In times of stringent emission standards for automotive and truck applications, exhaust gas recirculation (EGR) is used in IC engines to reduce NOx emissions by recirculating a portion of an engine’s exhaust gas. The amount of exhaust gas determined for EGR is withdrawn from the exhaust gas route and routed back into the combustion chamber. The recirculated exhaust gas acts as an inert gas and, when mixed with the pre-combustion mixture, helps to decrease the combustion temperature and thus NOx emissions. Designed for a diesel engine within a truck application, the turbine in this particular research project is fed by two cylinder groups, however, only the exhaust gas of one group is recirculated. The reduced mass flow in the small turbine scroll (EGR-scroll) through EGR withdrawal, along with the increased pressure required for EGR transport, leads to a massive reduction in the mass flow parameter of the EGR-scroll. The common turbocharger design process has been based on steady admission rather than unsteady admission given through the pulsating nature of multi-cylinder admission. This has lead to diverging results of turbochargers performing well on steady hot gas test rigs compared to performing badly in the final tests on the engine itself. In this paper however, unequal admission resulting from pulsating admission is taken into account. Based on unsteady admission, a methodology is proposed for steady computations with unequal admissions, and a thorough 3D CFD loss analysis is to be presented to understand the turbine behaviour, reveal the regions for improvements, and provide a framework for further development.

This article describes the first development phase of a centrifugal compressor with variable geometry which is designed to match the needs of future heavy-duty engines. Requirements of truck engines are analyzed, and their impact on the properties of the compressor map is evaluated in order to identify the most suitable kind of variable geometry. Our approach utilizes the transformation of engine data into pressure ratio and mass flow coordinates that can be displayed and interpreted using compressor maps. One-dimensional and three-dimensional computational fluid dynamics fluid flow calculations are used to identify loss mechanisms and constraints of fixed geometry compressors. Linking engine goals and aerodynamic objectives yields specific recommendations on the implementation of the variable geometry compressor.

A variable geometry concept for advanced turbocharger (TC) systems is presented. The variability of the device is based on outlet area changes as opposed to the more common systems that are based on inlet turbine geometry changes. In addition to the conventional variable turbine geometry (VTG), the new variable turbine type is termed variable outlet turbine (VOT). The flow variability is achieved by variation of the flow cross section at the turbine outlet using an axial displacement of a sliding sleeve over the exducer and provides a simple solution for flow variability. In order to predict the aerodynamic performance and to analyze the loss mechanisms of this new turbine, the flow field of the VOT is calculated by means of steady state 3D-CFD (computational fluid dynamics) simulations. The VOT design is optimized by finding a good balance between clearance and outlet losses. Furthermore, experimental results of the VOT are presented and compared to a turbine equipped with a waste gate (WG) that demonstrates an efficiency advantage of 5%. Additionally, engine performance measurements were carried out to investigate the influence of the VOT on fuel consumption and to asses the functionality of the new pneumatic actuating system. The VOT engine tests show also performance advantage in comparison to a WG turbine especially toward high engine loads. It is found that the use of the VOT at this condition shows a turbine efficiency advantage of 6% related to a reduction in engine fuel consumption of 1.4%. The behavior at part load is neutral and the peak turbine efficiency of the VOT is comparable with a fix turbine geometry.

This paper presents a detailed loss analysis of a centrifugal compressor stage with a vaned diffuser for application in a heavy-duty engine turbocharger. The analysis is carried out in order to investigate the loss distribution in the stage. To quantify the impact of different loss types and locations, a detailed validated steady-state three-dimensional (3D) computational fluid dynamics (CFD) solution is employed. The local entropy production rate is calculated for two operating points (full load and part load), which are most relevant to the real-world operation of the compressor in a truck application. Two methods are suggested as the procedure for the division of the whole fluid volume into subvolumes because this is key for the resulting loss distribution. The primary loss-generating mechanisms are shown at main operating conditions to reveal the regions of improvement. A detailed grid study was conducted to enable the calculation of the entropy ratio. It was possible to capture around 78% (partial load) and 70% (full load) of the entropy production with a mesh with circa 100 × 106 elements. Around half of the losses were due to the boundary layer friction, followed by losses associated with a boundary layer separation resulting from the back-flow at the shroud contour close to the impeller exit and back disk friction accounted for with 6–7% of the stage's losses.

Turbocharger turbine blades are subjected to resonant excitation that can lead to High Cycle Fatigue (HCF). In vaneless turbines the excitation primarily stems from asymmetries in the turbine housing such as the volute and the tongue. Given the nature of such asymmetries, the excitation is of a Low Engine Order (LEO) type. The present study deals with the effect of radial turbine housing design on LEO resonant excitation of turbine blades. The study focuses on two geometrical key design parameters of a twin-scroll turbine housing for a radial turbine which is the rotor-tongue distance and the circumferential angle between both tongues. The generalized force approach is used to identify the critical blade surface regions in order to understand the excitation mechanism of each specific design and to assess the differences of design variants with respect to the baseline design. The presented approach is highly practicable, because it is less expensive than full FSI-simulations. This approach is validated on tip timing test data from full-scale experiments. Correlation to test data shows that the presented approach is capable of capturing the relative trends reliably and hence can efficiently be employed in an industrial design process such as to minimize blade vibration amplitudes. It is shown that a reduction of blade vibration amplitudes by a factor of 10 could be achieved.