Infrared Multispectral Emissivity Assessment of Materials Within a Combustion Chamber

The study of dynamic temperature fluctuations within closed cavities is pivotal in numerous industrial applications. Infrared (IR) thermography is a useful tool to monitor and analyze these high-temperature environments, providing a non-intrusive means to identify hotspots, thermal gradients, and potential issues that could compromise system efficiency or safety. The remote nature of those measurements is often necessary; however, this brings the intrinsic complexity of the temperature and emissivity properties of a surface being intertwined in such data. Assessing a reliable emissivity through IR thermography is theoretically possible but challenging, particularly at high temperatures. An enclosed cavity leads to an additional challenge of a geometry-dependent apparent increase in emissivity. In this work, we describe a novel approach for solving this problem in the context of measurements within a model aircraft engine combustion chamber. By using thermocouples and a multi-spectral camera, we experimentally validate our radiometric model for the cavity. We first show how to evaluate the amplification factor of a cavity using numerical tools, and we then use these results to apply corrections on the camera signals for in-band radiance (IBR) measurements. The calculations are compared across 3 different wavebands to ensure their validity, with a difference lower than 2%. Finally, we showcase the importance of assessing the in-situ emissivity of a surface, which can change drastically with a large temperature variation and in a harsh environment. Using a calibration point given by a carefully placed thermocouple, the 2D temperature mapping of the whole scene is evaluated and compared in two different wavebands, leading to temperatures within ΔT = 10°C across the wavebands when the combustion chamber is at 700°C. As a non-invasive and non-destructive technique, this approach can be used to monitor in real time the evolution of the temperature and emissivity over a large temperature range. (Le poster peut être en français si souhaité)

Work In Progress