Performance improvement of an asymmetric twin scroll turbocharger turbine through secondary flow injection

Abstract

A powerful and efficient turbocharger turbine benefits the engine in many aspects, such as better transient response, lower NOx emissions and better fuel economy. The turbine performance can be further improved by employing secondary flow injection through an injector over the shroud section. A secondary flow injection system can be integrated with a conventional turbine without affecting its original design parameters, including the rotor, volute, and back disk. In this study, a secondary flow injection system has been developed to fit for an asymmetric twin-scroll turbocharger turbine, which was designed for a 6-cylinder heavy-duty diesel engine, aiming at improving the vehicle's performance at 1100 rpm under full-loading conditions. The shape of the flow injector is similar to a single-entry volute but can produce the flow angle in both circumferential and meridional directions when the flow leaves the injector and enters the shroud cavity. The preliminary design consists of ten design parameters, which is able to control circumferential area distributions, exit flow angles, and flow velocities. To investigate the availability of the injection system, a DOE study has been conducted with the creation of 200 different design candidates that cover the entire design space. Each design candidate is evaluated under ten different turbine operating points, which were picked from the engine exhaust pulse at 90 krpm, covering both equal and unequal admission conditions. To evaluate the turbine performance, a full-rotor steady-state simulation has been conducted using the commercial CFD solver ANSYS-CFX 19.2. This study found the injection system does not influence the original turbine matching during the idle operation (zero injection flow). Within the current DOE set-up, the mean turbine torque can be increased by 24.22%, but the improvement of energy-weighted mean turbine efficiency is limited because of the extra cost by introducing additional flow resources. The secondary flow injection system can be regarded as a novel turbocompounding technology, which can be used to increase the engine torque whenever needed. The current study reveals the availability of the novel system and provides a framework for further optimizations.