Design criterion for asymmetric twin-entry radial turbine for efficiency under steady and pulsating inlet conditions

Abstract

The internal combustion engine plays an important role in energy conservation and environmental protection. An efficient way to simultaneously reduce the engine fuel consumption and the emissions (NOx) is an asymmetric twin-entry turbine turbocharging system. The asymmetric twin-entry turbine uses a volute that has two scrolls in the axial direction with different throat areas. The smaller area scroll can increase the backpressure to support the exhaust gas recirculation system for lower NOx emissions; meanwhile, the larger area scroll can decrease the backpressure to reduce the exhaust resistance for lower fuel consumption. The area ratio is dependent on the required exhaust gas recirculation rate and fuel consumption. However, there are no guidelines for how to arrange the scrolls, and whether placing the big scroll on the hub side or the shroud side can provide improved results remains unknown. In this paper, two different design types are discussed for the asymmetric turbine, one with the big scroll on the hub side, while the other is on the shroud side. Also, the unsteady computational fluid dynamics (CFD) simulation is under steady and pulsating inlet conditions. The results show that when under steady inlet conditions, the efficiency of the asymmetric turbine with the big scroll on the shroud side is nearly 1.6% higher. However, when facing pulsating inlet conditions, the efficiency of the asymmetric turbine with the big scroll on the hub side is almost 1.1% higher. The difference is due to the different mass flow storage capacities of the two scrolls under pulsating inlet conditions. The design criterion for asymmetric twin-entry turbine states that if the turbocharger is designed for a large volume exhaust manifold, it is better to place the big scroll on the shroud side. If for a small volume exhaust manifold, it is better to set the big scroll on the hub side.