In the previous page we mentioned that there were several different types of combustion chamber. They all have one thing in common in that they all have an inner and an outer section.
Multiple combustion chambers.
The early jet engines used a number of individual combustion chambers. Each chamber has its own inner (liner) and outer section and are mounted externally around the engine. The air from the compressor is split up and directed into the individual chambers. One feature of the jet engine is that an ignition source or "spark" is normally needed when the engine is started. Once the engine is running, the flame in the combustion chamber will normally stay lit thus eliminating the need for the constant spark which internal combustion engines require. To avoid having to put an igniter plug in each chamber for starting purposes, the chambers are all linked by a hollow tube which allows the flame to spread around to all chambers. Two chambers will be fitted with igniter plugs to provide the initial sparks during engine start up. The advantages of the multiple combustion chamber are simplicity and ease of servicing. It is possible to replace individual chambers with relative ease. The disadvantages are its increased weight and bulkiness compared to the other types.
The externally mounted combustion chambers can be seen clearly on this early De Havilland Ghost engine.
Tubo-annular combustion chamber.
Tubo-annular combustion chamber.
The tubo-annular or can-annular system as it is sometimes called, is a number of individual liners but with a common outer casing. This arrangement is more compact than the multiple chamber system but is not so easy to maintain.
This cutaway picture shows the individual combustion liners enclosed between a single inner and outer casing.
Annular combustion chambers.
Annular combustion chambers.
The annular combustion chamber is the most common design fitted to modern jet engines. It consists of a single annular liner inside an annular combustion casing. This design is very compact, cheaper to manufacture and because it is more efficient it produces less pollution than the other types of combustion chamber
