Experimental Study of the Turbine Inlet Gas Temperature Influence on Turbocharger Performance

The influence of turbine inlet gas temperature on turbocharger performance is a topic discussed recently by many authors. Some studies present results on adiabatic operation by insulating the turbocharger from ambient conditions and report significant differences in compressor isentropic efficiency. Other authors perform non-adiabatic tests and report a significant influence on compressor isentropic efficiency only at the lowest turbocharger speed. In present work two different levels of gas temperature at the inlet of a Variable Geometry Turbine (VGT) have been tested at two different vane positions and two different corrected turbine speeds. Temperatures have been measured in the outer cases of turbine and compressor in order to determine the radiated power and their relative importance with respect to different power definitions obtained from turbocharger operative variables. The obtained results show the influence on both compressor and turbine isentropic efficiency. In addition, a thermodynamic analysis of the heat losses influence on the definition of isentropic efficiency has been performed in order to help in the analysis of the obtained results. The main conclusion is that diabatic operation occurs in the rear part of the compressor resulting in heat flux from the mass flow to the solid body. In the hot conditions, this heat flux is high enough to increase compressor efficiency (up to 4 points at some tested points) with respect to cold conditions. With respect to the turbine, small efficiency improvements have been observed in the hot test cases.