A variable geometry turbocharger with a pressure ratio of 3 has been designed for a DI diesel engine with a high power-weight ratio. New technical items are involved as follows. [1]Compressor with Variable Inlet Guide Vanes (VIGV) and a convex blade impeller. [2]Mixed flow turbine with a half vane type variable nozzle (HVN) that has variable vanes located between the fixed vanes. [3]Lightweight and high strength materials applied for rotating parts.

Through the numerical aerodynamic analysis and stress and vibration analysis of the compressor with VIGV and the turbine with HVN, the following advantages of the turbocharger were verified.
(1) The surge limit, rotating stall and adiabatic efficiency of compressors are improved by the prewhirl produced by VIGV. (2) Turbine efficiency and reliability of the variable nozzle is improved by HVN because the HVN has a small clearance between the variable vane and the housing wall and the fixed vanes of the HVN restrict the thermal distortion of the turbine housing. (3) The inertia moment (Ip) of the rotor is reduced by 44% and the critical speed of rotating vibration increases by 68% with the use of the TiAl turbine wheel, magnesium impeller and high modulus steel for the shaft.
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