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Proceedings Paper

Laser ignition of methane-air mixtures at high pressures and optical diagnostics
Author(s): Herbert Kopecek; M. Lackner; Kurt F. Iskra; Ch. Forsich; D. Rüdisser; Theo Neger; F. Winter; Ernst Wintner
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Paper Abstract

Laser-induced ignition of methane-air mixtures of varied composition was investigated experimentally using nano-second pulses generated by Q-switched Nd:YAG lasers (wavelength 1064 nm, 532 nm and 355 nm) at initial pressures up to 4 MPa. The minimum focal spot diameter was found to be about 20 μm for effective ignition, independent of the laser wavelength, indicating that small impurity particles provide the seeds for laser plasma generation. The minimum laser pulse energy needed for ignition ranged from 2-15 mJ decreasing reciprocally with initial pressure and with fuel equivalence ratio Φ in a mixing of Φ=0.91 to Φ=0.56. Corresponding threshold intensities ranged from 1010 to 1011 W/cm2. In this way, evidence for a non-resonant breakdown mechanism was established. Optical in-situ diagnosis of water vapor concentration covering the whole timespan of the combustion process in a stationary high pressure vessel with four optical windows was performed involving linear absorption measurements over the entire spectral absorption linewidth by rapidly tuned diode laser radiation at 2.55 μm. Additionally, planar laser-induced fluorescence was measured in a time-resolving fashion yielding 3D determination of the OH concentrations during the process. To the knowledge of the authors, these are the first results on laser-induced ignition under laboratory conditions well above atmospheric pressure being relevant for several technical combustion systems.

Paper Details

Date Published: 14 November 2003
PDF: 12 pages
Proc. SPIE 5147, ALT'02 International Conference on Advanced Laser Technologies, (14 November 2003); doi: 10.1117/12.543678
Show Author Affiliations
Herbert Kopecek, Technische Univ. Wien (Austria)
M. Lackner, Technische Univ. Wien (Austria)
Kurt F. Iskra, Technische Univ. Graz (Austria)
Ch. Forsich, Technische Univ. Wien (Austria)
D. Rüdisser, Technische Univ. Graz (Austria)
Theo Neger, Technische Univ. Graz (Austria)
F. Winter, Technische Univ. Wien (Austria)
Ernst Wintner, Technische Univ. Wien (Austria)

Published in SPIE Proceedings Vol. 5147:
ALT'02 International Conference on Advanced Laser Technologies
Heinz P. Weber; Vitali I. Konov; Thomas Graf, Editor(s)

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