Optimisation of a Turbocharger Compressor for Heavy-Duty Engines based on Aerodynamic Loss Analysis

Abstract

Within the last decades, the turbocharger has become a key part of the internal combustion engine and thus is no longer seen as optional. The turbocharger is especially crucial for heavy-duty engines for on-road truck applications as it addresses two main development goals simultaneously, which are typically oppose each other: lowest fuel consumption and meeting all emission regulations. To enable down-sizing, which is a common strategy to fulfil these two aims, the turbocharger must be well matched to the internal combustion engine and furthermore, must operate as efficiently as possible. The latter implies further optimisation of the turbocharger's components, e.g. the compressor, which supplies the engine with compressed air. As the compressor already achieves high efficiencies, further optimisation requires substantial efforts, a full understanding of the component and new development methods. To address the described challenges, a systematic methodology is developed and applied in this thesis to improve the efficiency of the baseline turbocharger compressor while achieving the same operating range. To also guarantee the mandatory, good matching between the engine and the turbocharger, the main operating points of the turbocharger compressor stage are defined for the real-world operation in a first step. A CFD setup is developed and validated extensively for the baseline geometry especially to analyse the flow field at these main operating points in detail. Two novel approaches are introduced and applied to the CFD results to determine the location and to further quantify the intensity of the most significant types of losses. Taking the resulting loss distribution into account, design parameters are defined which promise a high impact on specific kinds of losses and thus also on the stage's performance. In a next step, the selected design parameters are varied simultaneously applying a systematic Design of Experiments (DoE) plan. The resulting geometry variants are generated automatically using parameterised CAD models and they are evaluated via CFD simulation with an automated work flow. The optimisation is conducted based on mathematical surrogate models and results in design proposals promising improved compressor stage designs. Five of these design proposals are selected and their performance is validated against hot-gas test-rig measurements. Under real-world operation, the best performing compressor design is considered to achieve in average an approximately 1% higher efficiency. Additionally, the operating range is increased in average by around 10%. Furthermore, the best performing compressor design is compared to the baseline geometry in detail, also analysing the changes in the aerodynamic loss distribution leading to this improvement.