibration relationship between OC and dielectric constant will differ. In addition, each measurement must be accompanied by calibration procedures, which also affects the accuracy of measurements and the reliability of the results obtained.
A fairly expensive but effective Russian-made device is the OKTAN-IM octane meter (45-50 thousand rubles). Among its features is the presence of built-in memory that allows you to store up to 10 calibrations. The accuracy of the device is not satisfactory.
The PE-7300 M device is included in the same price category, and its “trick” is proprietary software that allows you to interface with a computer/laptop. The octane meter can take into account the temperature factor, which increases the accuracy of measurements (the dielectric constant has a weak dependence on the ambient temperature).
Approximately similar functionality is included in the SHATOX SX-100M device, which costs about $1,800. It is equipped with a temperature sensor and therefore measures this indicator more accurately than the PE-7300, which does this purely by software. Regardless of whether you measure 92 octane or 95 octane gasoline, if you have a reference fuel sample, the results should match the required accuracy, but within the same batch of gasoline. Other supplies, even from the same manufacturer, may require additional calibration of the instrument.
Compression ratio and RH
All possible types of gasoline are characterized by a very specific compression ratio, which is regulated by GOST. You can see the correspondence of the octane number to the compression ratio from the following table:
| Gasoline name | VERY | GOST | Compression ratio | |
| EYES | OHM | |||
| A72 | 72 | 208477 | 7.00 | |
| A76 | 76 | 208477 | 7.50 | |
| AI80 | 80 | 76 | 5110597 | 8.00 |
| AI91 | 91 | 82.5 | FS 5110597 | 9.00 |
| AI92 | 92 | 83 | TU 38001168/97 | 9.20 |
| AI93 | 93 | 85 | 208477 | 9.30 |
| AI95 | 95 | 85 | FS 5110597 | 9.50 |
| AI96 | 96 | 85 | TU 38001168/97 | 9.60 |
| AI98 | 98 | 87 | FS 5110597 | 10.00 |
Currently, you can no longer find 76/80 grade gasoline in the network of domestic gas stations. However, equipment designed specifically for these types of gasoline is still available and, as we noted above, it cannot work on gasoline with a higher octane number. So the need for low-octane gasoline remains at a fairly stable, albeit relatively low level. There is a way out of this situation - artificially reducing the octane number of gasoline to the required levels. This can also be done at home, but approximately. If, for example, you have a walk-behind tractor that was produced more than 10 years ago, you will need to lower the octane number from 95 to 80.
The easiest way is to just open . When interacting with air every day, the OC will decrease by about 0.5 units, so the procedure will take about a month. The obvious disadvantages of this method are the duration. The second, more common method is diluting gasoline with kerosene. And although it is considered the most common for cars running on low-octane gasoline, its main disadvantage is the difficulty of selecting the required proportion, that is, the accuracy of the method is very low. However, the same can be said about the first method, so in any case, you will need to measure the OC using an octane meter.
How to increase the octane number of gasoline
There are also opposite situations when only 92nd gasoline is available at a gas station, but 95/98 is required. In this case, you can try to independently increase the octane number of gasoline, for which a special substance, collectively called an anti-knock, is added to the fuel. Let's consider all the main additives used as an anti-knock agent. Ordinary ethyl (methyl) alcohol may well raise the OC by the required amount. By adding a liter of alcohol to 10 liters of 92 gasoline, you can get fuel with an octane rating of 95. Such a mixture, by the way, will be characterized by a less toxic exhaust composition, but this method also has disadvantages. One of them is considered to be an increase in the vapor pressure of the fuel assembly, which leads to an increase in the likelihood of plugging in the fuel line of the vehicle's power system. The second disadvantage of the alcohol mixture is the increase in hygroscopicity, which excludes the possibility of storing fuel for any long time in an open form due to the possibility of accumulation of a critical mass of water in gasoline.
Tetraethyl lead has physical characteristics that make it one of the most effective anti-knock agents. This includes high viscosity and a very high boiling point (about two thousand degrees). It was first used as a performance enhancing additive almost a century ago - in 1921. Allows you to increase your HP by 15-17 units. It is this substance that is most often used to increase the octane number of gasoline with your own hands. Unfortunately, tetraethyl lead also has disadvantages that limit its use. This is the formation of lead oxide during the combustion of diluted fuel. This substance forms a sediment that settles on the internal surfaces of pistons, valves and other components of the CPG.
To minimize the formation of such carbon deposits, special substances (diromethane, bromoethyl, dibromopropane) are added to tetraethyl lead, which bind lead combustion products, facilitating their removal to the outside through the exhaust tract.
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Gasoline is a flammable liquid that is colorless or has a slight yellowish tint (unless special additives are present). In order to improve the performance properties of motor fuel used by manufacturers, they 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 oil processing 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 enhanced by the high benzene content it contains, primarily affecting the environment, as it is a source of benzopyrene (a 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.
With a high degree of confidence, we can say that absolutely all car owners have heard about the octane number of gasoline, however, few of them know what this number actually represents, what it depends on, and what depends on it. This is what will be discussed in this article, but first let’s look at the phenomenon of detonation.
What is detonation and why is it harmful to the engine?
One of the main requirements for motor gasoline is its resistance to detonation. Under no circumstances should the combustible mixture in the cylinder ignite until it is ignited by a spark from the spark plug electrodes. In the event of self-ignition of the fuel mixture under the influence of high pressure, a detonation effect will inevitably occur in the cylinder - explosive combustion of the fuel, accompanied by a corresponding sound.
This phenomenon has a detrimental and sometimes even destructive effect on the parts of the piston group. The fact is that the speed of complete combustion of the fuel mixture in the cylinder, provided it is ignited by a spark, is 15-60 m/s, and when a detonation effect occurs, it burns at a speed of 2000-2500 m/s. And this is no longer combustion, but a real explosion, repeating with each cycle, causing resonance. The harmful effects of the latter lead to the destruction of the piston itself, piston pin, connecting rod and other engine parts.
Fortunately, modern cars are equipped with knock sensors that are able to detect its slightest signs and transmit the corresponding signal to the engine electronic control unit (ECU), which, in turn, either reduces the amount of fuel in the mixture or adjusts the ignition timing. However, the ECU cannot always cope with such a problem, especially if the tank contains low-quality gasoline or does not meet the engine requirements.
The concept of octane number
Each driver, refueling his car at a gas station, orders the operator the required amount of fuel, indicating its usual name (80, 92, 95, 98). In fact, this is not a name, not a brand, not a degree of flammability, and not even a measure of detonation, as some “experts” explain. The numbers in the name of gasoline indicate its octane number, which determines its resistance to detonation. It determines the percentage of the mixture of isooctane and n-heptane in gasoline. Why these particular substances? It's simple. The fact is that isooctane is practically non-explosive, which is why it cannot be detonated, and its detonation resistance is 100. In turn, n-heptane explodes at the slightest increase in pressure, so its resistance to detonation processes is equal to zero.
By mixing these substances in the required proportions and adding them to the fuel, we have the opportunity to regulate its octane number, thereby adapting gasoline for different engines.
How is octane number determined?
There are two generally accepted ways to calculate octane number: research and motor. The first method involves testing gasoline for its resistance to detonation processes under moderate load on the power unit. Tests are carried out on a special stand using a single-cylinder gasoline engine at variable load, speed 600 rpm, air temperature in the fuel mixture +52 0 C and ignition timing equal to 13 0. The engine first runs on the test fuel until detonation occurs. After fixing it, the engine at the same load is switched to reference fuel from a mixture of isooctane and n-heptane in different concentrations. Having recorded the moment of occurrence of the detonation effect, the tests are stopped. The amount of isooctane in gasoline at which the detonation process began is the so-called research octane number. And if the letter “I” (AI) is present in the gasoline labeling, this means that it was determined by the research method described above.
The motor method involves determining the resistance of fuel to detonation phenomena under real driving conditions at increased engine load (900 rpm at a fuel mixture temperature of +149 0 C and a variable ignition timing). The process for determining the octane number is similar to that described above.
There is another method for determining the octane number. Its essence is to measure the amount of isooctane with a special device - a digital octane meter. It is quite simple and easy to use. The principle of operation of the octane meter is to compare the composition of the gasoline under study with reference fuel samples, and is based on its dielectric properties. This method has not yet been certified in Russia, so the octane meter cannot be an official tool for conducting research.
The value of the octane number with different methods for determining it may differ slightly. Below is a table of the main brands of gasoline indicating their octane number
How does using gasoline with a high or low octane number affect engine performance?
For each make and model of car, the manufacturer provides gasoline with a certain octane number. You can find it out in the car's owner's manual. But what happens if you don’t follow the recommendations?
The use of fuel with a lower octane number, as we already know, leads to detonation. In addition, consumption increases, engine power decreases, and with prolonged load on it, valves may burn out, engine overheating, and failure of piston group parts. When using gasoline with a high octane number, nothing bad will happen, except that the dynamics will decrease slightly due to the longer combustion time of the combustible mixture.
Below is a table from which you can find out which fuel is best suited for engines with different compression ratios.
How to increase octane number
Until recently, fuel manufacturers used tetraethyl lead, a substance with high anti-knock characteristics, to increase its resistance to detonation. But, since it also turned out to be super-toxic, and also quickly damaged catalysts and oxygen sensors in the exhaust system, an alternative was quickly found.
Today, to increase the octane number, various aromatic (have a high octane number) and paraffinic hydrocarbons (have the lowest octane number), called boosters, are used. Many of them have high volatility levels, which often leads to the fact that the gasoline to which they were added can quickly change from 95 to, for example, 92 or 80 if the container is not sealed.
You can increase the octane number yourself. To do this, you need to purchase one of the additives and add it to the fuel. One such agent is methyl tert-butyl ether. This additive is considered practically harmless to the environment and engine elements, which cannot be said about ferrocene, which contains ordinary iron, which deposits a durable reddish coating on the electrodes of the spark plugs.
Most even new drivers regularly hear about gasoline octane numbers, but not everyone knows what they are for and what they indicate. In order to correctly install one or another filling hose, on which some conventional numbers that are not clear to everyone are indicated, it is necessary to understand the purpose of the octane number and what it affects.
The octane number of gasoline serves as direct evidence of a certain detonation point, reaching which the fuel begins to burn and explode, all this happens in the combustion chamber of every car. The fact is that too early and rapid combustion of the fuel, which began before the intake valves are closed, does not allow the fuel to reach its last mark; due to this circumstance, the power unit is forced to function at half capacity, the lack of full output and incorrect performance directly affect the poor performance of the entire vehicle.
An octane number that is too low will eventually require huge financial investments from the driver; most likely, long-term use of the substance will negatively affect almost all parts of the engine. The valves that are subject to early wear will be the first to suffer, then the seats. Eventually the entire device will become covered in additional carbon deposits. Another “surprise” that low-octane fuel that is not suitable for a specific engine is capable of is additional detonation, which is confused with a knock that occurs in the valves.
More precisely, their mixing determines the octane number. A mixture of substances such as isooctane and n-heptane can regulate the octane number. For example, isooctane is an absolutely non-explosive substance; even with a significant increase in pressure, it has a certain detonation resistance of 100 units. As for n-heptane, this kind of product, on the contrary, is resistant to detonation (it is self-detonating), it has a detonation resistance of 0. In addition to the previous substances, trimethylpentane is present in gasoline, only the octane number is practically not subject to it. A consumer can purchase gasoline with an octane number of more than 100 units; this type of substance contains isooctane, to which a lot of various additives are added.
The most common additives that increase octane number
Recently, chemists have been constantly working to create various types of additives that can maximize the octane number of gasoline. The increase is achieved by adding various aromatic and paraffin hydrocarbons to the main composition of gasoline; all such substances are alkanes with a branched structure. After adding such components, naturally, the octane number increases by several steps, but the acquired odor is several times more unpleasant than low-octane gasoline. Another disadvantage of gasoline equipped with additives is its volatility. When an open canister or container is exposed to the environment, the octane number of gasoline decreases, which is why it is better to use this kind of gasoline while it is “fresh.”
During the Soviet era, in order to significantly increase the octane number, tetraethyl lead was added to the fuel; such a substance was a toxic mixture, one of the components of which was lead. Despite the excellent effectiveness that tetraethyl lead has shown in practice, its toxic properties, coupled with the rapid destruction of catalytic converters and lambda probes, ubiquitous in almost all modern cars, over time forced scientists to abandon its active use. This additive was subsequently replaced by products based on manganese, although now they are also banned due to various environmental considerations.
A substance called ferrocene is quite common among “advanced” car enthusiasts. This kind of modern additive contains a large amount of iron, due to which, after prolonged use, a difficult-to-remove coating appears on the candles, which has excellent conductivity; you can notice it by its bright reddish tint. This deposit negatively affects the performance of the vehicle, while simultaneously reducing the performance and service life of the spark plugs.
In which an increase in octane number is achieved by adding other additives. The impurities used are capable of performing a wide range of different tasks, along with reducing various types of harmful impurities from the fuel (sulfur and water), they are able to clean the parts of the power unit and the entire fuel system. The most harmless additive for engine components today is an anti-knock additive called methyl tert-butyl ether. Recently, this particular additive has become widespread not only in Russia, but also in Ukraine and Europe. Through a high-quality admixture, the car owner can obtain high-quality fuel; such gasoline will have an octane number of 110 units. It is worth noting that this is a type of aviation fuel. Gas condensate is added to gasoline; its octane number always exceeds 100 units.
Combustion of gasoline with different octane levels
So, it was discussed a little higher that the octane number directly affects the burning rate of the fuel, or rather, its explosion. The high octane number of gasoline allows the fuel to burn longer. In this regard, the gas appearing in the combustion chamber does not allow the transfer of enormous loads to the pistons, which usually “come” with shocks and excessive resonant detonation. Using high-quality gasoline with a high octane rating, the car owner ensures uniform and smooth operation of his engine. The direction of the modern automobile industry is such that there are models of power units that run only on gasoline with a high octane number.
Determination of octane number
To correctly determine the octane number of fuel, you need to have a small device called an octane meter. Using such a simple unit, you can calculate the approximate octane number of fuel with an error of only 5–10 units. However, it is best to check the quality of gasoline using specialized laboratory tests.
Having the opportunity to find out the octane number in laboratory conditions, you should resort to one of two possible methods:
- MON, i.e. motor;
- RON, i.e. research.
US scientists, for example, in order to determine the octane number, or rather its index, compile the arithmetic average of all octane numbers of the same gasoline previously obtained by the motor and research method. The Japanese use an exclusively research method by which they designate fuel grades. In Russia, all gas stations also indicate octane numbers obtained only through a research method.
What are the consequences of using low-octane gasoline for the power unit?
The car owner does not always have the opportunity and means to buy only high-quality fuel. If it happens that you have to refuel your “steel horse” with fuel with an inappropriate octane number, you will have to periodically listen to the operation of the power unit. Stable operation of the engine, which begins to pull somewhat worse, requires the owner to simply gradually consume all the low-octane gasoline and further refuel the car with fuel with a standard octane number. You should try to avoid dynamic driving, which causes detonation in the engine.
If the power unit responds with unusual ringing sounds (not to be confused with the knocking of valves), most likely, the fuel mixture detonates before all the valves are completely closed. The fact is that the blast wave occurring in the combustion chamber additionally “covers” the power unit unit and the exhaust system. These kinds of sounds may indicate that all pistons and exhaust valves are about to burn out. The culprit will be the use of low-octane gasoline.
Arbitrary detonation can occur even when the car owner uses high-quality fuel; this happens in cases where the power unit is subjected to excessive loads, during sharp climbs uphill or when driving in high gears. It should be remembered that even such “natural” detonation is harmful to the engine; it is unacceptable to subject it to prolonged overloads, otherwise overheating of the power unit is inevitable, which will result in immediate damage to the cylinder head gasket or significant burnout of pistons and valves.
Conclusion
Despite the many advantages that high-quality high-octane gasoline allows you to get, not all cars can be filled with it. Some power units are simply not designed to use this type of fuel. The fact is that the design of the car, originally created for the use of low-octane fuel, is absolutely not suitable for the use of high-octane gasoline, the use of which can entail a complete reconfiguration of both all intake and exhaust gases. Along with this, you will even need to replace the motor components. Due to the longer burning time of the fuel, it will be necessary to rebuild the piston group; the expansion of the volume of the cylinder - piston should coincide in time with the burning time of gasoline, and everything should happen when the valves are completely closed. Instead of benefit, the car owner will receive a significant loss of power, therefore he will have to lower the octane number of gasoline.
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