Effect of inlet configuration and pulsation on turbocharger performance for enhanced energy recovery

Abstract

The future trends of internal combustion engines, especially automotive engines, are toward engine down-sizing along with air charging systems, such as turbomachinery technology, which have notable advantages. These advantages are: higher power density, improvement of fuel economy consumption and above all, it reduces carbon emissions. This thesis presents a novel variable geometry concept and assesses the experimental performance of a turbocharger turbine under different inlet conditions. The inlet conditions are defined by the pulsating characteristics and the inlet configuration of a variable geometry turbocharger. The inlet flow in a turbocharger turbine is highly pulsating as it responds to the exhaust valve operation of an internal combustion engine. The exhaust manifold is an important element of the boosting system as it influences the flow mixing and the energy level before the turbine inlet. The first part of this research presents an experimental investigation of turbocharger turbine with different manifold configurations. The experimental tests were conducted on two different volutes designs, twin entry and single entry, using three different manifolds: single entry, double entry and single divided entry. The results showed that for steady conditions the single entry volute with the single entry divided manifold performed better than the other possible combinations (single entry volute and single entry manifold and twin entry volute with double entry). Under both conditions, the single entry divided configuration performed better than the other two. The improvement was of up to 5 percentage points on steady conditions and 14 percentage points on unsteady conditions. The single entry divided configuration moves the mixing plane between the entries closer to the turbine, it has an effect on the fluid dynamics inside the volute and rotor; this work shows that this arrangement leads to better performance. Under unsteady conditions the single entry volute with single entry divided manifold showed an improvement in performance for all requencies. The second aspect of this research is focused on the design and assessment of a novel Variable Geometry Turbine (VGT). This new geometry has two degrees of freedom: the flow angle and the flow area. The aim of this research is to study the impact on efficiency and mass swallowing capacity for different combinations of those parameters at different operation points to enhance exhaust energy extraction. The steady results show that the turbine stage performance is heavily affected by the lack of guidance (misalignment) between the vane angle and the exit flow angle from the volute. The introduction of the two degrees of freedom on the VGT showed improvement for some cases relative to only changing one degree of freedom alone (as it is commonly done in current turbochargers). The unsteady results showed that settings with a higher area restriction applied by the sliding nozzle ring offered a better performance compared to their quasi-steady performance indicating that at low swallowing capacities these settings are more adequate to be used. The improvement, compared to a baseline set by the VGT operating as a pure sliding nozzle ring VGT and pure pivoting vane VGT has been measured on up to 2 percentage points in the higher mass flow region and 5 percentage points in the lower mass flow region. This is achieved with settings with a 60 to 70 vane angle and 38 to 93% opening sliding nozzle ring.