Experimental test results for vibration of a high speed diesel engine turbocharger

Diesel engine turbochargers are known to have operation into the self-excited unstable region. The operation in the nonlinear limit cycle has been tolerated on most applications to date. The need for a quieter and a smoother operation and in addition reduced emission levels have prompted new evaluations of the rotor bearing design for these systems. In this research, a commercial rotor-bearing dynamics computer program was used to evaluate the stability and transient response of a high-speed diesel engine turbocharger. Various models with varying bearing designs and properties were solved to obtain the linear stability threshold speeds and also the nonlinear transient response. The predicted whirl speed map shows two modes of instability and is very similar to recent on-engine test results conducted at Virginia Tech as part of a recent senior capstone design project. The development of the diesel engine test stand and the associated data acquisition system will be discussed. The results from the unloaded and the loaded engine testing will be compared to the analytical results. Future research will be devoted to the elimination of the large subsynchronous excitation.