Classification of fuel by production method. Liquid fuel and its characteristics. Conversion of fuel composition from one mass to another
Fuel is a flammable substance that, when burned, releases a significant amount of heat, which is used directly in technological processes and for heating, or is converted into other types of energy.
By state of aggregation Fuels of organic origin are divided into solid, liquid and gaseous (gaseous).
Based on their origin, organic fuels are divided into natural (natural) and artificial, obtained by various methods.
Table 1.1
Classification of fossil fuels
Depending on the nature of use, organic fuel can be divided into energy fuel (to produce thermal and electrical energy) and industrial (for high-temperature heat-technological installations and systems). Energy and industrial fuels are also defined by the term “boiler and furnace fuel”.
Elemental composition and technical characteristics of organic fuel
Organic fuel contains various compounds of combustible and non-combustible elements. Solid and liquid fuels contain flammable substances such as carbon C, hydrogen H, volatile sulfur S l, and non-combustible substances - oxygen O, nitrogen N, ash A, moisture W. Volatile sulfur consists of organic S or and pyrite S k compounds: S l = S op + S k. Organic fuel is characterized by:
Working mass;
Dry weight;
Combustible mass;
Organic mass.
The sulfur of the organic mass does not contain pyrite. You can recalculate the fuel composition from one mass to another using the appropriate coefficients (Table 1.2)
Table 1.2
Conversion of fuel composition from one mass to another
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Gaseous fuels are usually reduced to dry mass in volume fractions:
The most important technical characteristics of the fuel are the heat of combustion, heat output, ash and moisture content, the content of harmful impurities that reduce the value of the fuel, the yield of volatile substances, and the properties of coke (non-volatile residue).
Heat of combustion(calorific value) of fuel - the amount of heat released during complete combustion of a unit of mass (kJ/kg) or volume (kJ/m 3) of fuel. Heat of combustion is a characteristic that determines fuel consumption for the operation of fuel-using equipment. There are higher and lower calorific values of fuel. When designing boilers and technological units that do not use the latent heat of condensation of water vapor contained in fuel combustion products, calculations are traditionally carried out according to lower calorific valuecapabilities fuel.
In cases where the latent heat of condensation of water vapor is used in units, the calculations include higher calorific value fuel.
The lower heating value of fuel can be determined by knowing the higher heating value
The heat of combustion of fuel is determined experimentally in a calorimetric bomb or in a gas calorimeter. The operating principle of calorimeters is based on the fact that they burn a precisely measured mass or volume of fuel, the released heat of which is transferred to water, the initial temperature and mass of which are known. Knowing the mass of water and measuring the increase in its temperature, the amount of heat released and the heat of combustion of the fuel are determined. With a known fuel composition, its heat of combustion can be calculated analytically. The working lower heat of combustion of solid and liquid fuels can be approximately determined by the formula of D.I. Mendeleev, kJ/kg
Where 
– heat of combustion of each gas included in the fuel, MJ/m 3 ;C m H n,H 2 S,CO,H 2 – content of individual gases in the fuel, % vol.
The heat of combustion of individual gases included in the gaseous fuel is given in table. 1.3.
Heat of combustion various types fuel fluctuates within very wide limits. For comparison different types fuel, when determining consumption rates, reserves, and fuel economy, the concept of conventional fuel was introduced. Conventional fuel is a fuel whose lower calorific value is equal to Q c.t = 29310 kJ/kg (7000 kcal/kg).
To recalculate the consumption of any type of natural fuel into conventional fuel and vice versa, a thermal equivalent is used, which is the ratio of the lower calorific value of the working mass of natural fuel to the calorific value of conventional fuel
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.Introduction
General information about fuel
Fuel classification
Fuel properties
The concept of conventional fuel
Combustion processes
Combustion of gaseous fuel
Combustion of solid fuel
Combustion of liquid fuel
Conclusion
Bibliography
fuel burning volatile
Introduction
The role of fuel in the national economy is great and is growing all the time. Modern enterprises mechanical engineering are the largest consumers of energy and energy resources, in particular such type of energy as fuel. Fuel plays a very important role in human life, as fuel largely satisfies human needs. For example, gas. We heat our houses with gas and cook food on a gas stove. Many motorists switch from gasoline to gas because it is cheaper. Solid fuels such as coal and wood are also used to heat houses, mainly rural ones, and baths.
The main source of receipt liquid fuels is oil. For more rational use oil is distilled into individual components (fractions). To do this, it is heated to different temperatures, and the resulting vapors within certain temperature limits are cooled (condensed). In this way, various gasolines, naphtha, kerosene, diesel oil and waste fuel oil are produced, which are used in industry.
The purpose of this essay is to analyze the essence of fuel, its varieties, its application, and also to consider the main combustion processes of liquid, solid and gaseous fuels.
General information about fuel
Currently, the main source of energy on earth is chemical fuel energy. Natural fossil fuels account for 70 to 80% of all energy consumed.
Fuel is a substance that, when burned, releases a significant amount of heat and is used as a source of energy. Fuel can be natural, found in nature, or artificial, obtained by processing natural fuel.
Fuel consists of flammable and non-flammable parts. In solid fuel, the combustible part contains five elements: carbon, hydrogen, sulfur, oxygen and nitrogen. Carbon, hydrogen and combustible sulfur participate in the combustion of fuel, and nitrogen and oxygen make up the ballast of the combustible part (internal fuel ballast). The non-combustible part (external ballast) includes inorganic substances that turn into ash and moisture after burning fuel. Ash is a mineral residue obtained during complete combustion of fuel. Its composition includes the following oxides: MgO, CaO, Na2O, K2O, FeO, Fe2O3, etc. Refractory ash (with a melting point above 1425 °C) is an easily removable bulk mass, low-melting ash (with a melting point below 1200 °C) - solid residue (slag) in the form of a continuous sticky mass or individual pieces. Moisture is divided into external and internal. External moisture is the result of moisture from the environment entering the fuel. External moisture is removed by drying the fuel. Internal moisture is divided into hygroscopic (being in an adsorbed state with the surface of fuel particles) and hydrate (part of the molecules of certain compounds, i.e. chemically bound).
Solid and liquid fuels are a complex of complex organic and mineral compounds and consist of combustible and non-combustible parts.
The molecular and chemical structure of the combustible part has not been studied fully enough and so far cannot be deciphered in detail. Consequently chemical composition The flammable part is extremely difficult to identify. The structure and chemical compounds included in the non-combustible part, on the contrary, have been studied in sufficient detail.
Organic solid and liquid fuels are characterized by their elemental composition, which is conventionally represented as the sum of all chemical elements and compounds included in the fuel. Moreover, their content is given as a percentage of the mass of 1 kg of fuel. The elemental composition does not provide an idea of the molecular and chemical structure of the fuel. For solid and liquid fuels, the elemental composition can be written as follows:
C + H + Sл + O + N + A + W = 100%
The combustible part of the fuel includes carbon, hydrogen and sulfur (volatile). Volatile sulfur Sl is sulfur that is part of organic compounds and sulfur pyrites FeS2.
When studying the properties of solid and liquid fuels, their working, dry, combustible and organic masses are distinguished. The composition of each mass is assigned a corresponding index: working - p, dry - s, combustible - g and organic - o.
The fuel in the form in which it reaches the consumer and is burned is called working, and the mass and its elemental composition are called working mass and working composition, respectively. The elemental composition of the working mass is written as follows:
The dry mass of fuel, unlike the working mass, does not contain moisture and can be represented by the equality:
The ash content of fuel is always checked only by the dry weight of the fuel.
The combustible composition of the fuel does not contain external ballast, i.e. moisture and ash, and can be written as follows:
The name “combustible mass” is conditional, since its only truly combustible elements are C, H and Sl. The composition of the combustible mass of fossil fuel depends on the nature and conditions of origin of the fuel, as well as on its geological age (i.e., the depth of irreversible transformations that have occurred in organic substances).
The carbon content in solid fuel increases with its geological age, and the hydrogen content decreases. For example, the carbon content in peat is Cr = 50÷60%, in brown coal C = 60 ÷75%, in coal Sg = 75÷90%. With decreasing geological age, the content of plant residues in the fuel increases.
In all thermal engineering calculations, the composition of the fuel is taken according to its working mass, which is the most complete characteristic of the state of the fuel before its combustion.
Fuel classification
Depending on the nature of use, fuel is divided into energy, technological and complex. Recently, they have increasingly resorted to the integrated energy use of fuel, the essence of which is that the fuel is preliminarily subjected to technological processing in order to isolate from it valuable substances used as raw materials for chemical industry. The residual product is used as energy fuel (in the process of semi-coking, oil shale processing, etc.)
By maximum temperature, obtained through complete combustion, fuel can be of high heat output (more than 2000 °C - natural gas, oil products, coal) and low heat output (less than 2000 °C - brown coal, peat, firewood).
According to their state of aggregation, they are divided into solid, liquid and gaseous. Solid fuel is mainly formed from highly organized plants - wood, leaves, pine needles, etc. Dead parts of highly organized plants are destroyed by fungi with free access of air and turn into peat - a loose, vague mass of humus, so-called humic acids. The accumulation of peat turns into a brown mass, and then into brown coal. Subsequently, under the influence of high pressure and elevated temperature, brown coals undergo subsequent transformations, turning into coals, and then to anthracite. Liquid fuels include: petroleum products produced by distillation of crude oil; creosote, which is a product of low-temperature coking and sublimation of coal; synthetic oils resulting from the liquefaction of coal; other types of liquid fuel, for example, those produced from plants (potatoes, rapeseed, etc.) The composition of gaseous fuel is expressed by the content of individual gases in it as a percentage. Gaseous fuel also contains both its combustible part and its non-combustible part, which forms its ballast.
Fuel properties
1. Heat of combustion
The amount of heat released during complete combustion of solid, liquid or gaseous fuel under normal conditions is called the calorific value. The release of heat during fuel combustion is explained by the thermal effect of combustion reactions.
Not all components included in the working mass of fuel emit heat during combustion. The moisture in the fuel absorbs heat when it turns into steam; sulfur, which is part of sulfates, also absorbs heat during their dissociation. Conventionally, a distinction is made between the highest limit of the heat of combustion of fuel, if the moisture in the combustion products is taken into account in the form of liquid, and the lower limit of the heat of combustion, if the moisture in the combustion products is taken into account as steam.
Ash content and humidity
Ash and moisture reduce the quality of fuel and are undesirable impurities. Moisture reduces the heat of combustion and makes it difficult to ignite the fuel; wet fuel is more difficult to transport. Ash is a mineral mass. It can be contained in the substance that formed the fuel, or it can get into it when it occurs in the bowels of the earth as an accidental impurity. For example, coals with a porous structure such as brown coals contain salts crystallized from groundwater in their pores. Ash prevents complete combustion of fuel, forming an airtight layer on the surface of pieces of burning fuel. If the ash melts, then its sintered pieces form slag, which prevents coke from burning out even more than the crumbly ash residue.
Sulfur content
Sulfur is an undesirable impurity in fuel, despite the fact that it, in the form of sulfur pyrites, increases its heat of combustion. When sulfur burns, toxic sulfur dioxide gas is formed, the presence of which in the work area, even in small quantities, worsens working conditions. The presence of sulfur dioxide in the environment during heat treatment worsens the quality of the finished product. In a humid environment at low temperatures, sulfur dioxide forms sulfuric acid vapors, which cause corrosion of metal parts of heating installations.
Volatile flammable substances and coke residue
From solid fuel heated to a temperature of 870-1070K without access to an oxidizer, vapor-gas substances are released, which are called volatiles. Volatile substances are the breakdown products of complex organic substances contained in the organic mass of the fuel. The composition of volatile substances includes molecular nitrogen N2, oxygen O2, hydrogen H2, carbon monoxide CO, hydrocarbon gases CH4, C2H4, etc., as well as water vapor formed from the moisture contained in the fuel.
The chemical composition of volatile substances depends on the conditions of the fuel heating process. The sum of volatile substances is designated V and refers only to the combustible mass.
The solid residue that is obtained after heating the fuel (without access to the oxidizer) and the release of volatiles is called coke. Coke contains residual carbon and ash. Depending on the heating conditions, in addition to the ash, the solid residue may contain some of the elements (C, N, Bl, N) that are part of complex organic compounds, the thermal decomposition of which requires a higher temperature. In this case, the solid residue is called char.
According to their own mechanical properties the solid residue (coke) can be powdery, slightly baked or caked. The property of some coals (coking) to produce sintered, mechanically strong coke is used to produce metallurgical coke used in the blast furnace process.
The concept of conventional fuel
Conventional fuel is a concept introduced for more convenient comparison individual species fuels, summing them up and establishing the quantitative replacement of one type of fuel with another.
As a unit of standard fuel, 1 kg of fuel with a calorific value of 7000 kcal/kg (29.3 MJ/kg) is taken. The relationship between conventional fuel and natural fuel is expressed by the formula:
where By is the mass of the equivalent amount of standard fuel, kg;
Vn - mass of natural fuel, kg (solid and liquid fuel) or m3 (gaseous);
Lower calorific value of a given natural fuel, kcal/kg or kcal/m3;
Calorie equivalent.
Conversion of the amount of fuel of a given type into a standard one is carried out using a coefficient equal to the ratio of the heat content of 1 kg of fuel of a given type to the heat content of 1 kg of standard fuel.
The E value is taken as follows: for oil 1.4; coke 0.93; peat 0.4; natural gas 1.2.
The use of reference fuel is especially convenient for comparing the efficiency of various thermal power plants. For example, in the energy sector the following characteristic is used - the amount of equivalent fuel spent on generating a unit of electricity. This value of g, expressed in g of standard fuel per 1 kW × h of electricity is related to the efficiency of the installation by the ratio:
Reducing all types of fuel to conventional or oil equivalent makes it possible to compare the technical and economic indicators of the operation of fuel-consuming installations using different types of fuel. In addition, this makes it possible to compare reserves and production of various types of fuel, taking into account their energy value. Also, using standard fuel, you can create a fuel balance or the total energy balance of an industry, a country and the world as a whole.
Combustion processes
The fuel combustion process consists of combustion intermediate products its decomposition: volatile flammable substances and solid residue - coke. The volatiles burn first, then the coke. The combustion of volatile substances is preceded by their decomposition when heated into even simpler substances, which burn with a flame in the combustion chamber above the fuel layer when interacting with oxygen in the air. An increase in the concentration of oxygen in the air, good mixing of volatile substances with it, timely removal of combustion products - all this helps to accelerate the combustion process of volatile substances.
Fuel combustion is a chemical reaction of the combination of combustible fuel elements with an oxidizer at high temperature, accompanied by intense heat release. Oxygen is used as an oxidizing agent. It is known that at low temperatures the presence of fuel and oxidizer does not ensure their chemical combination, called combustion. Combustion begins only after the particles have warmed up to a temperature that provides them with an activation energy E sufficient to enter into a reaction.
Combustion is mainly a chemical process, because... as a result of its occurrence, qualitative changes occur in the composition of the reacting masses. But at the same time, the chemical combustion reaction is accompanied by various physical phenomena: heat transfer, diffusion transfer of reacting masses, etc. The fuel combustion time consists of the time of physical ( ) and chemical processes ():
= .
The time required for physical processes to occur consists of the time required to mix the fuel with the oxidizer ( ) and the time during which the fuel-air mixture is heated to the ignition temperature (tn):
tPHYS = tSM + tH
The burning time (tGOR) is determined by the speed of the slowest process.
Combustion of gaseous fuel
The combustion process of gaseous fuel is homogeneous, i.e. both the fuel and the oxidizer are in the same state of aggregation and there is no phase boundary. In order for combustion to begin, the gas must come into contact with the oxidizer. In the presence of an oxidizer, certain conditions must be created for combustion to begin. Oxidation of flammable components is also possible at relatively low temperatures. Under these conditions, the rates of chemical reactions are insignificant. As the temperature increases, the rate of reactions increases. When a certain temperature is reached, the gas-air mixture ignites, the reaction rates increase sharply and the amount of heat becomes sufficient to spontaneously maintain combustion. The minimum temperature at which the mixture ignites is called the ignition temperature. The value of this temperature for different gases is not the same and depends on the thermophysical properties of combustible gases, the content of fuel in the mixture, ignition conditions, heat removal conditions in each specific device, etc. For example, the ignition temperature of hydrogen is in the range of 820-870 K, and carbon monoxide and methane - 870-930 and 1020-1070 K, respectively.
The combustible gas mixed with the oxidizer burns in a torch. A torch is a certain volume of moving gases in which combustion processes occur. In accordance with general provisions Combustion theories distinguish two fundamentally different methods of burning gas in a torch - kinetic and diffusion. Kinetic combustion is characterized by preliminary (before combustion) mixing of the gas with the oxidizer. Gas and oxidizer are first supplied to the burner mixing device. The mixture is burned outside the mixer. In this case, the rate of the process will be limited by the rate of chemical combustion reactions.
Diffusion combustion occurs during the process of mixing combustible gas with air. Gas enters the working volume separately from air. The speed of the process in this case will be limited by the rate of mixing of gas with air.
A type of diffusion combustion is mixed (diffusion-kinetic) combustion. The gas is pre-mixed with some air. This air is called primary. The resulting mixture is fed into the working volume. The rest of the air (secondary air) enters there separately from it.
In the furnaces of boiler units, kinetic and mixed principles of fuel combustion are more often used. The diffusion method is most often used in technological industrial furnaces.
Gas combustion occurs in a narrow zone called the combustion front. The gas, pre-mixed with the oxidizer, burns in a combustion front, which is called kinetic. This front represents the interface between the fresh gas-air mixture and the combustion products. The surface area of the kinetic combustion front is determined by the rate of chemical reactions.
In the case of diffusion combustion of gas, a diffusion combustion front is formed, which is the interface between combustion products and a mixture of gas with combustion products diffusing towards the gas flow. The surface area of this front is determined by the rate of mixing of the gas with the oxidizer.
The most important characteristic of gaseous fuel combustion is the speed of normal flame propagation - the speed at which the combustion front moves normal to its surface in the direction of the oncoming gas-air mixture. The main factors on which the speed of normal flame propagation depends are the reactivity of the gas, its concentration in the mixture, and the temperature of preheating the mixture.
Other important feature combustion of gas-air mixtures - presence of concentration limits. There are lower (LEL) and upper (UEL) concentration flammability limits. The combustion of the gas stops if its concentration in the mixture is less than the concentration at the LEL, or greater than the concentration at the ERV. This is due to the fact that at low gas concentrations, heat becomes clearly insufficient to maintain the reaction. At high gas concentrations, there is a shortage of oxidizer, which also leads to a decrease in the amount of heat and a drop in temperature in the combustion front below the ignition temperature.
Combustion of solid fuel
The combustion process consists of the following stages:
Drying the fuel and heating it to the temperature at which volatile substances begin to release;
Ignition of volatile substances and their burnout;
Heating the coke until it ignites;
Burnout of flammable substances from coke.
Of all these stages, the decisive one is the stage of combustion of coke residue, i.e. the stage of carbon combustion, the intensity of which determines the intensity of fuel combustion and gasification as a whole. The decisive role of carbon combustion is explained as follows.
First, the solid carbon contained in the fuel is the main combustible component of almost all natural solid fuels. For example, the heat of combustion of anthracite coke residue is 95% of the heat of combustion of the combustible mass. With an increase in the yield of volatile substances, the share of the heat of combustion of the coke residue decreases and in the case of peat amounts to 40.5% of the heat of combustion of the combustible mass.
Secondly, the stage of combustion of coke residue turns out to be the longest of all stages and can take up to 90% of the total time required for combustion.
And thirdly, the coke combustion process is crucial in creating thermal conditions for the occurrence of other stages. Consequently, the basis for the correct construction of a technological method for burning solid fuels is the creation of optimal conditions for the carbon combustion process.
Combustion of liquid fuel
Each liquid fuel, just like any liquid substance, at a given temperature has a certain vapor pressure above its surface, which increases with increasing temperature.
Greatest practical use has a method of burning liquid fuel in an atomized state. Fuel atomization makes it possible to significantly accelerate its combustion and obtain high thermal stresses in the combustion chamber volumes due to an increase in the surface area of contact between the fuel and the oxidizer.
The boiling point of liquid fuels is always lower than their self-ignition temperature, i.e., the minimum temperature of the environment from which the fuel ignites and subsequently burns without an external heat source. This temperature is higher than the ignition temperature, at which the fuel burns only in the presence of an external ignition source (spark, hot coil, etc.). As a result, in the presence of an oxidizer, combustion of liquid fuels is possible only in the vapor state. This circumstance is essential for understanding the mechanism of the combustion process of liquid fuel. This process can be divided into the following stages:
Heating and evaporation of fuel;
Formation of a flammable mixture (mixing of fuel vapors with an oxidizer);
Ignition of a flammable mixture;
Combustion of the mixture.
A drop of liquid fuel entering a heated volume, the temperature of which is above the auto-ignition temperature, begins to partially evaporate. Fuel vapor mixes with air to form a steam-air mixture. Ignition occurs at the moment when the concentration of vapors in the mixture reaches a value exceeding its value at the lower concentration limit of ignition. Combustion is then maintained spontaneously by the heat received by the droplet from the combustion of the combustible mixture. Starting from the moment of ignition, the rate of the evaporation process increases, since the combustion temperature of the combustible steam-air mixture significantly exceeds the initial temperature of the volume into which the atomized fuel is introduced.
When a liquid fuel with a free surface is ignited, its vapor contained in the space above the surface ignites, forming a burning torch. Due to the heat emitted by the torch, evaporation increases sharply. In a steady state of heat exchange between the torch and the liquid mirror, the amount of evaporating, and therefore burning, fuel reaches its maximum value and then remains constant over time.
The temperature of a liquid fuel at which vapors above its surface form a mixture with air that can ignite when an ignition source is applied is called the flash point.
Since liquid fuels burn in the vapor phase, in a steady state the combustion rate is determined by the rate of evaporation of the liquid from its mirror.
The combustion process of liquid fuels from a free surface occurs as follows. In a steady-state combustion mode, due to the heat emitted by the torch, the liquid fuel evaporates. Air from the surrounding space penetrates into the upward flow of fuel, which is in the vapor phase, through diffusion. The mixture obtained in this way forms a burning torch in the form of a cone, spaced 0.5-1 mm from the evaporation mirror. Steady combustion occurs on the surface where the mixture reaches a proportion corresponding to the stoichiometric ratio of fuel and air. This assumption follows from the same considerations as in the case of diffusion gas combustion. The chemical reaction occurs in a very thin layer of the flame front, the thickness of which does not exceed a few fractions of a millimeter. The volume occupied by the torch and combustion zone is divided into two parts: inside the torch there are vapors of flammable liquid and combustion products, and outside the combustion zone there is a mixture of combustion products with air.
The combustion of liquid fuel vapors rising inside the torch can be represented as consisting of two stages: the diffusion supply of oxygen to the combustion zone and the chemical reaction itself occurring in the flame front. The speeds of these two stages are not the same: the chemical reaction when taking place high temperatures proceeds very quickly, while the diffusion supply of oxygen is a slow process that limits the overall combustion rate. Consequently, in this case, combustion occurs in the diffusion region, and the combustion rate is determined by the rate of oxygen diffusion into the combustion zone. Since the conditions for the supply of oxygen to the combustion zone when burning various liquid fuels from the free surface are approximately the same, it should be expected that the rate of their combustion relative to the flame front, i.e., to the side surface of the torch, should also be the same. The greater the evaporation rate, the greater the length of the torch.
A specific feature of the combustion of liquid fuels from a free surface is a large chemical underburning. Chemical underburning is primarily a consequence of a general or local lack of air in the combustion zone. Each fuel, which is a carbon compound when burned from a free surface, has its own chemical underburning value, which is, %:
for alcohol......... 5.3
for kerosene........ 17.7
for gasoline........ 12.7
for benzene......... 18.5.
The picture of the occurrence of chemical underburning can be presented as follows: vaporous hydrocarbons, when moving inside a cone-shaped torch to the flame front while being in the region of high temperatures in the absence of oxygen, undergo thermal decomposition until the formation of free carbon and hydrogen.
The glow of the flame is caused by the presence of free carbon particles in it. The latter, having become heated due to the heat generated during combustion, emit more or less bright light. Part of the free carbon does not have time to burn and is carried away in the form of soot by combustion products, forming a smoky torch. In addition, the presence of carbon causes the formation of CO. High temperature and low partial pressure of CO and CO2 in combustion products favor the formation of CO. The amounts of carbon and CO present in combustion products determine the amount of chemical underburning. The higher the carbon content in liquid fuel and the less it is saturated with hydrogen, the greater the formation of pure carbon, the brighter the torch, the greater the chemical underburning.
Thus, studies of the combustion of liquid fuels from a free surface have shown that:
Combustion of liquid fuels occurs after their evaporation in the vapor phase. The burning rate of liquid fuels from the free surface is determined by the rate of their evaporation due to the heat emitted by the combustion zone, under a steady state of heat exchange between the torch and the evaporation mirror;
The rate of combustion of liquid fuels from the free surface increases with increasing temperature of their heating, with the transition to fuels with a higher radiation intensity of the combustion zone, lower heat of vaporization and heat capacity and does not depend on the size and shape of the evaporation mirror;
The intensity of radiation from the combustion zone onto the evaporation mirror burning from the free surface of liquid fuel depends only on its physicochemical properties and is a characteristic constant for each liquid fuel;
The thermal stress of the diffusion plume front above the evaporation surface of liquid fuel practically does not depend on the diameter of the crucible and the type of fuel;
The combustion of liquid fuels from a free surface is characterized by increased chemical underburning, the magnitude of which is characteristic of each fuel.
Keeping in mind that the combustion of liquid fuels occurs in the vapor phase, the combustion process of a drop of liquid fuel can be represented as follows. A drop of liquid fuel is surrounded by an atmosphere saturated with vapors of this fuel. A combustion zone is established near the drop along the spherical surface. The chemical reaction of the mixture of liquid fuel vapor with the oxidizer occurs very quickly, so the combustion zone is very thin. The burning rate is determined by the slowest stage - the rate of evaporation of the fuel. In the space between the drop and the combustion zone there are vapors of liquid fuel and combustion products. In the space outside the combustion zone there is air and combustion products. Fuel vapor diffuses into the combustion zone from the inside, and oxygen diffuses from the outside. Here these components of the mixture enter into a chemical reaction, which is accompanied by the release of heat. From the combustion zone, heat is transferred outward and to the drop, and combustion products diffuse into the surrounding space and into the space between the combustion zone and the drop. However, the mechanism of heat transfer does not yet seem clear.
A number of researchers believe that the evaporation of a burning drop occurs due to molecular heat transfer through a stagnant boundary film at the surface of the drop.
As the droplet burns out due to a decrease in surface area, the total evaporation decreases, the combustion zone narrows and disappears when the droplet burns out completely.
This is how the combustion process proceeds of a drop of completely evaporating liquid fuels, which is at rest in environment or moving with it at the same speed.
The amount of oxygen diffusing to the spherical surface under other conditions equal conditions, is proportional to the square of its diameter, therefore, the establishment of a combustion zone at some distance from the drop causes a higher rate of its combustion compared to the same particle of solid fuel, during the combustion of which the chemical reaction practically takes place on the surface itself.
The burning rate of a liquid fuel droplet is determined by the evaporation rate, and its burnout time can be calculated based on the heat balance equation for its evaporation due to the heat received from the combustion zone.
Thus, the combustion process of liquid fuel can be divided into the following phases:
spraying liquid fuel;
evaporation and formation of a gas-air mixture;
ignition of the flammable mixture and combustion of the latter.
The temperature and concentration of the gas-air mixture vary across the cross section of the jet. As we get closer to external border As the jet flows, the temperature rises and the concentration of the components of the combustible mixture drops. The speed of flame propagation in the steam-air mixture depends on the composition, concentration and temperature and reaches its maximum value in the outer layers of the jet, where the temperature is close to the temperature of the surrounding flue gases, despite the fact that here the combustible mixture is highly diluted with combustion products. Therefore, ignition in an oil flame begins at the root from the periphery and then spreads deep into the jet over the entire cross-section, reaching its axis at a considerable distance from the nozzle, equal to the movement of the central jets during the time of flame propagation from the periphery to the axis. The ignition zone takes the form of an elongated cone, the base of which is located at a small distance from the outlet cross-section of the burner embrasure.
The position of the ignition zone depends on the speed of the mixture; the zone occupies a position in which at all its points an equilibrium is established between the speed of flame propagation and the speed of movement. The central jets, which have the highest speed, attenuate as they move through the combustion space, determining the length of the ignition zone by the place where the speed drops to the absolute value of the flame propagation speed.
The combustion of the main part of vaporous hydrocarbons occurs in the ignition zone, which occupies the outer layer of the torch of small thickness. The combustion of high molecular weight hydrocarbons, soot, free carbon and unevaporated liquid fuel droplets continues beyond the ignition zone and requires a certain space, determining the total length of the torch.
The ignition zone divides the space occupied by the torch into two areas: internal and external. In the internal region, the process of evaporation and formation of a flammable mixture occurs.
In the internal region, vaporous hydrocarbons are subjected to heating, which is accompanied by oxidation and splitting. The oxidation process begins at relatively low temperatures - about 200-300°C. At temperatures of 350-400°C and above, the process of thermal splitting occurs.
The process of oxidation of hydrocarbons favors the subsequent combustion process, since this releases a certain amount of heat and increases the temperature, and the presence of oxygen in the composition of hydrocarbons promotes their further oxidation. On the contrary, the process of thermal decomposition is undesirable, since the high molecular weight hydrocarbons formed in this process are difficult to burn.
Of the petroleum fuels, only fuel oil is used in the energy sector. Fuel oil is a residue from the distillation of oil at a temperature of about 300°C, but due to the fact that the distillation process does not occur completely, fuel oil at temperatures below 300°C still releases a certain amount of lighter vapors. Therefore, when a sprayed stream of fuel oil enters the furnace and is gradually heated, part of it turns into vapor, and part can still be in a liquid state even at a temperature of about 400°C.
Therefore, when burning fuel oil, it is necessary to promote the flow oxidative reactions and prevent thermal decomposition at high temperatures in every possible way. To do this, all the air necessary for combustion should be supplied to the root of the torch. In this case, the presence of a large amount of oxygen in the internal region will, on the one hand, favor oxidative processes, and on the other, lower the temperature, which will cause the splitting of hydrocarbon molecules more symmetrically without the formation of a significant amount of difficult-to-burn high molecular weight hydrocarbons.
The mixture resulting from the combustion of fuel oil contains steam and gaseous hydrocarbons, as well as solid compounds formed as a result of the breakdown of hydrocarbons (i.e., all three phases - gaseous, liquid and solid). Vapor and gaseous hydrocarbons, when mixed with air, form a flammable mixture, the combustion of which can proceed through all possible methods of gas combustion. The CO formed during the combustion of liquid droplets and coke burns similarly.
In a torch, droplets are ignited due to convective heating; A combustion zone is established around each drop. The burning of a drop is accompanied by chemical underburning in the form of soot and CO. Drops of high molecular weight hydrocarbons, when burned, produce a solid residue - coke.
The solid compounds formed in the torch - soot and coke - burn in the same way as heterogeneous combustion of solid fuel particles occurs. The presence of heated soot particles causes the torch to glow.
Free hydrocarbon and soot in a high temperature environment can burn if there is enough air. In the case of a local lack of air or an insufficiently high temperature, they do not burn completely with a certain chemical incompleteness of combustion, turning the combustion products black - a smoky torch.
Chemical underburning, characteristic of the combustion of liquid fuels from a free surface when burning them in a torch, can and should be reduced to almost zero by appropriate regime measures.
Thus, to intensify the combustion of fuel oil, good atomization is necessary. Preheating the air and fuel oil promotes gasification of the fuel oil, therefore it will favor ignition and combustion. All air required for combustion should be supplied to the root of the torch. The temperature in the flame must be maintained at a sufficiently high level and, to ensure intensive completion of the combustion process at the end of the flame, it must not be lower than 1000-1050°C.
Conclusion
Based on the above, the following conclusions can be drawn. Fuel is a substance that, when burned, releases heat from which energy can be obtained. Fuel can be in three physical states: solid, liquid and gaseous, each of which can have its own molecular composition. The combustion process for these types of fuel occurs differently. Thus, for solid fuels, the combustion process goes through the following stages: drying the fuel and heating to the temperature at which volatile substances begin to emerge; ignition of volatile substances and their burnout; heating the coke until it ignites; burning out of flammable substances from coke. The last stage is the main one, since it determines the intensity of fuel combustion and gasification as a whole.
Liquid fuel is usually burned in an atomized state. Fuel atomization makes it possible to significantly accelerate its combustion and obtain high thermal stresses in the combustion chamber volumes due to an increase in the surface area of contact between the fuel and the oxidizer. Combustion of liquid fuels occurs after their evaporation in the vapor phase. The rate of combustion of liquid fuels from the free surface increases with increasing temperature of their heating.
The combustion of gases is carried out in the combustion chamber, where the combustible mixture is supplied through burners. In the combustion space, as a result of complex physical and chemical processes, a stream of burning gas is formed, called a torch. Depending on the method of supplying air necessary for combustion, the following types of gas combustion are possible: combustion of a homogeneous gas mixture, when a pre-prepared combustible gas mixture is burned; diffusion combustion of gases, when gas and air are supplied separately; combustion of a mixture of gases with an insufficient amount of air, when the gas is supplied mixed with air, but the amount of the latter is not enough for complete combustion.
The combustion of all types of fuels produces thermal energy, which can be useful in all industries, but it also leads to adverse consequences, since during combustion harmful substances are released into the atmosphere.
It is also worth noting the reference fuel, which allows you to compare the thermal value of different types of fossil fuels.
Bibliography
1. Optimization of urban gas supply (Lyaukonis A. Yu.) Reviewer: Doctor of Engineering. sciences, prof. A. Yu. Garlyauskas L.: Nedra, 1989
Thermal equipment, Tsypkov V.Sh. Fokin K.F.; Moscow "Stroyizdat", 1973
Internet resource: www.knowhouse.ru
Internet resource: www.belenergetics.ru
Internet resource: www.xumuk.ru/teplotehnika/051
Internet resource: www.bibliotekar.ru/spravochnik-4/27
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Basic definitions, classification and origin of organic fuel. Elemental and technical composition of fuel. Heat of combustion of fuel and methods for its determination. Solid fuel. Liquid fuel. Gaseous fuel. Conditional fuel.
Fuel is a substance that can enter into a rapid oxidative process with oxygen in the air - combustion, releasing a significant amount of heat. Fuel is a complex organic compound containing combustible elements, ballasted with non-flammable components that have a significant impact on its quality.
Its main types are organic fuels: peat, oil shale, coal, natural gas, petroleum products.
By method of receipt A distinction is made between natural and artificial fuels. TO
Natural fuels include natural fuels: coal, shale, peat, oil, natural gases. Among solid fuels, synthetic fuels include coke, coal briquettes, charcoal. Liquids include fuel oil, gasoline, kerosene, diesel oil, and diesel fuel. Gases include blast furnace, generator, and coke oven gases. Peat, brown coals, bituminous coals and anthracites were formed in the process of successive carbonification of dead plant matter.
Further classification of each group can be made according to their state of aggregation for solid, liquid and gaseous fuels.
The composition and quality of the fuel is determined using chemical and technical analysis. To do this, a so-called average sample of a given batch of fuel is taken, which should most accurately reflect the properties and composition of the entire batch or layer from which the fuel is extracted. The selection of the average batch is carried out in accordance with specially developed instructions.
Fuel extracted from the subsoil, from the surface of the earth and delivered to the consumer is called working fuel. The composition of the working fuel includes: carbon (C), hydrogen (H), volatile sulfur (S l), which during combustion release a certain amount of heat, oxygen (O) and nitrogen (N), which represent the internal ballast of the fuel, and finally , ash (A) and moisture (W), making up the external fuel ballast. All of the above elements included in the fuel are given as a percentage by weight. The fuel in the form in which it reaches the consumer is called working, and the substance that composes it is called working mass. Its elemental chemical composition is expressed as follows:
C p + H p + O p + N p + S p + A p + W p =100%
Mineral impurities and humidity of the same type of fuel in different areas of its deposit and in different places can be different, and can also change during transportation and storage. The composition of the combustible mass of the fuel is more constant. With this circumstance in mind, for the comparative thermal technical assessment of various types of fuel, the conventional concepts of dry, combustible and organic mass were introduced, the components of which, expressed as a percentage, are denoted by the same symbols as the working mass, but respectively with the indices “c”, “g” " and "o" instead of the working mass index, "p".
Moisture. The moisture content in solid fuels varies widely - from 5% to 60%. The moisture content of liquid and gaseous fuels is low. Fuel moisture is divided into external (mechanical) W ext, %, and internal (hygroscopic) W gr, %. Their sum is the operating humidity
W р = W in + W gr, [%]
External moisture is removed from the fuel when it is naturally dried at room temperature. The reduction in fuel weight will stop when there is an equilibrium between the pressure of water vapor in the fuel and the partial pressure of water vapor in the surrounding air.
Internal moisture is retained in the pores of the fuel due to the presence of capillary forces and is removed from it only by heating the fuel. In a drying oven up to 105 0 C. The internal moisture content in solid fuel reaches 10%. However, the total moisture found in this way turns out to be less than the moisture actually found in the fuel, because a number of solid fuels contain crystallization or hydration moisture associated with some mineral components of the fuel: clay, silicates, organic substances. This moisture can be removed from the fuel only at a temperature of 800 0 C.
The presence of moisture in the fuel negatively affects its quality, and, consequently, the operation of the boiler installation, since moisture reduces the amount of flammable substances in the fuel, and, of course, reduces the amount of heat released during its combustion. In addition, part of the heat goes to evaporate moisture, and then leaves along with the vapors from the boiler plant, reducing its efficiency. It should also be noted that it is difficult to ignite fuel containing moisture and that the volume of flue gases increases, which in turn increases the energy consumption of smoke exhausters. At low temperatures of flue gases, the presence of water vapor in them causes the risk of condensation of the latter and the occurrence of corrosion of metal heating surfaces and chimneys.
Ash. The solid non-combustible residue resulting from the completion of transformations in the mineral part of the fuel during its combustion is called ash. The release of the gasifying part of the impurities reduces the mass of ash in relation to the initial mineral impurities of the fuel, and some reactions, for example, the oxidation of iron pyrites, lead to its increase. Typically, the mass of ash is slightly less than the mass of mineral impurities in the fuel, only in oil shale due to the decomposition of the ash carbonates contained in them
is obtained significantly less compared to the mass of mineral impurities.
There is no ash as such in the original fuel. It arises as a result of fuel combustion as a dry residue. In solid fuels, the ash content ranges from 2% to 60%. In liquid and gaseous fuels, the ash content is extremely low.
Ash is a mixture of various minerals trapped in the fuel. Ash is divided into three types. Primary ash enters the source material - wood - in the form of dissolved salts along with soil water and is evenly distributed in it. Secondary ash also enters the fuel from the outside with groundwater or as a result of mountain-forming processes that occurred in prehistoric times. Both types of this ash cannot be isolated from fuel. Tertiary ash is a random impurity in the form of rock captured during fuel extraction and separated from it as a result of enrichment.
In the combustion chamber at high temperatures, part of the ash melts,
forming a mineral solution called slag. Slag is removed from the furnace in a liquid or granular state. To assess the degree of contamination of the combustible mass of fuel, the ash content is related to its dry mass, expressing it as a percentage. Ash content is determined by burning a pre-dried fuel sample of a certain mass in a platinum crucible and calcination to a constant mass (solid fuels at a temperature of 800±25°C, and liquid fuels at 500°C). The ash content of fuel varies from fractions of a percent in fuel oil and wood to 40-60% in shale.
The ash formed during the combustion of fuel at high temperatures and a short residence time in the combustion chamber differs in its chemical and mineralogical composition from the ash formed when analyzing ash content by burning fuel in laboratory conditions.
Important properties of ash are its abrasiveness and fusibility characteristics. Highly abrasive ash causes severe wear on the convective heating surfaces of heat generators.
The fusibility of ash is determined by heating in a special furnace in a semi-reducing gas environment a triangular pyramid of standard dimensions with a height of 13 mm and a base edge length of 6 mm, made from a crushed sample of the tested ash (GOST 2057-49).
The following characteristics of ash fusibility are distinguished:
t 1 is the temperature at which deformation begins, at which the pyramid bends or its top is rounded;
t 2 - temperature of the onset of softening at which the top of the pyramid
tilts to its base or the pyramid turns into a ball;
t 3 - temperature of the onset of the liquid-melting state at which the pyramid
spreads on the stand;
t 0 - temperature of the beginning of the true liquid state, at which the melt
slag obeys Newton's laws of true fluid flow.
According to the characteristics of ash fusibility, steam coals are divided into three groups: with fusible ash t 3<1350 °С, с золой средней плавкости
1350< t 3 <1450 °С и с тугоплавкой золой t 3 >1450 °C.
The presence of ash in fuel significantly reduces its value and causes difficulties in the process of its combustion. Fly ash carried into the flues of the boiler unit abrades and contaminates heating surfaces, worsening the heat transfer coefficient. Ash and slag deposited in boiler units require special measures for their removal.
Carbon. Carbon is one of the most essential components of each fuel and is not included in its composition in a free state, but in the form of complex organic compounds with hydrogen, oxygen, sulfur and nitrogen. When burned, pure carbon releases 8130 kcal/kg (34.4 MJ/kg) and is the main source of fuel's calorific value. The carbon content in some solid fuels reaches 95%.
Hydrogen. Another important component of fuel is hydrogen, the content of which in the combustible mass of solid and liquid fuels ranges from 2 to 10%. A lot of hydrogen is contained in natural gas, fuel oil and oil shale, least of all in anthracite. In terms of calorific value, hydrogen is almost 4 times higher than carbon and its heat of combustion into water vapor is 10.8 MJ/m 3 (2579 kcal/m 3).e.
Sulfur. The sulfur content in solid fuels, with the exception of shale, is low. When burned, sulfur releases a small amount of heat. There are three types of sulfur in fuel. Organic sulfur S 0 and pyrite Sk make up the so-called flammable volatile sulfur:
S l = S 0 + Sk [%]
The third type of sulfur is sulfate sulfur - S a, which is already oxidized and therefore cannot release heat, as a result of which it is included in the fuel ash in the form of mineral compounds with iron and calcium. The total sulfur content in the fuel is
Sob = Sl + Sa [%]
Organic sulfur is part of complex high-molecular organic fuel compounds. Pyrite sulfur is its compounds with metals, most often with iron (FeS_2 - iron pyrite), and is included in the mineral part of the fuel. Organic and pyrite sulfur S l _is oxidized during fuel combustion, releasing heat. Sulfate sulfur enters the mineral part of the fuel in the form of sulfates CaS0 4 and FeS0 4 and therefore does not undergo further oxidation during the combustion process. Sulfate compounds of sulfur turn into ash during combustion. The combustible mass of fuel includes S o and S k, which, during fuel combustion, turn into gaseous compounds SO 2, and in small quantities into SO 3.
The sulfur content of solid fuels is usually low. In oil, sulfur is part of inorganic compounds; in natural gases it is practically absent; associated gases from some oil fields contain some sulfur in the form of hydrogen sulfide H 2 S and sulfur dioxide SO 2. The sulfur dioxide gas formed during fuel combustion, and especially the small amount of sulfur dioxide SO3 accompanying it, causes corrosion of the metal parts of heat generators and poisons the surrounding area. Due to the low heat of combustion - 9.3 MJ/kg (2220 kcal/kg), the presence of sulfur reduces the heat of combustion of the fuel. Therefore, sulfur is a harmful and undesirable impurity in fuel.
Nitrogen and oxygen refer to internal fuel ballast. Nitrogen is an inert gas. Its content in solid fuel is 1-2% and during fuel combustion it is released in a free state.
The oxygen content in fuel varies widely, reaching 40%. It is generally accepted that all the oxygen in the fuel is associated with hydrogen and when the fuel burns, they form water vapor. In addition, oxygen, when combined with hydrogen or carbon in the fuel, converts some of the combustibles into an oxidized state and reduces its heat of combustion. The oxygen content is high in wood and peat. When burning fuel in an air atmosphere, nitrogen does not oxidize and passes into combustion products in free form.
Motor fuel is easy to define – it is fuel for internal combustion engines. Traditionally, the classification of the main types of motor fuels is related to what they are produced from. That is, fuel is considered as a product of oil distillation. According to this criterion, petroleum products are divided into two groups - distillate and residual. The former include all types of gasoline, some types of diesel fuel, kerosene and some other little-known types. For example, gas oil and naphtha. But diesel fuel and fuel oil are residual types. Their fractions are obtained at maximum distillation temperatures.
Of course, Euro 4 diesel fuel refers to distillate products, and in its name we see another sign of the classification of motor fuel - environmental properties. But he's not the only one. The main characteristics for the intended purpose, that is, for use in the engine, are also influenced by other factors. For all types of fuel presented, for example, on the website http://oilresurs.ru/, the most important characteristic is flammability, that is, the ability of the air-fuel mixture to burn efficiently.
The volatility and viscosity of the fuel are also important, on which the ability to pump it through the engine fuel system depends, as well as the content of resinous substances. This characteristic, as well as the degree of coking and ash content, affect harmful deposits in the engine. High-quality fuel must have low chemical activity and be free of mechanical impurities. It is precisely these motor fuels of the types listed above that are offered by Oil Resource Group LLC.
However, they do not exhaust all types of fuel for engines. Only liquid petroleum products were discussed above, but natural gas is also widely used. Two types of it are used - compressed and liquefied. A liquefied mixture of propane and butane is the third most common type of fuel in the world. Advantages: possibility of use on conventional gasoline and diesel engines, environmental friendliness and reduced engine wear. Of course, and lower cost.
There are other types of motor fuel that are alternative to petroleum products. Traditional internal combustion engines also use alcohol as fuel. As a rule, this is not pure ethanol or methanol, but a mixture with gasoline in one proportion or another. Alcohol can also be added as an additive in small quantities to improve performance, but such a mixture is considered an alternative fuel if it contains more than 85% alcohol. Biodiesel fuel is produced from plant raw materials and even animal fats, however, in general, such types of motor fuel have not yet become widespread.
Requirements for fuel quality
When using and storing motor gasoline, the following requirements apply.
High energy and thermodynamic characteristics of combustion products. When burning gasoline, the maximum amount of heat should be released, the combustion products should have a low molecular weight, low heat capacity and thermal conductivity, and a high value of the product of the specific gas constant and the combustion temperature (RT). It is desirable to obtain a high RT value by increasing T.
Good pumpability. Gasolines must be reliably pumped through the fuel system of cars, pipelines, pumps, control systems and other units and communications under any environmental conditions - low and high temperatures, various pressures, dust and humidity.
Optimal evaporation. Under storage and transportation conditions, evaporation should be minimal. When used in an engine, gasoline must have such volatility to ensure reliable ignition and combustion of the fuel at an optimal speed in the combustion chambers of engines.
Minimal corrosiveness. Fuels must not contain components that destroy the engine’s structural materials, storage and transportation means.
High stability under storage and use conditions. Fuels should not change their physical, chemical and operational properties over a long period of time.
Non-toxic. Combustion products must also be non-toxic.
Properties of motor gasolines
Gasolines are fuels that boil off in the temperature range 28-2150C and are intended for use in internal combustion engines with forced ignition. Depending on their purpose, gasolines are divided into automobile and aviation.
The main indicators of gasoline are detonation resistance, saturated vapor pressure, fractional composition, chemical stability, etc. Tightening of environmental requirements for the quality of petroleum fuels in recent years has limited the content of aromatic hydrocarbons and sulfur compounds in gasoline.
Knock resistance
Detonation occurs if the speed of flame propagation in the engine reaches 1500-2500 m/s, instead of the usual 20-30 m/s. As a result of a sharp pressure drop, a detonation wave occurs, which disrupts the operating mode of the engine, which leads to excessive fuel consumption, a decrease in power, engine overheating, and burnout of pistons and exhaust valves.
Octane number (RON)
OCH is a conventional indicator characterizing the resistance of gasoline to detonation and numerically corresponding to the detonation resistance of a model mixture of isooctane and n-heptane.
The OR of isooctane is taken as 100 points, and n-heptane - as 0. For motor gasolines (except A-76), the OR is measured by two methods: motor and research. The octane number is determined in special installations by comparing the combustion characteristics of the test fuel and standard mixtures of isooctane and n-heptane. Tests are carried out in two modes: hard (crankshaft speed 900 rpm, intake mixture temperature 149 0C, variable ignition timing) and soft (600 rpm, intake air temperature 52 0C, ignition timing 13 degrees). The motor (MO) and exploratory (ROI) are obtained, respectively. The difference between the ROM and the RON is called sensitivity and characterizes the degree of suitability of gasoline for different engine operating conditions. The arithmetic average between the ROM and the RON is called the octane index and is equated to the road octane number, which is standardized by the standards of some countries (for example, the USA) and is indicated at gas stations as a characteristic of the fuel sold.
In the production of gasoline by mixing fractions of various processes, the so-called mixing grades (MBVs), which differ from the calculated values, are important. The ORV depends on the nature of the petroleum product, its content in the mixture and a number of other factors. For paraffinic hydrocarbons, the ORC is 4 points higher than the actual value; for aromatic hydrocarbons, the dependence is more complex. The difference can be significant and exceed 20 points. The blending octane number is also important to consider when adding oxygenates to fuel.
Fractional composition (FS)
The FS of gasoline characterizes the volatility of the fuel, which determines engine starting, fuel distribution among the engine cylinders, combustion completeness, and engine efficiency. Volatility is determined by the distillation temperature of 10, 50 and 90% (vol.) boiling of gasoline fractions. The boiling point of 10% gasoline characterizes the starting properties. At temperatures below the limit values, vapor locks may form in the engine power system, and at higher temperatures, starting the engine is difficult. In the USA, the starting properties of an engine are characterized by the amount of fuel boiling up to 70 0C. The boiling point of 50% characterizes the speed of the engine transition from one operating mode to another and the uniform distribution of gasoline fractions among the cylinders. The boiling point of 90% of the fractions and the end of boiling affect the completeness of fuel combustion and its consumption, as well as carbon formation in the combustion chamber in the engine cylinder. In GOST R 51105-97, which has been in force since January 1, 1999, the FS of gasoline is determined at boiling points of 70, 100 and 180 0C.
Saturated Vapor Pressure (SVP)
DNP gives additional information about the volatility of gasoline, as well as the possibility of gas plugs forming in the engine power system. The higher the saturated vapor pressure of gasoline, the higher its volatility. Based on the FS of gasoline, the volatility index is calculated.
Gasolines used in summer have a lower DNP. To ensure the necessary starting properties of commercial gasoline, it contains light components: isomerizate, alkylate, butane, fr. n.k. - 62 0С.
Chemical stability (CS)
During the storage, transportation and use of gasoline, changes in their chemical composition are possible due to oxidation and polymerization reactions. Oxidation leads to a decrease in the octane number of gasoline and an increase in its tendency to form carbon deposits. To assess cholesterol, indicators of the content of actual resins and the induction period of oxidation are used.
Active sulfur compounds contained in gasoline cause severe corrosion of the fuel system and transport tanks; The completeness of gasoline purification from these substances is controlled by analysis on a copper plate. Inactive sulfur compounds do not cause corrosion, but the gases formed during their combustion cause rapid abrasive wear of engine parts, reduce power, and worsen the environmental situation.
Among aromatic compounds, the most dangerous to human health and life are benzene and polycyclic compounds. Their toxic effect is explained by the possibility of its oxidation in the body. In this regard, the latest regulatory documents limit the permissible content of sulfur, benzene and aromatic compounds in gasoline.
Classification of motor gasolines
There are several types of classification of motor gasoline. The main ones (the most frequently used): volatility, fractional composition, octane number.
Classification by volatility
Depending on the climatic region of use, motor gasolines are divided into five classes (see Table 1.1). Along with determining the distillation temperature at a given volume, it is also possible to determine the volume of evaporated gasoline at a given temperature. The “volatility index” (IV) indicator has also been introduced. The AI of gasoline characterizes the volatility of gasoline and its tendency to form vapor locks at a certain combination of saturated vapor pressure and the volume of evaporated gasoline at a temperature of 70 0C. AI is calculated using the formula:
where DNP is saturated vapor pressure, kPa; V70 - volume of evaporated gasoline at a temperature of 70 0C, %.
Classification of motor gasoline by volatility
| Index | Class | ||||
| 1 | 2 | 3 | 4 | 5 | |
| Saturated vapor pressure, kPa | 35-70 | 45-80 | 55-90 | 60-95 | 80-100 |
| Fractional composition: | |||||
| beginning of boiling, 0 C, not lower | 35 | 35 | not standardized | ||
| 10%, 0 C, not higher | 75 | 70 | 65 | 60 | 55 |
| 50%, 0 C, not higher | 120 | 115 | 110 | 105 | 100 |
| 90%, 0 C, not higher | 190 | 185 | 180 | 170 | 160 |
| end of boiling point, 0 C, not higher | 215 | 215 | 215 | 215 | 215 |
| Amount of evaporated gasoline, % (vol.) at 70 0 C | 10-45 | 15-45 | 15-47 | 15-50 | 15-50 |
| Volatility index, no more | 900 | 1000 | 1100 | 1200 | 1300 |
Classification by fractional composition
Depending on the fractional composition, motor gasolines are divided into winter and summer: for winter, all boiling points are lower than for summer. This greatly facilitates engine starting at low temperatures in the case of winter and reduces the risk of vapor locks in the warm season in the case of summer.
Classification by octane number
Depending on the octane number, four brands of gasoline are established using the research method: “Normal-80”, “Regular-92”, “Premium-95” and “Super-98” (see Table 1.2). Normal-80 gasoline is intended for trucks along with AI-80 gasoline. Gasoline "Regular-92" is intended for use in cars instead of leaded A-93. Motor gasoline "Premium-95" and "Super-98" fully meet European requirements and are competitive in the oil market and are intended mainly for foreign cars operated in Russia.
Classification of motor gasoline by octane number
Research method | Stamps | |||
| "Normal-80" | "Regular-92" | "Premium-95" | "Super-98" | |
| Octane number, not less: | ||||
| motor method | 76,0 | 83,0 | 85,0 | 88,0 |
| research | 80,0 | 92,0 | 95,0 | 98,0 |
Characteristics of motor gasolines. Standards and requirements for their quality. Average composition components
All gasolines produced in accordance with GOST 2084-77, depending on volatility indicators, are divided into summer and winter. Winter gasolines are intended for use in the northern and northeastern regions during all seasons and in other areas from October 1 to April 1. Summer - for use in all areas except the northern and northeastern ones in the period from April 1 to October 1; in the southern regions it is allowed to use summer gasoline during all seasons.
Characteristics of motor gasolines
Indicators | AI-80 | AI-92 | AI-95 |
| Detonation resistance: octane number, not less than: | |||
| motor method | 76 | 85 | 85 |
| research method | 93 | 95 | |
| Mass content of lead, g/dm3, no more | 0,013 | 0,013 | 0,013 |
| Fractional composition: starting temperature of gasoline distillation, °C, not lower than: | |||
| summer | 35 | 35 | 30 |
| winter | |||
| 10% of gasoline is distilled at a temperature, °C, not higher than: | |||
| summer | 70 | 70 | 75 |
| winter | 55 | 55 | 55 |
| 50% of gasoline is distilled at a temperature, °C, not higher than: | |||
| summer | 115 | 115 | 120 |
| winter | 100 | 100 | 105 |
| 90% of gasoline is distilled at a temperature, °C, not higher than: | |||
| summer | 180 | 180 | 180 |
| winter | 160 | 160 | 160 |
| Boiling point of gasoline, °C, not higher than: | |||
| summer | 195 | 205 | 205 |
| winter | 185 | 195 | 195 |
| Residue in flask, %, no more | 1,5 | 1,5 | 1,5 |
| Remaining and losses, %, no more | 4 | 4 | 4 |
| Saturated vapor pressure of gasoline, kPa: | |||
| summer, no more | 66,7 | 66,7 | 66,7 |
| winter | 66,7-93,3 | 66,7-93,3 | 66,7-93,3 |
| Acidity, mg KOH/100 cm3, no more | 1 | 0,8 | 2 |
| Induction period at the gasoline production site, min, not less | 1200 | 1200 | 900 |
| 0,1 | 0,1 | 0,1 |
Source: GOST 2084 - 77
The parameters of motor gasoline produced in accordance with GOST 2084-77 differ significantly from accepted international standards, especially in terms of environmental requirements. In order to increase the competitiveness of Russian gasoline and bring their quality to the level of European standards, GOST R 51105-97 “Fuels for internal combustion engines. Unleaded gasoline. Technical conditions”, which comes into force on January 1, 1999. This standard does not replace GOST 2084-77, which provides for the production of both leaded and unleaded gasoline. In accordance with GOST R 51105-97, only unleaded gasoline will be produced (maximum lead content no more than 0.01 g/dm3).
Standards and requirements for the quality of motor gasoline and volatility characteristics in accordance with GOST R 51105-97 are given in the table.
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