Effect of balance valve on exhaust pulse energy of a heavy-duty diesel engine equipped an asymmetric twin-scroll turbine

Abstract

The exhaust pulse energy of engine is capable of driving the asymmetric twin-scroll turbine to run complicatedly in a wider flow range, which significantly causes more difficulty of an asymmetric twin-scroll turbine to match a diesel engine. In the present study, It was initially analyzed that an engine exhaust pulse energy of an asymmetric twin-scroll turbine with a balance valve. First, a pulsating flow model of asymmetric twin-scroll turbine was built to decouple the operation states of the small and large scroll turbines. Second, the experiments of asymmetric twin-scroll turbine were performed on a turbine test rig and an engine performance stand to determine the operation rules of turbine flow parameter, turbine efficiency, blade speed ratio, as well as turbine available energy. Asthe balance valve opens, the flow parameter of twin-scroll would perform more broadly around the swallow capacity curves of equal admission. Moreover, the fully-opened balance valve would make the exhaust pulse strength at the small and large scroll inlets sharply degrade by about 25% and 21%, the cycle turbine efficiency enhance by nearly 3%, the turbine available energy and BSFC degrade by about 8.15% and 2.9% at 800 rpm full load engine condition; At 1100 rpm full load engine condition, the exhaust pulse strength at the small and large scroll inlets only degraded by about 7.2% and 5.8%, the cycle turbine efficiency enhanced by about 4%, the turbine available energy and BSFC improved by about 3.7% and 2.1%. Lastly, this study delved into the distributions of the balance valve opening rate and the pulse strength at the small and large scroll inlets at full engine map.