An optical method for the measurement of combustion gas temperature in particle laden flows

Temperature measurements in combustion systems are challenging due to the physical limitations of measurement devices and the complexity of combustion flows. The objective of this work is to investigate the Integrated Spectral Band Ratio (ISBR) method for measuring the temperature of combustion product gases surrounded by radiating walls or within a mixture of gas and particles. Five conditions in a multi-fuel reactor were investigated using an optical probe. A Fourier Transform Infrared spectrometer provided detailed spectral measurements of hot gas and particle emissions at wavelengths of 1.69-2.15 μm, focusing on a spectral region where H2O is the dominant participating gas. These measurements were used to infer the gas temperature of the flows. It was found that the measurement path length needed to be at least 0.25 m in order to obtain a signal large enough to infer temperature accurately. For four of the five operating conditions tested, optically measured gas temperatures were found to be in good agreement with the average temperature along the measured path as taken with a suction pyrometer (aspirated thermocouple). For these four operating conditions the particle media were optically thin. Temperatures for the in-flame fine wood particle condition did not exhibit as good of agreement due to high particle loading causing optically thick zones along the line of sight. Modeling experiments showed that when particles and gasses are optically thin, the optical gas temperature measured with this technique will be near the arithmetic mean of the line of sight temperature.