ABSTRACT

Throughout the last decade, turbocharging the internal combustion engine has become the state-of-the-art technology when it comes to increasing power density and fuel economy of a given engine.

The investigation of the rotor dynamics is an important part in the turbocharger development process. This is especially true when it comes to advanced concepts such as new bearing technologies or matchings between turbine and compressor side as required for example for an electrically assisted turbocharger (eTC). Hence, the quantification and investigation of mechanical effects on the turbocharger (TC) and its components become more and more important in order to ensure long durability and high performance.

For the corresponding investigations, it is important to ensure realistic boundary conditions such as testing in combination with the original engine application on an engine test bench. However, in an early engine development phase, the latter might not yet be available or the desired measurement equipment can´t be installed due to limitations in available space. Before shifting such mechanical investigations on a component hot gas test bench, the impact of the engine boundary conditions on the results must be analysed.

Against this backdrop, the paper firstly covers the analysis of the TC shaft motion measured on-engine in different operating points. Thereto, the turbocharger of an 1.0 l three-cylinder spark ignited engine fuelled with compressed natural gas (CNG), has been equipped with shaft motion (displacement) sensors in order to quantify the relative movement of the turbocharger rotor assembly. While running the engine in most relevant operating points, possible effects of the exhaust pressure pulses upstream of the turbine on the rotor dynamics are analysed.

In a second step, the same investigations regarding the TC shaft movements are carried out on a component hot gas test bench using the identical turbocharger hardware. For these tests, a newly developed pulsation unit, the FEV PulseGen, is being installed between the stationary combustion chamber (exhaust gas generator) and the turbocharger itself. Upstream of the turbine, this unit enables the generation of exhaust gas pulsations that are realistic for real engine operation. For the first time a comparison of both measurement approaches is shown. This comparison has been carried out for the same engine like operating points which makes it possible to analyse the impact of the exhaust gas pulsations on the turbocharger shaft motion characteristics.