It is interesting to improve engine system performance with turbocharger technologies. In this study, a systematic simulation for engine and turbocharger matching to provide full utilization of the turbocharger potential and improve the engine performance without sacrificing the emission is developed. A velocity ratio concept was proposed to count the turbocharger performance impacts due to the diameter ratio of compressor and turbine wheels. A design of experiments was used to optimize the turbocharger and engine performance for different turbocharger factors. A better‐matched turbocharger was obtained. A multidisciplinary optimization method was used to design a mixed flow turbine wheel to reduce the turbine velocity ratio at peak efficiency and increase the overall turbocharger efficiency. Results showed that about 0.4% torque improvements and 1.2% reductions in the engine brake‐specific fuel consumption were obtained without making any other changes to the engine. This study demonstrated that systematic simulations for engine systems and considering turbocharger wheel diameter ratio effects could further improve the turbocharged engine system matching and the engine performance.

A gas-entraining diffuser exhaust gas recirculation (EGR) was proposed to induce the entry of the exhaust gas into the diffuser, to completely utilize the lower static pressure at the diffuser for reducing engine fuel consumption owing to the low engine backpressure. Thus, the induced structure was designed such that a large amount of exhaust gas enters the compressor diffuser. To improve the compressor efficiency and reduce the static pressure at the induced structure inlet, the design parameters of the induced structure (induced angle, induced effective inlet area, parallel part width, and position of the induced structure inlet) were investigated using numerical methods. The results show that the peak compressor efficiency reduced by 4% compared with the compressor prototype, and up to 90% of the compressor efficiency reduction is attributed to the induced gas entering the diffuser, except for the 10% induced gas ratio scenario over the near-choking point. This is because the entropy generation of the induced structure is close to 10% of the entropy generation increase in the diffuser system due to the induced gas at a medium flow rate. Second, in most cases, the compressor efficiency and static pressure of the induced structure inlet increase or decrease simultaneously as the design parameters vary. To select the best induced structure, it is necessary to compromise between the compressor efficiency and static pressure of the induced structure inlet. In fact, the compressor efficiency changes by less than 1% by varying the design parameters of the induced structure, compared with case ID1. This demonstrates that the design parameters have little effect on the compressor efficiency. Compared with the compressor efficiency, the static pressure of the induced structure inlet is more sensitive to the design parameters, particularly the induced effective inlet area and the position of the induced structure inlet.

When turbine blades of a radial turbocharger are subjected to an unsteady aerodynamic load excitation force, high cycle fatigue of the turbine blades will occur when the excitation force reaches a certain level. The fatigue of the radial turbine wheel is affected by both static and dynamic stresses, and high cycle fatigue occurs when the dynamic stress reaches a certain amplitude. In this study, a two-way fluid–structure interaction (FSI) analysis method was used to predict the dynamic excitation force and dynamic response of the turbine wheel, which can precisely predict the forced vibration of the turbine wheel under the condition of rotor–stator interaction. A resonance intersection point was excited by the stator (turbine housing vortex tongue) of the radial turbocharger as the operating boundary condition, and the aerodynamic excitation caused by the rotor–stator interaction and the vibration amplitude of the turbine blade was predicted and analysed. A turbine blade dynamic measurement system (tip timing) was used to measure the dynamic deformation of turbine blades for turbochargers in real time. The simulation and measurement results showed that the errors of the predicted vibration displacements and measured mistuning blades were within the acceptable range, and the two-way FSI analysis method can precisely predict the forced vibration of the model.