At Technische Universität Wien in Vienna and Technische Universität Graz in Graz, both in Austria, researchers have reported the results of their experiments into the laser-induced ignition of methane/air mixtures. The work, which they describe in the Sept. 20 issue of Optics Express, is part of investigations worldwide into the suitability of using lasers to take the place of spark plugs in combustion engines.

In the current study, the researchers used Schlieren photography and planar laser-induced fluorescence imaging to analyze the early stages of laser-induced ignition, from the deposition of the laser's energy to the development of a flame ball over a period of several milliseconds. The fuel/air mixtures varied from stoichiometric to lean and were tested at ambient to high pressures, and a Q-switched 1064-nm Nd:YAG laser from Quantel of Les Ulis, France, served as a source of attenuated 1- to 50-mJ ignition pulses.

The results from Schlieren photography indicated that the pulse energy influences the size of the plasma kernel and the velocity of the shock wave produced by a laser pulse. The fluorescence images revealed that the plasma kernel determines the turbulent geometry of the developing flame ball in the moments after ignition, which becomes laminar after a few milliseconds, depending on the local pressure, fuel composition and pulse energy.