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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) has been developing variable area radial turbine systems over the past several years for small turbochargers used in the passenger car and small truck markets. Several variable area concepts have been tested and evaluated by MHI on the engine dynamometer and in the vehicle. As a result of this research effort, a new variable area turbine coined “VARIABLE INLET” (VI) was developed. The VI turbocharger is characterized by its response improvement, good turbine efficiency, high reliability, and cost effectiveness.