The role of soot aggregate fusing in laminar flames: A study employing fusing models derived from carbon black

Abstract

The evolving morphology of carbonaceous aggregates has been previously ignored to a large extent in sooting flame studies. Soot aggregate fusing causes a reduction in surface area and the number of primary particles per aggregate. Despite soot aggregate fusing directly impacting the morphology of aggregates, there is no agreed model for the characteristic timescale for this process. Previous flame simulations used fusing timescale models based on other materials such as titania and silica, which feature different fusing mechanisms. Recently, a series of carbonaceous-based soot fusing models have been proposed that are intrinsically derived from carbonaceous materials such as carbon black or lab-produced ethylene soot. In the present work, these carbonaceous-material-based soot fusing models are implemented in a two population balance equation (PBE) framework and are further coupled with a reactive computational fluid dynamics (CFD) code in order to simulate the laminar Santoro series of flames across all three smoking conditions (non-smoking, incipient smoking, smoking). Predictions of soot volume fraction, total number density, number of primary particles per aggregate, and primary particle diameter are presented across all three flames and compared against experimental observations where possible. The importance of soot fusing is elucidated across various regions within flames and the predictive power of each fusing model is discussed.