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The exhaust emission gas regulations on truck diesel engines are becoming increasingly stringent in various countries in the coming years. The '94 EPA (U.S.A.) regulations include the entire working range of engines, including transient conditions; thus requiring a large-scale improvement in engine properties. For this reason, various engine components are now undergoing a series of improvements; in particular, the injection system has experienced a major renovation. However, the improvement of a naturally-aspirated engine has its own limit; and the turbocharged engine with inter-cooler becomes essential. Mitsubishi Heavy Industries has been pushing ahead with the development of turbochargers for use with the truck diesel engines. To assist the Diesel engine manufacture to meet these new emission regulations, we have developed various turbocharger options for improving engine performance, in addition to our continuing efforts for improving the aerodynamic properties.

Mitsubishi Heavy Industries, Ltd. (MHI) continued research to improve turbocharger compressor and turbine wheel aerodynamics has resulted in a new “G”-Series compressor wheel and “L”-Series turbine wheel. These new generation wheels offer lower inertia and improved performance in a smaller package size when compared to previous designs of similar flow capabilities. This paper discusses the design features of these state-of-the-art turbocharger wheel designs and presents performance improvements as demonstrated on the gas stand and engine dynamometer.

Mitsubishi Heavy Industries Ltd. is developing a ceramic turbine wheel to improve the response of the turbocharged engine. In this development, the Silicon Nitride Ceramic is considered most suitable for application to the turbocharger because of strength, reliability and adhesion to metal. This report introduces the development of the Silicon Nitride turbine wheel for a Mitsubishi turbocharger by showing the design strength and test results. Although further efforts for cost reduction are needed, the results of development demonstrated a satisfactory technical level and practical application in the near future is expected.