Abstract

Hydrodynamic interactions between an evaporating fuel spray and a turbulent reacting flowfield pose a considerable challenge for combustion modelers and experimentalists. Simultaneous imaging of critical species concentrations provides an opportunity for more detailed observation of these interactions than was previously possible. We report here on our work to obtain simultaneous images of reactive intermediates (OH or CH), based on planar laser-induced fluorescence, and fuel vapor, based on planar multiphoton dissociation. Earlier work¹ with single species imaging suggested that CH and OH images served to mark the instantaneous reaction zone and postcombustion zones, respectively, in a turbulent heptane-air spray flame. Photodissociation of C₂H₂ (a dominant pyrolysis product of the evaporating droplets) and imaging of the resultant CH fragment fluorescence enables tracking of the distribution of precombustion zones in the flow field. Using a tunable dye laser (Quanta Ray DCR-1 Nd:YAG pumped PDL) and an ArF excimer laser (Lambda Physik EMG 203 MSC), simultaneous images of pairs of these species distributions have been obtained. The laser radiation is formed into a thin sheet and focused into the flame. The resulting fluorescence is imaged onto an intensified photodiode array. The signal on the array is digitized and stored on an LSI 11/23 computer for processing and display. Near shot-noise-limited performance is often obtained, and molecular species detection limits are typically of the order of 10 ppm. In addition, we hope to infer droplet size fields from images of the Mie scattered light from a spectrally broad illumination source.

© 1986 Optical Society of America