Characterization of evaporating diesel sprays using exciplex laser-induced fluorescence measurements

摘要

Evaporating diesel sprays were investigated in a combustion-type spray chamber using the exciplex laser-induced fluorescence method at a density of 15 kg/m~3 and ambient temperatures of 800 and 1000 K.The vapor-phase exciplex fluorescence measurements were calibrated,but the liquid-phase measurements were used only to identify the liquid extent.The effects of peak injection pressure (60,90,and 150 MPa) and nozzle hole size (140,158,and200 mum) were studied.The spray penetration rate was found to be in good agreement with the Naber-Siebers model for all of the cases tested.The entrained air mass ascertained from the vapor-phase measurements was also found to agree with the model results.Radial profiles of the equivalence ratio showed significant shot-to-shot variability,but exhibited a Gaussian structure when averaged at a given downstream position and time.An overall mean equivalence ratio was obtained by normalizing the measured equivalence ratio by the cross-sectional average equivalence ratio of Naber and Siebers,and by normalizing the radial coordinate by the downstream distance.The resulting profile was Gaussian (1.2 at the peak with a 0.2 full-width half-maximum),but a progressive trend was observed with respect to the nondimensional downstream distance.This effect resulted from a slower observed decrease in the centerline equivalence ratio of the measurements compared to the model.