Spatio-Temporal Distribution of Soot Temperature for Flames Using Optical Pyrometry Under Unsteady Inlet Airflow Conditions

Abstract

Two pyrometric tools for measuring soot temperature response in fuel-rich flames under unsteady inlet airflow conditions are developed. High-speed pyrometry using a high-speed color camera is used in producing soot temperature distributions, with its results compared with those of global soot temperature response measured using a multi-wavelength pyrometer. For the former, the pixel RGB values pertaining to respective bandwidths of red, green and blue filters are used to calculate temperature and for the latter, the emission from whole flame at 660 nm, 730 nm and 800 nm is used to measure temperature. The combustor, running on Jet-A fuel, achieves unsteady inlet airflow using a siren running at frequencies of 150 and 250 Hz and with modulation levels (RMS) 20–50% of mean velocity. Spatiotemporal response of flame temperature measured by the high speed camera is presented by phase-averaged with average subtracted images and by fast Fourier transform at the modulation frequencies of inlet velocity. Simultaneous measurement of combustor inlet air velocity and flame soot temperature using the multi-wavelength pyrometer is used in calculating the flame transfer function of flame temperature response to unsteady inlet airflow. The results of global temperature and temperature fluctuation from the 3-color pyrometer show qualitative agreement with the local temperature response measured by the high speed camera. Over the range of operating conditions employed, the overall flame temperature fluctuation increases linearly with respect to the inlet velocity fluctuation. The two-dimensional map of flame temperature under unsteady combustion determined using a high-speed digital color camera shows that the local temperature fluctuation during unsteady combustion occurs over relatively small region of flame and its level is greater (∼10–20%) than that of overall temperature fluctuation (∼1%).