Planar laser-induced fluorescence imaging of shock-induced ignition

Abstract

Planar laser-induced fluorescence (PLIF) imaging has been developed for use in studies of shock-induced ignition. PLIF measurements of OH have been made in stoichiometric mixtures of H2 and O2 diluted in 90% Ar using two shock tube endwall configurations. These OH images, which serve as indicators of ignition, were first obtained in the weak and strong ignition limits in the gas behind a shock reflected from a planar endwall. In both limits the images exhibited planar combustion waves. The absence of observable ignition kernels in the weak ignition limit presumably results from lack of optical access to the corners of the shock tube where kernel formation is expected to occur. A grooved endwall was used to introduce thermal nonuniformities and thereby promote isolated regions of ignition within the imaged region. Sequences of PLIF images defining the temporal evolution of the ignition process were acquired in the weak and strong ignition limits for this endwall configuration. These images exhibit highly nonuniform structure and serve to illustrate the utility of 2-D imaging techniques for ignition studies.