System analysis and optimization of Variable Geometry Compressor for turbocharged diesel engines

Variable Geometry Compressors (VGC) have been recently considered as a solution for downsized, turbocharged engines to improve the stability of the compressor and increase its efficiency at low engine speed without compromising the operation at peak loads. This paper presents a system analysis of the air path dynamics of an automotive Diesel engine equipped with exhaust gas recirculation (EGR) variable geometry turbine (VGT) and VGC system. Starting from a validated model of the engine air path dynamics, a reduced-order model is designed to facilitate system analysis and control design. Then, a study of the steady-state and dynamic response of the air path system is conducted to understand the combined influence of the EGR-VGT-VGC actuators on the performance and transient behavior of the system. Finally, a multivariable optimization is performed to define a simple open-loop control strategy for the air path system. The work shown in this paper is intended as a preliminary study for the design of feedback control algorithms, which coordinate the available actuators to optimize the engine performance and the stability of the compressor.