Quantitative 2D single-shot imaging of NO concentrations and temperatures in a transparent SI engine
NO formation in a transparent spark-ignition engine was exptl. studied using a combination of planar laser-induced fluorescence and Rayleigh scattering. Simultaneous images were obtained after excitation with a single pulse from a tunable KrF excimer laser. Tuning the laser to 247.9 nm allows excitation of the NO A-X (0,2) band, and subsequent fluorescence emission is spectrally well sepd. to image Rayleigh scattering from the same laser pulse. The advantages of using the (0,2) band to excite NO under engine conditions are demonstrated, and quant. distributions of NO concns. are shown along with temp. fields calcd. from the Rayleigh images. Various engine operation conditions were examd. using propane and iso-octane fuels. Cycle-resolved measurements showed strong cycle-to-cycle variations of NO formation with peaks in spatial NO distribution, whereas the temp. field was nearly homogeneous, leading to the conclusion that small variations in temp. distributions lead to peak NO concns. via the Zeldovich mechanism.
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