Specific heat of combustion of fuel and combustible materials. Calorific value of various types of fuel
In this lesson, we will learn how to calculate the amount of heat that fuel releases during combustion. In addition, consider the characteristics of the fuel - the specific heat of combustion.
Since our whole life is based on movement, and movement is mostly based on the combustion of fuel, the study of this topic is very important for understanding the topic "Thermal phenomena".
After studying the issues related to the amount of heat and specific heat capacity, we turn to the consideration the amount of heat released during the combustion of fuel.
Definition
Fuel- a substance that in some processes (combustion, nuclear reactions) releases heat. Is a source of energy.
Fuel happens solid, liquid and gaseous(Fig. 1).
Rice. 1. Types of fuel
- Solid fuels are coal and peat.
- Liquid fuels are oil, gasoline and other petroleum products.
- Gaseous fuels include natural gas.
- Separately, one can single out a very common lately nuclear fuel.
Fuel combustion is a chemical process that is oxidative. During combustion, carbon atoms combine with oxygen atoms to form molecules. As a result, energy is released, which a person uses for his own purposes (Fig. 2).
Rice. 2. Formation of carbon dioxide
To characterize the fuel, such a characteristic is used as calorific value. Calorific value shows how much heat is released during the combustion of fuel (Fig. 3). In calorific physics, the concept corresponds specific heat of combustion of a substance.
Rice. 3. Specific heat of combustion
Definition
Specific heat of combustion- the physical quantity characterizing the fuel is numerically equal to the amount of heat that is released during the complete combustion of the fuel.
The specific heat of combustion is usually denoted by the letter . Units:
In units of measurement, there is no , since the combustion of fuel occurs at an almost constant temperature.
The specific heat of combustion is determined empirically using sophisticated instruments. However, there are special tables for solving problems. Below we give the values of the specific heat of combustion for some types of fuel.
|
Substance |
|
Table 4. Specific heat of combustion of some substances
From the given values it can be seen that during combustion a huge amount of heat is released, therefore the units of measurement (megajoules) and (gigajoules) are used.
To calculate the amount of heat that is released during the combustion of fuel, the following formula is used:
Here: - mass of fuel (kg), - specific heat of combustion of fuel ().
In conclusion, we note that most of the fuel that is used by mankind is stored with the help of solar energy. Coal, oil, gas - all this was formed on Earth due to the influence of the Sun (Fig. 4).
Rice. 4. Formation of fuel
In the next lesson, we will talk about the law of conservation and transformation of energy in mechanical and thermal processes.
Listliterature
- Gendenstein L.E., Kaidalov A.B., Kozhevnikov V.B. / Ed. Orlova V.A., Roizena I.I. Physics 8. - M.: Mnemosyne.
- Peryshkin A.V. Physics 8. - M.: Bustard, 2010.
- Fadeeva A.A., Zasov A.V., Kiselev D.F. Physics 8. - M.: Enlightenment.
- Internet portal "festival.1september.ru" ()
- Internet portal "school.xvatit.com" ()
- Internet portal "stringer46.narod.ru" ()
Homework
The tables present the mass specific heat of combustion of fuel (liquid, solid and gaseous) and some other combustible materials. Fuels such as: coal, firewood, coke, peat, kerosene, oil, alcohol, gasoline, natural gas, etc. are considered.
List of tables:
In an exothermic fuel oxidation reaction, its chemical energy is converted into thermal energy with the release of a certain amount of heat. The resulting thermal energy is called the heat of combustion of the fuel. It depends on its chemical composition, humidity and is the main one. The calorific value of fuel, referred to 1 kg of mass or 1 m 3 of volume, forms the mass or volumetric specific calorific value.
The specific heat of combustion of fuel is the amount of heat released during the complete combustion of a unit mass or volume of solid, liquid or gaseous fuel. In the International System of Units, this value is measured in J / kg or J / m 3.
The specific heat of combustion of a fuel can be determined experimentally or calculated analytically. Experimental methods for determining the calorific value are based on the practical measurement of the amount of heat released during the combustion of fuel, for example, in a calorimeter with a thermostat and a combustion bomb. For fuel with known chemical composition the specific heat of combustion can be determined from Mendeleev's formula.
There are higher and lower specific heats of combustion. The gross calorific value is equal to the maximum number heat released during complete combustion of the fuel, taking into account the heat spent on the evaporation of the moisture contained in the fuel. The lower calorific value is less than the higher value by the value of the heat of condensation, which is formed from the moisture of the fuel and the hydrogen of the organic mass, which turns into water during combustion.
To determine fuel quality indicators, as well as in heat engineering calculations usually use the lowest specific heat of combustion, which is the most important thermal and operational characteristic of the fuel and is given in the tables below.
Specific heat of combustion of solid fuel (coal, firewood, peat, coke)
The table shows the values of the specific heat of combustion of dry solid fuel in the unit of MJ/kg. The fuel in the table is arranged by name in alphabetical order.
Of the considered solid fuels, coking coal has the highest calorific value - its specific heat of combustion is 36.3 MJ/kg (or 36.3·10 6 J/kg in SI units). In addition, high calorific value is characteristic of coal, anthracite, charcoal and brown coal.
Fuels with low energy efficiency include wood, firewood, gunpowder, freztorf, oil shale. For example, the specific heat of combustion of firewood is 8.4 ... 12.5, and gunpowder - only 3.8 MJ / kg.
| Fuel | |
|---|---|
| Anthracite | 26,8…34,8 |
| Wood pellets (pillets) | 18,5 |
| Firewood dry | 8,4…11 |
| Dry birch firewood | 12,5 |
| gas coke | 26,9 |
| blast-furnace coke | 30,4 |
| semi-coke | 27,3 |
| Powder | 3,8 |
| Slate | 4,6…9 |
| Oil shale | 5,9…15 |
| Solid propellant | 4,2…10,5 |
| Peat | 16,3 |
| fibrous peat | 21,8 |
| Milling peat | 8,1…10,5 |
| Peat crumb | 10,8 |
| Brown coal | 13…25 |
| Brown coal (briquettes) | 20,2 |
| Brown coal (dust) | 25 |
| Donetsk coal | 19,7…24 |
| Charcoal | 31,5…34,4 |
| Coal | 27 |
| Coking coal | 36,3 |
| Kuznetsk coal | 22,8…25,1 |
| Chelyabinsk coal | 12,8 |
| Ekibastuz coal | 16,7 |
| freztorf | 8,1 |
| Slag | 27,5 |
Specific heat of combustion of liquid fuel (alcohol, gasoline, kerosene, oil)
The table of specific heat of combustion of liquid fuel and some other organic liquids is given. It should be noted that fuels such as gasoline, diesel fuel and oil are characterized by high heat release during combustion.
The specific heat of combustion of alcohol and acetone is significantly lower than traditional motor fuels. In addition, liquid propellant has a relatively low calorific value and, with the complete combustion of 1 kg of these hydrocarbons, an amount of heat equal to 9.2 and 13.3 MJ, respectively, will be released.
| Fuel | Specific heat of combustion, MJ/kg |
|---|---|
| Acetone | 31,4 |
| Gasoline A-72 (GOST 2084-67) | 44,2 |
| Aviation gasoline B-70 (GOST 1012-72) | 44,1 |
| Gasoline AI-93 (GOST 2084-67) | 43,6 |
| Benzene | 40,6 |
| Winter diesel fuel (GOST 305-73) | 43,6 |
| Summer diesel fuel (GOST 305-73) | 43,4 |
| Liquid propellant (kerosene + liquid oxygen) | 9,2 |
| Aviation kerosene | 42,9 |
| Lighting kerosene (GOST 4753-68) | 43,7 |
| xylene | 43,2 |
| High sulfur fuel oil | 39 |
| Low-sulfur fuel oil | 40,5 |
| Low sulfur fuel oil | 41,7 |
| Sulphurous fuel oil | 39,6 |
| Methyl alcohol (methanol) | 21,1 |
| n-Butyl alcohol | 36,8 |
| Oil | 43,5…46 |
| Oil methane | 21,5 |
| Toluene | 40,9 |
| White spirit (GOST 313452) | 44 |
| ethylene glycol | 13,3 |
| Ethyl alcohol (ethanol) | 30,6 |
Specific heat of combustion of gaseous fuel and combustible gases
A table of the specific heat of combustion of gaseous fuel and some other combustible gases in the dimension of MJ/kg is presented. Of the considered gases, the largest mass specific heat of combustion differs. With the complete combustion of one kilogram of this gas, 119.83 MJ of heat will be released. Also, a fuel such as natural gas has a high calorific value - the specific heat of combustion of natural gas is 41 ... 49 MJ / kg (for pure 50 MJ / kg).
| Fuel | Specific heat of combustion, MJ/kg |
|---|---|
| 1-Butene | 45,3 |
| Ammonia | 18,6 |
| Acetylene | 48,3 |
| Hydrogen | 119,83 |
| Hydrogen, mixture with methane (50% H 2 and 50% CH 4 by mass) | 85 |
| Hydrogen, mixture with methane and carbon monoxide (33-33-33% by weight) | 60 |
| Hydrogen, mixture with carbon monoxide (50% H 2 50% CO 2 by mass) | 65 |
| Blast Furnace Gas | 3 |
| coke oven gas | 38,5 |
| LPG liquefied hydrocarbon gas (propane-butane) | 43,8 |
| Isobutane | 45,6 |
| Methane | 50 |
| n-butane | 45,7 |
| n-Hexane | 45,1 |
| n-Pentane | 45,4 |
| Associated gas | 40,6…43 |
| Natural gas | 41…49 |
| Propadien | 46,3 |
| Propane | 46,3 |
| Propylene | 45,8 |
| Propylene, mixture with hydrogen and carbon monoxide (90%-9%-1% by weight) | 52 |
| Ethane | 47,5 |
| Ethylene | 47,2 |
Specific heat of combustion of some combustible materials
A table is given of the specific heat of combustion of some combustible materials (, wood, paper, plastic, straw, rubber, etc.). It should be noted materials with high heat release during combustion. Such materials include: rubber of various types, expanded polystyrene (polystyrene), polypropylene and polyethylene.
| Fuel | Specific heat of combustion, MJ/kg |
|---|---|
| Paper | 17,6 |
| Leatherette | 21,5 |
| Wood (bars with a moisture content of 14%) | 13,8 |
| Wood in stacks | 16,6 |
| Oak wood | 19,9 |
| Spruce wood | 20,3 |
| wood green | 6,3 |
| Pine wood | 20,9 |
| Kapron | 31,1 |
| Carbolite products | 26,9 |
| Cardboard | 16,5 |
| Styrene-butadiene rubber SKS-30AR | 43,9 |
| Natural rubber | 44,8 |
| Synthetic rubber | 40,2 |
| Rubber SCS | 43,9 |
| Chloroprene rubber | 28 |
| Polyvinyl chloride linoleum | 14,3 |
| Two-layer polyvinyl chloride linoleum | 17,9 |
| Linoleum polyvinylchloride on a felt basis | 16,6 |
| Linoleum polyvinyl chloride on a warm basis | 17,6 |
| Linoleum polyvinylchloride on a fabric basis | 20,3 |
| Linoleum rubber (relin) | 27,2 |
| Paraffin solid | 11,2 |
| Polyfoam PVC-1 | 19,5 |
| Polyfoam FS-7 | 24,4 |
| Polyfoam FF | 31,4 |
| Expanded polystyrene PSB-S | 41,6 |
| polyurethane foam | 24,3 |
| fibreboard | 20,9 |
| Polyvinyl chloride (PVC) | 20,7 |
| Polycarbonate | 31 |
| Polypropylene | 45,7 |
| Polystyrene | 39 |
| High density polyethylene | 47 |
| Low-pressure polyethylene | 46,7 |
| Rubber | 33,5 |
| Ruberoid | 29,5 |
| Soot channel | 28,3 |
| Hay | 16,7 |
| Straw | 17 |
| Organic glass (plexiglass) | 27,7 |
| Textolite | 20,9 |
| Tol | 16 |
| TNT | 15 |
| Cotton | 17,5 |
| Cellulose | 16,4 |
| Wool and wool fibers | 23,1 |
Sources:
- GOST 147-2013 Solid mineral fuel. Determination of the higher calorific value and calculation of the lower calorific value.
- GOST 21261-91 Petroleum products. Method for determining the gross calorific value and calculating the net calorific value.
- GOST 22667-82 Combustible natural gases. Calculation method for determining the calorific value, relative density and Wobbe number.
- GOST 31369-2008 Natural gas. Calculation of calorific value, density, relative density and Wobbe number based on component composition.
- Zemsky G. T. Flammable properties of inorganic and organic materials: reference book M.: VNIIPO, 2016 - 970 p.
(Fig. 14.1 - Calorific value
fuel capacity)
Pay attention to the calorific value (specific heat of combustion) various kinds fuel, compare performance. The calorific value of the fuel characterizes the amount of heat released during the complete combustion of fuel with a mass of 1 kg or a volume of 1 m³ (1 l). The most common calorific value is measured in J/kg (J/m³; J/l). The higher the specific heat of combustion of fuel, the lower its consumption. Therefore, the calorific value is one of the most significant characteristics of the fuel.
The specific heat of combustion of each type of fuel depends on:
- From its combustible components (carbon, hydrogen, volatile combustible sulfur, etc.).
- From its moisture and ash content.
| Table 4 - Specific heat of combustion of various energy carriers, comparative analysis of costs. | |||||||||
| Type of energy carrier | Calorific value | Volumetric matter density (ρ=m/V) | Unit price reference fuel | Coeff. useful action (efficiency) systems heating, % | Price per 1 kWh | Implemented systems | |||
| MJ | kWh | ||||||||
| (1MJ=0.278kWh) | |||||||||
| Electricity | - | 1.0 kWh | - | 3.70 rub. per kWh | 98% | 3.78 rubles | Heating, hot water supply (DHW), air conditioning, cooking | ||
| Methane (CH4, temperature boiling point: -161.6 °C) | 39.8 MJ/m³ | 11.1 kWh/m³ | 0.72 kg/m³ | 5.20 rub. per m³ | 94% | 0.50 rub. | |||
| Propane (C3H8, temperature boiling point: -42.1 °C) | 46,34 MJ/kg | 23,63 MJ/l | 12,88 kWh/kg | 6,57 kWh/l | 0.51 kg/l | 18.00 rub. Hall | 94% | 2.91 rub. | Heating, hot water supply (DHW), cooking, backup and permanent power supply, autonomous septic tank (sewerage), outdoor infrared heaters, outdoor barbecues, fireplaces, saunas, designer lighting |
| Butane C4H10, temperature boiling point: -0.5 °C) | 47,20 MJ/kg | 27,38 MJ/l | 13,12 kWh/kg | 7,61 kWh/l | 0.58 kg/l | 14.00 rub. Hall | 94% | 1.96 rub. | Heating, hot water supply (DHW), cooking, backup and permanent power supply, autonomous septic tank (sewerage), outdoor infrared heaters, outdoor barbecues, fireplaces, saunas, designer lighting |
| propane butane (LPG - liquefied hydrocarbon gas) | 46,8 MJ/kg | 25,3 MJ/l | 13,0 kWh/kg | 7,0 kWh/l | 0.54 kg/l | 16.00 rub. Hall | 94% | 2.42 rubles | Heating, hot water supply (DHW), cooking, backup and permanent power supply, autonomous septic tank (sewerage), outdoor infrared heaters, outdoor barbecues, fireplaces, saunas, designer lighting |
| Diesel fuel | 42,7 MJ/kg | 11,9 kWh/kg | 0.85 kg/l | 30.00 rub. per kg | 92% | 2.75 rub. | Heating (heating water and generating electricity are very costly) | ||
| Firewood (birch, humidity - 12%) | 15,0 MJ/kg | 4,2 kWh/kg | 0.47-0.72 kg/dm³ | 3.00 rub. per kg | 90% | 0.80 rub. | Heating (inconvenient to cook food, almost impossible to get hot water) | ||
| Coal | 22,0 MJ/kg | 6,1 kWh/kg | 1200-1500 kg/m³ | 7.70 rub. per kg | 90% | 1.40 rub. | Heating | ||
| MAPP gas (mixture of liquefied petroleum gas - 56% with methyl acetylene-propadiene - 44%) | 89,6 MJ/kg | 24,9 kWh/m³ | 0.1137 kg/dm³ | -R. per m³ | 0% | Heating, hot water supply (DHW), cooking, backup and permanent power supply, autonomous septic tank (sewerage), outdoor infrared heaters, outdoor barbecues, fireplaces, saunas, designer lighting | |||
(Fig. 14.2 - Specific heat of combustion)
According to the table "Specific calorific value of various energy carriers, comparative analysis of costs", propane-butane (liquefied hydrocarbon gas) is inferior in economic benefits and prospects of using only natural gas (methane). However, attention should be paid to the trend towards an inevitable increase in the cost of main gas, which today is significantly underestimated. Analysts predict an inevitable reorganization of the industry, which will lead to a significant rise in the price of natural gas, perhaps even exceed the cost of diesel fuel.
Thus, liquefied petroleum gas, the cost of which will remain virtually unchanged, remains extremely promising - the optimal solution for autonomous gasification systems.
specific heat of combustion- specific heat capacity - Topics oil and gas industry Synonyms specific heat capacity EN specific heat ...
The amount of heat released during the complete combustion of a fuel of mass 1 kg. The specific heat of combustion of the fuel is determined empirically and is the most important characteristic of the fuel. See also: Fuel Financial Dictionary Finam ... Financial vocabulary
specific heat of combustion of peat by bomb- Higher calorific value of peat, taking into account the heat of formation and dissolution of sulfuric and nitric acids in water. [GOST 21123 85] Inadmissible, non-recommended calorific value of peat according to the bomb Topics peat General terms peat properties EN ... ... Technical Translator's Handbook
specific heat of combustion (fuel)- 3.1.19 specific calorific value (fuel): The total amount of energy released under regulated conditions of fuel combustion. A source …
Specific heat of combustion of peat according to the bomb- 122. Specific calorific value of peat by bomb Higher calorific value of peat taking into account the heat of formation and dissolution of sulfuric and nitric acids in water Source: GOST 21123 85: Peat. Terms and definitions original document ... Dictionary-reference book of terms of normative and technical documentation
specific heat of combustion of fuel- 35 calorific value of a fuel: The total amount of energy released under specified fuel combustion conditions. Source: GOST R 53905 2010: Energy saving. Terms and definitions original document ... Dictionary-reference book of terms of normative and technical documentation
This is the amount of heat released during the complete combustion of a mass (for solid and liquid substances) or volumetric (for gaseous) unit of matter. It is measured in joules or calories. The heat of combustion, referred to a unit mass or volume of fuel, ... ... Wikipedia
Modern Encyclopedia
Heat of combustion- (heat of combustion, calorific value), the amount of heat released during the complete combustion of fuel. There are specific heat of combustion, volumetric, etc. For example, the specific heat of combustion of coal is 28 34 MJ / kg, gasoline is about 44 MJ / kg; voluminous ... ... Illustrated Encyclopedic Dictionary
Specific heat of combustion of fuel- Specific calorific value of fuel: the total amount of energy released under specified conditions of fuel combustion...
thermal machines in thermodynamics, these are periodically operating heat engines and refrigerating machines (thermocompressors). A variety of refrigeration machines are heat pumps.
Devices that perform mechanical work due to the internal energy of the fuel are called heat engines (heat engines). The following components are necessary for the operation of a heat engine: 1) a heat source with a higher temperature level t1, 2) a heat source with a lower temperature level t2, 3) a working fluid. In other words: any heat engines (heat engines) consist of heater, cooler and working medium .
As working body gas or steam is used, since they are highly compressible, and depending on the type of engine, there may be fuel (gasoline, kerosene), water vapor, etc. The heater transfers a certain amount of heat (Q1) to the working fluid, and its internal energy increases due to this internal energy, mechanical work (A) is performed, then the working fluid gives off a certain amount of heat to the refrigerator (Q2) and cools down to the initial temperature. The described scheme represents the engine operation cycle and is general; in real engines, various devices can play the role of a heater and a refrigerator. The environment can serve as a refrigerator.
Since in the engine part of the energy of the working fluid is transferred to the refrigerator, it is clear that not all of the energy received by it from the heater goes to doing work. Respectively, efficiency engine (efficiency) is equal to the ratio of the work done (A) to the amount of heat received by it from the heater (Q1):
Internal combustion engine (ICE)
There are two types of internal combustion engines (ICE): carburettor And diesel. In a carburetor engine, the working mixture (a mixture of fuel with air) is prepared outside the engine in a special device and from it enters the engine. In a diesel engine, the fuel mixture is prepared in the engine itself.
ICE consists of cylinder
, in which it moves piston
; the cylinder has two valves
, through one of which the combustible mixture is admitted into the cylinder, and through the other, the exhaust gases are released from the cylinder. Piston using crank mechanism
connects with crankshaft
, which comes into rotation during the translational movement of the piston. The cylinder is closed with a cap.
The cycle of operation of the internal combustion engine includes four bars: intake, compression, stroke, exhaust. During intake, the piston moves down, the pressure in the cylinder decreases, and a combustible mixture (in a carburetor engine) or air (in a diesel engine) enters it through the valve. The valve is closed at this time. At the end of the inlet of the combustible mixture, the valve closes.
During the second stroke, the piston moves up, the valves are closed, and the working mixture or air is compressed. At the same time, the gas temperature rises: the combustible mixture in the carburetor engine heats up to 300-350 °C, and the air in the diesel engine - up to 500-600 °C. At the end of the compression stroke, a spark jumps in the carburetor engine, and the combustible mixture ignites. In a diesel engine, fuel is injected into the cylinder and the resulting mixture ignites spontaneously.
When the combustible mixture is burned, the gas expands and pushes the piston and the crankshaft connected to it, performing mechanical work. This causes the gas to cool.
When the piston reaches its lowest point, the pressure in it will decrease. When the piston moves up, the valve opens and the exhaust gas is released. At the end of this cycle, the valve closes.
Steam turbine
Steam turbine represents the disk mounted on a shaft on which blades are fixed. Steam enters the blades. Steam heated to 600 °C is sent to the nozzle and expands in it. When the steam expands, its internal energy is converted into the kinetic energy of the directed motion of the steam jet. A jet of steam enters the turbine blades from the nozzle and transfers part of its kinetic energy to them, causing the turbine to rotate. Turbines usually have several discs, each of which receives a portion of the steam energy. The rotation of the disk is transmitted to the shaft, to which the electric current generator is connected.
When different fuels of the same mass are burned, different amounts of heat are released. For example, it is well known that natural gas is an energy-efficient fuel than firewood. This means that in order to obtain the same amount of heat, the mass of firewood to be burned must be significantly greater than the mass of natural gas. Consequently, various types of fuel from an energy point of view are characterized by a quantity called specific heat of combustion of fuel .
Specific heating value of fuel- a physical quantity showing how much heat is released during the complete combustion of fuel weighing 1 kg.
The specific heat of combustion is denoted by the letter q , its unit is 1 J/kg.
The value of specific heat is determined experimentally. The highest specific heat of combustion has hydrogen , the smallest - powder .
The specific heat of combustion of oil is 4.4 * 10 7 J / kg. This means that with the complete combustion of 1 kg of oil, the amount of heat 4.4 * 10 7 J is released. general case if the mass of fuel is m , then the amount of heat Q released during its complete combustion is equal to the product of the specific heat of combustion of the fuel q for its weight:
Q = qm.
Synopsis of a lesson in physics in grade 8 "Heat Machines. ICE. Specific calorific value”.