ABSTRACT
In axial-ow compressors, the stage pressure rise is very dependent on the axial ow velocity. To achieve the design pressure ratio in the minimum number of stages, a high axial velocity is essential; in many aircraft engines, compressor outlet velocities may reach 170 m/s or higher. It is, of course, impractical to attempt to burn fuels in air owing at such high velocities. Quite apart from the formidable combustion problems involved, the fundamental pressure loss would be excessive. For example, for an air velocity of 170 m/s and a combustor temperature ratio of 2.5, the pressure loss incurred in combustion would be approximately 25% of the pressure rise achieved in the compressor. Thus, before combustion can proceed, the air velocity must be greatly reduced, usually to about one-fth of the compressor outlet velocity. This reduction in velocity is accomplished by tting a diffuser between the compressor outlet and the upstream end of the liner.
