1. INTRODUCTION
The diesel engine uprating is achieved by raising the net mean effective pressure, which involves charging high-pressure air into the engine cylinder. This in turn makes it necessary to raise the turbocharger compressor pressure ratio. And a prerequisite for the turbocharger to operate at the higher levels of speed and pressure ratio than hitherto is to ensure its matching durability by resolving, in particular, the following two problems.
1] High-temperature creep rupture of aluminum alloy used as compressor impeller material resulting in short impeller service life.
2] Thrust bearing operating at a high operational speed and under a high bearing pressure suffering rapid wear from the effects of foreign particles contained in tube oil, hence premature failure.
Fig.1 below shows a cause-and-effect dia-gram illustrating how the increase in compressor pressure ratio results in shortening the service lives of the impeller and thrust bearing.
