Basic principles and objectives of supercharging Since the radial compressor will be discussed in detail in Chap. 5 in connection with exhaust gas turbocharging and as part of the exhaust gas turbocharger, at this point its function will only be addressed as the basis for its map characteristics. All flow compressors are based on the physical principle of the transformation of kinetic energy, which is supplied to the medium in the impeller, into a pressure rise via flow deceleration, partially in the impeller, partially in a diffuser. The complete process between compressor inlet and outlet can be clearly described using the. | 16 Basic principles and objectives of supercharging Since the radial compressor will be discussed in detail in Chap. 5 in connection with exhaust gas turbocharging and as part of the exhaust gas turbocharger at this point its function will only be addressed as the basis for its map characteristics. All flow compressors are based on the physical principle of the transformation of kinetic energy which is supplied to the medium in the impeller into a pressure rise via flow deceleration partially in the impeller partially in a diffuser. The complete process between compressor inlet and outlet can be clearly described using the first thermodynamic theorem for open systems v2 v2 wC -------2 h2 hi where wC is the added specific compressor work Vi are the medium absolute flow speeds at the intake 1 and outlet 2 and hi are the corresponding enthalpies. The latter describe the gas condition which enables directly from Eq. the calculation of the pressure and temperature at the compressor outlet or the compressor work. The danger of flow stalling exists in the flow compressor as in the diffuser. Therefore in a single compressor stage only a limited pressure ratio can be achieved. Since the radial compressor enables the highest per-stage pressure ratios it is the preferred choice for a compressor in exhaust gas turbochargers. In this layout the chargers can be of very compact design. Their disadvantage in comparison to axial compressors is lower efficiency. From all these facts it is clear that flow compressors show totally different map characteristics compared with displacement compressors. Additionally all turbo compressors deliver continuously except for the speed fluctuation at the compressor impeller exit caused by the finite blade thicknesses. Although they thus generally feature a better acoustic quality radial compressors are also sometimes equipped with silencer systems to eliminate these high-frequency noise excitations. The map characteristics of turbo .
