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The level of boost pressure has a significant effect on optimizing the steady-state and transient performance of turbocharged diesel engines. However the problem of matching the wide speed range diesel engine and the high pressure turbocharging system has to be resolved. The regulated two-stage (RTS) system is an effective method to improve the fuel economy, transient response and smoke emissions. Compared with the difficult matching problem of the RTS system, the problem of boost pressure control is more complex due to the frequently changing operating conditions. To overcome the limitations of an open-loop control strategy, a closed-loop boost pressure control strategy was studied numerically using a mean value model of a diesel engine with RTS system. The system identification was conducted for the transient response from the turbine bypass opening command to the boost pressure.

The concept of regulated two-stage turbocharging system is proposed to provide high boost pressure level over a wide range of engine speed by regulating the energy distribution of two turbochargers. However, the control strategy of turbine bypass valve becomes more complicated due to the frequently changing working of vehicle diesel engines. In this paper, a two-stage turbocharging system was matched for D6114 diesel engine to improve the low-speed torque. The effect of valve opening on the steady-state and transient performance was analyzed, and two different regulating laws were determined according to the different optimum aims. Then the transient response characteristics of two different regulating laws were studied and optimized at three speeds with the transient loading test. For steady-state performance, the output power and fuel efficiency were increased with the matched turbocharging system.