AbstractTurbocharged engines date back to the 1920s starting with aircraft and large ship engines. In recent decades, stringent restrictions on vehicle emissions and increasing demand for better fuel-efficient engines have accelerated developments in turbocharger technology in automotive industry. The turbocharger enabled solutions have significantly downsized the engines and improved efficiency without compromising power and torque performance, which has been primarily achieved by increasing the air density in the engine.
In order to improve the performance of a turbocharged engine, the turbocharger is required to operate at high efficiency during the breathing/operation line of the engine. In addition, it is crucial to match correct turbocharger with a specific engine to maximise performance. Failure to do so can lead to decreased engine efficiency and even engine failure. In order to maintain the low-end torque level, the turbocharger is required to work on low mass flow and high compression ratio, which leads to a stable operating limit. The flow in the centrifugal compressor is non-uniform and three dimensional in nature. An expert level of understanding is required to match the transient characteristics of an engine with a compressor. Furthermore, the structural integrity of the compressor stage components is a pivotal factor in compressor performance. Impeller is one of the most vulnerable components in the compressor stage due to several critical factors, such as high rotating operating speed, operating (sonic/supersonic flow) conditions and working environment. Impeller failure is one of the most common in compressor stage components, which is mainly caused due to High Cycle Fatigue (HCF), Low Cycle Fatigue (LCF) and Foreign Object Damage (FOD). Therefore, identification of emerging small failures on the impeller forms a vital part of the overall system fault detection and diagnosis. Appropriate actions can be taken by analysing the effects of the emerging small failures on local and global parameters to avoid performance loss and reduce further damage to the system.
Since the compressor stage of the turbocharger operates in transient conditions, the investigation presented in this thesis has focused on analysing the transient flow behaviours of the compressor stage of the turbocharger. The investigation has proceeded by mapping global and local transient flow characteristics of two compressors: one healthy and the other faulty. This has enabled the identification of flow instability in the compressor stage and a stall cell frequency in a healthy compressor. Moreover, it has identified the local flow variation due to the induced fault at the impeller. Further to the investigation, the generated flow field data has been used to compute dominant flow modes. The modes have been further leveraged to identify potential sensor locations to monitor the flow field. The locations identified have been further utilised in the investigation to monitor the effects of small impeller geometry deformation due to FOD on the local flow field, and consequently, on the global performance of the turbocharger. This work has proposed a principle-based methodology to use Computational Fluid Dynamics (CFD) to identify the local flow anomalies due to small failure in the compressor stage, which can be used to make necessary in-design modifications and adjustments to operating conditions in order to prevent further damage to the systems.
|Date of Award||13 Jul 2022|
|Sponsors||Cummins Turbo Technologies|
|Supervisor||Rakesh Mishra (Main Supervisor) & Muhammad Usman Ghori (Co-Supervisor)|