Identification and imaging of OH (ν″ = 0) and O_2 (ν″ = 6 or 7) in an automobile spark-ignition engine using a tunable KrF excimer laser

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Abstract
Planar laser-induced predissociative fluorescence is applied to image state-specific densities of OH and hot O2 inside an internal-combustion car engine. Improved instrumentation is described. It includes better imaging optics and a spectrometer that permits desired molecular quantum states to be selected and identified in real time. The OH (ν″ = 0) images are cleanly separated from the isooctane fuel and they display a thin superequilibrium region at the flame front. In contrast, vibrationally excited O2 (ν″ = 6 or ν″ = 7) is uniformly distributed behind the front. Uneven and broken flame fronts are commonly observed.