The Combustion Process

By Doug Hetsch

January 25, 2014

Chimney Maintenance, Fire Safety, Fireplace Maintenance

Combustion is when fuel reacts with oxygen to release heat energy. Put simply, combustion means to burn. For the combustion process to take place, fuel, oxygen, and an ignition heat source are required to start a chemical chain reaction. Combustion can be slow or fast depending on the amount of oxygen available. Getting a more solid grasp on the combustion process will enable you to get the most out of yourheatinginvestment.

The Role of Fuel in the Combustion Process

Fuels can be solids, liquids or gases. During the chemical reaction that produces fire, fuel is heated to such an extent that (if not already a gas) it releases gases from its surface. Only gases can react in combustion.Gasesare made up of molecules (groups of atoms). When these gases are hot enough, the molecules in the gases break apart and fragments of molecules rejoin with oxygen from the air to make new product molecules — water molecules (H20) and carbon dioxide (CO2) — and other products if burning is not complete.

The Fire Triangle

The heat generated by the reaction is what sustains thefire. The heat of the flame will keep remaining fuel at ignition temperature. The flame ignites gases being emitted, and the fire spreads. As long as there is enough fuel and oxygen, the fire keeps burning. In a campfire, for example, wood is the fuel, the surrounding air provides oxygen, and a match or lighter can ignite the fire. Increasing any of these elements will increase thefire’s intensity, while eliminating any one of them will cause the process to stop. If the campfire is smothered with water or dirt, for example, the oxygen can no longer get to the heat and fuel, and it goes out.

Complete Versus Incomplete Combustion

Incomplete combustion, the burning fuel will produce only water and carbon dioxide (no smoke or other products). The flame is typically blue. For this to happen, there needs to be enough oxygen to combine completely with the fuel gas. If there is not enough oxygen available during a chemical reaction,incomplete combustionoccurs, and products such as carbon (C) and carbon monoxide (CO) as well as water and carbon dioxide are produced. Less heat energy is released during incomplete combustion than complete combustion. In incomplete combustion, the burning flame is typically yellow or orange and there is smoke present.

Striving for as close to complete combustion as you can get will help to reduce the amount of creosote and other chemicals that can build up on the inside of your chimney. Even if you were able to achieve complete combustion, an annual chimneyinspectionandcleaningby aCSIA-certifiedchimney sweep is still recommended, as even a small amount of these substances is enough to cause a dangerous and potentially deadly chimney fire.

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