OCTANE NUMBER- a measure of the knock resistance of gasoline and motor oils.
A huge amount of gasoline is produced and consumed all over the world - as automotive fuel. In order for gasoline to burn in the cylinders of a car “correctly”, it must have a number of properties. One of the most important is the octane number. It is it that is written on all gas stations, and the quality and price of gasoline depends on it. When out exhaust pipe throws black smoke, and the engine makes sharp sounds, this means that gasoline in the cylinders, instead of burning at its prescribed speed of 15-60 m / s, begins to explode - detonate at a speed of 2000-2500 m / s ( cm. EXPLOSIVES). The detonation wave is repeatedly reflected from the walls of the cylinder, creating unpleasant sound, sharply reducing engine power and accelerating its wear.
The cause of detonation is the release of energy with an increased formation of ROOH hydroperoxides in gasoline vapors during their oxidation with atmospheric oxygen ( cm. PEROXIDES). If the concentration of hydroperoxides exceeds a certain limit, their explosive decomposition will occur. The explosion of peroxides proceeds by the mechanism of branched chain reactions ( cm. CHAIN REACTIONS). There are two ways to increase knock resistance. The first is to increase the proportion of branched and aromatic compounds in the composition of gasoline. The second is to introduce small amounts of special additives into the fuel. Usually both ways are used.
To determine the anti-knock properties of the resulting mixture, a special scale was proposed in the 1930s, according to which the knock resistance of a given gasoline is compared with the resistance of standard mixtures. Two substances were chosen as standards: normal heptane and one of the octane isomers, 2,2,4-trimethylpentane (it is called "isooctane"). A mixture of heptane vapor with air under strong compression easily detonates, so the quality of heptane as a fuel is considered to be zero. Isooctane, being a branched hydrocarbon, is resistant to detonation, and its quality is taken equal to 100. The octane number is determined as follows. Prepare a mixture of normal heptane and isooctane, which is equivalent in characteristics to the test gasoline. The percentage of isooctane in this mixture is the octane number of gasoline. There are flammable liquids with better anti-knock performance than isooctane. Additives of such liquids make it possible to obtain gasoline with an octane number of more than 100. To evaluate an octane number above 100, a conditional scale has been created in which isooctane is used with the addition of various amounts of tetraethyl lead Pb(C 2 H 5) 4 . It is known that this substance already in very small concentrations significantly increases the octane number of gasoline. Knowing how much tetraethyl lead must be added to gasoline in order to increase its octane number by one unit, it is easy to prepare standard mixtures from isooctane with an octane number of 101, 102, etc.
The octane number is determined in different ways. For motor gasoline, two methods are used - motor and research. In the first case, the operation of the engine is simulated under conditions heavy loads(moving on the highway at high speed), in the second - in urban conditions (the speed of movement is low and there are frequent stops). The letter "I" in the brand of gasoline AI-93 just means that the octane number of this gasoline was obtained by a research method. And if it is indicated that the octane number of gasoline is simply 76, then this means that it was obtained by the motor method.
The role of the hydrocarbon structure is clearly visible from the table, which shows the octane numbers of some pure chemical compounds obtained by the motor method:
It can be seen that chain branching, the introduction of a double bond, and the appearance of an aromatic ring contribute to an increase in the octane number. For example, if as a result of the isomerization of normal hexane (the process takes place in the presence of a catalyst) a mixture of branched isomers of this hydrocarbon is obtained:
n-C 6 H 14 ® (CH 3) 2 CHCH (CH 3) 2 + (CH 3) 2 CHCH 2 CH 2 CH 3 + CH 3 CH (C 2 H 5) 2, then the octane octane number of the mixture will increase immediately by 20 units.
Gasoline obtained from oil by simple distillation (such gasoline is called straight-run gasoline) has a low octane number - in the range of 41-56, so now such gasoline is not used. To increase the octane number, more modern methods of oil refining are used (thermal and catalytic cracking, reforming). Thermal cracking (from English cracking - splitting) is produced by heating oil to 450-550 ° C under a pressure of several atmospheres. At the same time, molecules of heavy hydrocarbons, which are abundant in crude oil, are split into shorter ones, among which there are many unsaturated ones. The world's first liquid oil cracking unit was patented by Russian engineers V.G. In thermally cracked gasoline, the octane number rises to 65–70. During catalytic cracking, the process is carried out in the presence of an aluminosilicate catalyst. In catalytic cracked gasoline, the octane number rises to 75–81. Reforming (from the English reform - to transform, improve) is carried out in the presence of catalysts that promote the aromatization of saturated hydrocarbons and increase the proportion of aromatic hydrocarbons from 10 to 60%. Previously, molybdenum and aluminum oxides were used as catalysts, now catalysts containing platinum are used (therefore, this process is called platforming). Catalytic reforming gasoline has an even higher octane rating of 77–86.
To increase the octane number, so-called high-octane components are also introduced into gasoline. These include aromatic hydrocarbons with a short branched side chain, for example, cumene C 6 H 5 CH(CH 3) 2 . Another additive is the so-called alkylate (alkylbenzene), a mixture of saturated hydrocarbons of isostructure, obtained by alkylation of isobutane with unsaturated hydrocarbons - alkenes, mainly butylenes. As a result, a mixture of isooctanes is formed:
CH 3 CH (CH 3) 2 + CH 3 CH \u003d CHCH 3 ® CH 3 C (CH 3) 2 CH (CH 3) CH 2 CH 3 (2,2,3-trimethylpentane); CH 3 CH (CH 3) 2 + (CH 3) 2 C \u003d CH 2 ® CH 3 C (CH 3) 2 CH 2 CH (CH 3) 2 (2,2,4-trimethylpentane). Alkylate has an octane rating of at least 90–91.5. It is very effective to add methyl- tert-butyl ether CH 3 -O-C (CH 3) 3 - non-toxic liquid with an octane rating of 117; up to 11% of this substance can be added to gasoline without reducing it performance characteristics. Thus, modern motor gasoline is a complex mixture of hydrocarbons obtained in various oil refining processes and special additives.
To increase the octane number of gasoline, the second method is also widely used: special substances are added to it - antiknock agents. The very first of these was relatively inexpensive and very effective tetraethyl lead, a colorless toxic liquid. At high temperature in the molecules of this compound, Pb–C bonds are easily broken, with the formation of ethyl radicals ( cm. FREE RADICALS):
Pb(C 2 H 5) 4 = Pb + 4C 2 H 5 . Lead atoms are easily oxidized by oxygen to lead oxides (depending on the temperature, mixtures of PbO and PbO 2 are formed), and the dioxide effectively destroys hydroperoxides with the formation of inactive compounds - aldehydes, alcohols, etc., for example: 2RCH 2 COOH + 2PbO 2 ® 2RCHO + 2PbO +O2. So that the lead oxides formed during the combustion of tetraethyl lead do not deposit on the internal parts of the engine, a special “scavenger” of lead (0.3–0.4%) is simultaneously introduced into gasoline, usually ethyl bromide C 2 H 5 Br and dibromopropane C 3 H 6 Br 2 . Then the lead is taken out with exhaust gases in the form of PbBr 2 bromide. A mixture of tetraethyl lead and ethyl bromide is called ethyl fluid, and gasoline with such an additive is called leaded (to distinguish leaded gasoline from regular gasoline, it is colored). The addition of just 0.1% tetraethyl lead can increase the octane number of gasoline by 10 units. Up to 0.3% tetraethyl lead is added to aviation gasolines. However, this compound is highly toxic: the maximum permissible concentration of its vapor in the air is only 0.005 mg / m 3 - much less than that of chlorine. In addition, toxic lead compounds heavily pollute near-highway areas of the earth. All this has led in many countries to a complete ban on leaded gasoline as a fuel. automotive fuel or to a significant limitation of its use.
Other, less toxic antiknock agents have been developed, for example, tricarbonyl (232-cyclopentadienyl) manganese Mn (CO) 3 (C 5 H 5), carbonyl (232-cyclopentadienyl) nickel 2 dimer, ferrocene Fe (C 5 H 5) 2. Unfortunately, these antiknock agents are too expensive, and in addition, they form hard deposits on the cylinder walls in much greater quantities than tetraethyl lead, so work in this area continues.
The role of increasing the octane number can be illustrated by the example of aviation gasoline during the Second World War. This war is often called the "war of engines". Motors are tanks, self-propelled guns, planes. Engines need fuel, and lack of fuel played a part in the defeat of Germany and its allies. A less well-known, but no less important factor is the fact that the countries of the anti-Hitler coalition have the best quality gasoline. The Germans and Japanese had an octane number of aviation gasolines that did not exceed 87-90, while their opponents had at least 100. Although the difference may seem small, the pilots fully appreciated it: it allowed a 30% increase in power aircraft engine during takeoff and climb; reduce fuel consumption by 20% and increase the flight range by the same amount, increase by 25% payload(and these are bombs, shells, additional weapons), increase by 10% top speed and 12% - flight altitude. As British Minister David Lloyd George noted, his country would not have been able to win the 1940 air "battle for Britain" if the British pilots had not had aviation gasoline of the 100 brand.
Mass production of "100" gasoline began in the United States in the late 1930s, when the industry switched to a catalytic oil refining process developed by French engineer Eugène Goudry. He immigrated to the United States in 1930, and already in June 1936, Goodry's semi-industrial plant began operating with a capacity of 2,000 barrels per day (an American barrel for crude oil and petroleum products is 139 liters). Successful work installation made it possible to put into operation a full-scale plant with a capacity of 15 thousand barrels per day in 10 months. Other oil companies also began to introduce Goodry installations at their enterprises, and in 1939, on the eve of World War II, their total productivity reached 220 thousand barrels per day. In 1940, Goodry managed to significantly improve the operation of reactors by replacing natural clays with a more efficient synthetic aluminosilicate catalyst. As a result, Goodry's gasoline had an octane number of 82, while previously it was not possible to obtain more than 72. Therefore, it was gasoline produced at Goodry's plants that became the basis for obtaining new high-quality gasoline (with an octane number unheard of at that time, reaching 100 or more) on a large scale.
As early as 1934, US Army officials became interested in gasoline with an octane rating of 100. Tests showed that it provides significant advantages and is a strategic product. But this gasoline was at that time very scarce. It was obtained by adding tetraethyl lead, isooctane, isopentane and other components to the best grades of aviation gasoline. The Goodry process halved the amount of expensive additives required to produce "gasoline-100". The merits of Goodry were appreciated by the American government: soon after the US entered the war, he became a citizen of this country. In 1941–1942, installations operating on the basis of the Goodry process produced 90% of all aviation gasoline of the countries of the anti-Hitler coalition. By 1944, the productivity of the installations was brought to a maximum - 373 thousand barrels per day.
Goodry received many patents for catalytic oil refining. Until now, petrochemical specialists use the terms “goodryflow”, “udriforming”, etc.; V English-Russian Dictionary of Chemistry and Oil Refining seven such terms are given.
Ilya Leenson
Most car owners have a vague idea of what an octane number is. As a rule, their knowledge is limited to the understanding that the higher this indicator, the better. Alas, this interpretation is far from the truth. And since novice drivers are taught so many things, but OC is not included in the training course, a bit of information on this topic will not hurt anyone.
Appointment of the octane number of gasoline and how to change it.
This incomprehensible term is understood as the degree of resistance of fuel in liquid form to detonation. In other words, what is the ignition threshold of gasoline under pressure, that is, under compression. A mixture of two hydrocarbons is taken as a reference: 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:
- ROI - research ROI;
- OCHM - motor OCH.
Since the instrumental mechanisms of these methods are not the same, there is a difference between the RON and RON values, which is called the sensitivity of the liquid fuel. Both methods are laboratory. And if we are talking about a real indicator obtained on a working power unit, they talk about the actual octane number. It is determined using a special stand on a running engine. But the closest indicator to reality is road octane, which is measured on a moving vehicle.
Isooctane is a substance that is practically incombustible under compression, so a mixture consisting of it alone has a maximum possible octane rating of 100. Conversely, a mixture consisting of only n-heptane has an octane number of zero. 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. It is they who arise if you use fuel with an inappropriate for a given power unit octane rating. Metallic ringing is formed as a result of the propagation of sound waves that appear as a result of too rapid combustion of fuel assemblies. Repeatedly reflected from the surface of the pistons / cylinders, they become clearly audible and recognizable experienced drivers. Thus, the octane number indicates how fast is happening in the engine's cylinders.
The influence of OC on the characteristics of the power unit
The relationship between the combustion rate of gasoline and OS has a linear form. The lower the octane number, the less time it takes to ignite the fuel assemblies, which directly affects the fuel consumption - if it burns faster than expected, then it enters the combustion chamber at a speed increased by the corresponding value. But this does not mean that by simply increasing the RH, we can save: if the combustion is slower than it should be, this is also bad, since the efficiency of the motor decreases, which leads to a loss of engine response and a deterioration in dynamic performance. By filling in an engine running on 95 gasoline, fuel with an OC equal to 92, you will get. If the situation is the opposite (instead of the working 92nd, we fill in the 95th), the flow rate will remain the same, and the engine power will decrease. So it is possible to use unsuitable gasoline, but it is undesirable. 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
OCHM, according to GOST 511/82, is measured using special installation UIT65M, consisting of the following components:
- a device that measures detonation;
- a single-cylinder engine characterized by a dynamic compression ratio and a degree of detonation;
- devices designed to control 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;
- make up a reference mixture characterized by the same amount of detonation, and the ratio of n-heptane to isooctane determines the OC of the original fuel.
GOST 8226/82 describes the procedure for measuring OC by the research method. In this case, the mode of operation of the motor is characterized by lower loads, as a result of which the RON is always obtained at par with a slightly larger MON. If it becomes necessary to independently measure the octane number, this can be done using devices that are commercially available. An example is an octane meter, which uses a measurement method based on the dielectric constant of liquid fuel (this value varies in proportion to the octane number).
The peculiarity of the method lies in the compilation of a calibration scale that allows one to determine the SP with acceptable accuracy. To build such a scale, you will need some amount of n-heptane and gasoline with a precisely set octane number. A similar procedure can be used to determine cetane number for diesel fuel. The possibility of applying this method is based on the fact that currently gasoline is produced without using the direct distillation method, but through the technology of camping, or mixing of components. However, the determination of the octane number of gasoline by this method also has disadvantages:
- to perform 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 gasolines of different types and produced in different ways;
- each instrument must be calibrated using reference devices;
- measurements must be carried out with care temperature regime given in the device specification.
All devices that measure SP use a similar measurement principle, and therefore their advantages and disadvantages are generally identical. Note that the octane number can be more than 100 due to the inclusion of certain additives in gasoline, however, none of these devices is able to work with such liquids.
One of the most affordable octane meters is domestic development OKTIS, which can be purchased for approximately 3,500 rubles. The German device Digatron is more accurate and reliable, however, it also costs several times higher, about 600 euros. However, it is he who is considered the most in demand on Russian market. For its operation, a reference fuel is needed, which is compared with the one under study, 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 an appropriate reference sample will be required, since in this case the calibration relationship between SP and permittivity will be different. In addition, each measurement must be accompanied by the implementation of calibration procedures, which also affects the accuracy of measurements and the reliability of the results obtained.
A rather expensive, but effective Russian-made device is the OKTAN-IM octanometer (45-50 thousand rubles). Among its features is the presence of a 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 “chip” is proprietary software that allows you to interface with a computer / laptop. The octanometer is able to take into account the temperature factor, which increases the accuracy of measurements (the dielectric constant has a weakly pronounced dependence on the ambient temperature).
Approximately similar functionality is incorporated into 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 PE-7300, which does this purely by software. Whether you are measuring 92 octane or 95 octane gasoline, with a reference fuel sample, the results should match to the required accuracy, but within the same batch of gasoline. Other shipments, even from the same manufacturer, may require additional instrument calibration.
Compression ratio and oct
All possible varieties of gasoline are characterized by a very specific compression ratio, which is regulated by GOST. You can get acquainted with the correspondence of the octane number of the compression ratio from the following table:
| Gasoline name | OC | GOST | Compression ratio | |
| EYES | HMO | |||
| 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, in the network of domestic gas stations, gasoline grades 76/80 can no longer be found. However, equipment designed specifically for these grades 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 - an artificial decrease in the octane number of gasoline to the required levels. At home, this can also be done, but approximately enough. If you, for example, have a walk-behind tractor manufactured 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, the OC will decrease by about 0.5 units daily, so the procedure will take about a month. The obvious disadvantages of the method are the duration. The second, more common method is the dilution of gasoline with kerosene. And although it is considered to be the most common in relation to cars running on low-octane gasoline, its main drawback lies in 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 it will be necessary to measure the RH using an octane meter.
How to increase the octane number of gasoline
There are also opposite situations, when only 92nd gasoline is available at the gas station, but 95/98 is required. In this case, you can try to independently raise the octane number of gasoline, for which a special substance, collectively referred to as an antiknock, is added to the fuel. Consider all the main additives used as an antiknock agent. Ordinary ethyl (methyl) alcohol may well raise the OCh by the required amount. By adding a liter of alcohol to 10 liters of 92 gasoline, you can get fuel with an OC of 95. By the way, such a mixture will be characterized by a less toxic exhaust composition, however this method also has disadvantages. One of them is considered to be an increase in the vapor pressure of fuel assemblies, which leads to an increase in the likelihood of plugs in fuel line car power systems. The second drawback of the alcohol mixture is an increase in hygroscopicity, which excludes the possibility of storing fuel for any long time in an open form due to the possibility of accumulating a critical mass of water in gasoline.
Tetraethyl lead has physical characteristics making it one of the most effective antiknock agents. This and high viscosity, and a very high boiling point (about two thousand degrees). It was first used as an OC booster nearly a century ago in 1921. Allows you to increase the SP 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 dilute fuel. This substance forms a precipitate that settles on the internal surfaces of pistons, valves and other components of the CPG.
To minimize the formation of such deposits, special substances (diromethane, bromoethyl, dibromopropane) are added to tetraethyl lead, which bind the combustion products of lead, facilitating their removal to the outside through the exhaust tract.
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Let's start with the basics
Octane number - important indicator quality of gasoline, characterizing its anti-knock resistance. Detonation is a spontaneous, independent of a spark on a spark plug, ignition of the working mixture in a cylinder under the influence of temperature and pressure, accompanied by its abnormally rapid combustion. Insignificant and short-term detonation, which occurs, as a rule, with a sharp increase in load, does not pose a particular threat, although it is manifested by knocks that are unpleasant for hearing and a characteristic “clatter”, which experienced motorists call “finger ringing”.
Under heavy load, detonation can be stronger and more destructive. The resulting knocks can be "masked" by the general noise of the engine. Prolonged detonation is extremely dangerous. It is capable of destroying the engine in a matter of hours (or even minutes).
In pursuit of additional power, engine builders throughout the last century followed the simplest path - they increased the compression ratio (i.e., the ratio of cylinder volumes when the piston is in the lower and upper dead spots). More high pressure compressed working mixture provoked detonation. Gasoline with an increasing octane number was required. If in the thirties of the last century, gasoline with an octane rating of 76 was considered the greatest achievement, now even 100 is not surprising.
The octane number of the fuel is determined on a special single-cylinder engine by comparison with a mixture of isooctane (an isomer of octane 2, 2, 4-trimethylpeptane) and η-heptane. The octane number of gasoline, for example, 92, means that its knock resistance corresponds to the resistance of a mixture of 92 parts of isooctane and 8 - η-heptane. Although both substances are usually included in gasoline, the octane rating does not mean that gasoline consists of only them. This is a much more complex "cocktail", the exact recipe of which is often not known even by its producers themselves. When the American Russell Marker of the Ethyl Corporation was developing a method for determining the octane number in 1926, he chose η-heptane as the zero standard for only one reason: a specific isomer of a high-purity hydrocarbon compound cannot be obtained from oil, but η-heptane can be produced from pine resin .
If, in principle, everything is clear with the octane number, we will begin to confuse everything. Octane numbers (and there are at least two of them) are not the only units of measure for antiknock resistance. Even on the same motor stand, two indicators are determined using two different methods.
The ASTM research method gives us, respectively, the research octane number or, more correctly, the research octane number (ROI). Remember the letter “and” in the labeling of our old gasolines?
During the test, a single-cylinder engine with forced variable degree compression works under controlled conditions with minimal stress.
To determine the octane number by the motor method (MOCH) supplied to the same engine working mixture is preheated, the crankshaft speed increases, the ignition timing adjustments change. Thus, gasoline is subjected to a tougher and closer to real-life test. Typically, the ROI of a fuel is 8–10 units greater than its ROI. This ratio is worth remembering, it can be useful for practical calculations.
There is no general, standard way of designating the knock resistance of gasoline in the world. In Europe and Australia, the research method is used. In our country, until recently, both walked, as evidenced by the mentioned letter "and" (or its absence -
evidence of the use of the motor method). New Zealand, Australia's neighbor, has more UOC operations. Even a study was carried out on reducing its minimum from 82 to 81 units. And here North America goes his own way. They use completely different names, fortunately, denoting the same parameter. In use here is the anti-knock coefficient 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 octane numbers obtained using two different methods is indicated, that is
AKI=IOCH+URI/2. AKI is 4–5 less than EI
(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 grade of gasoline instead of the octane number. At the same time, in different countries different numbers are hidden behind the same words. Moreover, there is no uniformity even in the individual states that make up the United States.
Let's start from the native stove. We have A-92 gasoline already served as Regular, A-95 as Premium and A-98 as Super. The A-76, disguised as the A-80, has not yet disappeared, but the imminent ban left the “old man” without a name. Data for some other countries are given in the summary table. Let's comment on it right now.
The mountainous states of the United States are no different from other mountainous regions of the world. The height above sea level is higher here, the air is thinner. No matter how hard you try, without boost, the pressure in the cylinder both at the beginning of the compression stroke and at its end will be lower than on the plain. Consequently, gasoline here may also have a reduced resistance to detonation. Keep this in mind when planning to go down the mountains for a long time. Slightly lowered requirements for OC in California are explained simply: you need to push the inhabitants of the richest state to buy the "hundredth" available in abundance. Ferrari and Porsche will say thank you. And oil traders too. In a number of European countries, the 95th has long been considered "standard" or "regular". They don't do worse.
But in some third world countries with Regular and Standard complications are possible: they may be similar to our A-76 (80). The information presented here, in addition to cognitive, has applied value. Knowing the country of origin of the purchased foreign car, its owner will be able to determine what gasoline should be served to his steel horse. Indeed, the vast majority of cars, except for sports, representative and tuning ones, as a rule, are content with the Regular / Standard grade without indicating the real octane number in the manual. These figures are also useful for servicemen, as they help to determine how to eliminate, for example, the “stupidity” of the machine. Just switch to higher O4 gasoline or change the expensive ECU. To the point, especially for mechanics, we note that strong detonation (and strong detonation) suffer more carbureted engines. Injection engines usually have a knock sensor in the form of a miniature piezoelectric microphone, on the signal of which electronic brains make ignition later, reducing detonation. The engine suffers less, the owner of the car suffers more. Due to deteriorating dynamics and rising fuel costs.
Back to topic
How does all this confusion relate to our colleague's car? His Mitsubishi came to us from the States. Let's turn to the table. Both as a “Japanese” and as an “American”, the car should be happy with our 92nd. And the transition to the 95th will not add any dynamics or efficiency to it.
It is most likely that our colleague unconsciously wishful thinking. He should install an on-board computer or at least refuel under a traffic jam at the same column for a week or two, regularly recording consumption and mileage data. Then repeat the measurements on another type of fuel. True, taking into account city traffic jams, the result will still turn out to be very approximate.
If the savings are nevertheless confirmed, there are several options for its occurrence.
The first and the easiest. A certain part of the machines, due to the summation of tolerances and other technological reasons, has characteristics that differ from the passport ones. And this must be taken for granted.
The second is 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, respectively, has increased. Which "adapted" the engine to gasoline with a higher octane rating. It is treated by regularly adding anti-carbon additives to gasoline, plus a long ride on high speed. An alternative to the additive could be the use of Shell V-Power "cleaning" gasoline, but you will have to pay for the lack of unnecessary hassle. If "chemistry" does not help, then "mechanics" remains. However, without more compelling reasons, it is better not to disassemble the engine. If the "chemistry" helps, most likely, the engine will have to be readjusted.
Third, the most difficult. The engine management system, ignition, exhaust gas recirculation system are buggy. Replacing the control unit is not difficult, but very expensive. It is worth consulting good diagnostician if one can be found. As well as a specialist in catalytic converters.
A little more theory
Numerous studies 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 hence the stored energy, is approximately the same for different types of fuel. High-octane gasoline produces the same amount of energy as standard gasoline, but burns more slowly. As a result, fuel that has not had time to burn can be thrown into the silencer (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 recommending high-octane gasoline, allow the use of standard gasoline without a threat to the engine, but with some deterioration in vehicle parameters.
What this deterioration is can be judged from the data published by Hyundai Motor. Powered by Premium 4.6-litre V8 engine Genesis sedan produces a maximum power of 375 hp. s., and on the standard (AKI-87) - 386, i.e. less than 2% less.
US manual smart fortwo same warning as for Mercedes cars: "To ensure a long reliable operation and high engine performance, Premium Unleaded gasoline should be used.” And on the bottom line: "Regular gasoline won't hurt your car."
We do not call for switching to low-octane gasoline. But if your car is “sharpened” for it, does it make sense to pay extra money? With the same chemical composition, equal energy intensity and independent of the octane number of use / non-use of additives, the only difference between gasoline grades is the amount of profit received by the fuel seller.
Useful formulas
When determining what kind of gasoline your car needs, it is helpful 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 (ROI);
MON - Motor Oil Number - octane number according to the motor method (MOCH).
As a result of fractional distillation of oil under the influence of different temperatures, various types of fuel are obtained (including gasoline), lubricants, as well as products for petrochemical synthesis. This, no doubt, is known to everyone who has been to chemistry classes at school. However, when approaching a gas station, you must have paid attention more than once to the mysterious figures dividing gasoline into different types. What is their real difference?
These same numbers in the markings of gasoline indicate its octane number. This is the main criterion by which various types of gasoline are classified. The term "octane number" characterizes the property of the fuel to burn freely in the engine, taking into account a variety of conditions. The higher this number, the more resistant gasoline is to self-ignition during compression. However, it is somewhat more difficult to obtain high-octane gasoline during production, in addition, it must be sufficiently pure.
Determination of anti-knock properties of gasoline
Each engine is designed to run on fuel with a specific octane rating. In Russia, most car owners use AI92. Such types of gasoline as AI95 and AI98, as a rule, are afforded by owners of premium class cars. Diesel fuel and AI80 are even less in demand.
Determination of the resistance of gasoline to detonation is carried out using standard mixtures. The fact is that gasoline is equivalent to a mixture of isooctane and heptane. Accordingly, if the octane number of gasoline is 92, it will spontaneously ignite as a composition of 92% isooctane and 8% heptane.
Increasing the octane number of gasoline
In production various kinds gasoline, the method of mixing fuel components is used. Otherwise, this process is called "compounding". As a result of all necessary processes products should be obtained that fully comply with state standards and have an accurate octane value.
Primary fractional distillation oil is produced by gasoline with an octane rating of 70. The quality of gasoline is improved not only with the use of compounding, but also through the use of special anti-knock additives. Previously, tetraethyl lead was used to improve the detonation properties of the fuel. Despite the fact that for a person this substance is a strong poison. Currently, ferrocene or methyl tert-butyl ether are used as high-octane additives, which do not have such a huge toxicity.
To understand whether this or that brand of fuel is suitable for a car, motorists look at its octane number (OC). But, not everyone understands what the 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 work car engine the mixture of air and gasoline vapors is compressed to a certain value by the pistons of the cylinders, after which it is ignited by an electric spark. The energy of combustion of gasoline vapors, in fact, is the force that rotates the wheels of the car.
However, if you squeeze fuel-air mixture too much, it may ignite spontaneously without waiting for spark ignition. This process is called detonation and results in increased wear and engine failure. IN modern cars they try to deal with this with the help of special sensors that detect detonation and send a signal to the on-board computer, which either corrects the fuel cycle, or, if the risk of detonation cannot be eliminated, simply blocks the engine.
But, modern technologies not enough for correct operation The engine needs the right fuel. The resistance of gasoline to self-ignition during compression is called the octane rating of the fuel. The higher the octane number, the higher pressure gasoline can withstand when compressed in the engine chamber.
Why is detonation dangerous?
As mentioned above, during the operation of an automobile engine, a mixture of gasoline and air is compressed by a piston, ignited by an electric spark and burned, releasing energy that is directed to the rotation of the wheels. The more you manage to compress the air-gasoline mixture, the higher the efficiency of the engine 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 elements of the engine, in contact with each other, make clanging sounds and after a short time become completely unusable. If the engine has been running on low-octane fuel for some time, then due to detonation:
- valves burn out;
- pistons melt and deform;
- connecting rods are bent;
- the engine is overheating.
All this inevitably leads to a quick breakdown. The destruction of engine components can be so severe that it will require complete replacement power unit.
How to increase the octane number of gasoline
In the second half of the 20th 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 the fuel to detonate. It is not difficult to manufacture tetraethyl lead industrially, and its cost practically does not affect the final price of fuel.
Currently, tetraethyl lead is banned for production in almost all countries of the world. Instead, aromatic and paraffinic hydrocarbons are used as octane boosters. Unfortunately, many of these substances evaporate extremely easily, so the octane rating of the fuel drops during long-term storage. If you fill an ordinary canister with 95th gasoline and leave it in the garage for several weeks, during this time it will spontaneously turn into 92nd or even 80th. Therefore, keep a supply of gasoline for modern car doesn't make sense.
How to lower the octane number
Until now in our country is used a large number of equipment designed for the use of low-octane gasoline - the 80th and even the 76th. We are talking not only about old brands of cars, but also about walk-behind tractors, gasoline generators and other devices. The purchase of new units will cost the owners too much, so the methods of lowering the octane number are quite relevant for our car owners.
Most in a simple way used by craftsmen is the evaporation of additives. It is believed that if you leave a can of gasoline open, then every day the octane number will decrease by 0.5. Thus, it will take two weeks to turn the 92nd gasoline into the 80th.
In some cases, mixing gasoline in a certain proportion with kerosene gives a similar effect. At one time, this method was widely used by owners of old cars. But, the method did not take root, since the proportion of dilution must be determined empirically each time.
Octane measurement
Unfortunately, even the purchase of fuel for filling station does not always guarantee compliance with the declared value of its octane number. However, it is extremely difficult to measure it at home, requiring special equipment and reference chemicals. In laboratories, the measurement is performed in two ways - motor and research. Both are based on a comparison of gasoline with a reference hydrocarbon, which has an octane rating of 100, and n-heptane, which has an octane rating of zero.
- motor way. 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 fuel grades.
- research method. fuel mixture fed into the engine without preheating, the speed is 600 rpm. This method is effective for measuring gasoline with an octane rating over 92.
In addition, special devices are used to measure the octane number. However, they are not very popular, as they give too large a scatter of results during measurements.
