Ultraviolet excimer laser-based ignition of H2/air and H2/O2 premixed flows

Very efficient ignition was demonstrated of H2/air and H2/O2 premixed flows at room temperature and atmospheric pressure using the radiation from a focussed ArF excimer laser (193nm). Incident pulse laser energies of less than 1 mj for H2/O2 and 6 mj for H2/air are required for ignition with the minimum occurring for lean mixtures. The ignition is due to efficient formation of microplasmas. Unlike the laser-produced microplasmas that are formed by non-resonant photon absorption processes, the resonant ones are easily controlled with respect to spark energy content and thus could be quite useful as potential igniters for the NASP plane and for other supersonic/hypersonic air breathing applications. It was also found that the atmospheric absorption of the ArF laser radiation strongly affects the values for the incident laser energy (ILE) that is required for ignition. Finally, the efficient ignition is reported of C2H2/air by the ArF laser which suggests that this UV laser ignition source may have a wider range of applicability.