Ball bearing turbocharger technology has started to be adopted for mass-production engines due to the potential benefit in transient performance and fuel consumption. Compared to the conventional journal bearing, the low friction of the ball bearing allows the turbocharger to accelerate faster so that the engine can be supplied with boost pressure more quickly following a transient torque request and under steady state offers reduced engine back pressure, which can reduce engine fuel consumption. In this study, the benefits of using a ball bearing turbocharger compared to a conventional journal bearing turbocharger were identified first in simulation and then validated in a back to back comparison of two otherwise identical turbochargers through extensive experimental analysis. The cold start engine performance was significantly improved as the ball bearing turbocharger was able to boost the engine to the full load level within a few engine cycles. The hot engine transient response was also improved, but the full potential of the ball bearing turbocharger in terms of the transient performance can be further exploited by recalibrating the engine. The fuel consumption of the engine was greatly reduced by the ball bearing turbocharger. However, closer scrutiny reveals that the insufficient EGR rate of the ball bearing turbocharger equipped engine was the main cause of the reduced BSFC, and that further engine calibration is a must before any fair evaluation of the BSFC benefit can be done.
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