Combustion chamber

 COMBUSTION CHAMBER

The combustion section houses the combustion process, which raises the temperature of the air passing through the engine. This process releases energy contained in the air/ fuel mixture. The major part of this energy is required at the turbine or turbine stages to drive the compressor. About 2/3 of the energy is used to drive the gas generator compressor. The remaining energy passes through the remaining turbine stages that absorb more of the energy to drive the fan, output shaft, or propeller. The primary function of the combustion section is, of course, to burn the fuel/air mixture, thereby adding heat energy to the air. 

The location of the combustion section is directly between the compressor and the turbine sections. The combustion chambers are always arranged coaxially with the compressor and turbine regardless of type, since the chambers must be in a through-flow position to function efficiently. All combustion chambers contain the same basic elements:

1. Casing

2. Perforated inner liner

3. Fuel injection system

4. Some means for initial ignition

5. Fuel drainage system to drain off unburned fuel after engine shutdown


Types of Combustion Chambers:

There are currently three basic types of combustion chambers, These types are:

1. Can Type or Multiple combustion chamber

2. Can-annular or Tubo-annular combustion chamber

3. Annular combustion chamber

1. Can or Multiple Combustion Chamber

Can type burner, consists of a cylindrical combustion liner installed within its own cylindrical shroud or air casing. A can type of burner arrangement is most frequently employed on centrifugal compressor engines. In this system, the air is divided as it leaves the diffuser, and is ducted to individual combustion cans, or cylinders, arranged around the of the burner section of the engine.
Each burner or can contains its own fuel nozzle and two burners are provided with igniter plugs.

Advantages of Can Type Combustion Chamber
1. Can be individually removed for inspection and maintenance.
2. Air-fuel patterns are easier to control than in other types.
3. Smaller diameter ensures higher strength resistance to War page

Disadvantages of Can Type Combustion Chamber
1. Longest length of all types of burners.
2. Does not efficiently utilize available space and results in a large diameter engine for a given airflow.
3. Large area for a given volume requires large amounts of cooling airflow and a large area of metal for construction.

2. Can-Annular or Turbo-Annular Combustion Chamber

Can-annular combustion chamber consists of a number of flame tubes fitted inside a common air casing.  Each can have two holes, which are opposite each other near the forward end of the can. One hole has a collar called a flame tube. When the cans are assembled in the annular chamber, these holes and their collars form open tubes between adjacent cans to enable a flame to pass from one can to the next during engine starting.

Advantages of Can-Annular Type Combustion Chamber

1. Individual liners may be replaceable
2. Better use of available space compared to can type combustion chamber
3. Lower pressure loss than that of the can type combustion Chamber.
4. Greater structural stability than annular type combustion Chamber.

Disadvantages of Can-Annular Type Combustion Chamber

1. Interconnect tubes required for flame propagation
2. Large cooling airflow required
3. Length is greater than annular combustion chamber


3. Annular Combustion Chamber

Annular Combustion chamber consists of a single flame tube, completely annular in form, which is contained in an inner and outer casing. The airflow through the flame tube is similar to that already described, the chamber being open at the front to the compressor and at the rear to the turbine nozzles. The liner of this type of burner consists of continuous, circular, inner and outer shrouds around the outside of the compressor drive shaft housing. In the annular combustion chamber, fuel is introduced through a series of nozzles.

Advantages of Annular Type Combustion Chamber

1. Less cooling air is required due to less surface-to-volume ratio comparable can burners
2. Makes more complete use of available space
3. Lower total pressure loss
4. Improved exit temperature distribution
5. Has the highest efficiency
6. Elimination of flame propagation problems

Disadvantages of Annular Type Combustion Chamber

1. Structural problems may arise due to the large-diameter
2. Entire combustor must be removed from the engine for inspection and repairs

 


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