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Pulse Combustion
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19126 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
1 / 1991 |
2,145 Words |
| Author
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Ben T. Zinn
Ben T. Zinn is Regent's Professor at the School of Aerospace
Engineering, Georgia Institute of Technology in Atlanta. |
Combustion processes affect nearly every aspect of our daily lives. They are used to generate the electricity that lights our homes and powers our appliances. They are used to cook our food, to heat our residences, and to power our cars, airplanes, buses, and trains. Combustion processes also provide the energy required to produce cement and asphalt; to dry food, paper, textiles, and pharmaceutical products; and to make steel, copper, aluminum, and metal alloys.
Combustion occurs when fuel and air molecules come in contact and are ignited by a third body (for example, a spark plug) that provides the energy needed to start heat-releasing chemical reactions. Greek mythology tells us that man obtained fire from Prometheus who stole it from Zeus, the god in charge of lightning and thunderbolts. Indeed it is likely that the first experiments of combustion research occurred about 600,000 years ago when a thunderbolt or a volcanic eruption ignited a combustible material such as dry wood.
Mankind's subsequent struggle with the control of combustion processes dealt with the need to have an ignition source readily available. This required that flames be kept continuously lit. Then about 30,000 years ago, man by accident discovered that sparks from the flint used in tool making ignited combustible materials. Thus man could start fires whenever he needed and the earnest development of the science of combustion was begun.
In practical applications today, in order to prevent premature explosions or undesired burning, the fuel and oxidizer are generally stored separately and injected separately into the combustion chamber (the combustor). If the fuel is in a gaseous form, the combustion process consists of injecting and mixing the reactants in a combustion chamber containing flames which ignite the resulting mixture. (Several additional steps are involved when a liquid or a solid fuel is burned.) The combustion process generates a stream of hot combustion products whose energy is used in a variety of applications. For example, they expand and push the pistons inside internal combustion engines, heat air in space heaters, steam in power stations, and calcine limestone in cement-making plants.
For centuries the community of scientists, engineers, industrialists, and entrepreneurs concerned with combustion had operated as if the supply of fuel resources and the environment's capacity to "absorb" combustion products (including pollutants) were unlimited. This attitude has changed drastically during the past two decades as the world has had
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