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Automotive
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The combustion chamber is defined as the “clearance space in the cylinder of an internal-combustion engine where the charge is compressed and ignited”. The combustion chamber is recessed in the cylinder head. Various shapes of combustion chamber have been used, the most common and used today are the “Wedge and Hemispherical “ combustion chamber. |
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The Combustion Chamber
- The combustion chamber is part of the cylinder head; a recessed area in the cylinder head.
- The shape of the chamber, to a large extent effects the engine performance, fuel efficiency, and the level of pollutants in the exhaust.
- Over the years manufacturers have designed several different shapes of combustion chambers. The two most popular are the "wedge" and the "hemispherical".
- Before we look at these two combustion chamber designs, two terms have to be defined.
- Turbulence: Turbulence is a very rapid movement of gasses which causes better
combustion because the air and fuel are mixed better.
- Quenching: Quenching is the mixing of gases by pressing them into a thin area. The area in which gasses are thinned is called the quench area
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- Q uench serves to focus the air and fuel mixture into the center of the combustion chamber, so that the force of igniting the mixture initially takes place over a smaller surface area. The same amount of force applied to a smaller surface equal’s greater work.
Wedge Chamber
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In the wedge-type combustion chamber, the spark plug is located at the widest part of the wedge.
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As the piston comes up on the compression stroke, the air/fuel mixture is squashed in the quench area.
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The quench area causes the air and fuel to mix thoroughly before combustion, which helps to improve the combustion efficiency or the engine.
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Spark plugs are positioned to allow for rapid and even combustion.
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When the spark occurs, a flame front moves from the spark plug outward.
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The wedge shaped combustion chamber is called a turbulence or swirl-type combustion chamber.
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On newer model cars, the quench area has been reduced, which helps reduce exhaust emissions.
Hemispherical Chamber
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The hemispherical or hemi combustion chamber gets its name from its basic shape.
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Hemi means half, and spherical means circle.
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The combustion chamber is shaped like a half circle.
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This type of cylinder head is also called the hemi-head.
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The piston top forms the base of the hemisphere and the valves are include at an angle of 60 to 90 degrees to each other, with the spark plug positioned between them.
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This design has several advantages.
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Produces efficient burning because the flame path from the spark plug to the piston head is short.
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Relatively free flow of gases in and out of the chamber due to the cross-flow arrangement of the inlet and exhaust valves.
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This results in a relatively free flow of gases in and out of the chamber.
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Little turbulence is produced in this type chamber which is called a non turbulence-type combustion chamber.
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On the compression stroke, the air/fuel mixture is compressed evenly.
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The spark plug is located directly between the valve.
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From the spark plug, combustion radiates evenly, completely burning the air/fuel mixture.
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Last but not least, unlike the wedge chamber which restricts the flow of air and fuel to a certain extent, the hemispherical chamber allows air and fuel to enter the chamber very easily.
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