Development of a high-speed temperature sensor based on ratiometric NIR water emission for hydrogen and methane flames

This study reports on a fast, inexpensive, non-intrusive, in situ temperature sensor that can be applied to a wide variety of combustion processes. The sensor is based on the detection of thermal radiation from water in the near-infrared, measured by two photodiodes at distinct wavelength bands centered at 1300 nm to 1500 nm and 1500 nm to 1700 nm. Validation tests are performed on well-characterized premixed hydrogen and methane flames, and the results are compared to reference values. Excellent agreement is obtained for lean and stoichiometric flames: matching the known results within a few tens of Kelvin at a rate of 9 kHz. The sensor's high-speed capability is demonstrated using a turbulent hydrogen-jet flame, resolving temperature fluctuations at a rate of 90 kHz. Larger deviations from the reference values are present at fuel-rich conditions, most likely resulting from a second reaction zone forming at the edges of these flames. The measurement precision is quantified, taking into account errors due to noise and equipment-related uncertainties. This sensor has a wide range of applicability and can enable real-time quasi-point thermometry in complex flames with minimal optical access.