An Investigation on Exhaust Pulse Characteristics of Asymmetric Twin-Scroll Turbocharged Heavy-Duty Diesel Engine

Abstract

The shape and energy distribution characteristics of exhaust pulse of an asymmetric twin-scroll turbocharged engine have a significant impact on the matching between asymmetric twin-scroll turbines and engines, as well as the matching between asymmetric twin scrolls and turbine wheels. In this article, the exhaust pulse characteristics of an asymmetric twin-scroll turbocharged engine was studied. Experiments were conducted on a turbine test rig and an engine performance stand to determine the operation rules of exhaust pulse strength, turbine flow parameters, turbine isentropic energy, and turbine efficiency. The results showed that the exhaust pulse strength at the inlets of both the small and large scrolls continuously decreased with the increase of engine speed. And the flow parameters at the inlets of the small and large scrolls exhibited a “ring” or “butterfly” shape with the change of expansion ratio depending on the pressure deviation of the extreme points at the troughs on both sides of the “secondary peak” of the exhaust pressure pulse, respectively. Besides, the distribution trend of turbine isentropic power was consistent with the trend of exhaust pressure pulse at the inlets of the small and large scrolls. Furthermore, when opening the balance valve, it caused the appearance of “concave” and “convex” features near the “main peak” and “secondary peak” of the turbine isentropic power pulses, respectively. Finally, as the engine speed increased, the fluctuation of turbine instantaneous efficiency gradually decreased. When calculating the instantaneous efficiency of the turbine, the influence of the rotor’s rotational inertia needs to be considered, otherwise, there may be a false phenomenon of exceeding 100% efficiency.