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