ABSTRACT
Twin scroll turbochargers are widely used in the Heavy Duty (HD) truck engines for long haulage applications. Such HD engines for pulse-turbocharging, non-EGR applications operate at higher pressure ratios compared to the automotive engines used for passenger cars and require wider operating ranges with correspondingly higher efficiencies. In order to minimize fuel consumption, the turbocharging system needs to be optimised as it is a vital component of the entire gas exchange system. This paper deals with testing of a twin scroll turbocharger turbine in a new gas stand (hot turbo test rig) facility at Scania CV AB, Sweden. Uniqueness of this gas stand is the ability to characterise a typical twin scroll turbine for a wide range of turbine loading coefficients (U/cs =0.52 to 0.83) on a dual combustor setup. In addition, it is also possible to run single, full and intermediate admission conditions (SPR=0.75 to 1.33) seamlessly on the twin scroll turbine without changing the turbocharger geometry. This is due to the capacity of the gas stand to control the compressor inlet pressure between 400 mbar to 3000 mbar, switching between open and closed loop configurations. Further, the twin scroll turbine stage is tested on a HD truck engine run at 1100 rpm full load from pressure ratios 1.3 to 3.75, to correlate the gas stand conditions and on-engine conditions. It was identified that the efficiency distribution between single admission and full admission was not linear and hence a linear interpolation must be avoided in 1D engine simulations. Further, intermediate admission maps are necessary to characterise the turbine stage and represent the on-engine conditions better. The goal of this work is to minimize the problem of interpolation & extrapolation in 1D engine simulations by characterizing a typical twin scroll turbine using gas stand measurements, by generating wider turbine maps at different admission conditions without changing the turbocharger geometry.
