A Validation System for the Compressor Side of an Electric Assisted Turbocharger

Abstract

This study focuses on investigating an alternative validation method to validate the compressor side of turbochargers. Nowadays, the performance of turbochargers is tested using hot gas stands. These hot gas stands are expensive. The application of an externally coupled e-motor to the turbocharger eliminates the need for a hot gas burner - significantly reducing the cost. However, the validation range with electric motors is limited. Therefore, it is investigated if the circulation of the compressor outlet flow provides additional shaft power by the turbine. Thereby it would be possible to generate a bigger range of compressor performance maps in terms of power and rotational speed with a limited electric motor.
In the first part of the study the test setup is designed. The original e-turbo hardware was not available. Therefore a test setup is designed with a relatively high power output but low maximum speed electric motor. The principle of range extension will be proven in the lower speed range. The test setup will be used in two configurations. One where the compressor is only powered using the electric motor and the other where the electric motor and turbine will power the compressor. For both configuration the input of the electric motor is kept constant in order to validate if by adding the turbine a shift can be measured in the operating points.
In the second part, a performance expectation model is set up. The existing compressor map, turbine map and electric motor characteristics are used to determine which operating point can be validated. When the available electric motor and turbine power and torque are higher as the compressor values, an operating point is considered in reach. The model outcome is a compressor map that indicated which operation points can be reached with only the electric motor and with the combination of the electric motor and the turbine.
The result of the model shows that the outlet flow in both configurations always remains above 1 bar and 0 oC. This means that no freezing gas is expected to be generated. Furthermore, the model shows that for a selected operating point it is possible, depending on the flow control, to push the operating point to a higher rotational speed or mass flow value.
The aim of the research was to use an alternative method to validate the compressor of the turbocharger whereby validation range could be extended by means of energy recovery with the turbine. This study shows a test setup design and a performance prediction model that shows that it is possible to eliminate the use of a hot gas burner for compressor validation and use an electric motor together with the turbine to extend the validation range in a compressor map. However, within the time frame of this study, no physical test was performed due to the unavailability of different electric motors. Nevertheless, this study shows the potential for an alternative way of compressor wheel validation for turbochargers and contributes to the development of the electric assisted turbocharger.