Development of fiber-optic sensors for combustion diagnostics

We focus on advancing fiber-optic sensor technologies for precise and robust measurement and analysis in practical combustion processes. These sensors are essential tools for monitoring temperature and gas compositions in harsh environments such as gas turbine combustion chambers. The optics are coupled to advanced water-cooled and gas-flushed sensor heads that stand the harsh conditions in industrial test rigs. Their application supports the improvement of efficiency and environmental performance of modern energy systems.

One of our key developments is in phosphor thermometry. This method involves using phosphorescent materials applied to surfaces, which are then excited by laser light. The temperature is determined from the emission spectrum or the decay time of the phosphorescence. We have developed a robust measurement technique suitable for high-temperature environments, such as future gas turbine combustion chambers, with surface temperatures up to 1700 K [1, 3].

In another significant advancement, we employ tunable diode laser absorption spectroscopy (TDLAS) to measure gas-phase temperatures and concentrations of CO, CO2, and H2O. Simultaneously capturing multiple absorption bands enables accurate species concentration and temperature determination. Successful field tests at gas turbine test rigs demonstrated the feasibility of this method under real-world conditions. This research is documented in a publication describing a compact, fiber-coupled NIR/MIR laser absorption instrument for simultaneous measurements [2].

Chemiluminescence detection via image-preserving fiber-optical probes is another area, where we have made substantial progress. This technique captures the natural light emission from flames, providing valuable information about flame location, turbulence, and stoichiometry. We have advanced this method for high-pressure burner test stands, enabling spatially resolved analysis of flame emission. This advancement is particularly beneficial for validating computational fluid dynamics (CFD) simulations. The robustness of endoscopic chemiluminescence measurements was successfully demonstrated in numerous tests at realistic gas turbine conditions, providing insight into flame behavior and its correlation with NOx emissions and pressure oscillations [4].

Our research has led to publications showcasing the capabilities and applications of fiber-optic sensors in combustion diagnostics. These include studies on fiber-coupled phosphor thermometry for wall temperature measurements in hydrogen-operated gas turbine combustors, compact fiber-coupled NIR/MIR laser absorption instruments for simultaneous measurement of multiple gas-phase species, and the application of phosphor thermometry in full-scale gas turbine combustion test rigs. We have also documented the use of endoscopic chemiluminescence measurements as a robust experimental tool in high-pressure gas turbine combustion tests.

The continued development of fiber-optic sensors will focus on enhancing their signal quality and expanding their industrial applications. This includes the miniaturization of sensors and their integration into various energy production and environmental monitoring systems. By advancing these technologies, we aim to contribute significantly to the optimization of combustion processes and the reduction of emissions, thereby supporting the competitiveness of the industry in the global market.

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  1. Nau, P., Müller, A., Petry, N., Nilsson, S., Endres, T., Richter, M., Witzel, B., Fiber-coupled phosphor thermometry for wall temperature measurements in a full-scale hydrogen gas turbine combustor. Measurement Science and Technology, 2023, 34:104003.
  2. Shi, L., Jeffries, J.B., Endres, T., Dreier, T., Schulz , C. , A compact fiber-coupled NIR/MIR laser absorption instrument for the simultaneous measurement of gas-phase temperature and CO, CO2, and H2O concentration. Sensors 22 (2022)1286.
  3. Nau, P., Görs, S., Arndt, C., Witzel, B., Endres, T., Wall temperature measurements in a full-scale gas turbine combustor test rig with fiber coupled phosphor thermometry. Journal of Turbomachinery 143 (2021) 011007.
  4. Goers, S., Witzel, B., Heinze, J., Stockhausen, G., van Kampen, J., Schulz, C., Willert, C., Fleing, C., Endoscopic Chemiluminescence Measurements as a Robust Experimental Tool in High-Pressure Gas Turbine Combustion Tests. in ASME Turbo Expo 2014: Turbine Technical Conference and Exposition. 2014. American Society of Mechanical Engineers. GT2014-26977.