Thermal Profiling of Automotive Turbochargers in Durability Tests

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. The Thermal History Coatings (THC) can offer a new and unique solution. THCs are applied to the surface of a component and, when heated, the coating permanently changes according to the maximum temperature of exposure. The technique 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 repeated cycling operation can test the response of the coating on the temperature measurements. 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. This information improves the interpretation of a durability test.

Simulation Research of Combustion Characteristics of Mixed Sodium Fire in a Columnar Flow

Sodium fire accident which was caused by the leakage of liquid sodium is the design basis accidents of sodium-cooled fast reactor. The column flow is a more realistic form of liquid sodium leakage due to the pipe system insulation structure and lower pressure in the sodium-cooled fast reactor. The leaked liquid sodium would combust in the form of columnar fire in the space and pool fire on the ground at the same time to form a mixed sodium fire in a columnar flow. In this paper, a numerical calculation model is established to simulate mixed sodium combustion in a columnar flow. This model is based on the turbulence model, discrete phase model and finite-rate model in Fluent software, and combined with chemical kinetic of sodium combustion. Several variables like spatial temperature, oxygen concentration and pressure during combustion of mixed sodium fire are calculated, and validated with experimental data collected in previous mixed sodium combustion experiment. Besides, the oxygen concentration and the temperature field are calculated for further study of the experiment. The result shows that the spatial temperature calculated by the code coincides well with the experiment, but the chamber pressure cannot be predicted precisely. The oxygen concentration in the center of the sodium flow would decline rapidly in the early stage, then remains at around 5%, but the oxygen concentration in the distance is relatively high. This study could provide reference for evaluation and prevention measures of sodium fire.

“Thermal Eraser” to Mitigate Screening Current by Optimal Control on Spatial Temperature Distribution in a High Temperature Superconductor Magnet

The so-called “screening current” in high temperature superconductor (HTS) is a well-known phenomenon that has detrimental effects on performance of an HTS magnet. To date, many research efforts have been devoted to suppressing screening current in an HTS magnet. Here we report a customized electric-heater, named “Thermal Eraser”, to mitigate the screening current. The key idea is to optimally control spatial temperature distribution in an HTS magnet using the customized heater and the consequent temperature-dependent local critical current of HTS wires of the magnet. To validate the idea, a Thermal Eraser was designed, constructed, and installed in an actual single-pancake HTS coil. And the Thermal Eraser plus test coil system was operated at temperatures ranging 7-40 K in our in-house conduction-cooling cryogenic facility. The feasibility of the Thermal Eraser was demonstrated in terms of two aspects: 1) creation of the designated spatial temperature distribution within the HTS test coil as designed; and 2) quantitative evaluation of its effectiveness to mitigate screening current using both experimental and numerical results. We confirmed that the screening current induced field in the test coil was reduced by 0.6 mT after activation of the Thermal Eraser, which implies 60% reduction of screening current in the HTS test coil. The results demonstrate that the Thermal Eraser is a viable option to effectively reduce the screening current in an HTS magnet.

Time-Resolved Endoscopic Evaluation of Spatial Temperature and Soot Distribution in a Butanol-Diesel Blend Fuelled Direct Injection Compression Ignition Engine

In-situ spatial soot and temperature distributions were investigated experimentally for B20 (20% v/v butanol and balance mineral diesel blend), vis-a-vis mineral diesel using endoscopic visualization. Endoscopy captured in-cylinder combustion images in a production-grade direct injection compression ignition (DICI) engine at varying engine operating points. A comparative combustion data analysis using pressure-crank angle history, and the captured endoscopic images was performed, and an attempt was made to correlate the results of these two experimental investigations. Combustion duration (CD) obtained from the endoscopic images was found to be relatively long compared to CD calculated from the thermodynamic analysis. The majority of the research on soot and NOx emitted from an engine using a raw exhaust gas emission analyser provides bulk, time-averaged, and cycle-averaged information about the pollutant formation. This investigation is unique wherein the spatial or time-resolved soot and NOx formation (Via spatial temperature distribution) is evaluated and the findings of this study support the research finding available in the open literature, which uses emission analyser. This study and the technique therein on deployment of engine endoscopy as an emerging optical technique is potentially useful to original automotive manufactures (OEM's) in designing more efficient engines to meet upcoming stringent emission norms.

Thermal Profiling of Automotive Turbochargers in Durability Tests

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 (THC) 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.