| Summary: | When trace quantities of an alkali element are added to a flame,
its optical and electrical properties change significantly. Addition of
alkali seed to both premixed and diffusion flames has been used in the
development of two new techniques, one for flame temperature measurement
and the other for enhanced mixing.
Advantage has been taken of the spectral characteristics of alkali
seeds in the development of a non-invasive optical flame temperature
measurement technique. The strongest resonance line of alkalis is in
fact a doublet, and the two peaks can be subjected to different optical
treatment. A cesium-seeded flame was exposed to radiation which was
selectively filtered to yield different apparent source temperatures at
the wavelengths corresponding to the doublet resonance lines. The ratio
of the emission peak heights at the two wavelengths relates directly to
flame temperature. This technique allows real-time measurement of flame
temperatures up to 2800 K.
A second process has been investigated which takes advantage of the
enhanced electrical conductivity of alkali-seeded diffusion flames. The
study first required a characterization of electrical discharges through
planar diffusion flames. Because of the increase in conductivity,
alkali-seeded diffusion flames can carry current when a transverse
electric potential is applied. The behavior of diffusion flames
carrying electrical current has been investigated. The dependence on
electrode position and gap is reported and the behavior is contrasted
with that described in the literature for premixed flames.
A planar diffusion flame was subjected to a steady magnetic field
parallel to the flow direction while an orthogonal, oscillating current
passed through the flame sheet. A Lorentz body force was induced on the
flame sheet which acted to move it alternately toward the fuel and
oxidizer streams, improving bulk mixing in the flame. High-speed video
images of the oscillating flame were analyzed to obtain its maximum
lateral velocity. The results compared well with predictions from a
simple theoretical model. === Graduation date: 1992
|
|---|
