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Combustion, which is simply the burning of something, is a rather complex chemical process. We rely quite heavily on combustion technologies for energy. For example, we burn gasoline to power our cars; we often burn oil or gas in home heating systems; and power plants usually burn coal, oil or natural gas to generate electricity.
Many families, particularly in the developing world, burn wood and other biomass to cook food and heat their homes. However, burning wood and other solid fuels produces a lot of smoke, which is harmful to health and the environment. In fact, the World Health Organization reports that approximately 4 million people die every year from diseases related to smoke inhalation from burning wood and other solid fuels in their homes for cooking and heating. Many of these deaths are young children.
Why does burning wood create so much pollution? The short answer is incomplete combustion.
In order to get something to burn you need three things, all in the proper combination: fuel (such as wood, oil or gas), oxygen and heat. These requirements are referred to as the “combustion triangle.” With solid fuels, like wood and other biomass, it’s really difficult to get good mixing of the fuel, oxygen and heat in the proper ratio. For example, wood fires, especially those on the ground, don’t receive enough oxygen for the wood to burn completely. Similarly cool breezes can reduce the heat needed to sustain a flame. As a result, you are often left with unburned fuel, particulates, ash, carbon monoxide and nitrogen oxides. These types of compounds are what make up smoke.
Watch the animation above to learn more about the chemistry of combustion.
This Science Spotlight video is part of our Engineering Is: Saving the World with Cookstoves e-book, and is a companion to our Darfur Stoves Project video. The e-book tells the story of how Professor Ashok Gadgil and his team at Lawrence Berkeley National Laboratory designed a cookstove to help internally displaced persons in Darfur. They are now working on designing a new wood-burning stove to reduce indoor air pollution. The e-book includes videos, interactives and media making opportunities that explore the science and engineering principles behind this project.