Table of specific heat of combustion of some types of fuel. Thermal machines. ICE. Specific heat of combustion of fuel. How is specific heat of combustion measured?

(Fig. 14.1 - Calorific value
fuel capacity)

Pay attention to the calorific value ( specific heat combustion) various types fuel, compare the indicators. The calorific value of a fuel characterizes the amount of heat released when complete combustion fuel weighing 1 kg or volume 1 m³ (1 l). Most often, calorific value is measured in J/kg (J/m³; J/l). The higher the specific heat of combustion of the fuel, the lower its consumption. Therefore, calorific value is one of the most significant characteristics fuel.

The specific heat of combustion of each type of fuel depends on:

  • From its flammable 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
density of matter
(ρ=m/V) 		Unit price
standard fuel 		Coeff.
useful action
(efficiency) of the system
heating, % 		Price per
1 kWh 		Implemented systems
MJ kWh
(1MJ=0.278kWh)
Electricity - 1.0 kWh - 3.70 rub. per kWh 98% 3.78 rub. 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(sewage), street infrared heaters, outdoor barbecues, fireplaces, baths, 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, baths, 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 rub. Heating, hot water supply (DHW), cooking, backup and permanent power supply, autonomous septic tank (sewerage), outdoor infrared heaters, outdoor barbecues, fireplaces, baths, 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 is very expensive)
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, baths, designer lighting

(Fig. 14.2 - Specific heat of combustion)

According to the table “Specific Heat of Combustion of Various Energy Carriers, Comparative Analysis of Costs,” propane-butane (liquefied petroleum gas) is inferior in economic benefits and prospects for use only to natural gas (methane). However, attention should be paid to the tendency towards an inevitable increase in the cost of main gas, which is currently significantly underestimated. Analysts predict an inevitable reorganization of the industry, which will lead to a significant increase in the price of natural gas, perhaps even exceeding the cost diesel fuel.

Thus, liquefied petroleum gas, the cost of which will remain virtually unchanged, remains extremely promising - optimal solution for autonomous gasification systems.

Thermal machines in thermodynamics, these are periodically operating heat engines and refrigeration machines (thermocompressors). Variety refrigeration machines are heat pumps.

Devices that perform mechanical work due to internal energy fuels are called heat engines (heat engines). For the operation of a heat engine, the following components are required: 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, refrigerator and working fluid .

As working fluid gas or steam are used, since they are well compressed, 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 is performed (A), then the working fluid gives off a certain amount of heat to the refrigerator (Q2) and is cooled to the initial temperature. The described diagram represents the engine operating cycle and is general; in real engines, the role of a heater and a refrigerator can be played by various devices. 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 the energy it receives from the heater is used to perform work. Respectively, efficiency engine (efficiency) is equal to the ratio perfect work(A) to the amount of heat received by him from the heater (Q1):

Internal combustion engine (ICE)

There are two types of engines internal combustion(ICE): carburetor And diesel. In a carburetor engine, the working mixture (a mixture of fuel and air) is prepared outside the engine in 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 ; there are in the cylinder two valves , through one of which the combustible mixture is admitted into the cylinder, and through the other, exhaust gases are discharged from the cylinder. Piston using crank mechanism connects with crankshaft , which begins to rotate with the translational movement of the piston. The cylinder is closed with a lid.

The internal combustion engine operating cycle 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 intake 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 a carburetor engine heats up to 300-350 °C, and the air in a 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 spontaneously ignites.

When a 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 the lowest point, the pressure in it will decrease. When the piston moves upward, the valve opens and exhaust gas is released. At the end of this stroke the valve closes.


Steam turbine

Steam turbine It is a disk mounted on a shaft on which the blades are mounted. Steam enters the blades. Steam heated to 600 °C is directed into the nozzle and expands in it. When steam expands, its internal energy is converted into kinetic energy of the directed movement of the steam jet. A jet of steam comes from the nozzle onto the turbine blades and transfers part of its kinetic energy to them, causing the turbine to rotate. Typically, turbines have several disks, each of which transfers part of the steam energy. The rotation of the disk is transmitted to a shaft to which an electric current generator is connected.

When different fuels of the same mass are burned, they release different quantities warmth. For example, it is well known that natural gas is an energy-efficient fuel than firewood. This means that to obtain the same amount of heat, the mass of wood that needs to be burned must be significantly greater than the mass of natural gas. Consequently, different types of fuel from an energy point of view are characterized by a quantity called specific heat of combustion of fuel .

Specific heat of combustion of fuel- a physical quantity showing how much heat is released during complete combustion of fuel weighing 1 kg.

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

The specific heat value is determined experimentally. Has the highest specific heat of combustion hydrogen , the smallest - powder .

The specific heat of combustion of oil is 4.4*10 7 J/kg. This means that with complete combustion of 1 kg of oil, the amount of heat released is 4.4 * 10 7 J. In the general case, if the mass of fuel is equal to 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 to its mass:

Q = qm.

Physics lesson notes in 8th grade “Thermal engines. ICE. Specific heat of combustion".

    specific heat of combustion - specific heat— Topics oil and gas industry Synonyms specific heat capacity EN specific heat ...

    The amount of heat released during complete combustion of 1 kg of fuel. The specific heat of combustion of fuel is determined experimentally and is the most important characteristic fuel. See also: Fuel Financial Dictionary Finam... Financial Dictionary

    specific heat of combustion of peat by bomb- Higher heat of combustion of peat, taking into account the heat of formation and dissolution of sulfuric and nitric acids in water. [GOST 21123 85] Inadmissible, not recommended calorific value of peat for a bomb Topics peat General terms properties of peat EN ... ... Technical Translator's Guide

    specific heat of combustion (fuel)- 3.1.19 specific heat of combustion (fuel): The total amount of energy released under regulated conditions of fuel combustion. Source …

    Specific heat of combustion of peat by bomb- 122. Specific heat of combustion of peat by bomb Higher heat of combustion 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 specific heat of combustion of 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 complete combustion of mass (for solids and liquid substances) or volumetric (for gaseous) units of a substance. Measured in joules or calories. Heat of combustion per unit mass or volume of fuel, ... ... Wikipedia

    Modern encyclopedia

    Heat of combustion- (heat of combustion, calorie content), the amount of heat released during complete combustion of fuel. There are specific heat of combustion, volumetric heat, etc. For example, specific heat of combustion coal 28 34 MJ/kg, gasoline about 44 MJ/kg; volumetric... ... Illustrated Encyclopedic Dictionary

    Specific heat of combustion of fuel- Specific heat of combustion of a fuel: the total amount of energy released under specified combustion conditions...

Humanity, in the process of its evolution, has learned to receive thermal energy by burning different types of fuel. The simplest example is a fire made of wood, which was lit primitive people, and since then peat, coal, gasoline, oil, natural gas - all these are types of fuel, burning which a person receives thermal energy. So what is specific heat of combustion?

Where does the heat come from during the combustion process?

The process of fuel combustion itself is a chemical, oxidative reaction. Most fuels contain large amounts of carbon C, hydrogen H, sulfur S and other substances. During combustion, the C, H, and S atoms combine with oxygen atoms O 2, resulting in molecules CO, CO 2, H 2 O, SO 2. In this case, there is a separation large quantity thermal energy that people have learned to use for their own purposes.

Rice. 1. Types of fuel: coal, peat, oil, gas.

The main contribution to the heat release is made by carbon C. The second largest contribution to the amount of heat is made by hydrogen H.

Rice. 2. Carbon atoms react with oxygen atoms.

What is specific heat of combustion?

Specific heat of combustion q is a physical quantity equal to the amount of heat released during complete combustion of 1 kg of fuel.

The formula for specific heat of combustion looks like this:

$$q=(Q \over m)$$

Q is the amount of heat released during fuel combustion, J;

m—fuel mass, kg.

The unit of measurement for q in the International System of Units (SI) is J/kg.

$$[q]=(J \over kg)$$

To denote large values ​​of q, off-system energy units are often used: kilojoules (kJ), megajoules (MJ) and gigajoules (GJ).

The values ​​of q for different substances are determined experimentally.

Knowing q, we can calculate the amount of heat Q that will result from the combustion of fuel with mass m:

How is specific heat of combustion measured?

To measure q, instruments called calorimeters are used (calor - heat, metreo - measure).

A container with a portion of fuel is burned inside the device. The container is placed in water with a known mass. As a result of combustion, the heat released heats the water. The magnitude of the mass of water and the change in its temperature make it possible to calculate the heat of combustion. Next, q is determined using the above formula.

Rice. 3. Measurement of specific heat of combustion.

Where can you find q values

Information on the specific heat of combustion values ​​for specific types fuels can be found in technical reference books or in their electronic versions on Internet resources. They are usually presented in the following table:

Specific heat of combustion, q

Explored resources, modern species fuels are limited. Therefore, in the future they will be replaced by other energy sources:

  • atomic, using the energy of nuclear reactions;
  • solar, converting the energy of sunlight into heat and electricity;
  • wind;
  • geothermal, using the heat of natural hot springs.

What have we learned?

So, we found out why a lot of heat is released when fuel burns. To calculate the amount of heat released during the combustion of a certain mass m of fuel, it is necessary to know the value q - the specific heat of combustion of this fuel. The values ​​of q were determined experimentally by calorimetry methods and are given in reference books.

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Lesson developments (lesson notes)

Line UMK A.V. Peryshkin. Physics (7-9)

Attention! The site administration is not responsible for the content methodological developments, as well as for compliance with the development of the Federal State Educational Standard.

“To warm others, a candle must burn”

M. Faraday.

Target: Study the issues of using the internal energy of fuel, heat release during fuel combustion.

Lesson objectives:

educational:

  • repeat and consolidate knowledge on the material covered;
  • introduce the concept of fuel energy, specific heat of combustion of fuel;
  • continue to develop skills in solving calculation problems.

developing:

  • develop analytical thinking;
  • develop skills in working with tables and drawing conclusions;
  • develop students’ abilities to put forward hypotheses, argue them, and correctly express their thoughts out loud;
  • develop observation and attention.

educational:

  • cultivate a careful attitude towards the use of fuel resources;
  • cultivate interest in the subject by showing the connection between the material being studied and real life;
  • develop communication skills.

Subject results:

Students should know:

  • specific heat of combustion of fuel is a physical quantity showing how much heat is released during complete combustion of fuel weighing 1 kg;
  • When fuel burns, significant energy is released, which is used in everyday life, industry, agriculture, at power plants, in road transport;
  • unit of measurement of the specific heat of combustion of fuel.

Students should be able to:

  • explain the process of energy release during fuel combustion;
  • use the table of specific heat of combustion of fuel;
  • compare the specific heat of combustion of fuel various substances and the energy released during the combustion of various types of fuel.

Students must apply:

  • formula for calculating the energy released during fuel combustion.

Lesson type: lesson of learning new material.

Equipment: candle, plate, glass, plant leaf, dry fuel, 2 alcohol lamps, gasoline, alcohol, 2 test tubes with water.

During the classes

1. Organizational moment.

Greeting students, checking readiness for the lesson.

It is known that the great scientist M.V. Lomonosov worked on the treatise “Reflections on the Cause of Heat and Cold” back in 1744. Thermal phenomena play a huge role in the world around us, in the life of humans, plants, animals, as well as in technology.

Let's check how well you have mastered this knowledge.

2. Motivation for educational activities.

Do you have any questions about homework? Let's check how you handled it:

  • two students present solutions to homework problems on the board.

1) Determine the absolute air humidity in a storage room with a volume of 10 m 3 if it contains water vapor weighing 0.12 kg.

2) The water vapor pressure in the air is 0.96 kPa, the relative humidity is 60%. What is the pressure of saturated water vapor at the same temperature?

  • 1 student (Dima) fills out the diagram on the board;

task: label next to each arrow the name of the processes and the formula for calculating the amount of heat in each of them

  • In the meantime, the guys are working at the board, you and I will complete another task.

Look at the text shown on the slide and find in it the physical errors that the author made (suggest the correct answer):

1) On a bright sunny day, the guys went hiking. To make it not so hot, the guys dressed in dark suits. In the evening it became fresh, but after swimming it became warmer. The guys poured themselves hot tea into iron mugs and drank it with pleasure, without getting burned. It was very cool!!!

Answer: dark colors absorb more heat; during evaporation, body temperature decreases; The thermal conductivity of metals is greater, so it heats up more.

2) Waking up earlier than usual, Vasya immediately remembered that at eight in the morning he agreed with Tolya to go to the river to watch the ice drift. Vasya ran out into the street, Tolya was already there. “This is the weather today! – instead of greeting, he said admiringly. “What sunshine, and the temperature in the morning is -2 degrees Celsius.” “No, -4,” Vasya objected. The boys argued, then realized what was going on. “I have a thermometer in the wind, and you have it in a secluded place, so yours and shows more", Tolya guessed. And the guys ran splashing through puddles.

Answer: in the presence of wind, evaporation occurs more intensely, so the first thermometer should show a lower temperature; At temperatures below 00C, water freezes.

Well done, you found all the errors correctly.

Let's check the correctness of solving the problems (students who solved the problems comment on their solution).

Now let's check how Dima coped with his task.

Did Dima name all the phase transitions correctly? What happens if you place a wooden stick into a flame? (She'll burn)

You correctly noted that the combustion process occurs.

You probably already guessed what we will talk about today (they put forward hypotheses).

What questions do you think we will be able to answer at the end of the lesson?

  • understand physical meaning combustion process;
  • find out what determines the amount of heat released during combustion;
  • find out the application this process in life, in everyday life, etc.

3. New material.

Every day we can watch natural gas burn in a stove burner. This is the process of fuel combustion.

Experience No. 1. The candle is fixed to the bottom of the plate using plasticine. Let's light a candle, then cover it with a jar. A few moments later the candle flame will go out.

A problematic situation is created, in which students come to the conclusion: the candle burns in the presence of oxygen.

Questions for the class:

What accompanies the combustion process?

Why does the candle go out? What are the conditions under which the combustion process occurs?

How is energy released?

To do this, let’s remember the structure of matter.

What does the substance consist of? (from molecules, molecules from atoms)

What types of energy does a molecule have? (kinetic and potential)

Can a molecule be divided into atoms? (Yes)

To divide molecules into atoms, it is necessary to overcome the attractive forces of atoms, which means doing work, that is, expending energy.

When atoms combine into a molecule, energy, on the contrary, is released. This combination of atoms into molecules also occurs when fuel is burned. Regular fuel contains carbon. You correctly determined that combustion is impossible without access to air. During combustion, carbon atoms combine with oxygen atoms in the air to form a carbon dioxide molecule and release energy in the form of heat.


Now let's conduct an experiment and see the simultaneous combustion of several types of fuel: gasoline, dry fuel, alcohol and paraffin (Experiment No. 2).

What is common and how does the combustion of each type of fuel differ?

Yes, the combustion of any substance produces other combustion product substances. For example, when wood burns, ash remains and carbon dioxide, carbon monoxide and other gases are released. .

But the main purpose of fuel is to provide heat!

Let's look at another experience.

Experience No. 3:(on two identical alcohol lamps: one filled with gasoline, the other with alcohol, the same amount of water is heated).

Questions about experience:

What energy is used to heat water?

How to determine the amount of heat that went into heating the water?

In which case did the water boil faster?

What conclusion can be drawn from the experience?

Which fuel, alcohol or gasoline, released more heat during complete combustion? (gasoline has more heat than alcohol).

Teacher: Physical quantity, showing how much heat is released during complete combustion of fuel weighing 1 kg, is called the specific heat of combustion of the fuel, denoted by the letter q. Unit of measurement J/kg.

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

The results of the experimental data are given in the textbook table (p. 128).

Let's work with this table.

Questions about the table:

  1. What is the specific heat of combustion of gasoline? (44 MJ/kg)
  2. What does this mean? (This means that the complete combustion of 1 kg of gasoline releases 44 MJ of energy).
  3. Which substance has the lowest specific heat of combustion? (firewood).
  4. Which fuel produces the most heat when burned? (hydrogen, because its specific heat of combustion is higher than the others).
  5. How much heat is released when 2 kg of alcohol is burned? How did you determine this?
  6. What do you need to know to calculate the amount of heat released during combustion?

They conclude that to find the amount of heat, you need to know not only the specific heat of combustion of the fuel, but also its mass.

Means, total heat Q (J) released during complete combustion of m (kg) of fuel is calculated by the formula: Q = q · m

Let's write it down in a notebook.

How to find the mass of fuel burned from this formula?

Express the specific heat of combustion from the formula. (You can call the student to the board to write down formulas)

Physical education minute

We are tired. Let's warm up a little. Straighten your back. Straighten your shoulders. I will name the fuel, and if you think it is solid, lower your head down, if it is liquid, then raise your hands up, and if it is gaseous, pull your hands forward.

Coal is solid.

Natural gas is gaseous.

Oil is liquid.

Wood is hard.

Gasoline is liquid.

Peat is hard.

Anthracite – hard.

Kerosene is liquid.

Coke gas is gaseous.

Well done! The most attentive and sporty among us... Sit down.

Teacher: Guys! Let's think about the question: “Is the combustion process a friend or foe to man?”

Experience No. 4. Let's repeat the experiment with a burning candle, but now we'll put a plant leaf next to the candle.

Look what happened to the plant next to the candle flame?

That. When using fuel, one should not forget about the harm of combustion products to living organisms.

4. Consolidation.

Guys, please tell me, what is fuel for you and me? IN human body Food plays the role of fuel. Different types of food, like different types fuels contain different amounts of energy. (Show the table on the computer “Specific Heat of Combustion of Food Products”).

Specific heat of combustion of fuel q, MJ/kg

Wheat bread

Rye bread

Potato

Beef

Chicken's meat

Butter

Fat cottage cheese

Sunflower oil

Grape

Chocolate roll

Ice cream

Kirieshki

Sweet tea

"Coca Cola"

Black currant

I suggest you join groups (desks 1 and 2, 3 and 4) and complete the following tasks (according to the handouts). You are given 5 minutes to complete, after which we will discuss the results.

Group assignments:

  • Group 1: when preparing for lessons, you spend 800 kJ of energy within 2 hours. Will you restore your energy levels if you eat a 28g pack of chips and drink a 200g glass of Coca-Cola?
  • Group 2: to what height can a person weighing 70 kg rise if he eats a sandwich with butter (100g of wheat bread and 50g of butter).
  • Group 3: is it enough for you to consume 100 g of cottage cheese, 50 g of wheat bread, 50 g of beef and 100 g of potatoes, 200 g of sweet tea (1 glass) during the day? Required amount energy for an 8th grade student is 1.2 MJ.
  • Group 4: at what speed should an athlete weighing 60 kg run if he eats a sandwich with butter (100g of wheat bread and 50g of butter).
  • Group 5: How much chocolate can a 55 kg teenager eat to replenish the energy he expended while reading a book while sitting? (In one hour)

Approximate energy consumption of a teenager weighing 55 kg per 1 hour during various types of activities

Washing dishes

Preparing for lessons

Reading to yourself

Sitting (at rest)

Physical exercise
  • Group 6: Will an athlete weighing 70 kg restore his energy reserve after swimming for 20 minutes if he eats 50 g rye bread and 100 g of beef?

Approximate energy consumption of a person for 1 hour during various types of activities (per 1 kg of weight)

Groups present the solution to the problem on a piece of Whatman paper, then take turns going to the board and explaining it.

5. Reflection. Lesson summary.

Let's remember what tasks we set for ourselves at the beginning of the lesson? Have we achieved everything?

The guys in a circle speak in one sentence, choosing the beginning of a phrase from the reflective screen on the board:

  • today I found out...
  • it was interesting…
  • it was difficult…
  • I completed tasks...
  • I realized that...
  • Now I can…
  • I felt that...
  • I purchased...
  • I learned…
  • I managed …
  • I was able...
  • I will try…
  • I was surprised...
  • gave me a lesson for life...
  • I wanted…

1. What new did you learn in the lesson?

2. Will this knowledge be useful in life?

Giving lesson grades to the most active students.

6. D.z

  1. Paragraph 10
  2. Task (1 to choose from):
  • Level 1: how much heat does 10 kg produce during combustion? charcoal?
  • Level 2: complete combustion of oil released 132 kJ of energy. How much oil was burned?
  • Level 3: how much heat is released during complete combustion of 0.5 liters of alcohol (alcohol density 800 kg/m3)
  • Comparison table: types of fuel (advantages and disadvantages)

    • Read also