The diesel engine is known for its high efficiency, performance, and durability. With stringent fuel economy and emission regulations, diesel engines face increasing challenges. To accommodate emission regulations, fuel economy and performance requirements, modern diesel engines are equipped with the variable geometry turbocharger (VGT) and exhaust gas recirculation (EGR) system. VGT extracts energy from the exhaust gas to drive the compressor to improve transient response, steady-state performance, and fuel efficiency under a wide range of engine flow conditions. Meanwhile, EGR dilutes fresh air with exhaust gas to reduce the formation of mono-nitrogen oxides NO and NO2 (NOx). The VGT and EGR control design is complicated due to the natural coupling between VGT and EGR, and high nonlinearity of diesel engine air-path system. The extra assisted power and regenerative power on the turbocharger shaft further increase the control system complexity. In this dissertation, new approaches for turbocharger system modelling and multivariable control design for the coordinated actuation of the VGT-EGR system are investigated. The control design is further extended to hydraulic regenerative assisted turbocharger system.New modelling approaches for turbocharger system are proposed based on turbomachinery physics. Proposed turbine and compressor models eliminate the interpolation error, and especially, allow smooth extrapolation outside the mapped region. A high fidelity reduced order mean value model of a diesel engine for automotive application is developed based on developed turbocharger model. Further, new models for high-speed hydraulic turbines and centrifugal pumps are developed for hydraulic assisted and regenerative turbochargers.A regenerative hydraulic assisted turbocharger (RHAT) system is investigated in this dissertation. A system level approach based on 1-D simulations is used to understand the assist benefits and design trade-offs. Simulation results show that 3-5% fuel economy improvement for FTP 75 driving cycle, depending on different sub-component sizing. The study also identifies technical challenges for optimal design and control of RHAT systems.A linear controller design approach is proposed in this dissertation for regulating both boost pressure and EGR mass flow rate of the VGT-EGR system. The linear quadratic control with integral action is designed based on the linearized system. Local controllers are scheduled based on engine operational parameter: engine speed and fuel injection quantity. The gain scheduled liner controller is validated against baseline controller based on the nonlinear plant. Results show that designed multi-input and multi-output (MIMO) controller can well manage the trade-offs between boost pressure tracking and EGR mass flow tracking, compared to baseline controller (two single input single output (SISO) controllers). A novel approach is proposed for closed-loop control design with respect to engine performance and engine emission trade-offs. The controller design is further extended to assisted and regenerative turbocharger system with VGT and EGR. The results show that emission reduction, engine performance and fuel economy improvement can be achieved at the same time with external power applied to the turbocharger shaft.
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