Turbocharging plays a key role not only in improving automotive engine performance, but also in reducing fuel consumption and exhaust emissions for Spark Ignition and diesel engines. In depth experimental investigations on turbochargers are therefore necessary to better understand their performance. The availability of experimental information on realistic turbine steady flow performance is an essential requirement for optimizing engine-turbocharger matching calculations developed in simulation models. This is most evident with regards to the turbine efficiency, as its swallowing capacity can be accurately assessed by measuring the mass flow, inlet temperature and pressure ratio across the machine. In fact, in the case of a turbocharger radial flow turbine, the isentropic efficiency evaluated directly starting from the measurement of the thermodynamic parameters at the inlet and outlet sections can give significant errors. This inaccuracy is mainly related to the difficulty of a correct evaluation of the turbine outlet temperature due to the flow field and the temperature distribution at the machine outlet. The purpose of this work is to obtain a reliable measurement of the turbine outlet temperature thanks to a specific device installed before the standard measurement section to dissipate the flow structures dominated by vorticity, thus obtaining a uniform distribution of the flow fields and of temperature to the measurement section. This measurement allows to optimize turbocharger experimental performance implemented in simulation models, obtaining a better control of the after-treatment device generally adopted downstream of the turbine. To this aim, a non-intrusive 3-hole probe was adopted to perform measurement of the flow field, pressure, and temperature downstream the turbine. The main results obtained through the non-standard measurements are compared with those achieved through a direct measurement of turbine outlet temperature by three probes inserted in pipe with a different protrusion. The experimental campaign concerns investigations also developed in almost adiabatic conditions and to be adopted to carry out a realistic measurement of the turbine outlet temperature in a simpler and less time-consuming way.

Turbocharging plays a fundamental role not only in improving the performance of automotive engines, but also in reducing the fuel consumption and exhaust emissions of spark-ignited biofuel, diesel, liquid, and gaseous engines. Dedicated experimental investigations on turbochargers are therefore needed to evaluate a better understanding of its performance. The availability of experimental information on the steady flow performance of the turbocharger is an essential requirement to optimize the matching calculation. It is interesting to know the isentropic efficiency of the turbine in order to improve the coupling with the engine, in particular it is difficult to identify the definition of the turbine efficiency through a direct evaluation. In a radial turbine, the isentropic efficiency, evaluated directly starting from the measurement of the thermodynamic quantities at the inlet and outlet sections, can be affected by significant errors. This inaccuracy is mainly related to the incorrect evaluation of the turbine outlet temperature, due to the non-uniform distribution of the flow field in the measurement section. For this purpose, a flow conditioner was installed downstream the turbine. Tests were performed at different values of the rotational speed, and in quasi-adiabatic conditions. The flow field downstream the de-coupler was analysed through a hand-made three-hole probe with an exposed junction thermocouple inserted in the pipe with different protrusions. Thanks to this experimental campaign, it was possible to measure pressure, velocity, mass flow and temperature profiles necessary to examine the homogeneity of the flow field. As the turbocharger is fitted with a twin entry turbine, the thermodynamic quantities have been properly taken into account referring to each sector.

<div class="section abstract"><div class="htmlview paragraph">Turbochargers are still one of the most common solutions to improve internal combustion engines performance. The correct evaluation of turbochargers characteristic maps is one of the main issues to achieve a good matching with internal combustion engines. In a 1D procedure the accuracy of performance maps constitutes the basis of the turbocharger matching with the engine. The classical quasi-steady approach assumes that compressor and turbine characteristic maps are evaluated under the hypothesis of adiabatic turbocharger behavior. The aim of the paper is the investigation of the effect of heat transfer phenomena on the measured turbocharger maps. A model to correct compressor efficiency evaluated starting from measured data, thus removing the heat transfer effects, is proposed. The compressor steady flow behavior has been analyzed through specific tests performed at the test rig for components of propulsion systems of the University of Genoa, under various heat transfer conditions. The experimental campaign was conducted on a water-cooled turbocharger for spark ignition engines and on an uncooled turbocharger for diesel engines considering the effect of different heat transfer conditions. Then, measurements were carried out under quasi-adiabatic conditions, maintaining a constant temperature between the compressor - intermediate casing - turbine to validate the proposed model. Thanks to this specific campaign it was possible to validate the proposed model highlighting a high degree of accuracy. The main advantage of the method presented here compared to others developed by the authors or found in the open literature is its ease of use, thus requiring a small amount of geometric and physical information that can be obtained in a standard turbocharger test bench.</div></div>