Automobile gasolines. What gasoline consists of, what is the octane number The ignition temperature of gasoline is 92

The range and quality of gasoline produced and used is determined by the structure of the country's car fleet (over the past decade, the number of cars has increased by 1.7 times, while the share of foreign cars has increased), the technical capabilities of the domestic petrochemical industry, as well as environmental requirements, which in Lately became decisive. In order to reduce harmful emissions, cars began to be equipped with catalytic exhaust gas aftertreatment systems, which caused tougher requirements for the quality of gasoline used.

1. Obtaining motor gasoline and their component composition

The manufacture of fuel for internal combustion engines is a complex process that includes obtaining its primary components, mixing them and improving them with additives to commercial quality indicators in accordance with the requirements of standards. The mixing of straight-run fractions with components of secondary processes and additives is called compounding.

Automobile gasolines of the same brand, manufactured at different enterprises, have a slightly different composition, which is associated with an unequal set of technological equipment. However, they must comply normative documentation. The average component composition of gasolines of different grades is given in Table. 3.

The basic component for the production of motor gasolines are usually catalytic reforming or catalytic cracking gasolines. Catalytic reforming gasolines are characterized by low sulfur content, they contain practically no olefins, so they are highly stable during storage. However, the high content of aromatic hydrocarbons in them is a limiting factor from an ecological point of view. Their disadvantages also include the uneven distribution of detonation resistance by fractions.

The share of the catalytic reforming component in the gasoline fund of Russia exceeds 50%.

Table 3Average component composition of gasolines of different grades

Catalytic cracking gasolines are characterized by a low mass fraction of sulfur, octane numbers according to the research method 90…93. The content of aromatic hydrocarbons in them is 30...40%, olefinic - 10...25%. They have relatively high chemical stability (induction period 800…900 min). Compared to catalytic reforming gasolines, catalytic cracking gasolines are characterized by a more uniform distribution of knock resistance over fractions. Therefore, a mixture of catalytic reforming and catalytic cracking components is used as a base for the production of motor gasoline.

2. Requirements for the quality of motor gasoline

The power of a gasoline engine, its economy, reliability, fuel and oil consumption, exhaust gas toxicity largely depend on the quality of the fuel used.

Motor gasolines are blends of straight run, thermal cracked, platformed and catalytically cracked gasoline distillates. With the improvement of catalytic cracking and reforming processes, the proportion of distillates of these processes in motor gasoline increases due to a decrease in the proportion of direct distillates and thermal cracking.

To ensure reliable operation of automobile engines in all modes, gasolines must meet certain requirements.

Combustion of gasoline mixed with air in the combustion chamber must occur with normal speed without the occurrence of detonation in all engine operating modes in any climatic conditions. This requirement establishes standards for the knock resistance of gasoline. In order to improve anti-knock properties, anti-knock additives - anti-knock agents - are added to some gasolines. Various high-octane components are added to gasolines designed for engines with a high compression ratio.

It is necessary that gasoline has a high calorific value, a minimum likelihood of deposits in the fuel and intake systems, as well as carbon deposits in the combustion chamber. Combustion products must not be toxic or corrosive. The volatility of gasoline should ensure the preparation of a combustible mixture at any engine operating temperature. This requirement regulates such properties and quality indicators of gasoline as fractional composition, saturated vapor pressure, and the tendency to form vapor locks. To improve the starting properties of the engine, gas gasolines are added to gasolines.

The production of motor gasoline is associated with a complex set of different technological processes oil refining.

The requirements for the quality of produced gasoline, due to the technical capabilities of domestic oil refining, impose restrictions on the fractional and hydrocarbon composition, sulfur content and various antiknock agents.

The conditions of mass production require the possibility of using petroleum feedstock with the widest variation in hydrocarbon and fractional composition and the content of various sulfur compounds, which in a certain way affects the establishment of standards in the specifications for the corresponding quality indicators of gasoline.

In order to increase the yield of gasoline from processed petroleum feedstock, production is interested in raising the end point of boiling, and the efficient use of gasoline in an engine is possible with a certain limitation of the content of high-boiling fractions.

The standards for the index of detonation resistance are set at a level achievable using existing technological processes, components and additives approved for use in gasoline.

The requirements of car manufacturers very often conflict with the requirements of refiners, and in these cases it is necessary to determine the optimal economically viable level of these requirements. An example of such a compromise is the octane index, which characterizes the knock resistance of American gasolines.

The US automakers proposed to introduce the octane number of gasolines into the specification by the research method, and oil refiners - by the motor method. As a result, an indicator was introduced equal to half the sum of octane numbers for research and motor methods.

The requirements associated with the transportation and storage of gasoline are due to the need to maintain their quality for several years.

Automobile gasoline from the manufacturer is supplied to large regional transshipment tank farms. From these storage bases, gasoline is delivered to oil depots that supply gas stations (gas stations), and then by truck tanks to gas stations.

Transportation, storage and use of gasoline directly on cars are carried out in various climatic conditions at an ambient temperature of -50 to 45 ° C, while it is necessary to ensure the normal operation of the engine. Requirements related to transportation and storage regulate such properties of motor gasoline as physical and chemical stability, tendency to losses from evaporation and formation of vapor locks, water solubility, content of corrosive compounds, etc. For long-term storage, as a rule, summer-type gasolines with high chemical stability (induction period of at least 1200 minutes) are received.

The impact of gasoline on the environment when used in automotive technology is associated with the toxicity of compounds that enter the atmospheric air, water, soil directly from the fuel (evaporation, leakage) or with its combustion products.

Sources of toxic vehicle emissions are exhaust gases, crankcase gases and fuel vapors from the intake system and fuel tank. Exhaust gases contain carbon monoxide, nitrogen oxides, sulfur, unburned hydrocarbons and products of their incomplete oxidation, elemental carbon (soot), combustion products of various additives, such as lead oxides and lead halides when using leaded gasoline, as well as nitrogen and oxygen not consumed for fuel combustion air.

To reduce emissions of harmful substances, modern cars are equipped with catalytic exhaust gas aftertreatment systems that allow afterburning unburned hydrocarbons and carbon monoxide to CO 2, and reducing nitrogen oxides to nitrogen.

The environmental properties of gasoline are provided by restrictions on the content of individual toxic substances, on the group hydrocarbon composition, on the content of low-boiling hydrocarbons, as well as sulfur and benzene. These limits ensure the reliable operation of the catalytic aftertreatment system and contribute to the reduction of pollution. environment.

In table. 4 shows the requirements for motor gasoline in the countries of the European economic community(EEC).

In connection with the accession Russian Federation and the Republic of Belarus to the European environmental programs there was an urgent need to organize industrial production motor gasolines that meet European requirements (EN 228). The technology for the production of motor gasoline that meets the requirements of EURO-2, EURO-3, EURO-4, EURO-5 must guarantee the established standards for the content of sulfur, aromatic and olefinic hydrocarbons and benzene.

Table 4Requirements for motor gasoline EEC

Thus, gasolines as fuel should:

• have good volatility and form a combustible mixture that is homogeneous in composition in all cylinders;
• have high detonation resistance, i.e. burn without detonation under various engine operating modes;
• provide easy start-up and stable operation of the engine in various modes, high efficiency;
• have an optimal fractional composition;
• have a low content of resinous and carbon-forming compounds and corrosive substances;
• have high physical and chemical stability during storage, transportation, etc., do not cause corrosion of containers, refueling facilities, engines (gasoline combustion products should also not cause corrosion of engine parts);
• burn completely with minimal formation of toxic and carcinogenic substances;
• have a minimal tendency to form carbon deposits on engine parts;
• ensure maximum engine power and minimum oil consumption;
• have good low temperature properties;
• not have increased hygroscopicity and a tendency to form ice;
• do not contain mechanical impurities and water.

The properties of gasoline that fully meet all operational requirements include: physical and chemical properties, volatility and fractional composition, detonation resistance, their stability and anti-corrosion properties. IN separate group properties of gasolines, environmental requirements are highlighted.

3. Chemical and hydrocarbon composition of gasolines

The chemical composition of gasolines is characterized by a group hydrocarbon composition, i.e. the content of aromatic, olefinic, naphthenic and paraffinic hydrocarbons in them.

In addition to hydrocarbons, gasoline contains a small amount of heteroatomic hydrocarbon compounds, which include sulfur, oxygen and nitrogen. They get into gasoline from processed oil, and oxygen compounds are formed during the oxidation of hydrocarbons during gasoline storage.

The components of gasoline do not contain organometallic compounds of oil, which are concentrated, as a rule, in high-boiling fractions. In order to improve the physicochemical and operational properties of motor gasolines, oxygen-containing components (ethers and alcohols), as well as special anti-knock additives, including metal-containing ones, are added to their composition in limited quantities.

To limit the content of antiknock additives in the specifications for gasoline, the maximum allowable concentrations of lead, manganese, and iron are provided.

The main restrictions on the chemical and hydrocarbon composition of motor gasoline include: the content of sulfur, aromatic hydrocarbons, and primarily benzene; the content of olefinic hydrocarbons, oxygenates (total by oxygen concentration and by individual alcohols and ethers).

With an increase in the content of sulfur compounds in gasoline, increased carbon formation and wear of engine parts, aging of engine oil occur. In addition, it has a significant negative impact on the environment.

An increase in the content of aromatic hydrocarbons in gasoline contributes to an increase in benzene emissions into the environment. The conducted studies have established that there is a linear relationship between the content of benzene in gasoline and its concentration for all types of emissions of unburned hydrocarbons: in exhaust gases; in fumes from the fuel system; while refueling the vehicle. For vehicles not equipped with a catalytic converter, the main source of benzene emissions into the atmosphere is exhaust gases (about 70%), the intake with evaporation plays a lesser role (20%), losses during refueling play an even lesser role (10%).

• cut from gasoline catalytic reforming fraction 60 ... 85 ° C, containing more than 20% benzene, with its subsequent use to obtain benzene. At the same time, the content of benzene in commercial gasoline decreases by almost 3 times, and the octane characteristic of reforming gasoline after separation of the fraction 60 ... 85 ° C increases by 1 ... 1.5;
• an increase in the share of high-octane components that do not contain benzene in the composition of commercial gasoline: alkylate, isomerizates, oxygenates (alcohols, ethers, etc.), as well as the use of non-toxic anti-knock agents;
• selection of raw materials and reducing the rigidity of the reforming process, extraction, as well as selective hydrogenation of benzene in cyclohexane or alkylation of benzene to alkylaromatic hydrocarbons.

It is possible to combine several methods based on the characteristics of the refinery, the availability of raw materials, the concept of processing and integration with chemical production.

The maximum content of olefinic hydrocarbons in commercial gasoline should not exceed 18%, since they are the main source of formation of resinous substances in gasoline. An increase in the content of olefinic hydrocarbons increases the emissions of harmful substances into the environment with exhaust gases.

Oxygenates have a high detonation resistance, which allows them to replace aromatic hydrocarbons, in addition, they help reduce the toxicity of exhaust gases from cars. However, when the content of oxygenates in gasoline is more than 2.7% in terms of oxygen, an increase in mass and specific fuel consumption is observed due to their low calorific value, as well as loss of engine power. Therefore, from environmental prerequisites, the content of oxygenates in gasoline should be 2.0 ... 2.7% of oxygen.

The specifications for motor gasoline also introduced standards for the maximum content of individual oxygenates.

4. Physical and chemical properties of gasolines

The physicochemical properties of motor gasolines and the adjustment parameters of engines must be carefully coordinated with each other.

The assessment of the physicochemical properties of motor gasoline is carried out according to appearance, the presence of mechanical impurities, water-soluble acids and alkalis, as well as their density. In the same group of operational requirements for fuels, the low-temperature properties of gasolines are also considered.

By the appearance of gasoline, its color and transparency are evaluated. Gasoline is colorless. A possible yellowish tint of gasoline is due to the presence of resinous substances in it.

The transparency of gasoline in accordance with GOST is determined in a glass cylinder. Gasoline poured into the cylinder must be completely transparent and must not contain foreign impurities suspended and settled on the bottom of the cylinder, including water. The turbidity of gasoline at room temperature is usually associated with the presence of water (in the form of an emulsion) or mechanical impurities in it. Such fuel is subjected to settling and filtration before use. The presence of water in gasoline is especially dangerous in winter, when the ice crystals that form disrupt the dosage of gasoline and can even cause a complete cessation of its supply. In addition, water increases the corrosivity of gasoline in relation to the metal parts of fuel systems.

The specification for gasoline provides for the absence of water in it. However, water in gasoline can be in dissolved form, as well as get into fuel tanks and accumulate in them in a free state. The amount of water in the free state depends on the conditions of transportation and storage. Therefore, for the reliable operation of equipment, storage tanks and means of pumping gasoline, it is important that they not only be not aggressive themselves, but also have the ability to reduce the rate of electrochemical corrosion in the fuel-metal-water system.

Mechanical impurities can get into gasoline when using dirty or faulty (leaky) containers or contaminated filling equipment. The presence of mechanical impurities is determined external inspection samples of gasoline are also in a glass container. The presence of even the smallest mechanical impurities in gasoline is not allowed. The use of gasoline containing mechanical impurities causes wear of the fuel equipment, clogging of fuel metering systems, and if it enters the engine cylinders, wear of the engine cylinder-piston group.

In the process of application, motor gasolines come into contact with various metals and alloys, causing their corrosive destruction. Corrosion is exposed to fuel tanks, pipelines, etc.

Water-soluble acids and alkalis, which cause corrosive wear of engine parts, may end up in gasoline due to a violation of its purification technology. So, after sulfuric acid cleaning, the presence in gasoline of residues of both the acid itself and its derivatives (sulfonic acids and acid esters) is not excluded due to their incomplete neutralization. Alkali gets into gasoline when it is poorly washed during the cleaning process. Thus, organic acids remain in gasoline after oil refining, and are also formed during oxidation during storage, and their content increases from the moment of gasoline production to its consumption.

Organic acids are especially strong destroy non-ferrous metals - lead and zinc. Acids, interacting with metals, form soaps insoluble in gasoline, which precipitate in the form of clots, clogging the engine power system.

Sulfur compounds contained in gasoline are conventionally divided into active and inactive. Active compounds include elemental sulfur, hydrogen sulfide, mercaptans, while inactive compounds include sulfides, disulfides, etc. Active sulfur compounds corrode metal even at low temperatures, so their presence in gasoline is unacceptable.

By themselves, inactive sulfur compounds found in gasoline do not cause corrosion of metals. The products of combustion of sulfur compounds - sulfuric and sulfurous anhydrides - have high corrosive aggressiveness. When starting the engine, especially in the cold season, at a relatively low temperature of the combustion products, condensation of water vapor resulting from fuel combustion is possible. Anhydrides dissolve in water, forming sulfuric and sulphurous acids. Under the action of these acids, low-temperature liquid corrosion of metals occurs. If the temperature of the combustion products is high enough, then water vapor does not condense, but high-temperature gas corrosion occurs. Sulfur oxides in exhaust gases cause exhaust system corrosion. Corrosive wear largely depends on its technical condition, oil quality, operating conditions and the amount of sulfur contained in the fuel. With an increase in the sulfur content in gasoline from 0.05 to 0.1%, the corrosion wear of engine parts increases by 1.5–2.0 times, from 0.1 to 0.2% - by another 1.5–2.0 times , from 0.2 to 0.3% - by 1.3–1.7 times.

The process of removing sulfur from gasoline is very laborious and expensive. Therefore, part of the sulfur compounds, mostly inactive, in an amount that does not affect engine wear, is usually left in the fuel.

The maximum sulfur content in domestic motor gasoline is regulated by STB ISO 20846–2005 and should not exceed 50 mg/kg.

5. Fuel stability, tendency to form deposits and carbon deposits

Under fuel stability understand its ability to maintain properties within acceptable limits for specific operating conditions. The stability of fuels depends on their physical and chemical properties, the presence of various impurities, etc. Under operating conditions, when the fuel is exposed to such external factors as air oxygen, unstable temperature, moisture pollution and mechanical impurities, its fractional and chemical composition. Conditionally distinguish between the physical and chemical stability of the fuel.

Physical stability fuel determines its ability to maintain fractional composition (changes are caused by the loss of the lowest-boiling fractions as a result of their evaporation) and uniformity.

The physical stability of gasoline is evaluated by saturated vapor pressure and the presence of light fractions. Insufficient physical stability of gasoline causes its high volatility.

The design of fuel tanks should exclude the possibility of free communication of their internal volume with the atmosphere.

To prevent evaporation, the fuel tanks are protected from direct sunlight.

The physical stability of the fuel is controlled by periodically determining the density, fractional composition, saturated vapor pressure, cloud point and crystallization temperature, and other indicators.

Chemical stability characterizes the ability of gasoline to maintain its original chemical composition unchanged when long-term storage, pumping and transportation. The chemical stability of gasolines is associated primarily with the presence of unsaturated hydrocarbons in their composition, which are characterized by an increased tendency to oxidize. Hydrocarbons with conjugated double bonds, especially cyclic ones, are most prone to oxidation. Low resistance to oxidation and aromatic hydrocarbons with a double bond in the side chain.

The most prone to oxidation are gasolines obtained by thermal and catalytic cracking, coking, pyrolysis and containing a lot of olefinic and diolefinic hydrocarbons. More chemically stable are gasolines obtained by catalytic reforming and direct distillation, as well as alkyl gasoline.

On the way from the manufacturer to the car tank, auto-oxidation of gasoline occurs, i.e. oxidation of its unstable compounds by the oxygen of the surrounding air with the formation of products of complex composition. The longer gasoline is stored, the longer the transportation route and the more transshipment points, the greater the possibility of the formation of oxidation products - resinous substances and various acidic compounds (organic acids, hydroxy acids, etc.). Most of the resulting oxidation products are in gasoline in a dissolved state, and a smaller part precipitates. The oxidation of gasoline is accelerated by various sludges and sediments that accumulate in tanks, as well as due to the catalytic effect of metals (for example, copper). The more unsaturated hydrocarbons in gasoline, the faster it oxidizes. Oxidation changes the color of gasoline. For example, unleaded gasoline takes on a light yellow to intense yellow color. A sharp smell appears, an oil layer is formed at the bottom of the tank, slightly soluble in gasoline, the acidity of gasoline increases, i.e. its corrosiveness increases.

Chemical stability is characterized by the following indicators:

• induction period;
• actual resin content;
• the total amount of oxidation products;
• acidity.

The acidity and the content of the actual resins characterize the content of end products of oxidation in gasoline at the time of their determination. According to them, one can judge the stock of gasoline quality, i.e. about the difference between the allowable and actual content of oxidation products. The induction period and the amount of oxidation products characterize the rate of gasoline oxidation during storage and use.

Under long-term storage conditions, some of the compounds (sulfur, oxygen, nitrogen and organometallic) can enter into oxidation, polymerization and condensation reactions. Such negative phenomena as oxidation and gumming of gasolines, precipitation of an antiknock agent are due to insufficient chemical stability of the fuel.

The content of actual resins is an indicator of the level of chemical stability of gasolines and is normalized by standards. To improve the chemical stability of gasolines, antioxidant additives (inhibitors) are introduced into them: wood-resin antioxidant DSA (0.05 ... 0.15%), a mixture of phenols FCh-16 (0.03 ... 0.10%), synthetic inhibitors - ionol (0.03 ... 0.10%), agidol-1, agidol-12 (up to 0.3%).

The hydrocarbon composition of gasolines is one of the main factors determining their tendency to carbon formation in the engine. An analysis of the available data shows that the tendency of motor gasolines to carbon formation depends mainly on the content of unsaturated and aromatic hydrocarbons in them.

The structure of unsaturated hydrocarbons, their chemical activity and tendency to transformations under the action of high temperatures largely determine the possibility of carbon formation in motor gasoline. The structure of aromatic

hydrocarbons has a significant effect on carbon formation. With an increase in the molecular weight of the hydrocarbon and its boiling point, the likelihood of carbon formation, as a rule, increases. High-boiling aromatic hydrocarbons undergo oxidative transformations under the influence of high temperatures and, obviously, serve as the main source of soot formation.

Aromatic hydrocarbons are valuable components of motor gasolines, as they have high knock resistance. However, their content in commercial gasoline should be limited due to increased carbon formation in the engine. A direct comparison of the knock resistance of gasolines and their tendency to carbon formation, depending on the content of aromatic hydrocarbons, made it possible to propose a norm for the content of aromatic hydrocarbons in commercial motor gasoline. It has been established that the specific increase in the amount of carbon deposits in the combustion chamber, i.e. an increase in soot deposits, as a result of the addition of aromatic hydrocarbons in an amount corresponding to an increase in the detonation resistance of the fuel by 1 octane unit, remains practically unchanged for various aromatic hydrocarbons, when their content in gasoline varies from 0% to 40 ... 45%. With a higher content of aromatic hydrocarbons, the specific increase in the amount of soot sharply increases. Thus, the content of aromatic hydrocarbons in commercial motor gasoline should not exceed 40%.

Specifications EURO-3 and EURO-4 also mandatory determine the presence of detergent additives in motor gasoline that reduce the effects of carbon formation.

6. Compatibility of gasolines with non-metallic materials

Motor gasolines must not adversely affect the materials with which they come into contact during manufacture, transportation, storage and use. When exposed to gasolines, rubbers, seals, and other materials can swell, crack, lose their strength characteristics, and collapse. The aggressive effect of fuel on rubbers and sealants is mainly associated with the leaching of the antioxidant from them and further destruction due to the formation of peroxides during oxidative processes occurring in the fuel itself. In this regard, the compatibility of gasolines containing oxygenates with rubber materials is evaluated by the results of their direct impact on rubber. The essence of control is reduced to determining the preservation of the properties of samples of rubber materials and the purity of fuel during testing.

The change in the physicochemical properties of rubber under the influence of gasoline is determined by the change:

• sample volume;
• elongation at break;
• sample tensile strength and Shore hardness.

Tests for the compatibility of gasolines with rubber materials are carried out when they are put into production.

7. Evaporation of gasolines

Gasoline is a complex mixture of a number of individual hydrocarbons boiling at various temperatures, so it does not have a fixed boiling point.

The volatility of gasoline, i.e. the ability to pass from liquid to gaseous state lies in the temperature range from 35 to 195 °C.

The volatility of gasoline is assessed by fractional composition and volatility (vapor pressure, evaporation loss and tendency to form vapor locks).

The volatility of gasoline should ensure the optimal composition of the air-fuel mixture in all engine operating modes, regardless of the method of its preparation. A homogeneous combustible mixture must enter the engine cylinders, in which the concentration of fuel, which is in a vapor state and evenly distributed throughout the volume, is sufficient to ignite it from an electric spark.

The speed and completeness of the transition of fuel from a liquid to a gaseous state depend on its chemical composition and external conditions, such as temperature, gas flow velocity. Since these conditions are not the same in different engines, the requirements for fuel volatility are related to the design of the engine for which it is intended. Combustion is always preceded by evaporation liquid fuel and mixing its vapors with air (the formation of a combustible mixture). With poor volatility, part of the fuel does not go into a gaseous state and does not burn.

To assess the volatility of the fuel, a conditional indicator is used - the fractional composition. Start-up, warm-up time, throttle response and engine wear, fuel and oil consumption, exhaust gas toxicity depend on the fractional composition of gasoline. Since motor gasoline is a complex mixture of various hydrocarbons boiling over a wide temperature range, its volatility is estimated from the boiling points of individual parts - fractions.

On fig. 1 shows the distillation curve of gasoline and indicates the volumes of its main fractions - starting, working and trailing. The distillation temperature of 10% gasoline characterizes the starting properties of the fuel. If there are not enough low-boiling fractions in gasoline, then when starting a cold engine, part of the gasoline does not have time to evaporate and enters the cylinders in a liquid state. The combustible mixture entering the cylinders turns out to be over-depleted and does not ignite from an electric spark, and therefore starting the engine sometimes becomes impossible at all.

Rice. one.

Unevaporated gasoline, remaining in a drop-liquid state, enters the engine cylinders and washes oil from their surface, and when it enters the crankcase, it dilutes the oil. Therefore, at the time of start-up and for some time during subsequent warm-up, semi-dry friction of the parts of the cylinder-piston group occurs, since there is not enough oil on their surfaces to provide a strong oil film. This causes intense wear of the rubbing parts of the engine, called starting wear.

To ensure the engine start, the starting fraction must contain a sufficient amount of low-boiling hydrocarbons, which create a mixture that can be ignited by an electric spark. Knowing the boiling point of 10% gasoline t 10%, it is possible to approximately determine the air temperature t in, above which the engine can be started on this fuel, according to the formula

tw ≥ 0.5t 10% - 50.5. (8)

The starting properties of gasolines improve as the starting fraction becomes lighter. Winter gasolines make it possible to start a cold engine at an air temperature of -26 ... -28 ° С.

The start temperature of the distillation of summer grades of motor gasoline should not be lower than 35 °C, and 10% of gasoline should be distilled at a temperature not exceeding 75 °C.

The distillation temperature of 50% gasoline characterizes the warm-up rate and engine acceleration. Warming up the engine lasts from the moment it is started until the start of uninterrupted, stable operation. At the end of warm-up at idle, almost complete evaporation of gasoline in the intake manifold is achieved. The lighter the fractional composition and the lower the distillation temperature of 50% gasoline, the faster the engine warms up. Gasoline with a low distillation temperature of 50% evaporates faster in the intake pipe, filling the cylinder with a combustible mixture improves, and engine power increases.

Saturated vapor pressure is determined by the presence of light fractions in gasoline. Saturated vapor pressure of a liquid fuel refers to the pressure of vapors that are in equilibrium with a liquid at a given temperature and a certain ratio of the volumes of the liquid and vapor phases. The more light fractions in gasoline, the higher the saturated vapor pressure.

The susceptibility of gasoline to the formation of vapor locks, its possible losses during storage, transportation and refueling of the car, and the ease of starting the engine depend on the pressure of saturated vapors. The more hydrocarbons with a low boiling point in gasoline, the higher its volatility and saturated vapor pressure, and hence the tendency to form vapor locks. The higher the saturated vapor pressure of gasoline, the greater its loss during storage, transportation, pumping, refueling and directly from the car tank. Saturated vapor pressure decreases with decreasing temperature and increasing the ratio of vapor and liquid phases.

The value of saturated vapor pressure for all types of gasoline (STB EN 13016) should be in the range from 45 to 100 kPa. The reason for limiting the upper level of the pressure of saturated vapors of gasoline is the possibility of the formation of vapor locks, and the lower one is the deterioration of its starting properties.

The formation of vapor lock depends on the volatility of gasoline, temperature and engine design. The higher the saturated vapor pressure of gasoline, the lower the distillation temperature of 10% and the greater the volume of the fraction that boils away at temperatures up to 70 ° C, the greater its tendency to form vapor locks. This relationship is linear and can be expressed as follows:

IPP = 10DND + 7V 70°С, (9)

where IPP is the vapor lock index; DNP is the pressure of saturated vapors of gasoline, kPa; V 70 °С - the volume of gasoline boiling off at temperatures up to 70 °С.

The density and viscosity of gasoline are regulated parameters of its quality. The use of gasoline with a significantly reduced density can lead to an increase in its level in the carburetor float chamber and spontaneous leakage from the atomizer. The volatility of gasoline significantly depends on its density. Distinguish between absolute and relative density of matter.

Absolute density substances (kg / m3) is the mass contained in a unit volume. The mass of 1 m3 of distilled water at a temperature of 4 °C is taken as a unit of density.

Relative density substance is the ratio of its mass to the mass of distilled water at 4 ° C, taken in the same volume. Relative density is a dimensionless quantity.

Oil products and water have different coefficients of expansion. In this regard, it is necessary to indicate the temperature values ​​of the oil product and water at which their density was determined. The relative density of petroleum products is determined at a temperature of 20 °C. The density of an oil product can be measured at any temperature, but the result is given at 20 or 15 °C. In foreign and some domestic standards, density limits are set at 15 °C.

In accordance with the current standard, the density of an oil product is designated 20. Here, the number 20 indicates that the density of the oil product is referred to normal temperature 20 °C, and the number 4 means that the density of the oil product is related to the density of water at 4 °C, taken as a unit.

The relative density of motor gasoline is 0.70…0.78, and the absolute density in the SI system is 700…780 kg/m3 at 20 °C.

Density is not standardized in fuel standards, but it is mandatory to determine it. This is necessary to account for the consumption and movement of petroleum products at oil depots and filling stations, since the income is recorded in units of mass (kg, t), and the consumption when refueling tractors and cars is taken into account in units of volume (l). Therefore, in order to convert fuel from mass units to volume units and vice versa, it is necessary to know the density of received and sold oil products.

The density of gasoline increases by about 1% for every 10°C decrease in temperature.

Density (kg/m3) of gasolines is determined at 15°C in accordance with STB ISO 3675–2003 and STB ISO 12185–2007.

The low-temperature properties of gasoline should not affect the performance of fuel systems at low temperatures. At low temperatures, the supply of gasoline to the engine may stop due to the precipitation of ice crystals or the formation of ice deposits on the parts of the carburetor and intake system (carburetor icing). Since most of the hydrocarbons that make up gasolines solidify at very low temperatures, and the pour point of motor gasolines is below -60 ° C, this indicator is not regulated for them.

The greatest complications during engine operation at low temperatures are associated with the formation of ice crystals in gasoline. Gasoline may contain only a few hundredths of a percent of water (in a dissolved state). At high humidity and positive temperatures (car parking in a warm, damp, poorly ventilated garage), the water content even in dehydrated gasoline almost instantly reaches its maximum value. With the rapid cooling of gasoline, moisture that has not had time to pass into the air is released in the form of small drops, which at low temperatures turn into ice crystals. These crystals clog fuel filters and pipes and disrupt the flow of gasoline to the engine. In addition, the water contained in leaded gasoline leads to the decomposition of tetraethyl lead, which greatly increases the corrosiveness of gasoline.

The solubility of water in gasoline improves with an increased content of aromatic hydrocarbons, in particular benzene. Therefore, to reduce the risk of ice crystals formation during cooling of gasoline, the content of aromatic hydrocarbons, including benzene, is limited.

If you suspect the presence of water in the fuel tank of the car, as well as for preventive purposes, its owner (driver) can add one of the special preparations that “bind” water to gasoline. At a nominal dosage, these drugs, as a rule, do not affect the condition of engine parts and its operation.

8. Antiknock properties

One of the main indicators of the quality of motor gasolines is their detonation resistance, on which reliability, power increase, efficiency and service life of a car engine depend to the greatest extent.

As an indicator of the antiknock properties of gasoline, called the "octane number", the content of isooctane in a mixture with normal heptane, which is equivalent in its antiknock properties to the test fuel, is taken.

Different structure of hydrocarbons at close physical properties causes a sharp difference in their detonation resistance. The octane number of isooctane (C 8 H 18) - a hydrocarbon of the paraffin series of an isomeric structure, characterized by high detonation resistance (begins to detonate only in engines with a very high compression ratio), - is taken as 100 units. The octane number of highly detonating C 7 H 16 heptane, a hydrocarbon of the paraffin series with a normal structure, is taken as 0 units.

Composing mixtures of isooctane with normal heptane in volume percent, it is possible to obtain reference mixtures with knock resistance from 0 to 100 units.

The various octane meters of domestic and foreign production that have appeared recently, working on the principle of measuring the dielectric constant, hydrocarbon composition, have nothing to do with engine installations, on which the octane numbers of gasoline are found.

Knock resistance of motor gasolines is determined on single-cylinder units. When finding octane numbers according to the motor method (GOST 511–82), the UIT-85 or IT9-2M units are used, which allow testing with a variable compression ratio (from 4 to 10 units). They compare the knock resistance of the studied gasoline with the reference fuel, which includes two hydrocarbons: isooctane and normal heptane. A mixture of isooctane and normal heptane has an octane number equal to the percentage (by volume) of isooctane in it.

Detonation intensity is measured and recorded by a special device - a detonometer.

In practice, it was found that the octane number determined by the motor method correlates with the detonation requirements of full-size engines when operating at maximum power and intense thermal conditions and does not fully reflect the entire characteristic of the detonation resistance of motor gasoline under operating conditions. In this regard, a research method for determining octane numbers was developed, which characterizes the detonation resistance of motor gasolines under conditions of engine operation at partial load and lower thermal tension (city traffic). The research method (GOST 8226–82) determines the detonation resistance of gasoline on UIT-65 or IT9-6 units (IT9-6 unit allows you to determine octane numbers by both methods) of domestic production and Vokesha units (USA). Moreover, the detonation resistance is determined in the mode of operation of a passenger car when it is moving in a city. In this case, the letter I is included in the brand of gasoline, for example, AI-95 is motor gasoline with an octane rating of at least 95 according to the research method.

The difference between the octane numbers according to the research and motor methods of the same gasoline is 7 ... 10 units (with the research method, the octane number is higher) and is called sensitivity. The lower the sensitivity, the better the antiknock properties of gasoline. For example, one AI-95 gasoline has an octane number equal to 95 according to the research method, and 86 according to the motor method, and the second gasoline has 95.6 and 85, respectively. The sensitivity in the first case is less and, therefore, the anti-knock properties are better.

The octane number (OC), which approximates the research octane number, can be determined by the formula

(10)

where t cf is the average fuel distillation temperature, °C; ρ 4 20 - fuel density at a temperature of 20 °C.

The average fuel distillation temperature is determined by the formula

(11)

where t n.r - the temperature of the beginning of the dispersal of the fuel, ° C; t k.r - temperature of the end of the distillation of the fuel, °C.

The obtained value of the octane number is compared with the GOST standards for gasoline and it is concluded whether the given gasoline, in terms of octane number determined by a specific test method, corresponds to the GOST standards for this brand of gasoline.

High-octane components (isooctane, alkyl gasoline, toluene, isopentane) or antiknock agents are added to fuels whose antiknock properties do not meet operational requirements. When adding 15...40% of high-octane components to base grades of fuel, gasolines with high knock resistance are obtained.

Antiknock are called organometallic compounds, the addition of which in a small amount sharply increases the anti-knock properties of gasoline. The cheapest of them is tetraethyl lead (TES) or tetramethyl lead (TMS) in the composition of ethyl liquid. TPP and TMS are poisonous.

As an alternative to TES and TMS, manganese compounds, iron pentacarobonyl, iron dicyclopentadienyl, or ferrocene, and iron pentacarbonyl diisobutylene complex, as well as oxygen-containing compounds are used to increase the knock resistance of gasolines. Detergent, antioxidant, anticorrosive and other components are introduced into multifunctional additives and additives.

In Russia and abroad, methyl tertiary butyl ether (MTBE) is widely used in the production of high-octane gasolines.

Anti-knock additive based on MTBE is non-toxic, has a higher calorific value, mixes well with gasoline in any ratio, and is not aggressive to structural materials. With the addition of 10% MTBE, the octane number of gasoline increases by 2.1 ... 5.8 (according to the research method), with the addition of 20% - by 4.6 ... 12.6. In addition, with the introduction of MTBE into gasoline in an amount of 11%, the minimum cold start temperature of the engine is reduced by 10...12 °C. The maximum allowable content of MTBE (TU 103704-90) or its mixture "Feterol" (TU 301-03-130-93) in domestic gasoline is 15%. However, the production of MTBE is planned to be reduced, although it does not pose a threat to health. The reason is that MTBE easily penetrates into groundwater and has an unpleasant odor. It is found in small amounts in many water sources.

Compositions containing manganese and iron are also used as antiknock additives. They have high anti-knock properties and are less toxic compared to TPPs. However, gasolines with manganese antiknock agents (CTM, MCTM) form deposits on the surfaces of spark plugs and afterburner catalysts, reducing their efficiency. In addition, manganese compounds, when inhaled, have a neurotoxic effect and, when massively used in crowded places in closed parking lots or in repair areas, can exceed the maximum allowable concentration.

The GOST R 51105–97 standard for automobile gasolines provides for the production of Normal-80 and Regular-91 gasolines with a manganese content of 50 and 18 g/dm3, respectively.

Iron-containing additives (ferrocenes) are non-toxic, relatively cheap and effective, but cause increased wear of engine parts, intense carbon formation and the deposition of varnish films. At ferrocene concentrations up to 40 mg/kg, the wear rate of parts decreases, but remains higher than when using gasoline without additives. Antiknock agents based on ferrocene are approved for use with the iron content in gasoline of all grades not exceeding 37 mg/dm3.

Based on the ever-increasing requirements for the reliability and environmental performance of engines, leaded gasoline is recognized as not meeting the technical level.

EN 228 standard, therefore its production in Russia and other countries of the world has been discontinued. The use of gasolines with metal additives is considered as a temporary alternative to leaded gasolines.

Appendix 9 lists the most commonly used anti-knock fuel additives.

9. Ecology of motor gasolines

Combustion products of motor fuels are one of the main air pollutants. As fuel consumption increases, the content in the air of the most toxic components of engine exhaust gases, such as lead compounds, nitrogen oxides, carbon monoxide, unburned aromatic hydrocarbons, especially benzene, increases. The solid product of incomplete combustion of fuels, soot, is also dangerous. The harmful effect of soot on humans is associated with the adsorption of many combustion products by its particles, which stimulate the formation of malignant tumors.

During the combustion of gasoline, the most aggressive compounds in the exhaust gases are lead compounds, benzo (α) pyrene and nitrogen oxides. Gasoline vapors also pose a great threat to human health, the content of which in the atmosphere also increases with the increase in the production of petroleum products. Thus, the toxicity of exhaust gases and motor fuel vapors depends on their hydrocarbon composition and the presence of various additives. To improve the quality of gasoline in order to increase environmental safety their application is possible by optimizing the hydrocarbon and chemical composition of fuels. Guidelines for the development and implementation of gasolines with improved environmental performance are the norms of European standards for gasolines EN 228, as well as the actual quality indicators of European fuels, which, as a rule, are higher than the norms regulated by international standards.

The quality of motor gasoline can be improved through the following measures:

• refusal to use lead compounds in gasoline;
• reduction of sulfur content in gasoline to 0.05%, and in the future - to 0.003%;
• reducing the content of aromatic hydrocarbons in gasoline to 45%, and in the future - up to 35%;
• normalization of the concentration of actual resins in gasoline at the place of use at a level not exceeding 5 mg per 100 cm3;
• division of gasoline by fractional composition and saturated vapor pressure into 8 classes, taking into account the season of operation of vehicles and the ambient temperature characteristic of a particular climatic zone. The presence of classes allows the production of gasoline with properties that are optimal for real ambient temperatures, which ensures the operation of engines without the formation of vapor locks at air temperatures up to 60 ° C, and also guarantees high volatility of gasoline and easy engine start at temperatures below -35 ° C;
• the introduction of detergent additives that prevent contamination and gumming of fuel equipment parts.

Annex 10 lists the Customs Union requirements for environmental classes of motor gasoline (TR CU 013/2011).

The concentration of actual resins in domestic gasoline at the place of production should not exceed 5 mg per 100 ml (GOST 31077-2002, STB 1656-2011). The actual content of resins in gasoline, especially those coming from the State Reserve after many years of storage, often exceeds this level, which contributes to the rapid resinization of fuel equipment parts.

The environmental friendliness of the use of automotive fuels is achieved by:

• improving the quality of gasoline to the level of the European standard for the content of sulfur and benzene. In the absence of lead, the environmental aggressiveness of exhaust gases is reduced by 4%;
• the use of MTBE, which reduces the aggressiveness of exhaust gases by 3%, mainly due to the replacement of the aromatic components of gasoline with an oxygen-containing additive and more complete combustion of the fuel (reduction of CO by 12%);
• the use of a detergent additive that reduces the aggressiveness of emissions by 5%.

The total reduction in aggressiveness due to all measures to improve the quality of gasoline is 12%, while the increase in the cost of producing gasoline with improved environmental performance is relatively small and does not exceed 5...8% of the cost of gasoline production.

In accordance with STB 1656–2011 “Fuel for internal combustion engines. Unleaded gasolines” in Belarus provides for the production of gasolines that meet the environmental requirements of European standards EN 228:2008.

US legislation has adopted amendments to the Clean Air Act, which, in connection with changes in environmental requirements for fuels after the ban on lead antiknocks, provide for a transition to the use of reformulated gasolines. In accordance with the adopted amendments, more stringent requirements have been put forward for gasoline in terms of: saturated vapor pressure; fractional composition; the content of aromatic hydrocarbons, benzene, olefins, sulfur. The obligatory addition of oxygen-containing compounds (not less than 0.8% oxygen) and detergent additives to reformulated gasolines is provided.

10. Range of gasolines

Currently, the following are operating on the territory of the Republic of Belarus: regulations, which determine the properties of motor gasolines:

• STB 1656–2011 “Fuel for internal combustion engines. unleaded gasoline";
• GOST 31077–2002 “Fuel for internal combustion engines. unleaded gasoline";
• technical regulation of the Republic of Belarus TR 2008/011/BY “Motor gasoline and diesel fuel. Security";
• technical regulation of the Customs Union TR CU 013/2011

"On the requirements for automobile and aviation gasoline, diesel and marine fuel, jet fuel and fuel oil".

On the territory of the Russian Federation, the standard for motor gasolines GOST R 51313-99 “Motor gasolines. General technical requirements".

Consider the basic requirements for motor gasoline according to GOST 31077–2002 (Table 5).

Table 5Quality indicators of motor gasoline (GOST 31077–2002)

All motor gasolines produced according to specifications, must be certified for compliance with the general technical requirements of GOST 31077–2002.

In order to improve the quality of gasoline to the level of European standards EN 228:2008, STB 1656-2011 was developed. Motor gasolines must comply with the requirements of this standard, which allows the use of dyes and labeling substances, provided that they do not adversely affect the engine and fuel supply system. The standard establishes brands of unleaded gasolines and their

kinds. At the same time, the requirements for AI-95-Euro type I and AI-98-Euro type I gasolines comply with the requirements of the European standard. The requirements for AI-92-Euro gasoline, as well as AI-95-Euro and AI-98-Euro type II gasolines, are additionally established and take into account the provisions of the technical regulation of the Republic of Belarus TR 2008/011/BY (Table 6).

Table 6Quality indicators of motor gasoline (TR 2008/011/BY)

In the labeling of AI-92, AI-95 and AI-98 gasolines, the letter A means that gasoline is automobile, the letter I followed by a number is the octane number determined by the research method.

The toxicity of gasoline combustion products is largely determined by the content of sulfur, benzene and aromatic hydrocarbons in them. The high sulfur content in motor gasoline increases the emissions of sulfur oxides, which have a detrimental effect on human health, flora and fauna, and structural materials. Therefore, depending on the content of sulfur and aromatic hydrocarbons, gasolines are divided into two types: I and II (see Table 6).

When benzene is burned, polycyclic aromatic hydrocarbons (benz(α)pyrenes) are formed, which have carcinogenic properties, i.e. cause cancer. Exhaust gases, which contain more than 300 harmful compounds, also pollute the environment.

To ensure the reliable operation of vehicles in various seasonal and climatic conditions, 10 classes of gasoline are distinguished by volatility: A, B, C, C 1 , D, D 1 , E, E 1 , F, F 1 . With an increase in class, the minimum and maximum pressure saturated vapors, as well as the volume fraction of evaporated gasoline at 70 °C. On the territory of the Republic of Belarus it is recommended to use the following classes of gasoline:

• class B - during the summer period (from April 1 to September 30);
• class D 1 - in transition period(from 1 to 30 October);
• class D - in winter period(from November 1 to March 31). Simultaneous use of summer and winter varieties of gasoline

on or their mixtures during the transition of engines from summer to winter operation and vice versa is allowed within a month. The rest of the time, gasoline must comply with climatic conditions. The use of summer grades of gasoline in winter, for example, leads to an excessive consumption of fuel by 3 ... 5%.

Gasoline "Normal-80" is used mainly for trucks and outdated engine models with a compression ratio of 6.5 ... 7.

Gasoline with octane numbers 91, 92, determined by the research method, are intended for medium-boosted engines cars with a compression ratio of 8 ... 11 and some trucks. AI-95, "Premium-95", AI-98, "Super-98" gasolines are used in passenger car engines with a compression ratio of 8 ... 12. Compliance of brands of automobile gasolines with factory instructions for this car should be observed.

Consider the basic requirements for motor gasoline according to GOST R 51313–99 (Table 7). The requirements established by this standard should be included in all regulatory documents of the Russian Federation for motor gasoline. The standard allows the production of leaded motor gasoline only grade A-76 (AI-80), which is intended for the operation of obsolete trucks of the ZIL and GAZ types, the share of which in the vehicle fleet is declining, and, consequently, the demand for this gasoline is decreasing.

Table 7Quality indicators of motor gasoline (GOST R 51313–99)

However, the requirements of GOST R 51313–99 do not comply with accepted international standards, especially environmental requirements. In order to improve the quality of gasoline to the level of European standards, GOST R 51105–97 was developed, which provides for the production of unleaded gasolines of the Normal-80, Regular-91, Premium-95 and Super-98 brands (Table 8) .

Table 8Quality indicators of motor gasoline (GOST R 51105–97)

Note. All gasolines pass the copper plate test.

Premium-95 and Super-98 gasolines fully meet European requirements and are intended mainly for imported cars.

To provide big cities and other regions of Russia with a high density of road transport using environmentally friendly fuel, at the present stage it is planned to produce unleaded gasolines with improved environmental performance ("City" AI-80EK, AI-92EK, AI-95EK, AI-98EK; "Yar-Marka 92E" and "Yar-Mark 95E"). Compared to gasolines according to GOST R 51105–97, these gasolines are subject to more stringent standards for benzene content, aromatic hydrocarbons regulation and the addition of detergent additives.

Also, a number of gasolines in Russia are produced according to technical specifications. According to TU 401-58-220-98, automobile unleaded gasolines are produced containing anti-knock additive APC of the following grades: A-76, Normal-80, Regular-91, AI-92, AI-93, Premium-95 "," Super-98 ". According to TU 401-58-235-99

they produce automotive compounded gasoline obtained by compounding commercial motor gasoline AI-93 and A-80 with isopentane-pentane fraction and anti-knock additives "Oktan Maximum", "Super Octane", etc.

Depending on the ratio of components, two grades of gasoline are produced: AKZ-1 winter (octane number 93 according to the research method) and AKZ-2 summer (octane number 92 according to the research method).

According to TU 401-58-240-99, automobile unleaded gasoline is produced, produced from gasoline fractions and gas condensate with the addition of anti-knock additives

Super Octane, MTBE, etc. They produce gasoline of the following grades: A-76, Normal-80, Regular-91, AI-92, AI-93, Premium-95 (AI-95), " Super-98" (AI-98).

According to TU 401-58-244-99, unleaded motor gasolines containing ethanol are produced. These gasolines are used for both carbureted and direct injection engines. Gasoline is produced by compounding unleaded gasolines with ethyl alcohol. Ethanol is used as the high octane blending component. It can be used as a substitute for gasoline. Installed

the following brands of gasoline containing ethanol: AI-92E, AI-93E, AI-95E, AI-98E.

According to TU 401-58-264-00, unleaded motor gasoline (city) is produced for use in densely populated areas of the country. Various additives and additives have been introduced into the composition of gasoline, increasing its operational properties.

According to TU 401-58-95-94, unleaded gasolines with improved environmental and operational properties are produced: AI-80F, AI-91F, AI-92F, AI-93F. They add the antiknock additive "Ferro 3" and the detergent additive "Afen" or "Automag".

According to the technical specifications, Euro-Super-95 and AI-95 Super Plus all-season motor gasolines are produced, in which the oxygen-containing component MTBE is present.

According to TU 401-58-288-01, automobile unleaded gasoline is produced in four grades containing methanol: AI-80M, AI-92M, AI-95M, AI-98M. These specifications include standards for cloud point, methanol and iron content.

Summer grades of gasoline are used in all regions of Russia, except for the northern and northeastern regions, from April 1 to October 1, and in the southern regions - all year round. Winter grades of gasoline are used in the northern and northeastern regions as an all-weather fuel, and in other regions - from October 1 to April 1.

The priority tasks to be solved in the field of domestic motor gasoline production are as follows:

• implementation of a complete transition to the production and use of unleaded gasoline only;
• increase in the production of unleaded gasoline with octane numbers over 91 (according to the research method);
• increase in the production of motor gasoline containing various alcohols;
• organizing the supply of gasoline with improved environmental properties to cities and areas with a high density of vehicles.

Gasoline is used as fuel for most cars. It is a mixture of hydrocarbons having a boiling point of 30 to 205 degrees Celsius. In addition to hydrocarbons, gasoline contains impurities containing nitrogen, sulfur and oxygen.

Depending on the number of certain compounds, motor gasoline is divided into different grades that have slightly different performance properties:

• AI-92;
• AI-95;
• AI-98.

With the tightening of environmental requirements, gasolines with a lower octane number, such as A-76 or AI-80, and, consequently, a "dirtier" chemical composition, are not currently being produced.

Basic properties

The main properties of gasoline are its chemical composition, the ability to evaporate, burn, ignite, form deposits, as well as corrosiveness and resistance to detonation.

The physical and chemical properties of gasoline vary depending on which hydrocarbons and in what proportions it contains. The freezing point of gasoline reaches -60 degrees Celsius, in the case of the use of special additives, this value can be lowered to -71 degrees. Gasoline actively evaporates at temperatures above 30 degrees, and with increasing temperature, evaporation occurs more intensively. When the concentration of its vapor in the air reaches 74 - 123 grams per cubic meter, an explosive mixture is formed.

The fractional composition of gasoline directly affects the performance properties. In production, it is important to achieve the correct ratio of light and heavy fractions in order, on the one hand, to ensure a sufficiently high volatility at low temperatures, and on the other hand, to prevent interruptions in the operation of the engine due to the formation of vapor locks in the fuel line, which may occur due to intense evaporation a lot of light fractions. In this regard, gasolines used in places with a hot climate and in the Arctic Circle have a different chemical composition in order to provide the necessary performance properties.

There are several ways to get gasoline: direct distillation of oil and the selection of certain fractions (this method was used at the beginning of the era of motorization), in the middle of the last century, cracking and reforming began to be used. The main component of gasoline obtained by direct distillation is alkane chains. During cracking and reforming, they are converted into branched alkanes and aromatic compounds.

The last two methods make it possible to obtain high-octane fuel grades AI-92, 95 and higher.

Octane number

The name of the brand of gasoline consists of an alphanumeric designation. The letters A or AI indicate the method for determining the octane number:

1. motor (A)
2. research (AI)

and the figure determines the octane number (92, 95, etc.).

The value of the octane number indicates such a property as the resistance of gasoline to detonation. This number is relative. Isooctane is taken as a standard, the detonation resistance of which is very high and is taken equal to 100. The octane number scale was proposed at the beginning of the last century. It was determined by the content of isooctane in a mixture with normal heptane (its detonation resistance is very low and is assumed to be zero). Accordingly, AI-92 gasoline is equivalent in its resistance to detonation to a 92% mixture of isooctane with heptane, AI-95 is 95%, and so on. The octane number can be higher than 100 if the anti-knock properties of the fuel are even higher than those of pure isooctane.


This value is very important, since detonation leads to the rapid destruction of the cylinder-piston group. This is explained by the speed of propagation of the flame front - up to 2.5 km / s, while under normal conditions the flame spreads at a speed of no more than 60 m / s.

To increase the anti-knock properties, one can either add additives containing lead compounds (tetraethyl lead) or change the fractional composition upon receipt. The first method is easily obtained from AI-92 gasoline AI-95, or 98, but it has now been abandoned. Since, although such additives significantly increase the performance properties of the fuel and have a low cost, they are also very toxic and have a much more detrimental effect on the environment than pure gasoline, and also destroy the car’s catalytic converter (the combustion temperature of leaded gasoline is higher than that of unleaded, as a result, the ceramic elements of the neutralizer simply sinter, and the device fails).

Other compounds that are less toxic, such as ethyl alcohol or acetone, can also be used as additives. For example, if you add 100 ml of alcohol to a liter of AI-92 gasoline, then the octane number will increase to 95. However, the use of such additives is not economically viable.

Chemical stability

Considering the chemical properties of gasoline, the main emphasis should be on how long the composition of hydrocarbons will remain unchanged, since during long-term storage, lighter compounds evaporate and performance deteriorates greatly. This problem is especially acute if a higher grade gasoline (AI-95) was obtained from a fuel with a lower octane number (for example, AI-92) by adding propane or methane to its composition. Their antiknock properties are higher than those of isooctane, but they also evaporate very quickly.

The state standard requires that the chemical composition of gasoline of any brand, whether AI-92, 95 or 98, remains unchanged for at least five years, subject to storage rules. However, in reality, often even freshly purchased fuel already has an octane number lower than the declared one (for example, not 95, but 92). This is due to the dishonesty of sellers who add liquefied gas to tanks with fuel whose shelf life has expired and the composition does not comply with GOST. As a rule, different amounts of gas are added to the same gasoline in order to obtain an octane rating of 92 or 95. An obvious confirmation of such tricks is the strong smell of gas at gas stations. It is likely that the performance properties of such gasoline will noticeably deteriorate right before our eyes, before the time the fuel tank is empty.

Petrol is a liquid hydrocarbon fuel, which is a mixture of paraffinic, olefinic, naphthenic and aromatic organic substances. These are the main components of gasoline that determine its properties. Also, the composition of gasoline may include compounds of sulfur, nitrogen and oxygen, the so-called impurities.

The main parameter of gasoline is octane number, which shows resistance to detonation. Moreover, this is not an indicator of the quality of gasoline, but the requirements that the fuel must satisfy in order to be compatible with a certain type of engine.

The octane number is determined by the research or motor method and is indicated by an alphanumeric combination. Fuels with different octane numbers have different specifications according to GOST.

AI-76 GOST, specifications

Gasoline AI-76 this moment not issued. It matches today AI-80. AI-76 was used in carburetor engines and motor vehicles. This is a colorless hydrocarbon fuel of the second class with a boiling range of 33-205⁰С. Gasoline AI-76 could be leaded and unleaded. Acids, alkalis, mechanical impurities and water did not contain.

AI 80 GOST, specifications

Brand of gasoline AI-80 "Normal" refers to unleaded. It has a low sulfur content up to 0.05%, lead - up to 0.15 g/l. The density of AI-80 is up to 0.755 g/cm3. The composition does not contain metal-containing impurities. This is practically the same AI-76 fuel, but with slightly improved characteristics and anti-knock additives.

AI-92 GOST, specifications

Fuel AI-92, "Regular"- until recently it was the most common in our country. Used in injection and carbureted piston engines with spark ignition technology. The properties of gasoline allow you to start the engine at temperatures from -35 to + 60⁰С.

The boiling point of AI-92 is in the range of 33-205⁰С, the amount of lead is up to 0.1 g/cm3, sulfur is up to 0.05%, and the density is up to 780 kg/m3. There are no more than 5 mg of resins per 100 cm3 of fuel. The 92nd belongs to the EURO-4 gasoline group according to the European system, or the 4th environmental class. But a well-refined 92 can also be class 5 gasoline. The environmental class of gasoline does not depend directly on the octane number.

AI-95 GOST, specifications

AI-95 "Extra" characterized by improved qualities and a higher octane number, so it is widely used in high-speed engines of modern cars. This brand contains a small amount of additives, is characterized by high resistance to detonation and an increase in the dynamics of the vehicle. It is characterized by a low content of benzene (up to 5%) and an increased density - up to 0.780 g/cm3.

To increase the octane number are used high octane gasoline components . They are aromatic or aliphatic mixtures of hydrocarbon composition. In base gasoline, such additives can be from 5 to 40%.

Previously, tetraethyl lead was used to increase the octane number. But at the same time, the fuel became poisonous and acquired a reddish tint. Today, dangerous leaded gasoline is banned from production. According to the technical regulations, only lead-free unleaded gasoline is produced.

The main requirements of GOST for gasoline are regulated by the document 32513-2013 Motor fuels. It contains the following characteristics:

• High energy and thermodynamic properties.
• Reliable pumpability through the fuel system.
• Minimum evaporation.
• anti-corrosion qualities.
• The invariance of physico-chemical and operational properties.
• No toxicity.
• Detonation resistance.

Gasoline can be manufactured specifications (TU) while maintaining all the above qualities. Gasoline according to specifications it also has high characteristics in terms of traction and dynamic properties of the car.

Gasoline: hazard class

Gasoline is a flammable liquid, hazardous to health due to aspiration, toxicity, skin irritation. Extremely dangerous if swallowed and inhaled. According to the UN scale regulating the transportation of dangerous goods, gasoline has the 3rd hazard class.

Gasoline production technology

The process of oil refining is aimed at obtaining gasoline and other petroleum products. All oil fractions have their own boiling point, so they are separated at different stages of processing:

1. Vacuum distillation.
2. Thermal cracking.
3. catalytic cracking.
4. Alkylation.
5. Polymerization.
6. Reforming.
7. Hydrocracking.
8. Isomerization.

Excise taxes on gasoline components

Excises on gasoline and diesel fuel are levied on entrepreneurs and organizations. At the same time, the calculation and payment mechanism requires each participant in the turnover of fuel products to calculate the payment independently and transfer this obligation to the next counterparty. According to this scheme, the distribution of excise taxes on gasoline.

The composition and use of gasoline

Gasoline consists of hydrocarbons with a boiling point of 30-205⁰С and impurities of organic substances. Fractional composition determines the performance of gasoline. The correct ratio of heavy and light fractions allows the fuel to evaporate well even in cold climates and prevent engine failure.

Classification of gasolines composition:

• straight-run,
• gas,
• pyrolysis,
• cracked gasolines.

By destination and the use of gasoline can be distinguished:

• automobile (marking A),
• aviation (marking B),
• industrial gasoline (non-toxic and low-hazard),
• technical gasoline (used as a solvent, for washing parts, etc.).

The use of gasoline by brand is determined by the vehicle manufacturer. It is they who indicate in the instruction manual what kind of fuel it is preferable to fill the car. As a rule, the use of gasoline of higher grades than indicated in the recommendation (for example, 95 instead of 92) has a good effect on the traction and dynamic properties of the car. But the use of a grade lower than recommended can lead to engine damage.

The use of gasoline in the production of chemical products for the production of ethylene is widely developed. Here, oil fractions are used, boiling up at temperatures up to 180⁰С. Gasolines used in petrochemistry are called Naphtha.

Gasoline: problems and prospects

The main problem regarding gasoline in our country today is the high cost of a liter of fuel, the growth of which is ahead of inflation. This is due to high excise taxes on gasoline, which account for over 60% of the cost, and fluctuations in the oil market. The situation is already widely discussed at the level of the government of the country.

The main fuel producers today are the companies of the big three VIOCs: Rosneft, Lukoil, Gazpromneft. They are engaged in both wholesale and retail sales of gasoline. In the future, the situation will not change.

And its characteristics. Mixture, flammable, of light hydrocarbons with a boiling point of 33 to 205 °C. Density is about 0.71 g/cm³. Calorific value approximately 10,200 kcal/kg (46 MJ/kg, 32.7 MJ/liter). Freezing point -72 °C if special additives are used. Gasoline is a product of oil refining. Represents fuel with low detonation characteristics. There are: natural gasoline, gasoline of the cracking process, polymerization products. Also liquefied petroleum gases and all products used as industrial motor fuels. Gasoline is the most common fuel for most modes of transport.

Reciprocating internal combustion engines

Gasolines are intended for use in piston internal combustion engines with forced ignition (from a spark). Depending on the purpose, they are divided into automobile and aviation. Despite the differences in the conditions of use, automobile and aviation gasolines are characterized mainly by general quality indicators. Their physicochemical and operational properties are different. Modern automotive and aviation gasolines must meet a number of requirements.

They must ensure economical and reliable operation of the engine (Gasoline and its characteristics). Operation requirements: have good volatility, allowing to obtain a homogeneous air-fuel mixture of optimal composition. At any temperature; have a group hydrocarbon composition that provides a stable, detonation-free combustion process. In all modes of engine operation, do not change its composition and properties. During long-term storage, do not have a harmful effect on parts of the fuel system, tanks, rubber products, etc. In recent years, the environmental properties of fuel have come to the fore.

The composition of gasolines

Gasoline - is a mixture of hydrocarbons consisting mainly of limiting 25-61%, unsaturated 13-45%, naphthenic 9-71%, aromatic 4-16% hydrocarbons with a hydrocarbon molecule length from C 5 to C 10 and the number of carbon atoms from 4 -5 to 9-10 with an average molecular weight of about 100D. Also, the composition of gasoline may include impurities - sulfur-, nitrogen- and oxygen-containing compounds. Gasoline is the lightest fraction of liquid oil fractions (Gasoline and its characteristics). This fraction is obtained in a number of different oil sublimation processes. Therefore, the ease and reliability of starting the engine, the completeness of combustion, the duration of warm-up, the throttle response of the car and the intensity of wear of engine parts depend on the fractional composition of gasolines. The fractional composition of gasoline is determined according to GOST 2177-99.

Light fractions of gasoline characterize the starting properties of the fuel - the lower the boiling point of the fuel, the better the starting properties. To start a cold engine, it is necessary that 10% of gasoline boil away at a temperature not exceeding 55 degrees (winter grade) and 70 degrees (summer grade) Celsius. Winter grades of gasoline have a lighter (than summer) fractional composition. Light fractions are needed only for the period of starting and warming up the engine. The main part of the fuel is called the working fraction. From its evaporation depend: the formation of a combustible mixture under different engine operating modes, the duration of warm-up (transfer from idling to load), throttle response (the ability to quickly switch from one mode to another). The content of the working fraction should coincide with 50% distillate. The minimum temperature range from 90% to the end of the boil improves the quality of the fuel and reduces its tendency to condense, which increases efficiency and reduces wear on engine parts. The boiling point of 90% of the fuel is sometimes called the dew point.

Properties of gasolines

Gasolines are flammable colorless or slightly yellow (in the absence of special additives) liquids with a density of 700-780 kg / m? Gasolines are highly volatile and have a flash point in the range of 20-40 degrees Celsius. The boiling point of gasolines is in the range from 30 to 200 C. The pour point is below minus 60 degrees. The combustion of gasoline produces water and carbon dioxide. At vapor concentrations in the air of 70-120 g/m3, explosive mixtures are formed.
Motor gasolines, due to their physical and chemical characteristics, must have the following properties:

• Homogeneity of the mixture;
• Fuel density - at +20 °С should be 690…750 kg/m2;
• Low viscosity - with its increase, the flow of fuel through the jets becomes more difficult, which leads to a depletion of the mixture. Viscosity is highly dependent on temperature. When the temperature changes from +40 to -40 ° C, the consumption of gasoline through the jet changes by 20 ... 30%;
• Evaporation - the ability to change from a liquid to a gaseous state. Automobile gasoline must have such volatility to ensure easy engine start (especially in winter), its rapid warm-up, complete combustion of fuel, and the formation of vapor locks in the fuel system is also excluded;
• Saturated vapor pressure - the higher the vapor pressure during the evaporation of fuel in a confined space, the more intense the process of their condensation. The standard limits the upper limit of vapor pressure in summer - up to 670 GPa and in winter - from 670 to 930 GPa. Gasolines with higher pressure are prone to the formation of vapor locks, when they are used, the filling of cylinders is reduced and engine power is lost, evaporation losses increase when stored in car tanks and in warehouses;
• Low temperature properties - the ability of gasoline to withstand low temperatures;
• combustion of gasoline. By "combustion" in relation to automobile engines is understood the rapid reaction of the interaction of fuel hydrocarbons with atmospheric oxygen with the release of a significant amount of heat. The vapor temperature during combustion reaches 1500...2400 °C.

Automobile gasolines

In Russia, motor gasolines are produced in accordance with GOST 2084-77, GOST R 51105-97 and GOST R 51866-2002, as well as in accordance with TU 0251-001-12150839-2015 Gasoline AI 92.95 (Alternative).
Automobile gasolines are divided into summer and winter ones (winter gasolines contain more low-boiling hydrocarbons).
The main brands of motor gasoline GOST R 51105-97:
Normal-80 - with an octane rating of at least 80 according to the research method;
Regular-92 - with an octane rating of at least 92 according to the research method;
Premium-95 - with a research octane rating of at least 95;
Super-98 - with a research octane rating of at least 98

Marking of motor gasolines

In accordance with GOST R 54283-2010, motor gasolines are marked with three groups of characters separated by a hyphen (for example, "AI-92-4"):

• the letters "AI" (automotive gasoline with an octane number measured by the research method GOST 8226-82);
• octane number measured by the research method (for example, 80, 92, 95 or 98);
• number 2, 3, 4 or 5 - class of gasoline; the number matches the number of the environmental standard of the Euro series, which gasoline must comply with (2 for Euro-2, 3 for Euro-3, etc.).

Example. The AI-92-4 brand stands for motor gasoline with an octane rating of 92, measured by a research method, corresponding to the fourth environmental class (Euro-4 standard). Since the production of harmful leaded gasoline has officially ceased in Russia since 2003, all gasolines are considered unleaded, and this fact is not displayed in the labeling.

Raw materials for gasoline production

The raw material for producing gasoline is oil. Oil is a natural liquid mixture of various hydrocarbons with small amounts of other organic compounds; a valuable mineral often found together with gaseous hydrocarbons (associated gases, natural gas). Crude oil compounds are complex substances consisting of five elements - C, H, S, O and N, and the content of these elements varies between 82-87% carbon, 11-15% hydrogen, 0.01-6% sulfur, 0–2% oxygen and 0.01–3% nitrogen. Hydrocarbons are the main components of oil and natural gas. (Gasoline and its characteristics) The simplest of them - methane CH4 - is the main component of natural gas.

All hydrocarbons can be divided into aliphatic (with an open molecular chain) and cyclic, and according to the degree of unsaturation of carbon bonds - into paraffins and cycloparaffins, olefins, acetylenes and aromatic hydrocarbons. Conventional well crude oil is a greenish-brown flammable oily liquid with a pungent odor. Chemically, oils are very different and vary from paraffinic, which consist for the most part from paraffinic hydrocarbons, to naphthenic or asphalteneic, which contain mainly cycloparaffinic hydrocarbons; there are many intermediate or mixed types. Paraffin oils, compared to naphthenic or asphaltene oils, usually contain more gasoline and less sulfur and are the main raw material for obtaining lubricating oils and paraffins. Naphthenic types of crude oils generally contain less gasoline but more sulfur and fuel oil and asphalt.

Vladimir Khomutko

Reading time: 11 minutes

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What is the combustion temperature of gasoline?

Gasoline is used as fuel for many cars. It is a mixture of hydrocarbons that has a boiling point of 30 to 205 degrees. In addition to hydrocarbons, gasoline contains impurities of nitrogen, sulfur and oxygen. Depending on the number of certain components, gasoline for cars is divided into various brands that have different performance qualities:

• AI 92.
• AI 95.
• AI 98.

With the tightening of environmental requirements, gasolines with a lower octane number (A 76 or AI 80), which means a dirtier chemical composition, are not manufactured today.

Main qualities

The main qualities of the fuel are its chemical composition, the ability to evaporate, burn, self-ignite, deposit formation, as well as corrosion resistance and fire resistance.

Physico-chemical characteristics depend on which hydrocarbons and in what proportions are present in the fuel. The freezing point of the fuel is -60 degrees, in the case of using special additives, this figure can be reduced to -71 degrees.

Fuel actively evaporates at a temperature of +30 degrees, and with increasing temperature, the evaporation process is more active. When the degree of its vapor in the air is 74-123 grams per m3, an explosive mixture is formed.

The composition of the fuel fraction affects the performance. During manufacture, it is imperative to obtain the optimal ratio of light and heavy compounds in order to obtain a sufficiently high evaporation at low temperatures and prevent engine malfunctions due to the creation of vapor locks in the fuel line, which can appear due to the active evaporation of a large number of light compounds.

In view of this, gasolines that are used in areas with a hot climate and in the regions of the Arctic Circle have different chemical composition in order to provide the desired performance. Gasoline is obtained in several ways:

• by direct distillation of oil;
• by selecting specific fractions;
• cracking;
• reforming.

The main component of the fuel, which is obtained by direct distillation, is alkane compounds. During cracking and reforming, they are transformed into branched alkanes and aromatic components. The last two methods make it possible to obtain fuel with a high octane number of grades AI 92 and 95.

Octane number

The name of the brand of fuel consists of letters and numbers. The letters A or AI mean the method for detecting the octane number:

And the number means octane number (92, 95).

The name of the octane number shows such a quality as the resistance of the fuel to ignition. This number is conditional. Isooctane is used as a reference, the fire resistance of which is very high, and equals 100. The octane rating was created at the beginning of the last century. It was revealed by the composition of isooctane mixed with normal heptane.

Accordingly, AI 92 brand fuel is equivalent in its resistance to ignition to 92% of a mixture of isooctane with heptane, AI 95 - 95%. The octane number can be higher than 100 if the anti-knock qualities of the gasoline are higher than those of pure isooctane.

This value is very important, since ignition leads to a rapid deformation of the cylinder-piston group. This is due to the speed of the spread of flames - up to 2.5 km per second, while under optimal conditions the fire spreads at a speed of no more than 60 meters per second.

To increase the anti-knock qualities, you can either add additives that contain lead, or change the fractional composition upon receipt. The first option can be easily obtained from AI 92, AI 95 or 98 fuel, but today it has been abandoned.

Since, although such additives greatly increase performance characteristics gasoline and have a low cost, they are also very toxic and have a detrimental effect on the environment than clean fuel.

They also destroy the catalytic converter of the vehicle (the combustion temperature of leaded fuel is higher than that of unleaded fuel, as a result, the ceramic compounds of the converter are sintered, and the device is damaged).

Other compounds that are less toxic, such as acetone or ethyl alcohol, can also be used as additives. For example, if you pour 100 ml of alcohol into a liter of AI 92 fuel, then the octane number will increase to 95. But the use of such funds is not economically feasible.

Chemical stability

Considering the chemical qualities of gasoline, the main focus should be on how long the composition of hydrocarbons will remain unchanged, since with long storage, lighter components disappear and performance is greatly reduced.

In particular, the problem is acute if gasoline with a minimum octane number is used to produce fuel of a higher grade (AI 95) by adding propane or methane to its composition. Their antiknock qualities are higher than that of isooctane, but they dissipate instantly.

According to GOST, the chemical composition of fuel of any brand must be unchanged for 5 years, subject to storage rules. But in fact, often even newly purchased fuel already has an octane number below the specified one.

Unscrupulous sellers are to blame for this, they add liquefied gas to containers with fuel, the storage time of which has expired, and the content does not meet the requirements of GOST. Usually, different amounts of gas are added to the same fuel to obtain an octane rating of 92 or 95. Confirmation of such tricks is the sharp smell of gas at gas stations.

Boiling temperature of gasoline

Any person who decides to find information about the boiling point, combustion or ignition temperature of a fuel will find an interesting thing: even in fairly well-known sources, there is a difference between the indicated indicators of the same parameter. Why does this happen and what are the real indicators?

Boiling point of gasoline

The boiling point of gasoline is an interesting quantity. Today, few young motorists know that once upon a time high temperatures air, boiled fuel in the fuel line or carburetor could block the vehicle. This phenomenon contributed to the formation of failures in the system.

The light fractions were strongly heated and separated from the heavier fractions in the form of combustible gas bubbles. The car cooled down, the gases turned into liquid - and it was possible to continue moving. Today, gasoline used at gas stations will boil at about +80 degrees.

Fuel flash point

The flash point of a fuel is the thermal threshold at which freely separated, lighter fractions of the fuel begin to burn from an open fire source when this source is located above the test sample.

In practice, it is shown that the flash point is determined by the method of heating in an open crucible. The fuel to be tested is poured into a small open container. Then it is slowly heated without involving an open flame.

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At the same time, the temperature is monitored in real time. Each time when the temperature of the fuel rises by 1 degree, a flame source is carried out at a small height above its surface. At this moment, when a fire occurs, the flash point is determined.

In other words, the flash point determines the threshold at which the concentration of volatile fuel in the air reaches a value sufficient to ignite under the influence of open source fire.

This indicator reveals the maximum temperature created by burning gasoline. And there is also no unambiguous information that answers this question with one number. Surprisingly, but it is for the combustion temperature that the conditions of the process, and not the composition of gasoline, play a key role.