Thin-Filament Pyrometry in Flickering Laminar Diffusion Flames
William M. Pitts
This paper describes an experimental system for thin-filament pyrometry (TFP) in acoustically phase-locked flickering laminar methane/air diffusion flames. The physical basis of the technique is discussed. The experiment utilizes a 15-mu m beta-SiC fiber, which is simultaneously imaged at 540 points over a length of 27.5 mm using a cooled CCD camera. This arrangement provides measurements over a 1200-2100-K temperature range having a spatial resolution of ~100 mu m, a temporal resolution of 1.5 ms, and a precision of 1.5 + 1.0 K for temperatures on the order of 2000 deg. K. The TFP is calibrated assuming that the strongest filament emission at a height 7 mm above the burner for a steady laminar flame corresponds to a temperature of 2000 deg. K. Temperatures at different positions along the filament are then determined by recording relative emission intensities and assuming that the filament acts as a gray-body emitter. Measured filament temperature profiles are found to be in good agreement with earlier radiation-corrected thermocouple results by Richardson and Santoro for the same steady laminar flame. The calibrated TFP is then used to make filament temperature measurements at various heights and phases of a previously studied flickering flame entering a low-velocity air flow. The use of a two-dimensional CCD allows a baseline to be determined, and measurements can be made in the presence of background luminosity, which is observed in sooting regions. In order to demonstrate the effectivenss of the approach, measurements are well-characterized flame for calibrating TFP is discussed. Knowledge of flow velocities and molecular composition in both the calibration and flickering flames is required to improve the accuracy of flame temperature measurements using TFP.
Combustion Institute, Symposium (International) on Combustion, 26th. Proceedings. Volume 1.