22-09-2016, 12:22 PM
1455683571-combustionchambers2.pptx (Size: 1.35 MB / Downloads: 6)
Combustion chamber is the space enclosed between the piston head and cylinder head when the piston is at top dead center position.
Depending upon the location of the spark plug, valves and type of cylinder head , the combustion chambers in SI engines are of the following shapes:
I-shape
L-shape
T-shape
F-shape
The basic requirements of a good combustion chamber are to provide:
High power output
High thermal efficiency
low specific fuel consumption and
Smooth engine operation
Advantages:
Additional turbulence during compression stroke is possible as gases are forced back through the passage.
By varying throat area of passage designed degree of additional turbulence is possible.
This design ensures a more homogeneous mixture by scoring away the layer of stagnant gas clinging to chamber wall. Both the above factors increase the flame speed and thus the performance.
Disadvantages :
With compression ratio of 6, normal speed of burning increases and turbulent head tends to become over turbulent and rate of pressure rise becomes too rapid leads to rough running and high heat losses.
F- Head combustion chamber
such a combustion chamber one valve is in head and other in the block. This design is a compromise between L-head and I-head combustion chambers. One of the most F-head engines (wedge type) is the one used by the Rover Company for several years. Another successful design of this type of chamber is that used in Willeys jeeps
Its advantages are :
1.High volumetric efficiency
2. Maximum compression ratio for fuel of given
octane rating
3. High thermal efficiency
4. It can operate on leaner air-fuel ratios without misfiring.
The drawback
This design is the complex mechanism for operation of valves and expensive special shaped piston.
Open combustion chamber
Open combustion chamber is made like groove inside the top of the piston.
The injector fitted at the center of the cylinder head so that it injects the fuel in the combustion chamber.
This type of combustion chamber is also called an Open combustion chamber. In this type the entire volume of combustion chamber is located in the main cylinder and the fuel is injected into this volume
Pre-combustion chamber
In pre-combustion chamber there are two combustion chambers – one is auxiliary combustion chamber and the other is main combustion chamber.
The auxiliary combustion chamber is smaller in size than the main combustion chamber and is called pre-combustion chamber.
Fuel is injected into the pre-combustion chamber where it partly burns. This partly burnt fuel goes through a small orifice in the main combustion chamber, where the complete combustion takes place.
The turbulence created in the combustion chamber helps to ignite the fuel completely.