Evaluation of Performance Gain by Interstage Injection in a Four-Stage Axial Compressor

Abstract Recently, the energy market has seen a shift towards renewable energies due to changing demands. Gas turbines are used as a transitional technology to cope with grid fluctuations. The changing conditions have increased the interest in applying Wet Compression in order to increase the power output during peak demands. The novelty of this paper arises from the experimental results of Interstage Injection by analysing the stage and overall pressure ratios at different operating points in the four stage axial compressor “eco.MAC” (“evaporative cooling Multiphase Axial Compressor”). An innovative injection design is realized with twin jet nozzles in the trailing edge of SLM printed stator blades. A variation of water mass fraction, inlet temperature and rotational speed is performed and shows a gain in pressure ratio up to 1.5 %. Moreover, a polynomial approach is used for the dry data to compare wet and dry results at equal air mass flow rates. For the first time, a linear dependency of the pressure gain on the compressor’s gas temperature is experimentally found. It can be concluded that Interstage Injection is an effective technology to be applied in later stages of axial compressors due to the strong influence of local gas temperatures on the evaporation rate and thus the pressure gain. Furthermore, reducing the local injection rate decreases aerodynamic losses between the liquid and gas phase. Hence, a multiple injection and reduced local injection rates should be targeted.