Steady-state, transient and WLTC drive-cycle experimental performance comparison between single-scroll and twin-scroll turbocharger turbine

Abstract

The use of twin-scroll turbocharger turbine in automotive powertrain has been known for providing better transient performance over conventional single-scroll turbine. This has been accredited to the preservation of exhaust flow energy in the twin-scroll volute. In the current study, the performance comparison between a single and twin-scroll turbine has been made experimentally on a 1.5L passenger car gasoline engine. The uniqueness of the current study is that nearly identical engine hardware has been used for both the single and twin-scroll turbine volutes. This includes the intake and exhaust manifold geometry, turbocharger compressor, turbine rotor and volute scroll A/R variation trend over circumferential location. On top of that, the steady-state engine performance with both the volutes, has also been tuned to have matching brake torque. Such highly comparable setup enabled a more precise evaluation on the effect of pulse-isolation in the twin-scroll turbine volute during transient process. The steady-state performance comparison shows the amplitude of exhaust pulse in the twin-scroll volute is substantially higher than in the single-scroll volute, hence confirming the preservation of pulse exhaust energy. As a result, twin-scroll volute is found to be able to accelerate the engine boost pressure at a faster rate, therefore results in better transient response. The ultimate advantage of the twin-scroll turbine is further exemplified via engine Worldwide harmonized Light vehicles Test Cycle (WLTC) testing, where approximately 2.7% of averaged reduction in fuel consumption has been recorded. Majority of this improvement has been contributed by low to medium speed driving condition.