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Effects of Finite Time Response and Soot Deposition on Thin Filament Pyrometry Measurements in Time-Varying Diffusion Flames.


pdf icon Effects of Finite Time Response and Soot Deposition on Thin Filament Pyrometry Measurements in Time-Varying Diffusion Flames. (841 K)
Pitts, W. M.; Smyth, K. C.; Everest, D. A.

Combustion Institute, Symposium (International) on Combustion, 27th. Proceedings. Volume 1. August 2-7, 1998, Boulder CO, Combustion Institute, Pittsburgh, PA 563-569 pp, 1998 AND Chemical and Physical Processes in Combustion. Fall Technical Meeting, 1996. Eastern States Section/Combustion Institute. Proceedings. December 9-11, 1996, Hilton Head, SC, 107-110 pp, 1996, 1998.

Keywords:

combustion; diffusion flames; soot; flame flicker; methane; Rayleigh light scattering; temperature measurements; thermal radiation

Abstract:

Prior work has shown that thin filament pyrometry (TFP) is a powerful approach for making highly precise, spatially and temporally resolved line measurements of temperature in time-varying laminar diffusion flames. The technique has been previously used to map out temperature distributions as a function of phase angle for acoustically locked flickering diffusion flames with two different levels of forcing. During these measurements two small errors in the temperature measurements have been identified for certain heights and phases. The first error source is shown to be due to the limited time response of the TFP to a rapidly changing temperature field by comparing temperatures determined by TFP with line measurements using Rayleigh light scattering (RLS). The TFP measurements yield lower temperature readings when the flame front is moving at its fastest rate, but the RLS measurements show that these lower temperatures are an artifact which is attributed to the finite time response of TFP. The second source of error occurs for a limited number of cases in which soot is thermophoretically deposited on the filament and is not subsequently burned off. The soot modifies both the emissivity of the filament surface and, for large amounts of deposition, its diameter. These modifications lead to lower measured filament temperatures for low levels of soot deposition and to increasing measured temperatures as the soot builds up. Approaches are suggested for identifying the presence of these errors and minimizing their effects.