Photochemical Ignition Studies. II. Oxygen-Atom Two-Photon Resonance Effects.
ARMY BALLISTIC RESEARCH LAB ABERDEEN PROVING GROUND MD
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Ultraviolet lasers have recently been used to activate and ignite reactive gas mixtures through multiphoton photochemical means. The observation of this new phenomenon opens up the possibility of using uv lasers as primary ignition or ignition augmentation sources for igniting propellants or their pyrolysis products. The first report in this series describes the ignition of hydrocarbonair, N2O mixtures by the excimer laser lines KrF 248 nm and ArF 193 nm. In this report, a sharp wavelength dependence on the amount of incident laser energy necessary to ignite a premixed flow of H2O2 at atmospheric pressure is described. This wavelength dependence exhibits a spectral profile similar to the two-photon fluorescence excitation curve for flame oxygen atoms and the respective peaks correspond to exactly the same wavelength near 225.6 nm. This similarity clearly indicates that oxygen atom production and subsequent excitation is an important step in the efficient ca. 0.5 mJ laser ignition of H2O2 flows in this wavelength region. In addition, the dependence of the incident laser energy on the equivalence ratio reveals that the most efficient ignition occurs far into the fuel-lean region. This behavior further underscores the importance of the interaction between the uv laser and the oxidizer O2 component in the ignition of this reactive mixture.
- Radiation and Nuclear Chemistry
- Combustion and Ignition