Making fire

The fire has changed the course of human evolution. It has helped us protect ourselves and create energy (change energy to a usable form). It makes the stars burn, as it does the human soul.

While researching on how to make a stove that uses the firewood efficiently to turn it into heat and doesn’t give out smoke, we realised it was important to observe fire more closely.

When we burn wood, the wood itself doesn’t burn. Because of very high temperatures, the wood releases wood gas (a mixture of hydrogen, nitrogen, carbon monoxide and traces of methane). Wood gas is combustible and at high temperatures, in presence of oxygen, it bursts into flames. The remaining solid residue, char, is then combusted to form carbon dioxide. Complete combustion of wood (or wood gas) results in two byproducts: carbon dioxide and water vapour. In contrast, incomplete combustion creates unburned particles that cause pollution and health hazards for users. The smoke coming out of the wood is really wood gas that doesn’t burn, which can be due to several reasons discussed below.

A good clean (without smoke) fire can be made by keeping the following things in mind:

1. Metering the fuel
Cutting the wood into small pieces and feeding them to the fire at regular intervals. A big log of wood will cool down the combustion chamber, restrict passage of air and create smoke.

2. Stack it like a grid
A good fire needs a good amount of oxygen. By stacking the firewood such that enough air passes below and above it, will help in complete combustion.

3. Making a hot combustion chamber
While starting a fire, smoke cannot be avoided. It takes a while for the combustion chamber to heat up and burn all of the wood gas. By insulating the combustion chamber properly, high temperatures can be achieved rather quickly.

4. Keeping the wood gas in the chamber for longer
By increasing the time for which the wood gas is in the combustion chamber, complete combustion can be achieved.

5. Creating a draft
By creating a draft in the combustion chamber, the velocity of the incoming air can be increased. This will create a turbulence in the combustion chamber allowing for better mixing of the wood gas and oxygen.

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Reference:
Combustion Engineering, Borman & Ragland, 1998

 

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