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Experimental investigation and numerical simulation of gas flow through wastegated turbine of gasoline turbocharger
Author(s): Seyed Shahabeddin Alaviyoun, M. Ziabasharhagh, Mojtaba Farajpoor
Keywords: Gasoline engine; Pressure distribution; Turbine housing; Turbocharger; Wastegate
Turbochargers are generally used in the combustion engine due to their ability to increase the specific power. This paper investigates the performance of the turbocharger turbine which is mounted in a gasoline engine. Different working points, including close and open wastegate positions, are studied in a steady-state condition. The experimental test of this article has been performed on an engine test cell. The movement of the wastegate linkage in different working conditions of the engine was measured in the test cell. Furthermore, the static pressure was measured at the different positions of the turbine housing. Comparison of the simulation and the experimental results show good agreement. Simulation results show that at maximum engine speed, the wastegate bypass flow reaches 32 percent of the total turbine flow. Results show that as the wastegate starts to open, maximum loading happens. However, increasing the waste-gate opening angle will decrease the force which is caused by the passing gas. It was found that at 2 degrees opening angle of the wastegate, there is 80 kPa pressure difference between two sides of the wastegate valve. When the wastegate has a small opening angle, the pressure distribution on the flat surface of the valve is not symmetric which means the gas does not provide a 360° flow distribution around the valve. Moreover, streamlines show that the high-speed flow passing bypass passage disturbs the flow exiting the turbine blades. Results show that the opening of the wastegate flap can reduce the turbine’s power. When the turbocharger speed assumed constant, the 6 degrees opening of the wastegate causes a 31 percent power reduction at pressure ratio 2 and 34.5 percent reduction at pressure ratio 3. Moreover, the simulation results of the turbine’s characteristic map show that at constant mass flow rate 0.01 kg/s, the opening of the wastegate from the closed position to 6 degrees causes the pressure ratio to decrease 26 percent.