Investigation of soot formation in n-dodecane spray flames using LES and a discrete sectional method

Considering stricter regulations on soot emissions, the detailed soot modeling approaches facilitating prediction of soot particle size distributions (PSD) are increasingly in demand. In this context, the transient evolution of soot is numerically investigated for two high-pressure turbulent sprays from the Engine Combustion Network (ECN), namely, Spray C (SC) and Spray D (SD). The 900-K ambient temperature (Tam) sprays are studied. This is because the two cases tend to produce a similar amount of soot at Tam=900K, despite the significantly different spray development. To predict the soot formation with information on PSD, a discrete sectional method is applied within the large-eddy simulation (LES) framework. The applied modeling strategy favorably captures the experimentally observed similar soot mass for SC and SD in the characteristic field-of-view (FOV) frustum. Moreover, the transient dynamics of soot within the FOV frustum is well captured, and the onset of soot is well predicted. It is observed that for SC and SD, soot formation is more prominent in fuel-rich (2<π<4) and high-temperature (T>1500K) regions. Despite the stronger fuel dilution in the downstream area of the spray, soot is predominantly present in the head of the spray during the whole combustion progress, corresponding to larger particle sizes and higher soot number density. Although the spray development of SC and SD are different, the FOV approach bridges the two cases. The unique correlation between soot mass and FOV volume recognized in experiments was found to hold for the complete quasi-steady sooting region. Moreover, PSD analysis suggests very similar soot size and number density with respect to the FOV volume. This is attributed to the similar LOL for SC and SD in the normalized coordinates, and the same FOV volume corresponding to similar locations in the normalized coordinates.