Calorific value of diesel fuel mJ kg. Fuel combustion heat

An important thermotechnical characteristic of fuel is its specific heat of combustion.

Specific heat of combustion of fuel

Distinguish between specific higher and lower calorific value. Specific heat combustion of the working fuel, taking into account the additional heat that is released during the condensation of water vapor located in the combustion products, is called higher specific calorific value of working fuel. This additional amount of heat can be determined by multiplying the mass of water vapor generated from the evaporation of fuel moisture /100 and from the combustion of hydrogen 9 /100 , for the latent heat of condensation of water vapor, equal to approximately 2500 kJ / kg.

Specific lower heating value of fuel – the amount of heat that is released under normal practical conditions, i.e. when water vapor does not condense, but is released into the atmosphere.

Thus the relationship between higher and lower specific heat of combustion can be expressed by the equation - = =25(9 ).

64. Conditional fuel.

fuel is any substance that, during combustion (oxidation), releases a significant amount of heat per unit mass or volume and is available for mass use.

Natural and derivative organic compounds in solid, liquid and gaseous states are used as fuel.

Any organic fuel consists of carbon, hydrogen, oxygen, nitrogen, volatile sulfur, while solid and liquid fuels consist of ash (mineral residues) and moisture.

An important thermotechnical characteristic of fuel is its specific heat of combustion.

Specific heat of combustion of fuel is the amount of heat that is released during the complete combustion of a unit amount of fuel substance.

The lower the specific heat of combustion of the fuel, the more it is consumed in the boiler unit. For comparison various kinds fuel, according to their thermal effect, the concept of conventional fuel was introduced, the specific heat of combustion of which was taken = 29.3 MJ / kg.

The ratio of Q N R of this fuel to Q sp of standard fuel is called the equivalent of E. Then the conversion of the consumption of natural fuel V N into standard fuel V UT is carried out according to the formula:

Conditional fuel- the unit of accounting for fossil fuels, that is, oil and its derivatives, natural and specially obtained during the distillation of shale and coal, gas, peat, adopted in calculations, which is used to calculate the useful action of various types of fuel in their total accounting.

In the USSR and Russia per unit reference fuel(c.u.) was accepted calorific value 1 kg of coal = 29.3 MJ or 7000 kcal. International Energy Agency ( IEA) took the unit of oil equivalent, usually denoted by the abbreviation TOE(English . Tonne of oil equivalent). One tonne of oil equivalent equals 41.868 GJ or 11.63 MWh. The unit is also used - a barrel of oil equivalent ( BOE).

65. Excess air coefficient.

The number showing how many times the actual air flow is greater than the theoretically required amount of air is called excess air coefficient, i.e. actual air flow L (in kg/kg) or V (m 3 / m 3) is equal to its theoretically required amount L o or V o > multiplied by the coefficient of excess air a

V= aV 0 .

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 issues related to the amount of heat and specific heat, let's consider the amount of heat released during the combustion of fuel.

Definition

Fuel- a substance that in some processes (combustion, nuclear reactions) gives off 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 - physical quantity, which characterizes 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, so 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.

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Homework

specific heat of combustion- specific heat capacity - Topics Oil and gas industry Synonyms specific heat 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- The higher calorific value of peat, taking into account the heat of formation and dissolution in sulfuric and nitric acid. [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 mass (for solid and liquid substances) or volumetric (for gaseous) units 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...

It is known that the source of energy used in industry, transport, agriculture, in everyday life, is the fuel. These are coal, oil, peat, firewood, natural gas, etc. When fuel is burned, energy is released. Let's try to figure out how energy is released in this case.

Let us recall the structure of the water molecule (Fig. 16, a). It consists of one oxygen atom and two hydrogen atoms. If a water molecule is divided into atoms, then it is necessary to overcome the forces of attraction between atoms, i.e., to do work, and therefore to expend energy. Conversely, if atoms combine to form a molecule, energy is released.

The use of fuel is based precisely on the phenomenon of energy release when atoms combine. For example, the carbon atoms contained in the fuel are combined with two oxygen atoms during combustion (Fig. 16, b). In this case, a molecule of carbon monoxide - carbon dioxide - is formed and energy is released.

Rice. 16. Structure of molecules:
a - water; b - connection of a carbon atom and two oxygen atoms into a carbon dioxide molecule

When designing engines, an engineer needs to know exactly how much heat the fuel being burned can release. To do this, it is necessary to determine experimentally how much heat will be released during the complete combustion of the same mass of fuel of different types.

The physical quantity showing how much heat is released during the complete combustion of a fuel weighing 1 kg is called the specific heat of combustion of the fuel.

The specific heat of combustion is denoted by the letter q. The unit of specific heat of combustion is 1 J/kg.

The specific heat of combustion is determined experimentally using rather complex instruments.

The results of the experimental data are shown in Table 2.

table 2

This table shows that the specific heat of combustion, for example, of gasoline is 4.6 10 7 J / kg.

This means that with the complete combustion of gasoline weighing 1 kg, 4.6 10 7 J of energy is released.

The total amount of heat Q released during the combustion of m kg of fuel is calculated by the formula

Questions

What is the specific heat of combustion of fuel?
In what units is the specific heat of combustion of fuel measured?
What does the expression “specific heat of combustion of fuel equal to 1.4 10 7 J / kg” mean? How is the amount of heat released during the combustion of fuel calculated?

Exercise 9

How much heat is released during complete combustion charcoal weighing 15 kg; alcohol weighing 200 g?
How much heat will be released during the complete combustion of oil, the mass of which is 2.5 tons; kerosene, the volume of which is 2 liters, and the density is 800 kg / m 3?
With the complete combustion of dry firewood, 50,000 kJ of energy were released. How much firewood burned?

The task

Using Table 2, build a bar graph for the specific heat of combustion of firewood, alcohol, oil, hydrogen, choosing the scale as follows: the width of the rectangle is 1 cell, the height of 2 mm corresponds to 10 J.

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