Investigation of the limit-stable operating conditions of centrifugal turbocharger compressors
File(s)
Author(s)
Schwarz, David
Type
Thesis
Abstract
Turbochargers are a key component to achieve today‘s challenging requirements for commercial vehicle engines. They recover energy from the exhaust gases and supply denser air to the engine, improving efficiency and thus reducing fuel consumption. CO2 and emission regulations and the challenging customer demands require highest turbo efficiency and broad operating range.
Three of the most crucial design targets for turbochargers are: efficiency and pressure ratio for optimal performance and fuel economy, maximum choke mass flow for brake performance, and sufficient surge margin to allow safe engine operation.
While compressor performance at design conditions and close to choke can be predicted with reasonable accuracy, predicting surge remains challenging. This introduces significant risk in compressor development, often leading to application of conservative design rules, limiting the theoretically achievable performance. Therefore, a comprehensive understanding of surge is crucial.
In this work, surge is first investigated on component level using a validated URANS simulation. Findings indicate that a combination of diffuser stall and disturbed inlet flow conditions due to the ported shroud is the surge trigger.
Subsequently, the system level is examined by considering pulsating environments and engine operation, with experiments conducted on a hot gas test rig and an engine test rig. Results show that surge margin shifts are heavily dependent on operating conditions and specific compressor design features. These findings reconcile seemingly contradictory results in literature and bridge the gap between industry experience and academic research.
Finally, the findings are integrated into a fully automated compressor optimization scheme that considers all thermodynamic aspects of compressor performance. The optimization process yields superior results compared to the previous design, significantly enhancing efficiency while improving map width.
This work adresses a critical gap in compressor development, contributing to more efficient and cleaner engines and provides an experimental foundation for future research in transient environments.
Three of the most crucial design targets for turbochargers are: efficiency and pressure ratio for optimal performance and fuel economy, maximum choke mass flow for brake performance, and sufficient surge margin to allow safe engine operation.
While compressor performance at design conditions and close to choke can be predicted with reasonable accuracy, predicting surge remains challenging. This introduces significant risk in compressor development, often leading to application of conservative design rules, limiting the theoretically achievable performance. Therefore, a comprehensive understanding of surge is crucial.
In this work, surge is first investigated on component level using a validated URANS simulation. Findings indicate that a combination of diffuser stall and disturbed inlet flow conditions due to the ported shroud is the surge trigger.
Subsequently, the system level is examined by considering pulsating environments and engine operation, with experiments conducted on a hot gas test rig and an engine test rig. Results show that surge margin shifts are heavily dependent on operating conditions and specific compressor design features. These findings reconcile seemingly contradictory results in literature and bridge the gap between industry experience and academic research.
Finally, the findings are integrated into a fully automated compressor optimization scheme that considers all thermodynamic aspects of compressor performance. The optimization process yields superior results compared to the previous design, significantly enhancing efficiency while improving map width.
This work adresses a critical gap in compressor development, contributing to more efficient and cleaner engines and provides an experimental foundation for future research in transient environments.
Version
Open Access
Date Issued
2025-10-07
Date Awarded
2026-05-01
Copyright Statement
Attribution-NonCommercial 4.0 International Licence (CC BY-NC)
License URL
Advisor
Martinez-Botas, Ricardo
Publisher Department
Department of Mechanical Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)