This paper reports the application of optical tomography and Chemical Species Tomography (CST) to the characterisation of the in-cylinder
A novel opto-electronic scheme for line-of-sight Near-IR gas absorption measurement based on direct absorption spectroscopy (DAS) is reported. A diode-laser-based, multiwavelength system is designed for future application in nonintrusive, high temporal resolution tomographic imaging of H2O in internal combustion engines. DAS is implemented with semiconductor optical amplifiers (SOAs) to enable wavelength multiplexing and to induce external intensity modulation for phase-sensitive detection. Two overtone water transitions in the Near-IR have been selected for ratiometric temperature compensation to enable concentration measurements, and an additional wavelength is used to account for nonabsorbing attenuation. A wavelength scanning approach was used to evaluate the new modulation technique, and showed excellent absorption line recovery. Fixed-wavelength, time-division-multiplexing operation with SOAs has also been demonstrated. To the best of our knowledge this is the first time SOAs have been used for modulation and switching in a spectroscopic application. With appropriate diode laser selection this scheme can be also used for other chemical species absorption measurements.
The operating temperature of turbomachinery components are increasing the drive towards higher efficiency, lower fuel consumption and reduced emissions. Accurate thermal models are required to simulate the operating temperature of gas turbine components and hence predict service life or other qualities. These models require validation through measurement. Therefore, the quality of the models and prediction are dependent on the uncertainty of the measurements used to validate them. Currently available temperature measurement techniques have limitations in the harsh operating conditions inside gas turbines. Thermocouples are widely used, however, are practically very challenging to apply on rotating components and only provide point measurements. Furthermore, over 80% of the surface must be measured to validate complex thermal models. A new technique under development called thermal history paints (THP) and coatings (THC) overcomes some of these limitations. While the uncertainty estimation model described in this work is directly related to THP, the principles can be applied in general to thermographic phosphors. The paint comprises a proprietary phosphor powder and a water-based silicate binder. The paint is applied to the surface of the test component. When the component is operated the paint records the maximum temperature of exposure across the complete surface of the component. After operation, the paint is read-out using automated instrumentation. The measurements are related to temperature through calibration to deliver a high-resolution temperature profile. An uncertainty model has been developed and described for the first time. The model assesses the uncertainty sources related to the generation of the calibration data and the measurement of the component. It has been applied to determine the uncertainty of the THP in the temperature range 400–750 °C. The estimated uncertainty in this case was, for most samples, ±3–6 °C (67% confidence level). The maximum estimated uncertainty was ±6.3 °C or ±13 °C for 67% or 95% confidence levels respectively. This is believed to be well within the uncertainty of thermal models and the requirements for temperature measurements in harsh environments on gas turbines. These results combined with the fact that the THP can record the temperature at many locations demonstrates that it is a very useful tool for the validation of thermal models and lifing predictions. The uncertainty model was validated by measuring separate test samples and comparing the temperature measured from the THP with the thermocouple data from the heat treatment. The difference was within ±7 °C and the uncertainty bounds determined by the model.
Compliance with incoming new emission standards such as Euro6d and China6b will require new approaches to the design of thermally loaded automotive components e.g. turbochargers, exhaust valves and manifolds. However, the validation of those new designs and the need for a rapid market entry will require new temperature measurement technologies to provide accurate data across the entire component. A limited number of techniques are currently available, and all have limitations in the harsh operating conditions of turbomachinery. A new technique, called Thermal History Paint (THP), has been developed to overcome these limitations to enable accurate temperature profiles to be recorded in harsh environments. There are limited publications that cover the use of this technique and this paper demonstrates the capability of the THP through the implementation on turbocharger turbine wheels. A cooled, hollow radial turbine wheel was designed, manufactured via 3D printing and tested. A solid wheel of the same external dimensions was manufactured and tested under the same conditions to act as a baseline. The THP was used to measure the temperature profile of the blade surfaces and to quantify the effectiveness of the cooling. The paint exhibited good durability through the tests of both wheels in a hot gas rig at the University of Bath. Specific calibration data were generated for the test and the repeatability of the measurements was determined to be within 8K. Both the cooled and baseline wheels were measured at many locations and the THP recorded a significantly higher temperature on the baseline solid wheel. The measured temperature profiles were in good agreement with expectation and CFD simulations. The results enable the validation of thermal models and demonstrate the capability of the new measurement technique.
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.
The requirement for reduced emissions and the growing demand on gas turbine efficiency are in part met through increasing firing temperatures. However, development budgets leave only limited time for dedicated thermal testing. Consequently, manufacturers are seeking novel temperature measurement technologies to validate new engine designs. This paper will demonstrate how a new temperature mapping technology can be utilized for non-dedicated (multi-cycling) testing while still delivering high-resolution temperature data in a non-dedicated test on a combustor of an industrial gas turbine. Typically, thermocouples are used to monitor the temperature during tests, but they only provide one data point. Colour changing thermal paints are used to deliver measurements over complete surfaces, but they require dedicated testing with short-duration exposure, necessitating dismantling and re-assembling the engine for further testing. Thermal History Coatings (THC) present an alternative solution to providing high-density temperature information. This coating permanently changes consistent with the maximum temperature of exposure during test. A laser-based instrumentation technique is then used to obtain temperatures. The maximum temperature profile of the surface can be determined through a customized calibration. Given the complex cooling system of a combustor, the high temperatures and the long-time exposure, this case offers a unique possibility for the testing of the coating under real engine conditions. The coated region covered the external surface of the can. Highly significant is the number of measurement points in excess of 7,000 (2 × 2 mm resolution, which enables advanced analysis. This provides insight into the impact of local features, e.g. the region adjacent to a cooling hole. The temperature profile is compared to a CFD-CHT model and thermocouple measurements for the calibration of cooling pre-design methods.
The requirement for reduced emissions and the growing demand on gas turbine efficiency are in part met through increasing firing temperatures. However, development budgets leave only limited time for dedicated thermal testing. Consequently, manufacturers are seeking novel temperature measurement technologies to validate new engine designs. This paper will demonstrate how a new temperature mapping technology can be utilized for non-dedicated (multi-cycling) testing while still delivering high-resolution temperature data in a non-dedicated test on a combustor of an industrial gas turbine. Typically, thermocouples used to monitor the temperature during tests can only provide one data point. Colour changing thermal paints are used to deliver measurements over complete surfaces require dedicated testing with short-duration exposure. Thermal History Coatings (THC) present an alternative solution to providing high-density temperature information. This coating permanently changes consistency with the maximum temperature of exposure during test. The maximum temperature profile of the surface can be determined through a customized calibration. Given the complex cooling system of a combustor, the high temperatures and the long-time exposure, this case offers a unique possibility for the testing of the coating under real engine conditions. The coated region covered the external surface of the can. Highly significant is the number of measurement points in excess of 7000 (2x2 mm resolution), which enables advanced analysis. The temperature profile is compared to a CFD-CHT model and thermocouple measurements for the calibration of cooling pre-design methods.
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.
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