30-08-2013, 04:32 PM
Combustion Engines
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Combustion Engine Definiton
Combustion engines are machines that deliver mechanical work through a linked thermal and combustion process: mechanical work is obtained from the chemical bound energy of the fuel (fuel energy) through combustion by means of thermal energy.
Heat engines can be classified as; external combustion type in which the working fluid is entirely separated from the fuel- air mixture (ECE), and the internal - combustion (ICE) type, in which the working fluid consists of the products of combustion of the fuel- air mixture itself.
History of Internal Combustion Engine
They became widely used at around the 1900's. The first internal combustion engine was built in 1859 by Etienne Lenoir. It ran on street-lightning gas, which was ignited by an electric spark. It ran smoothly, but it wasn't very powerful because the fuel and the air weren't compressed so it didn't burn fast enough. Even though they took a lot of fuel people still bought them. Next in 1862 Alphonse Beau de Rochas took it a step farther. He took it to compression and the four-stroke cycle, but Alphonse never built an engine. The first-stroke cycle was built by Nikolaus A. Otto in 1876. They named it the Otto Cycle in his honor.Today technological advances have been made, such as pollution control, computerization, fuel injection, and supercharging.
The Combustion Process
In the internal combustion engines the combustion is the fundamental process which converts the chemical energy of the fuel in thermal energy inside the combustion chamber. This thermal energy is then converted into mechanical energy through the piston-con rod- crankshaft system. The combustion is a chemical reaction between the air and the fuel generally composed by a mixture of different hydrocarbons molecules. The reaction can be simplified as follows:
The ideal combustion process should produce only carbon dioxide (CO2) and water vapor (H2O). Instead the real combustion process produces also some exhaust gases which are the products of an uncompleted oxidation as carbon monoxide (CO), unburnt hydrocarbons (HC), nitrogen oxides (NOx) and per particulate matter (PM).
Modern Developments of I.C.E.:
The modern I.C.E. is a product of research and developments extending over a long period of time many engines were proposed and tested, these include:
1. Stratified charge engine.
2. Dual Fuel and Multi- Fuel engines.
3. Sterling engine.
4. Free Piston engine.
5. Variable compression Ratio engine.
6. Combination of reciprocating engine with gas turbine.
Use of the Engine:
1. Marine engine: for propulsion of ships at sea.
2. Industrial engine: for power generation on land.
3. Automotive engine: for transport.