Dual-stage boosting systems: Modeling of configurations, matching and boost control options.

摘要

Among many technical innovations and improvements in power train technologies, engine downsizing (reduction in displacement volume and/or the number of cylinders) is one of the most effective methods to reduce fuel consumption. Engine downsizing is achieved by running with high levels of pressure boosting at full load using a supercharger or turbocharger. In order to downsize Diesel engines that are typically turbocharged, it is necessary to raise the boost level well above the capability of the single-stage boosting system.However, when the displacement of the engine is reduced substantially, its dependence on boosting system increases and it needs high boost pressure to produce enough torque for acceleration. Although very effective, some characteristics of the turbocharged engines remain unsatisfactory and matching a turbocharger to an engine to achieve efficient turbocharger operation over a wide range of engine speed is a difficult and often compromising process.This study presents a simulation-based methodology for dual-stage turbocharger matching, through an iterative procedure predicting optimal configurations of compressors and turbines for given operating conditions. Different types of boost control schemes for the dual-stage turbocharging system are evaluated for performance and fuel economy benefits. In order to further enhance the low end torque and transient characteristics of the downsized engine, hybrid dual-stage boosting systems are also investigated. The hybrid dual-stage boosting systems incorporate different types of boosting devices, such as a mechanically driven supercharger, an electrically driven supercharger, and a variable geometry turbine, into a dual-stage system with only turbochargers on both stages.The simulation results suggest that the hybridization of the boosting system results in fewer compromises in the boosting system matching resulting in substantial reduction in fuel consumption without too much compromise in performance. In addition, the assessment of the different types of dual-stage boosting systems presented in the study and the methodology used in the process provide valuable means to evaluate and develop a new boosting system that requires excellent low end torque and transient boosting characteristics as well as the fuel economy benefit from the downsized engine.