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.
