Infrared imaging for two-dimensional soot and temperature measurements in laminar premixed and non-premixed flames

Spectral soot emission (SSE) is an effective flame imaging technique for retrieving soot and temperature field. Currently, the application of SSE is focused on the visible to near-infrared range, but the accuracy is strongly related to the complex wavelength-dependence of soot absorption function of E(m)_λ. Our previous study in a premixed flat flame has demonstrated high-fidelity SSE measurements by using an infrared spectral range. Here, we extend previous work to investigate, for the first time, the reliability of SSE-based infrared imaging for two-dimensional temperature measurements in both premixed flat flames and non-premixed coflow flames. The performance of SSE measurements within different wavelength ranges have been evaluated through a cross-comparison with other established techniques and with numerical predictions. It is found that SSE measurements using wavelength in the infrared range of 1100–1400 nm could provide more reliable temperature results in both premixed and non-premixed flames, showing improved accuracy than the visible-SSE measurements in the spectral range of 660–905 nm. The reason could be correlated to the weak (strong) sensitivity of E(m)_λ to spectral variation in the infrared (visible) region, as inferred from the parallel two-dimensional extinction-based soot measurements at different wavelengths of 660–1400 nm. The present study demonstrates the benefits of infrared imaging for accurate extinction-based soot and SSE-based temperature measurements. The results are expected to guide the development of accurate and cost-effective two-dimensional SSE-pyrometry.