Numerical investigation on the effect of cold climate on the thermodynamic behavior and exergy distribution in the two-stage radial turbine

The internal heat transfer process and thermodynamic behavior in turbochargers as diabatic machines, especially in low ambient temperature scenarios such as plateaus, requires further clarification. This study investigates the aerothermodynamics and flow exergy losses in two sets of two-stage turbochargers matched with V-6 diesel engines under different heat transfer conditions. Based on fundamentals of heat transfer combined with several possible low temperature scenarios for the engine, inner wall temperatures of the two-stage turbine were estimated. Next, thermal sensitivity analyses of the aerodynamic parameters and thermodynamic processes in the two-stage turbine were revealed. By applying an exergy budget analysis, the flow exergy losses in the whole and in the components of the two-stage turbine were evaluated. Results showed that the maximum flow exergy loss (including entropy generation and heat exergy loss) could be close to 50% of the net flow exergy passing through the two-stage turbine. Although the adiabatic efficiency in the two stage-turbine was more than 80%, the maximum exergy efficiency was still less than 15%, indicating that the potential for recycling available energy from exhaust gases was still great. Furthermore, downstream components require greater attention. Heat exergy losses in the low-pressure turbine were about 1.3 times those in the high-pressure turbine, suggesting that the volute and interstage ducts require greater adiabatic protections. The present work can provide an informed and directed manner for optimal design of a two-stage turbocharger under diabatic conditions.