Development of detection techniques and diagnostics for airborne carbon nanoparticles. Page: 3 of 18
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SAND2003-8666
Unlimited Release
Printed November 2003
Development of Detection Techniques and Diagnostics
for Airborne Carbon Nanoparticles
H. A. Michelsen
Diagnostics and Remote Sensing Department
P. O. Witze
Engine Combustion Department
T. B. Settersten
Diagnostics and Remote Sensing Department
Sandia National Laboratories
MS 9055
P. O. Box 969
Livermore, CA 94551
Abstract
We have recorded time-resolved LII signals from a laminar ethylene diffusion flame over a
wide range of laser fluences at 532 nm. We have performed these experiments using an
injection-seeded Nd:YAG laser with a pulse duration of 7 ns. The beam was spatially filtered
and imaged into the flame to provide a homogeneous spatial profile. These data were used to aid
in the development of a model, which will be used to test the validity of the LII technique under
varying environmental conditions. The new model describes the heating of soot particles during
the laser pulse and the subsequent cooling of the particles by radiative emission, sublimation, and
conduction. The model additionally includes particle heating by oxidation, accounts for the
likelihood of particle annealing, and incorporates a mechanism for nonthermal photodesorption,
which is required for good agreement with our experimental results.
In order to investigate the fast photodesorption mechanism in more detail, we have recorded
LII temporal profiles using a regeneratively amplified Nd:YAG laser with a pulse duration of 70
ps to heat the particles and a streak camera with a temporal resolution of -65 ps to collect the
signal. Preliminary results confirm earlier indications of a fast mechanism leading to signal
decay rates of much less than a nanosecond.
Parameters to which the model is sensitive include the initial soot temperature, the
temperature of the ambient gas, and the partial pressure of oxygen. In order to narrow the model
uncertainties, we have developed a source of soot that allows us to determine and control these
parameters. Soot produced by a burner is extracted, diluted, and cooled in a flow tube, which is
equipped with a Scanning Mobility Particle Sizer (SMPS) for characterization of the aggregates.3
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Michelsen, Hope A.; Witze, Peter O. & Settersten, Thomas B. Development of detection techniques and diagnostics for airborne carbon nanoparticles., report, November 1, 2003; United States. (https://digital.library.unt.edu/ark:/67531/metadc878784/m1/3/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.