Different Measurement Techniques for Wider Small Radial Turbine Performance Maps

Abstract

Engine downsizing usually requires the use of a turbocharger. This component’s related data are reduced. This is caused by the small range of stable functioning of its centrifugal compressor at high boost pressures. That is why the measurement of the data of both the compressor and the turbine is limited. Numerical simulations are used by automotive manufacturers for internal combustion engines simulations, so it is necessary to have an accurate and reliable extrapolation model of the turbine performance maps. Once an extrapolation model is established, the new performance map can be used for internal combustion engines calibration. This study presents different experimental techniques to measure the widest performance map of a small radial turbine. This turbine is a part of a turbocharger of a small diesel engine. Experiments were held on a traditional turbocharger test rig at first. The turbine inlet temperature was changed to extend the mass flow rate measurement range. Then there was the compressor force-feeding where air was blown through the compressor inlet and exit. This technique allowed the extension of the map by increasing and decreasing the power consumed by the compressor rotor and moving its surge and choking limits. After that, the compressor was replaced by another one with a reversed rotational direction. Blowing air to the new compressor exit enabled us to use it as a turbine and hereby extend the data map. We measured very low mass flow rates using a hot wire anemometer. This sensor also allowed us to measure negative mass flow rates to reach the expansion ratio of one zone. These techniques gave an almost complete mass flow rate performance map with an expansion ratio going from 1 to 6 for some rotational speeds. As for the efficiency, data were measured in adiabatic conditions. This allowed the calculation of the turbine total-to-static isentropic efficiency and the turbocharger mechanical efficiency separately. These data enabled us to calculate the turbine efficiency according to the manufacturer’s method.