Gernot Hertweck

Innovative Variable Turbine Concept for Turbochargers

New concepts for the optimisation of supercharging systems have been analysed to improve fuel consumption, emissions and transient diesel engine response. In addition to the conventional VTG (Variable Turbine Geometry) where the variability takes place upstream of the turbine impeller, a new innovative variable turbine geometry called VOT (Variable Outlet Turbine) is investigated in this paper where the variability takes place at impeller exit. The flow variability is achieved by variation of the flow cross-section at the turbine outlet using an axial displacement of a sliding sleeve over the exducer and provides a simple solution for flow variability. The flow field of the VOT is calculated by means of steady state 3D-CFD simulations to predict the aerodynamic performance as well as to analyse the loss mechanisms. The VOT design is optimised by finding a good balance between clearance and outlet losses to improve the turbine efficiency. Furthermore, experimental results of the VOT are presented and compared to a turbine equipped with a waste gate (WG) that verify the efficiency advantage of the VOT. In general, it is found that the use of the VOT at high specific speed is important to reduce the outlet losses and to improve the turbine efficiency over a wide operating range.Copyright

Micro Jet Engine Oil Consumption Measurement Technique

Oil consumption of micro gas turbine engines plays a significant role with regards to their practical application in aerospace. In this context an oil consumption measurement device has been developed on behalf of Daimler AG for the application to vehicle turbo chargers. This device has been used to measure the oil consumption of an own design micro jet engine of 400 N thrust. The design of the device is based on the principle of gravimetric weighting. In the past, volumetric principles have been applied to engine oil consumption measurements. Technical advances in the field of piezoelectricity have improved the accuracy of gravimetric weighting in such a way that today its accuracy is comparable to volumetric gauging. Moreover, unlike volumetric gauging gravimetric weighting is not influenced by the density or the amount of emulsified gas in the oil. Hence, application of gravimetric weighting represents a more robust and more efficient way to evaluate oil consumption in micro gas turbine engines. Unlike non-conventional measurement strategies like emission measurement and tracer techniques, gravimetric weighting allows very simple and convenient oil consumption measurements [3]. The device was validated using defined laboratory measurements. Experimental results are shown.Copyright