Abstract

In the engine exhaust manifold, pressure pulses from several cylinders can interfere with exhaust phases of two different cylinders taking place simultaneously. In four-cylinder engines, interference between exhaust pulses can be reduced by double scroll (DS) turbines. These can ensure pulse separation and improve performance at low engine speeds where the exhaust pulsing effect is more predominant. However, high speed power of the engine can be limited by the increased restriction caused by the DS turbine, in comparison to a single scroll solution. Therefore, IHI developed a regulated Scroll Connection Valve (SCV) to allow increased connection area between scrolls, reducing the restriction at high engine speeds.

Prediction of performance using 1D models can be challenging under open SCV conditions. The opening of the SCV simultaneously affects the connection between scrolls and the wastegate ratio, influencing turbine performance. This paper shows an approach to overcome the modeling challenges of DS turbines with SCV, using additional data retrieved from gasstand testing and 3D CFD simulations to update efficiency and discharge coefficient, respectively. The validation of the 1D model is performed on a four-cylinder gasoline engine from General Motors with an IHI turbocharger, equipped with a DS turbine and SCV. The model predicts performance at full load with a maximum error of 4% in BSFC at 2500rpm. No error was recorded by the model prediction during the time-to-torque at 1500rpm, showing correct prediction when SCV is kept fully closed. Finally, while keeping the valve fully open, base boost pressure was underpredicted by about 5%.

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