An on-engine twin-scroll turbine performance estimation
In this study the main objective was to estimate the instantaneous turbine shaft power and turbine efficiency of a turbocharger mounted on a 6-cylinder 13 literheavy-duty diesel engine. The work was carried out at Scania CV AB in Södertälje, Sweden from January to June 2015 as master thesis under the division of Internal Combustion Engines at the Royal Institute of Technology KTH, Stockholm, Sweden. Normally the turbine performance is estimated during off-engine conditions in a gas flow bench during steady flow. When the turbocharger is mounted on the engine, the flow is far from being steady. The exhaust gas flow is pulsating and every thermodynamic property with it as well. In this thesis theturbine performance is estimated 1 crank angle degree resolved with 1 crank angle degree resolved pressures and turbocharger speed. Parameters difficult to measure crank angle resolved such as temperature and exhaust mass flow rate are estimated utilizing methods found in literature. The turbine efficiency is defined as the utilized turbine shaft power divided with the isentropic turbine power. The utilized shaft power consists of the power consumed by the compressor, which is assumed to be constant in this thesis, the power lost due to bearing friction and the acceleration power of the rotating parts. The result of the used method revealed a fluctuating turbine efficiency, very seldom at the same levels as the optimal efficiency obtained during steady flow during one engine cycle. The results where promising, but lacked the needed accuracy to estimate the instantaneous turbine performance with proven confidence. Primarily this is believed to be caused by the instantaneous exhaust mass flow rate approximation based on a calculated dynamical pressure. Another factor impacting the overall accuracy is the assumed constant compressor power. Further development of the method is needed and could yield results with better confidence in the future.
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