Advanced Thermal Profiling of Turbocharger Compressor Wheels Using Phosphorescence Thermal History Coatings

Abstract

Compliance towards future emissions legislation requires internal combustion engines (ICE) to utilize highly efficient combustion concepts (e.g. Miller cycle), which, are often associated with increased boost pressure requirements, leading to increased mechanical stress on turbocharger components. This is especially the case for compressor wheels due to the increased speed and temperature loading. To offer cost competitive products, IHI seeks to further exploit the limits of conventional state-of-the-art materials used in automotive turbochargers and refine their component development processes. While knowledge of the exact boundary conditions under which turbocharger components are operating is essential, the actual material temperature components experience under real operating conditions is a significant source of uncertainty. Temperature measurements are usually conducted during turbomachinery durability tests to validate thermodynamic models and assess component lifetime. Temperature measurement techniques typically include thermocouples, optical sensors and thermal paints. However, the former methods are limited mostly to stationary components and can only provide point measurements, while the latter only offers low resolution data for short durations and involves highly toxic materials. Thermal History Paint & Coating technology developed by Sensor Coating Systems (SCS) offers a unique solution for thermal mapping in harsh environments. The technology is based on a phosphor material which is applied as a paint or coating on the surface of the components to be measured. The luminescent properties of the coating material are permanently changing depending on the maximum exposure temperature during the test. The THP/C luminescent properties are measured in multiple locations using a laser-based instrumentation system and a robotic arm. High-resolution thermal maps directly on the 3D CAD models of the component are generated. For this application, the THP material has been applied for the first time on the surface of three turbocharger compressor wheels tested under different cooling conditions. The THP material exhibited excellent durability during testing at high circumferential speeds above 580 m/s. More than 2,000 temperature measurements were obtained on pre-selected locations on the surface of the wheels. The test demonstrates that THP can be used on components with complex geometries such as turbocharger compressor wheels. Additionally, temperatures as low as 120 °C have been resolved for the first time.