Combustion in pure form represents a chemical reaction with heat extraction; during this reaction from simple substances (carbon and hydrogen), when they interact with oxygen other substances are produced.
During efficient combustion if air is used as oxidant, the output is carbon dioxide (as a result of carbon combustion), water vapors as a result of hydrogen combustion and nitrogen as a component of the air used for combustion, which represents 4/5 of the output volume. Actually, due to nonuniform mixing of fuel with air, it should be supplied at a rate of 1.6 to 2.4 times the theoretical amount required. Therefore, in the firebox there is always a surplus of air with increased nitrogen content that did not really take part in the combustion process plus the water vapors from water normally present in fuel. All these gases are called ballast gases, that is, they do not take part in combustion but only get heated from the combustion of carbon and hydrogen. In other words, they reduce the useful heat.
In the system of forced gas movement (forced gas movement system) all these gases are mixed to form a single flow. As a result of mixing of hot and cold ballast gases the temperature in the firebox decreases, thus the conditions for fuel combustion worsen. At the same time the flow diluted with cold ballast gases acts on the heat exchanger and further comes into the chimney. The design of forced-air installations is now so efficient that there is practically no room for improvement.
At present during combustion of any type of fuel in any type of firebox when air is used as oxidant, the main aim is to reduce the negative influence of ballast gases as the temperature of the flow in which the conditions of fuel combustion get worse, and the heat content of combustion products decreases, depends on their quantity. This also refers heat generators used in all branches of industry.
For this purpose the following is used:
- dry fuel, including pellets, briquettes, etc., product of power-consuming technique and expensive production technology;
- minimization of quantity of the supplied air to the level, which ensures complete combustion and absence of surplus of air.
The system of “Free gas movement” in interpretation of Kuznetsov, I. V., (hereinafter referred to FGM) assumes another mechanism of reduction the negative influence of ballast gases on the process of fuel combustion, as well as usage of extracted heat. It is based on the nature laws.
It is possible to improve the conditions of fuel combustion in the firebox, by removing ballast gases from the combustion zone. Thus the efficiency of energy extraction from the fuel is increased, that is the heat content of combustion products is increased. In other words, the heat content of combustion product depends on the type of oxidant and on the quantity of ballast gases.
The basics of theory of free gas movement were laid by a Russian scientist and metallurgist, Correspondent Member of the Academy of Sciences of the USSR, Professor V.M. Grum-Grzhimailo (1864-1928). Further this work was developed using the principle of “Free gas movement” (FGM) by Grum-Grzhimailo’s follower PhD. I.S. Podgorodnikov (1886-1958). He proposed building the stoves using “double bell” scheme.
The main idea lying at the basis of FGM theory that was formulated by V.E.Grum Grzhimailo is as follows: hot gas stream being surrounded by cold gas stream will rise up being lighter. While making stove design in each of its part it is necessary to preset such a direction of gas movement, that would reflect their natural strive, hot gas up, and colder gas down. In their works V. E. Grum Grzhimailo and I. S. Podgorodnikov didn’t manage to solve the most important question regarding natural gas movement in the firebox in accordance with this classical determination.
Natural movement of hot gases in the firebox can be ensured only in a heat generator built in accordance with certain rules. The heat generator scheme is shown in Fig.1 featuring:
1-firebox; 2-«dry joint»; 3-lower bell; 4-heat exchanger; 5-upper bell; 6-pipe. The stove’s lower level and the fire box through “dry joint” are combined to form a single space creating a lower bell”
The bell represents a vessel turned upside down. Cold particles in it are pushed out to go down and the hot ones rise up. In this design the availability of “dry joint” is compulsory. The dry joint represents a 2- 3 cm vertical crevice between the firebox and the bell. The firebox may be different both with regard to its design and principle of fuel combustion. Any type of fuel can be used for combustion.
The essence of the rules: Here we speak about fuel combustion in the firebox located in the bell and combined with it through 2-3 cm vertical crevice (dry joint) to form a single space. Such arrangement makes it possible to create both in the bell and in the firebox conditions, in which the movement of gases provides for their natural behavior: hot gas rises up and the streams of cold gas go down. In this case the lower and the upper limit of the specific heat stress of the firebox volume can be maintained. This formula corresponds to the theory of V.E. Grum Grzhimailo.
The main goal of the concept is to obtain maximum heat during fuel combustion and maximize the use of the heat obtained. The design of the heat generator to meet functional requirements and ensure optimum heat emission.
It is possible to produce an effective combustion process and obtain maximum energy but use this heat inefficiently. On the other hand, it is possible not to extract the energy contained in fuel completely and use it effectively. Therefore, the total efficiency of a particular installation is made up of the efficiency of energy extraction from the fuel and the efficiency of heat usage. The combustion efficiency equals what percent of the total energy resource can be transferred into heat during combustion.
The efficiency of energy use in the system of free gas movement and in the system of forced gas movement and what is the difference between them? The combustion efficiency equals what percent of the total energy resource can be transferred into heat during combustion.
The efficiency of energy usage in the system of free gas movement and in the system of forced gas movement and what is the difference between them?
Moving gas flow in the heat generator with any convective system transfers heat energy and combustion products. The convective system is a tool for using the extracted heat energy, which can be used for heating of boiler of hot-water heating, radiator, etc. In order to clarify the difference of gas flow movement mechanism in the system of free gas movement and that in the system of forced gas movement let’s imagine that an electric heater is the source of heat. In this case there’s no need to remove the combustion products.
Let’s fill the bell К1 shown in Fig.A1 with a portion of hot air, Fig.2. Designations in Fig.2 are the following: К1, К2, К3, and so are the bell numbers 1, 2, 3 in the direction of movement of hot gases; В- heat exchanger; С- electric heater; D- blast; T- draft; Hot air being lighter will rise up and pulls out cold air from the bell. It will remain inside the bell until it heats the bell’s walls. If hot air generated by electric heater C is constantly supplied to the bell, then part of the flow heat will be absorbed by the bell’s walls and the heat exchanger B placed inside it. If the heat is generated in quantity larger than the bell with the heat exchanger can accumulate, the surplus of heat (cooled air from the lower zone of the bell) will flow over to the second bell К2 and then further to К3, if К2 won’t accumulate the full amount of heat. Hot air movement in the bells takes place without chimney draft due to forces of nature and doesn’t require external energy. In the forced gas movement system the heat transfer is possible only due to the chimney draft.
If hot air flow passes through the lower zone of the bell K1 shown in Fig.2 with blast (D) equal to draft (T) Fig.A2, then the flow heat under the influence of Archimedes force rises up, to the zone where the heat exchanging processes take place. The heat of hot air will be radiated to the bell’s walls and to the heat exchanger placed inside the bell, and the surplus of heat (cooled air) comes outside to bells К2, К3 etc, if they are available.
Water boiler register, air heater, retort for fuel gasifying and process materials, etc. can be used as a heat exchanger. Theoretically it is possible to select such a heat exchanger that will be capable of accumulating all the heat. In this case it is possible to say that the efficiency of use of the extracted heat will be close to 100%.
Heat transfer from gas to the heat exchanger depends on the following factors:
- the heat exchange contact area;
- temperature difference;
- contact duration.
The larger they are the larger is the heat transfer. The bell may have any shape and volume, into which the heat exchanger can be inserted, that is to increase the heat exchange. At such arrangement of heat generator the area of the heat exchange and the time of contact of hot gases with the heat exchanger are increased, thus the heat exchange is improved.
We will get the same if the gas flow received during combustion of any type of fuel in another firebox at any type of combustion process when air is used as oxidant, (see K1 in Fig.A2, Fig.2) will be passed through the lower zone of the bell, at blast (D) equal to draft (T). The flow contains combustion products, which represent a mixture of various gases, including ballast gases. Their molecules are totally independent, that is, they are not coupled with each other. The products of combustion are: carbonic acid (СО2) from combustion of carbon; water vapors from combustion of hydrogen, as well as ballast gases - water vapors of fuel; nitrogen (in mixture); and surplus of air.
This gas flow passing through the lower part of the bell is distributed according to the components. Each particle of the gas flow has its own state: weight, temperature, energy and occupies a location in the bell determined by this state during the total time of free movement through the bell. The hot component of the flow under the action of Archimedes force tends to flow upward exerts an influence on the heat exchange and is being present there all the time until the gases get cooled. Cold, heavy and harmful gases of the flow pass through the lower part of the bell not exerting much influence on the heat exchange. Most cold jets having maximum velocity pass through the lower zone of the bell not influencing much on the heat exchanger. Most cold jets having maximum velocity pass through the lower zone of the bell not influencing much on the heat exchanger.
Therefore: When the gas flow passes through the bell the efficiency of use of the extracted energy increases as the influence of the ballast gases on the heat exchange decreases. In a forced gas movement system all combustion products pass through the firebox and channels of convective systems of heat generator, mix into a single flow, in other words, decrease temperature and useful heat emission of the flow. Chimney draft is the driving force of the flow.
Hence an important conclusion: Optimum use of the exhaust energy received as a result of any type of fuel combustion in any firebox when air is used as oxidant is realized due to the use of convective bell-shape system.
To ensure the efficiency of operation of heat generator, reduce exhaust gas emissions, complete fuel combustion shall be ensured. Four conditions for complete fuel combustion are known, namely, proper design of the firebox, good mixing of air with the fuel, high firebox temperatures and optimum supply of primary and secondary air.
During combustion concentration of initial matters, fuel and oxidant fall down sharply. The concentration of combustion products and temperature level also rise sharply. In any system secondary air shall be supplied higher than the fuel to be able to burn fuel gases from fuel thermal decomposition.
In the system of forced gas movement, movement of oxidant and fuel gases takes place in incidental direction. During the flow movement the flow is more and more mixed with ballast gases. At the end-stage of combustion flame concentration of fuel and oxidant is decreased. The initial matters are separated by a large amount of combustion products. The possibility of quick contact of reacting molecules is rather difficult. In this case it is essential to provoke intensive turbulence. It is also required to ensure adequate amount of air for combustion, to make its amount optimum that is minimize it and exclude incomplete combustion or air surplus. However there is always a surplus of air, nitrogen and water vapors from water normally present in fuel in the firebox, which reduce the flow temperature, thus worsening the conditions of fuel combustion. The energy that is present in the fuel is not extracted completely. The extracted heat is used incompletely as it is used for heating of ballast gases present in the flow.
Therefore: In order to improve the efficiency of heat extraction, that is, burn fuel more efficiently, it is necessary to reduce the negative influence of ballast gases and increase the temperature in the firebox.
In forced-gas installations, there is no good place for the heat exchanger so that the conditions of fuel combustion correspond to the conditions of use of extracted heat. If heat exchangers are placed inside the firebox, the conditions for fuel combustion worsen. That is the more heat is used (the efficiency of use increases), the worse are the conditions of fuel combustion (the efficiency of energy extraction from fuel is decreased). The heat exchangers placed in the firebox (cold core) decrease temperature, that is worsen the conditions of fuel combustion. When the channel area is increased to be able to place a heat exchanger the energy of the gas flow in it is getting diluted, that is the temperature in the flow is decreased.
Combustion of fuel in the bell is also possible without a firebox. However in this case it is not possible to achieve good fuel combustion: high temperature, optimum air supply for combustion, its proper mixing and preliminary heating. Due to this reason combustion of fuel shall be performed in the restricted volume where the specified requirements can be met.
Unlike a forced-gas system, fuel combustion in a new system of free-gas movement takes place in other conditions.

Firebox 1(Fig.3) is walled from all the sides and from top with a catalyst 2 (fire grate made of fire brick). The firebox is provided with “dry joint”3, connecting it with the bell.
The walls are provided with chambers 4 through which via openings 5 secondary air is supplied above the fuel from the ash-pit. The major part of the secondary air being heated all the way through the chambers made in the firebox walls and is supplied due to Archimedes force to the end-stages of combustion under the catalyst. The air is also transferred through the 25 mm crevice in front of the firebox door, which is especially needed during kindling when secondary air cannot rise through the chambers.
The “bell conditions” are created in the firebox where each particle of the gas flow has its own motion path determined by its state during the total time of its free movement through the firebox. In other words, hot particles are in the upper part and those that are less heated cannot go up. Secondary air comes out from holes located under the catalyst 5, enters the bell zone and is pulled down being heavy in the direction opposite the direction of the flow. Unlike a forced-gas system, the movement of oxidant and fuel gases goes in the opposite direction relative each other and due to that turbulence is ensured, and the molecules of fuel contact with the molecules of oxidant much more often. The combustion catalyst ensures turbulence of the outlet flow and high temperature in the firebox due to reflection of radiant heat. Such character of tubular exchange determines the speed of gas mixture formation, making this zone especially important. The fuel gas particles interact with oxygen of the air and extract heat turning into carbon dioxide, water vapor and other combustion products.
The hot gases tend to flow up the bell creating high temperature zone and acting on the heat exchanger fitted outside the firebox. Ballast gases being cold can’t go up and are pulled out into the lower zone of the firebox; further they are transferred through the dry joint into the bell and then for reuse or into the chimney.
In this case continuity of dry joint from hearth and higher than the holes of secondary air supply must be ensured. This is taboo. In winter when we slightly open the window in the house (by 2-3 cm) heavy heat exchange takes place (cold air will enter the house through the lower part of the slit and warm air comes out through the upper part of the slit. Similar heat exchange takes place in the heat generator through dry joint. Water vapors of the fuel being heavy can’t go up into combustion zone. This is especially important for fuel combustion with high moisture content, for example, brown coal containing 45-55% of water, and is not suitable for combustion in a forced-gas system.
Fuel gas combustion process is expressed with the help of chemical equations showing in what ratio and in what way separate matters interact with each other (D.B. Ginzburg).
С+О2=СО2+7940 kcal/kg, or (33190 kJ/kg);
Н2+1/2О2=Н2О+2579 kcal/Nm3 Н2, or (10780 kJ/Nm3);
СО+1/2О2=СО2+3018 kcal/Nm3 СО, or (12615 kJ/Nm3);
Thus in the firebox of heat generator of free gas movement system these ratios of separate matters reacting with each other are maintained as well as their content. That is carbon - С and hydrogen - Н2 react with oxygen - О2, in quantity determined by chemical equation. Other matters cannot react. These are ballast gases including the released nitrogen (air with increased nitrogen content).
Therefore the quantity of air shall be sufficient enough to avoid chemical underburning, also the correct ratio of primary and secondary air supply shall be maintained. Waste gases being cold are pulled out to the lower part of the firebox and through the dry joint and the bottom of the bell are thrown into the chimney. In other words, chemical reaction in the heat generator of free gas movement system theoretically runs with a factor of air surplus equal to 1. In heat generators of forced gas movement system, unlike heat generators of free gas movement system, even during fuel combustion with air surplus equal to 1, the released conditionally cold nitrogen, dilutes combustion products thus decreasing the flow temperature.
In «Gasification» section it is pointed out that reactivity of coke, that is its capability to interact with oxygen of the air, CO2 and water vapor is an important feature for gasification. When water vapor interacts with hot coke the following reactions run between it and carbon in the gasification zone: С + Н2О = СО+Н2; and С + 2Н2О = СО2 + 2Н2.
As a result of the first reaction we get only fuel gases (50%СО and 50% Н2). The calorific value of mixture of these gases is 2802 kcal/Nm3.
In the second reaction partially fume gases and partially non-fume gases are produced (33,3% СО2 and 66,7% Н2). Calorific value of mixture of these gases is 1714 kcal/Nm3.
The products of combustion include water vapors of the fuel. In our system of FGM water vapors of the fuel being heavy cannot rise to the upper zone of the firebox, pass above the fuel and exert an influence on burning hot coal (carbon). Decomposition of water vapors takes place in accordance with the above reactions with extraction of fuel gases, which are burnt there. It is probable that due to this reason no condensation of fuel water vapors takes place, and the energy content of combustion products is above normative.
The smoke is not present:
stove 2;
stove 3;
Below are the results of independent tests of FGM-system stoves carried out in Sweden and France where the stoves of FGM system showed high efficiency and high purity of combustion.
(Translation of the text: In January 2009 Swedish Boiler Association (svenska ångpanneföreningen AB) measured the quality of waste gases on a massive stove mounted on Gothland island. The quality of waste gases was far below the permitted levels, and thermal effectiveness proved to be 95 %. Please read the document with test result here. Our conclusion regarding test results: there’s no fireplace that can be comparable with the one built on the principle of free gas movement in terms of the results of waste gas quality and thermal effectiveness. You can find the document at ).

Compare Fig.4 featuring combustion of recently cut wood in the fireboxes of boilers of constant firing. The top of the photo features a boiler with forced gas movement system. The bottom photo features a boiler built in accordance with a new free gas movement system, in which the registers are fitted in the bell. The boilers function without blasting.
In the boiler of free gas movement system it is obvious that in high-temperature field a uniform heating of wood and a thermal destruction of wood (pyrolysis) takes place. The conditions of the fuel combustion in the firebox change. Separation of cold ballast gases takes place, thus high-temperature combustion process is formed. That ensures heating and gasification of fuel as well as high purity of combustion. The mixture that is not capable of self-ignition at lower temperature is becoming capable of self-ignition at high temperature. The arrangement of the heat exchanger in the bell beyond the fuel combustion zone provides for energy extraction from fuel without decreasing the efficiency of energy extraction from fuel, thus increasing the efficiency of extracted heat.
During fuel combustion in heat generators of a free-gas movement system when air is used as oxidant the heat content of combustion products increases due to decrease of influence of ballast gases on the oxidation process.
The calorific value of wet wood is lower than the calorific value of dry wood. That means that during combustion of wet wood the amount of ballast gases increases. The influence of ballast gases on combustion process and fuel calorific value can also be traced on acetylene combustion during welding. The calorific value of acetylene combustion products depends on the type of oxidant used, in other words, on the quantity of ballast gases. If air is supplied into the combustion zone instead of oxygen, the combustion temperature and the energy extracted from acetylene will be insufficient for metal cutting and welding.
In heat generators of a free-gas movement system the process of fuel combustion is natural, self-regulated and optimal. The conditions of fuel combustion are much better and the efficiency of energy extraction increases.
The free-gas movement system acquired a wide application and development in the design and construction of furnaces and boilers using wood for fuel. The system is marked with a high degree of flexibility that made it possible to create thousands of highly efficient stoves and boilers for various applications. There is a possibility of creation of a great number of heat generators of various shape, capacity and purpose, including multi-purpose and multi-storey heat generators as well as industrial ones. Continuously operated wooden boilers show wonderful results and efficiency. High-temperature combustion process takes place in their firebox. This ensures heating and gasification of fuel at approximately 1060 о С. They are used at present for heating houses with area of several thousand square meters; in this case the movement of heat carrier is performed without a pump. When we measure the quantity of wood being burnt a day we get the result that the energy content is less than the energy radiated by the boiler. This is not very probable but that’s a fact, which has to be confirmed or disproved by tests.
The free-gas movement system is being introduced in many countries of the world. The efficiency of the stoves built in accordance with our system as per the results of tests conducted in the U.S.A., Canada, France, Sweden, Russia and Germany is about 90%. After some improvements as per experiments made in France we managed to achieve high purity of combustion. The tests of the stove made by the independent Swedish company “AF-Kontrol AB” performed in January 2008 showed that exhaust of СО and organically bound carbon are much more below the permissible norms. The efficiency is more than 90%. The system of free gas movement is a new high-quality level of technology of biofuel combustion, which is unique in the world. This is an example of real energy saving.
In retorts (tight metal tanks) heated from outside without access of air it is possible from organic domestic or industrial waste to produce solid, rich in carbon coke, vapor-gas (product of pyrolysis) and different components. This is metal from car tires, cables and other waste, pyrolysis fuel, activated charcoal, etc. The coke can be processed into gas if we exert an influence of water vapor at high temperature. This gas is high-quality gas with calorific value of 2802 kcal/Nm3. The extracted gas and coke can be used for receiving heat by burning it.
Gas plant of free gas movement system may have 1, 2 or more bells with retorts, one or more bells with a heat exchanger and heat-accumulating bell with a firebox. Each retort is located in its own bell where it is heated by the heat extracted from vapor-gases being combusted in the firebox or in the bell. The adjustment of heating is performed due to redistribution of direction of hot gas flows produced during combustion of vapor-gases in the firebox or as a result of change of amount of vapor-gases being combusted in the bell with retort. The production of high-quality combustion products from biomass processing in maximum volume is ensured by pyrolysis process control in every retort during all the cycles, which is not possible to do in other systems. The plants don’t require external energy. They operate due to the energy extracted by raw materials during pyrolysis process.
Similar plants (modules) are produced by German company “Meta Pyrolyse-Anlagen GmbH", driven by electricity. Only in this case they managed to achieve control at every stage of fuel pyrolysis as well as produce high-quality products and payback of their production. Nowadays in many countries of the world combustion of solid fuel is performed in two stages:
1 stage - costly and energy-consuming stage to produce pellets and briquettes, etc; 
2 stage - combustion of pellets, with regard to automation, it corresponds to the level of gas and diesel fuel combustion.
In the system of free-gas movement it is possible to use wet fuel as its drying is performed with the help of waste gas heat. The expensive and energy-consuming stage of fuel preparation is excluded. The adjustment of combustion capacity takes place without decreasing of efficiency.
A free-gas movement system provides for creating mechanism of vacuum drying of fuel due to the heat of waste gases. There is also a possibility of improvement of vapor-gas produced at low-temperature pyrolysis until the molecular decomposition degree to prepare for efficient combustion or processing.
Further work regarding improvement of free-gas movement system requires participation of a wide range of experts in different fields and performing experimental jobs. All this requires creation of material and technical basis. In developing the free-gas movement system continuity is required, otherwise its Russian priority will be lost.
This job requires a political and financial support and should be leaded by a strong economic manager.
List of reference:
1. I.S. Podgorodnikov . Household stoves. Publisher HIC RSFSR. Moscow - 1960
2. K. Myakelya. Furnaces and fireplaces. Moscow. Stroyizdat 1987
3. I.I. Gringauz . Steam boilers. NKEP USSR. State Energy Publishing. Moscow, Leningrad, 1940
4. D.B. Ginsburg. Gasification of solid fuel. State Publishing House of Literature on construction, architecture and building materials. Moscow, 1958
5. Edited by Y.D. Yudkevich , S.N. Vasiliev , V.I. Jagodin . Production of chemical products from wood waste. St. Petersburg, 2002
6. E.D. Levin. The theoretical basis of the production of charcoal. Timber industry. Moscow,. 1980
7. A.N. Kislitsin. The pyrolysis of wood: chemistry, kinetics, products, new processes. Moscow. Timber industry, 1990
About a new method of fuel combustion in individual heating stoves
CONTINUED (Annex). About some new properties of free gas movement system
The principle difference of two systems is the following:
In forced gas movement system the gas particles move along the convective system channels up, down and aside due to chimney draft and get mixed to form a single flow.
In free gas movement system the gas particles move through the bell (convective system) not only due to the chimney draft but also up to the bell under the action of Archimedes force of gases. They are also influenced by the heat-exchange processes taking place in the bell that cool the particles changing their motion path. This is not considered during calculation of gas flow movement. Water vapors of fuel being cold cannot rise up and move above fuel interacting with hot carbon of fuel.
In order to better understand what we speak about, let’s recall some of the properties of different parts of household stoves (heat generators), fireboxes and convective systems.
The basic parts of furnaces of any systems are as follows:
• firebox (also hearth firebox), it is intended for fuel combustion;
• convective system, that is intended for accumulation and use of waste gas heat; it determines the character of gas flow movement;
• Chimney with natural draft (or mechanical blast-draft) is intended for combustion product removal and is common for stoves of any system.
This article describes operation and compares only firebox and convective system of stoves of different systems, i.e free gas movement and forced gas movement systems. Chimney with natural draft is regarded as a mechanism for forced removal of combustion products in any system, therefore its operation is not considered.
Why it is not possible to create complex multi-purpose stoves in forced gas movement system while in the system of free gas movement there is a possibility to create a great number of energy generators of various purpose and power?
Heat transfer from gas fluid to heat emission surface depends on the following main reasons: temperature difference, square, contact time, material, shape and mass of heat emission surface.
Gas pressure force the resultant force of which is directed upward exerts an influence on the body (particle) immersed into gas. This is a gas supporting (Archimedes) force.
The supporting force of gas (Fa) is equal to gas weight in volume of body immersed into gas. Fa= ρgV, where ρ – gas density, g – acceleration of gravity, V – volume of immersed body. (Elementary physics, under edition of G.S.Landsberg).
In descending channel (gases move down from top) the flow energy is equally distributed over the cross section. This phenomenon is called «self-adjustment» and is explained by the fact that the moving forces of gases, draft and Archimedes force of gases are directed in different directions. The draft is directed down, and Archimedes force of gases tends to go up. If in certain place of the horizontal section of the channel the flow temperature is higher, then Archimedes force there is larger. So in this place the braking force increases, and the flow is distributed to the place where it is easier for it to run. Temperature decrease over the channel section arises near the channel walls where heat exchange processes take place, and its value depends on the wall material and channel shape.
In the ascending channel (gases upwards) channel draft and Archimedes force of gases are both directed upward and summed up. For that reason the flow movement over the channel section is unequal, it is greater where the temperature is higher. The heat exchange processes over the channel section are distributed unequally. This specially concerns the channels with large section area.
When the gas flow moves along the channel of a convective system of any direction due to the chimney draft, the following takes place:
When the channel cross section is reduced, the gas flow gets packed, the speed of its movement, energy (temperature) increases and, as a result, the heat exchange also increases. In the forced gas movement system the gas particles fly with high speed over the heat emission surface of the convective system due to the chimney draft. However in this case the friction force of the flow increases; this leads to noise formation, and at the end the channel cannot pass the whole volume of gas formed during combustion. It should be noted that this refers to the case when the gases coming out from the firebox run in one way. If other ways are available, in this case the gases run where it’s easier for them to flow, and in this case nothing from the above described happens in the channel with reduced cross section. For example, if the firebox is provided with two exits, it’s not possible to reduce the channel cross section due to decrease of stove heating. When the channel has a larger section, the flow dilutes and its movement, energy (temperature) decreases. In this case the heat exchange processes run under low temperatures of the flow.
With larger sections of vertical channels (gases move down from top) in the system of forced gas movement comparable with horizontal section of the bell in the system of free gas movement, the gas flow is diluted across the section, its temperature decreases, the flow passes due to the chimney draft and its heat is badly accumulated in the channel. In such convective systems the heat exchange is inefficient. For that reason it is not possible to create complex multi-purpose stoves in the forced gas movement system.
Unlike the system of forced gas movement, in free gas movement system the bell can be of any form and volume. The heat exchange in the bell takes place as if it were in single space together with the firebox with consideration of movement of the gases through the “dry” joint (when draft and blast are equal). The heat emission from the gas fluid to heat emission surface increases when the mass of heat emission surfaces also increases. This happens in coverings, in the corners and thicknesses of the walls where the gas temperature is reduced. This can be proved by experiments’ results.
Cold gases that gave up their heat flow from the bell. Heat exchanger can be inserted into the bell. The time of contact of hot gases and their temperature increases. All this increases the heat exchange, thus increasing the efficiency of use of extracted energy. In this case in the top zone of the bell and at the lateral surfaces the temperature of hot gases decreases due to effectiveness of the heat exchange.
This can be compared with reduction of air temperature when someone comes closer to the window and the walls during winter. This is obvious from the diagram of stove heating by height that E.V. Kolchin obtained during tests. The stove is provided with two bells. The height of the first one is 2/3, and the height of the second one is 1/3 of the stove height. The diagram of temperature distribution of outcoming gases along the height of dry joint is of the same character.
If we use material with a low coefficient of heat conductivity for the bell’s walls, then the temperature in the top zone will be the highest. Effective heat exchange takes place also along the lateral walls of the bell. This provides for a possibility to create a great number of energy plants of different purpose and power. As it was pointed out previously, unlike in forced gas movement system, the use of extracted energy in our system is close to 100% as the particles of hot gases remain in the bell until they cool down. This refers to the case when the heat emission surface with the heat exchanger can accumulate more energy than the firebox actually produces. The following example is provided to prove the fact that the stoves built in accordance with our system are more efficient than the stoves built on the principle of counterflow.  

Two stoves, one using principle of free gas movement, and the other one using forced gas movement principle, were built in practice in the U.S.A. during the МНА workshop in 2008 in which I was lucky to participate. The stove built on the counterflow principle warmed up much more badly even in its top although its firing started earlier. This could be seen on the photo. People were warming themselves around our stove while around the counterflow stove they were not. The counterflow stove is worse and it warms up the house incorrectly. At the same time the counterflow stove is considered to be the best in its class and is used more often in various developed countries of the world.
One more important feature of free gas movement system shall be pointed out (as regarded by I.V. Kuznetsov). Several times it was noted and pointed out that during temperature decrease of outcoming gases below 100 ° C, no condensation of water vapors takes place in the chimney. This wonderful feature was first noted during stove test at Jean Claude’s in France, The same was noted during other tests.
It was also required to understand and explain the difference in the combustion of wood shown in the photo, «Fig.4», and also the fact that measuring taken several times regarding the quantity of wood burnt during 24 hours in constant action boilers showed that their energy content was less than the energy produced by the boiler. There are no wonders, energy cannot appear from nothing. At that time I could not explain these phenomena. During boiler test at Polushkino (a settlement near Moscow), with participation of assistant professor of heat engineering faculty of USTU-UPI, Ph..D. Mikula, V.А., leading specialist on energy audit of Sverdlovsk oblast, interesting data were obtained. The lower working calorific value of 12.5 kg of burnt fuel made 3650 kcal/kg. The heat extracted during combustion of that amount of fuel (12,5 kg) made 3650х12,5= 45625 kcal, and useful used heat measured during the test made 57141 kcal, 51341*+ 5800 kcal (heat for water heating + heat through lining). That means that the boiler produced more energy than the heat content of the combusted wood!!! If we do calculation with consideration of possible errors caused by the use of flow meter with high velocity of heat carrier and absence of certificate data with regard to thermal capacity of the heat carrier, then the boiler efficiency may be within the range 66 to 125 % and more/. 51341* - According to certificate of the flow meter, the range of speed measuring of heat carrier is 0,3-8 m/s. This flow meter is not rated for our speed range 0,1-0,22 m/s, therefore the data cannot be true. The measuring error in this range is unknown. The only known error is the error on the low measuring limit. At a speed of 0,3 m/s the error is 10%. Therefore the accuracy of heat determination is doubtful.
The result of tests performed cannot be considered true, but it makes everybody think again. Due to importance of this issue, this fact needs clarification and explanation, therefore the tests shall be continued with participation of scientists of heat engineering faculty of USTU-UPI taking into account corrections pointed out by them. I personally and our partnership have no possibility to finance continuation of tests. Money is required for acquisition or rent of certain tools, payment of travel costs, accommodation and work of specialists in Moscow. We are looking for sponsors. We will express our gratitude and mention their names in the name of the article.
To increase trustworthiness of the tests, Mukula, V.A, recommends undertaking the following measures:
To measure speed (consumption) of heat carrier forced circulation shall be arranged pr use flow meter with a low speed of heat carrier;
Precise data are required regarding the content of the heat carrier (composition of matters and their share);
To reduce the influence of stove inertia and heating of the heating system, it is recommended to increase duration of tests up to 24 hours;
To obtain more precise information on the calorific value of wood, it is required to take 4 small cubes (weighing1-2 g) from the lot of wood used from different logs, pack them in sealed polyethylene bags or small glass jars and then using calorimetrical method determine the calorific value.
In my opinion, the time of experiment should have been taken as «passed time interval, starting from the value of initial temperature of boiler lining till the end temperature, equal to initial temperature».
Now I have an idea, why the above-mentioned phenomena take place. In section «Gasification» it is pointed out that reactivity is an important feature for gasification of coke, i.e. its ability to interact with oxygen in the air, carbon dioxide and water vapor. When water vapor exerts an impact on hot coke, the following reactions run between it and carbon in the gasification zone: С + Н2О = СО+Н2; and С + 2Н2О = СО2 + 2Н2.
As a result of the first reaction we get only fuel gases (50%СО and 50% Н2). The calorific value of mixture of these gases is 2802 kcal/Nm3.
As a result of the second reaction we get partially flammable and partially nonflammable gases (33,3% СО2 and 66,7% Н2). The calorific value of mixture of these gases is 1714 kcal/Nm3. When the temperature is higher the first reaction runs more intensively. When the temperature is lower – the second reaction. Recovery of carbon oxide or decomposition of carbon dioxide in accordance with reaction С+СО2=2СО doesn’t take place in our case due to absence of required temperature 1150 °С in the firebox. (D.B.Ginsburg).
Combustion products comprise water vapors normally present in the fuel. In our system of free gas movement water vapors being heavy cannot rise up to the top zone of the firebox, pass over the fuel and exert an impact on hot coal (carbon). Decomposition of water vapors takes place in accordance with the above-mentioned reactions with extraction of fuel gases that are burnt there. Probably due to this reason there’s no condensation of water vapors of the fuel in the chimney, and the energy content is above normative. These facts were observed during operation of boilers of constant firing. Taking into consideration the importance of increasing of effectiveness of energy sources, this must be proved or denied by tests.
Combustion does not always run till the end as the matter that burns does not always add maximum possible amount of oxygen. If the combustion process has not ended, flammable matters will be formed capable of adding oxygen that is capable of combustion again (D.B.Ginsburg. Gasification of solid fuel, Gosstroiizdat, 1958).
At the finishing stage of combustion when there are only hot coals in the firebox the level of CO output increases above permissible limit. This refers to heat generators of any systems and is confirmed by the tests. When air exerts an impact on hot carbon, which takes place at the finishing stage of combustion, in the gasification zone oxygen of the air impacts on fuel carbon forming carbon dioxide, product of complete combustion and carbon oxide, product of incomplete combustion, fuel gas, in accordance with reactions С+О2=СО2; 2С+О2=2СО So an increased output of CO is explained by that. Carbon oxide CO ignites at approximately 700 °С and burns with a blue flame in accordance with equation 2СО + О2 = 2СО2+ 135 kcal. Such temperature is not available in the firebox at this time; therefore carbon oxide does not burn.
In this case another means of carbon combustion must be found. For example, we can supply a certain amount of overheated water vapor at the finishing stage of fuel combustion. The combustion reaction at low temperatures runs in accordance with equation С + 2Н2О = СО2 + 2Н2. Temperature of hydrogen ignition is 350 °С. Such temperature probably exists in the firebox at this time, hydrogen burns completely, and there is no emission of carbon oxide. This can be proved or disproved only by carrying out experiments, which I cannot perform due to lack of technical possibility and due to financial reasons.
In my opinion, current test methods and Testo tools are suitable only for forced gas movement system and cannot be applied for free gas movement system, as the gas flows movement and heat exchange processes are different in these systems.
The advantages of heat generators application in free gas movement system are shown during construction of household stoves. They provide high efficiency, a possibility of creating a large number of stoves with new useful functions; they show good test results with reference to purity of combustion obtained in different countries, and they are in high demand. It should be pointed out that ordinary multi-purpose stoves were subject to tests, not specially prepared and brought to perfection stoves, as a result of experiments, just ordinary simple stoves. The forced gas movement system has been developing and improving for a number of centuries, including development under laboratory conditions. We have to develop free gas movement system without experimental works and lapping, always at our own expense.
It should be mentioned that free gas movement system as regarded by I.V. Kuznetsov is widely used by different stove-makers. But this is only the top of the iceberg. Fuel gasification is the bottom of the iceberg, its nontouched part that requires further development. In this field there are boundless opportunities for biofuel processing and creating different devices on this base.
27.05.2013© Igor Kuznetsov "Kuznetsov's stoves"
I.V. Kuznetsov phone: 8 (343) 307 7303
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