Design of a variable geometry turbine constrained by geometric and aerodynamic parameters to improve engine low-speed characteristics at high-altitude

Abstract

High-altitude environment with low atmospheric pressure will significantly reduce the torque and power of diesel engines at low-speeds. To enhance the low-speed characteristics of an existing diesel engine at high-altitude of 4500 m, a variable nozzle is designed and integrated with the fixed-geometry turbine. Based on the mean-line thermodynamic calculations assisted by genetic algorithm optimization, the three-dimensional modeling and simulations, and the one-dimensional engine simulation, a design method for variable geometry turbine (VGT) under the constraints of geometric and aerodynamic parameters is established. Under the constraints of maintaining the prototype turbine volute geometry and achieving equivalent flow capacity and efficiency at the design rotating speed, the fixed-geometry turbine is modified to be a VGT. The newly designed VGT has increased the turbine efficiency by 2% at the design rotating speed, and expanded the flow adjustment range by 31%. Based on the calibrated one-dimensional simulation model of the diesel engine, the VGT is evaluated at high-altitude of 4500 m. Compared to the diesel engine with the fixed-geometry turbine, the engine with the VGT shows improvements in torque and power by 10.41%, 19.28%, and 23.28% at engine speeds of 800, 1000, and 1200 rpm respectively.