Effects of fuel droplet size distribution on soot formation in spray flames formed in a laminar counterflow

The effects of fuel droplet size distribution of the fuel spray on the soot formation of spray flames, which is stabilized in a laminar counterflow field, were investigated numerically and experimentally. To investigate the effects of droplet size distribution of fuel spray on soot formation, fuel sprays with quasi-mono-dispersed droplet size distribution (QM-DSD) spray and poly-dispersed droplet size distribution (P-DSD) spray were generated using a frequency-tunable vibratory orifice atomizer. The differences in the spray flame structures and soot formation characteristics between QM-DSD and P-DSD were examined in detail using an experiment with two-dimensional laser induced incandescence of soot and using three-dimensional direct numerical simulations (3D-DNS) employing a CIP method. Results showed that the soot formation area in the cases of P-DSD decreased compared to the cases of the QM-DSD under the same Sauter mean diameter (SMD) condition. This tendency was caused by differences of the flame structures. The results of the fuel and oxygen concentration and temperature obtained from the 3D-DNS indicated that the portion of the premixed-like flame structure increased in the case of P-DSD. As a result, the combustion reaction region of the spray flames is enlarged in axis direction in the case of P-DSD in the counterflow field. (C) 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.