Local gas heating in sooting flames by heat transfer from laser-heated particles investigated using rotational CARS and LII

• Soot particles strongly absorb radiation in the visible and infrared spectral regions, and the soot interaction with laser light during laser diagnostic interrogation leads to particle heating and often to subsequent sublimation. Consequently, laser-heated particles transfer heat to the ambient gas leading to local gas heating, a process that has received minor attention so far in the diagnostic community. In the present work, this specific local gas heating is measured in a pump-probe-type experiment. A 1064-nm laser beam heated the soot particles in an ethylene/ air diffusion flame (on a Gulder-burner) with known soot volume fraction, and a two-beam rotational coherent anti-Stokes Raman spectroscopy (CARS) setup was used to probe the local gas temperature on time scales from nanoseconds to milliseconds. The temperature of the heated particles was simultaneously probed using a two-color laser-induced incandescence (2C-LII) detection system. The results show that laser heating of soot particles from flame temperatures to sublimation temperatures leads to local gas heating of similar to 100 K at a soot volume fraction of 4 ppm, in good agreement with theoretical predictions. The implication of these results to the application of laser diagnostic techniques is briefly discussed. (C) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Subject headings

NATURVETENSKAP  -- Fysik -- Atom- och molekylfysik och optik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Atom and Molecular Physics and Optics (hsv//eng)

Keyword

Local gas heating

Soot

Rotational coherent anti-Stokes Raman

spectroscopy

Laser-induced incandescence

Publication and Content Type

art (subject category)

ref (subject category)