=Paper=
{{Paper
|id=None
|storemode=property
|title=Continuous Wave LII in an Atmospheric Pressure Kerosene Flame

|pdfUrl=https://ceur-ws.org/Vol-865/Black.pdf
|volume=Vol-865
}}
==Continuous Wave LII in an Atmospheric Pressure Kerosene Flame
==
<pdf width="1500px">https://ceur-ws.org/Vol-865/Black.pdf</pdf>
<pre>
         Continuous Wave LII in an Atmospheric Pressure
                       Kerosene Flame
                         John D. Black and Paul Wright
       School of Electrical and Electronic Engineering, University of Manchester, UK
                             John.black-2@manchester.ac.uk

       Fibre and diode lasers with sufficient power to heat soot particles to
incandescent temperatures are readily available at lower cost than the nanosecond
pulsed lasers traditionally used in LII. There are less stringent safety restrictions on
the use of CW lasers and they can be delivered with excellent beam quality through
standard optical fibres, making them more suitable for LII in practical environments.
Using the collimated beam from a diode laser at 803 nm in the power range 5 – 30
W, LII was easily observable in a highly sooting kerosene flame (Fv ~10-5). However,
the laser causes major changes in the combustion, increasing soot burn out rates
and transferring heat to other regions of the flame.

         In contrast to short pulse LII, soot
particles experience laser heating and cooling by
heat transfer at rates comparable with their
reaction rate. Their residence time in the beam
and other processes such as photophoresis and
optical trapping also have to be considered.
Hence, modeling is much more complicated than
for short pulse LII, and the processes are not well
understood.

         Visible emission spectra were collected
using a traversable fibre optic probe from a
magnified projected image of the flame shown in
Figure 1. There is a good match between
predicted emission spectra based on the                 Figure 1: LII in a quasi-2-D
                                                        kerosene lamp flame with 28 W
blackbody curve and observed spectra from the
                                                        1 mm diameter cw laser beam
flame in the wavelength range 590 – 790 nm.             photographed through a BG3 filter
From these spectra estimated soot temperature
in the absence of the laser is 2150 K, rising to 2600 K in the region of a 28.5 W laser
beam. Temperature rise is linear in laser power. Local soot temperature is increased
both above and below the beam when the laser is present. Above the laser beam,
light emitted at 700 nm decreases quadratically with distance from the height of the
centre of the laser beam to the edge of the visible flame, although the soot particle
surface temperature remains at ~2350 K in this upper part of the flame. The intensity
of light emitted at 700 nm at the centre of the laser beam at varying laser power is in
good agreement with a prediction based on blackbody radiation. This indicates that
the mechanism of increased light emission is particle heating (LII) and not creation of
additional soot by laser stimulated reactions in the flame.

        Although cw LII is at a very early stage of development, the potential for
combustion diagnostics – soot concentration, temperature, velocity by flow tagging,
etc. – is obvious. The observations described here should provide a basis for future
investigation of the processes involved.




             5th international workshop on Laser-Induced Incandescence
              May 9-11, 2012, Palais des Congrès, Le Touquet, France

</pre>