Laser ignition of methane-air mixtures at high pressures and optical diagnostics

H. Kopecek, M. Lackner, K. Iskra, Ch Forsich, D. Rüdisser, T. Neger, F. Winter, E. Wintner*

*Corresponding author for this work

    Research output: Chapter in Book/Report/Conference proceedingConference contribution

    Abstract

    Laser-induced ignition of methane-air mixtures of varied composition was investigated experimentally using nanosecond 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 regime 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 3-dimensional 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.

    Original languageEnglish
    Title of host publicationProceedings of SPIE - The International Society for Optical Engineering
    Subtitle of host publicationThe International Society for Optical Engineering
    EditorsH.P. Weber, V.I. Konov, T. Graf
    Pages331-342
    Number of pages12
    Volume5147
    DOIs
    Publication statusPublished - 2003
    EventALT'02 International Conference on Advanced Laser Technologies - Adelboden, Switzerland
    Duration: 15 Sep 200220 Sep 2002

    Conference

    ConferenceALT'02 International Conference on Advanced Laser Technologies
    CountrySwitzerland
    CityAdelboden
    Period15/09/0220/09/02

    Keywords

    • Absorption spectroscopy
    • Diode laser
    • High-pressure gas mixtures
    • Laser ignition
    • Laser-initiated combustion
    • Lean gas mixtures
    • Multipoint ignition
    • OH concentration
    • OH-radicals
    • PLIF

    ASJC Scopus subject areas

    • Electrical and Electronic Engineering
    • Condensed Matter Physics
    • Atomic and Molecular Physics, and Optics

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