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

Herbert Kopecek, Max Lackner, Johann Klausner, Ernst Wintner, Christian Forsich, Soren Charareh, Franz Winter, Günther Herdin

Research output: Contribution to journalConference articlepeer-review

17 Citations (Scopus)

Abstract

Methane-air mixtures at high fill pressures up to 30 bar and high temperatures up to 200°C were ignited in a high pressure chamber with automated fill control by a 5 ns pulsed Nd:YAG laser at 1064 nm wavelength. Both, the minimum input laser pulse energy for ignition and the transmitted fraction of energy through the generated plasma were measured as a function of the air/fuel-equivalence ratio (λ). The lean side ignition limit of methane-air mixtures was found to be λ = 2.4. However, only λ < 2.2 seems to be practically usable. As a comparison, the limit for conventional spark plug ignition of commercial natural gas engines is λ = 1.8. Only with excessive efforts λ = 2.0 can be spark-ignited. The transmitted pulse shape through the laser-generated plasma was determined temporally as well as its dependence on input laser energy and properties of the specific gases interacting. For a first demonstration of the practical applicability of laser ignition, one cylinder of a 1 MW natural gas engine was ignited by a similar 5 ns pulsed Nd:YAG laser at 1064 nm. The engine worked successfully at λ = 1.8 for a first test period of 100 hours without any interruption due to window fouling and other disturbances. Lowest values for NOx emission were achieved at λ = 2.05 (NOx = 0.22 g/KWh).Three parameters obtained from accompanying spectroscopic measurements, namely water absorbance, flame emission and the gas inhomogeneity index have proven to be a powerful tool to judge laser-induced ignition of methane-air mixtures. The following effects were determined by the absorption spectroscopic technique: formation of water in the vicinity of the laser spark (semi-quantitative); characterization of ignition (ignition delay, incomplete ignition, failed ignition); homogeneity of the gas phase in the vicinity of the ignition and the progress of combustion.

Original languageEnglish
Pages (from-to)147-154
Number of pages8
JournalAmerican Society of Mechanical Engineers, Internal Combustion Engine Division (Publication) ICE
Volume40
DOIs
Publication statusPublished - 2003
Externally publishedYes
EventProceedings of the 2003 Spring Technical Conference of the ASME Internal Combustion Engine Division - Salzburg, Austria
Duration: 11 May 200314 May 2003

Keywords

  • High pressure
  • Laser ignition
  • Laser-induced plasma
  • Linear absorption spectroscopy
  • Methane-air mixtures

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