Performance of the Automotive Turbocharger Compressor With Various CO₂-Air Mixtures

The automotive low pressure exhaust gas recirculation or closed-cycle gas turbine engines are among applications where an alternative fluids to air are used. This paper analyses compressor performance measured while operating with substitute gas. Several compressor performance maps were generated and compared on a steady-state turbocharger test facility run in a closed-loop mode. The automotive centrifugal compressor was mapped with pure air, CO2-air mixtures (3%, 5%, 10% CO2 by mass) and pure CO2. The analysis of the obtained data has indicated that the use of reduced speed parameter and reduced mass flow parameter formulas worked well in the process of the compressor map correction for the CO2-air mixtures. The corrected (with reduced mass flow and speed parameters) compressor performance map generated for the case of pure CO2 has shown a shift in both choke and surge lines and changes in measured pressure ratio and efficiency. Further efficiency and pressure ratio corrections based on the method proposed by Roberts and Sjolander [1] have shown no match between the predicted and measured values of efficiency for CO2. The series of adiabatic 3D CFD simulations indicated that this was likely caused by the heat transfer between the uninsulated turbomachinery components.