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Three-phase sequential turbocharging system with two unequal-size turbochargers is developed to improve fuel economy performance and reduce emission of the automotive diesel engine, which satisfies wide range of intake flow demand. However, it results in complicated transient control strategies under frequently changing operating conditions. The present work aims to optimize the control scheme of boost system and fuel injection and evaluate their contributions to the improvement of transient performance. A mean value model for diesel engine was built up in SIMULINK environment and verified by experiment for transient study. Then a mathematical model of optimization issue was established. Strategies of control valves and fuel injection for typical acceleration and loading processes are obtained by coupled calculating of the simulation model and optimization algorithm.

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.

During cold start of DI diesel engine, exhaust gas comprises a great deal of unburned hydrocarbon, fuel vapor, and product of partial oxidation reaction. If these compositions are reintroduced into cylinder by EGR, the positive effects may shorten ignition delay, and thus promote ignition. Furthermore, considering thermal effect of EGR and its minor dilution effect during cold start, the combustion performance of cold start could also be promoted through introducing EGR. Through experiments conducted on a 135 single cylinder DI diesel engine, effects of EGR on combustion and emission performance during cold start process were investigated. Comparison of combustion performance between cold start processes with and without EGR suggested that it is an effective measure to improve cold startability of DI diesel engine by controlling EGR system during cold start.

A newly developed turbocharging system, named MIXPC, is proposed and the performance of the proposed system applied to diesel engines is evaluated. The aim of this proposed system is to reduce the scavenging interference between cylinders, and to lower the pumping loss in cylinders and the brake specific fuel consumption. In addition, exhaust manifolds of simplified design can be constructed with small dimensions, low weight and a single turbine entry. A simulation code based on a second-order FVM+TVD (finite volume method + total variation diminishing) is developed and used to simulate engines with MIXPC. By simulating a 16V280ZJG diesel engine using the MPC turbocharging system and MIXPC, it is found that not only the average scavenging coefficient of MIXPC is larger than that of MPC, but also cylinders of MIXPC have more homogeneous scavenging coefficients than that of MPC, and the pumping loss and BSFC of MIXPC are lower than those of MPC.