To understand how it works the stove need to know, at least basically, what is burning and fire. This well-known phenomenon, although seemingly simple, is a combination of many processes, whose full description needed serious knowledge.
Not aim to achieve scientific and technical precision, but little to illuminate the issue of fire. For simplicity, we will look up in the tree.
What comprises the tree dry and dead wood as a fuel material?
Tree, each material substance is made up of atoms arranged in molecules that, in turn, build-forming cells of different tissues. Around 40-45% of the wood consists of cellulose, 23-32% – hemicellulose, from 15 to 25% -lignin several percent water and a variety of substances for brevity and simplicity we shall call “other”.
Cellulose is crystalline unbranched biopolymer, odorless and tasteless, insoluble in water, composed of carbon, hydrogen and oxygen. Hemicellulose is called any one of a group heteropolymers and unlike cellulose is amorphous, its chains are branched to form a weak structure.
Lignin is a complex polymer made of aromatic alcohols called monolignini. This is the most abundant polymer in the world after cellulose. It lignin gives specific qualities of each tree – strength and stiffness. It is unusual, there are highly branched heterogeneous structure. Thanks lignin every blade of grass, every bush and generally each plant is upright and withstand the wind and tapping the bystanders.
And now some of combustion temperature and heat, flame and light:
For better understanding of combustion have to know what is the temperature.Temperature is a measure for the degree of movement of atoms and molecules that make up the fabric. Theoretically, it can vary from zero to infinity. But in fact, the absolute zero can not be reached, it exists only in the imagination of scientists. Absolute zero means absolute lack of movement. Similar quality is contrary to the nature of life and energy.
So when we start to heat a substance its constituent particles begin to accelerate their dance. Heat the means to import energy.
Heat, for brevity, we call heat. Heat is produced from the burning of wood, for example and not only.
Combustion is a rapid oxidation of a substance, which for brevity will be called a fuel, resulting in evolution of heat, light, and a mixture of the starting materials, preferably solid particles, gases and water.
Each material has a critical temperature at which burning begins. When there is the necessary quantities of fuel, oxygen and temperature combustion can start.
To get back to the tree and mentally built a fire. Here stacked thin and thick branches, they are our source of fuel around us is full of oxygen we breathe every breath. Now you need only to raise the temperature of some of the branches to bring critical as energy.You can rub a little or you can just get a source of heat, such as a cigarette lighter.Energy source starts to accelerate the building blocks of dance, their movements are gaining ground, a process of destruction. The movements are so strong that they overcome the forces that hold atoms in molecules and molecules in cells. Everything vibrates and vibrates! Slowly but surely, cellulose and lignin begin to decompose, long chains begin to crumble, we see smoke – small pieces of wood airborne. Temperature rises further apart becomes even stronger around appear gases (remember alcohol lignin) and behold, a person is our fuel mix – smoke particles, mixed with a variety of gaseous hydrocarbons. All that was formed from the breakdown of cellulose and lignin, but still no combustion. Combustion preceded by sputtering and gasification of cellulose and lignin (pyrolysis). Now the molecules of these gases are pushing increasingly with the free oxygen in the air, until at some point the blows were so powerful that oxygen is inserted into the gas molecule, binds to a part of it and it breaks, explodes is – boom !Burning is started. The energy of the flight cages debris is what we call heat and not only!
The reaction is accelerated, each oxidized molecule decay, releases energy and give part of it to other molecules. The process becomes so intense that around began to appear flames light. Atoms and molecules collide violently each other, increasing its internal energy that is released after a moment out in the form of light. Infrared, visible and ultraviolet even. Light also shines. Especially infrared. The higher the temperature becomes, the brighter are the flames.
Light also apply part of the thermal energy released during combustion. It is called radiant energy.
Flames are visible from the fire. They are emitted by hot gases and particles.
What are the stoves?
Stoves are devices that by burning fuel, emit heat, serving different purposes and needs. Effectiveness of each stove is mainly determined by two things – first, how fully burn fuel and, second, how much of the heat remains usable.
The most inefficient form of combustion is the open fire. So we invented and stoves first.Nowadays all stoves and fireplaces to work well, they need a chimney. The chimney takes exhaust gases and unburned smoke particles out of your home. Also chimney bringing “thrust” of the heater and drawing in air and in this way brings oxygen into the combustion chamber.
The chimney draft depends on its height and the temperature difference between the exhaust gas and ambient air. The passage section of the chimney is an important factor.In our most popular size of flue pipe has a diameter of 13 cm. Hence the minimum section of the chimney must be 13 cm. In fact, the chimney can have several flue, allowing one stack to include several stoves, but each requires a separate stove flue with a corresponding passage section.
Constrictions, sharp bends and even rough surfaces and make it difficult to disturb the movement of gases.
The chimney must be positioned so that it is the highest part of the roof, close to no high hills and buildings because the wind passing these hills, creating zones with different pressure, which affects the operation of the chimney.
Second, good isolation is required in order that the chimney remains warm in which more effectively supports the elevation of exhaust gases. If the chimney is cold, the gas which moves in the cool, shrinks, becomes heavier and falls down. Also create conditions for condensation.
So chimneys are an integral part of the stove. And they require maintenance. Must be cleaned. But why? Ideally combustion, all that remains is water and carbon dioxide. But it is nowhere. Even the internal combustion engine and any smoke and combustion gases spewing all, though they are quite sophisticated devices and work with well refined fuels.
In most burning stoves with low efficiency, which means that a small part of the fuel burned. The rest, which is a mixture of exhaust gases, unburned gases, smoke particles, ash and water vapor travel chimney and fall into the atmosphere. While traveling through the chimney, smoke and ash particles clump and stick to it, assisted by heat, moisture and gases. These layers reduce the effective area of the chimney and impede the movement of the gas stove and usually begins to smoke back into the room. These deposits appear and flues (pipes).
Maintain traction in a stove requires constant discharge of hot gas through the chimney.Here is the second factor behind the efficiency of the stove as a whole. First, about 50-70% of the fuel becomes heat, and secondly, only a portion of this heat is usable. The rest left in the chimney.
Main advantages of rocket stove.
Now, as we threw little light around the stove and burning, will be easier to understand how it works and why it is more effective a rocket stove.
The picture below shows the schematic structure of such a stove. At the base of the stove body is made of fireproof and insulating material, which in shape resembles the letter J. As seen in the picture, the branches are placed in short vertical part, the fire burning in a horizontal combustion chamber and gases and smoke travel through central chimney then fall into an area bounded by a cylindrical metal housing and is discharged to the flue pipe and chimney. Nothing complicated right? Which still makes the stove more efficient? Basically two things.
First look at the central chimney. As already mentioned, this body is made of heat resistant and heat insulating material. So hem withstand high temperatures, yet does not conduct heat well. The low thermal conductivity is important. Due to this capacity, the main stack is heated to high temperatures of the order of 800 to 1000 degrees. This course is not immediately as flammable stove. It is necessary here above about 20 to 30 minutes, depending on the intensity of combustion to heat the well central chimney.When this happens we say that the stove is working or “rocket” mode.
And now take a step back to the imaginary fire that lit. To imagine that the burning is started and the central chimney is warm, that the stove is in operation. What is going on here, which is different from an ordinary stove. What happens is the following – a mixture of burned and unburned gases, smoke and water vapor resulting from the combustion of the material in the horizontal combustion chamber, passing through the hot central chimney comes in contact with hot walls and what is not burned in the horizontal camera burns here. This means that the higher the central chimney, the better we will burn. This is called secondary combustion. Constituent particles (atoms) of the material from which the central chimney vibrate with great intensity, but it remains in place, the material does not disintegrate. Therefore, it is said to be heat resistant. The molecules of the gas mixture, bringing it closer to the walls, get extra energy and accelerate its movement (filament) and in contact with oxygen burn in which heat is released, part of which leaves the chimney, and another maintains its temperature. So the role of the central chimney.A very important element which, together with the horizontal combustion chamber are the heart of the rocket stove.
Another interesting phenomenon that occurs as a result of the structure of the rocket stoves is thrust. Rocket stove creates its own power. This means that it can operate without a chimney! You can just spend smokestack through the window and voila.However chimney support its effectiveness and power. How is self-propelled or “missile” thrust? The hot gas mixture leaving the central chimney, locked into the space between it and the cylindrical shell, chilled. This is because the cylindrical housing that is made of metal, is in contact with ambient air, which has a temperature of, say about 22 degrees, and the gas mixture leaving the main stack has a temperature of more than 400 degrees. The cooled gas is compressed and the pressure in the space around the stack drops – formed by vacuum by means of which the stove “sucks” air through the opening of the combustion chamber. It is therefore important to have a tightness of the outer casing.
Rocket thrust is a big plus. It enables us to absorb the utmost heat produced in the combustion process. This is done by run exhaust gas through long enough flue pipes, which act as heat exchangers. It is important to mention that it is not possible to adjust the thrust of the rocket stove through the valve in the flue pipe. This is because the “missile” thrust “pushes” the gas and if we put a barrier in the way he started in the compounds of the pipes and invaded the room.
Working with rocket stove has its subtleties. And here we have the perfect combustion at all times. Yet even car engines emit smoke and smoke sometimes. Optimum combustion is achieved by optimum ratio between heat, fuel and oxygen.
Rocket stove allows us to enjoy the semi-open fire, fires up quickly and easily and gives us better control over the intensity of burning.
2 thoughts on “What is burning”
I made a rocket mass heater. Out of bricks. The outer bells is only 3 sided. I’m thinking I made a mistake. There is no space between the inner bell and outer bell on the back wall. How important is it to have 360 degree space between the bells? I’m thinking that is what causes the rocket action similar to a tornado.
I beleve You are right.
We have model (Gamera) that is with excentrical mounted cylinders and there are 4 pipes inside the wider area between but still all shapes are roound and there is still place for the gas to circulate all around.
Even with square bodies i know people are making there are free space all around.
The gas allways try to move on spirals so if there is no possible you have a lot of bad draft.