Thermal Profiling of Automotive Turbochargers in Durability Tests

Abstract A major portion of the development of an automotive powertrain system is devoted to robustness and durability testing to ascertain the viability of the design. For turbochargers, thermo-mechanical fatigue is often considered as life-limiting failure mechanism for the turbine section; therefore, these tests involve repeated and continuous cycling of the turbocharger for hundreds of hours. Thermocouples are used to monitor the temperature during the test; however, they only provide information at the location to which they are attached, are practically challenging to apply to all areas of interest, and are prone to fail due to the thermal cycling throughout the test. As a result, there may be very limited temperature data at the end of the test. If a failure occurred in the system during the testing, the lack of temperature data can inhibit the understanding of the cause. Further testing may be required and delay product release, which add significant expense to the product development. The thermal history coatings (THCs) developed by Sensor Coating Systems can offer a new and unique solution to provide complimentary temperature information for this purpose. THCs are applied to the surface of a component and, when heated, the coating permanently changes according to the maximum temperature of exposure. A laser-based instrumentation system is then used to measure the coating or paint, and through calibration, the maximum temperature profile of the surface can be recorded. Although this technique is relatively new, it has been used in several turbomachinery, and other applications to capture the spatial temperature distribution of critical components. However, the turbocharger durability test presents new challenges for the technique. It has not been tested in this type of application and the extended and repeated cycling operation can test the durability of the coating and will influence the response of the coating, hence, the temperature measurements. The internal surfaces of the turbocharger will also be exposed to the exhaust gases of the combustion process. In this paper, the capability of the THC for this application was investigated. For the first time, the effect of cyclic operation on the THC is reported. The measurement capability was demonstrated on two turbine housings tested on a gas stand, one for a single cycle, another for 10 cycles. The results show that the surface temperature profile of the two turbine housings can be accurately recorded and the results are validated against the installed thermocouples. The demonstration indicates that the THC can be used to acquire accurate and detailed spatial temperature distributions, which significantly enhance the information from thermocouples alone. This information can be used to improve the interpretation of the durability test and hence accelerate new product release.