A review of soot formation and evolution in turbulent swirling flames

Abstract

Many practical combustion systems, such as aviation engines, stationary gas turbines, diesel engines, etc., rely on turbulent swirl flames to operate efficiently and reliably. One of the primary concerns in developing these combustion systems is the reduction of particulate matter (i.e., soot) emissions. This is due to the fact that soot emissions have adverse effects on human health and the environment. In this context, mitigating soot emissions from these combustion systems requires a comprehensive understanding of the physicochemical pathways from fuel to soot particles in turbulent, swirling flames. Moreover, fundamental studies of soot emissions in turbulent swirling flames can help elucidate the processes of soot formation and evolution in complex reacting flows. In this work, we intend to provide a comprehensive review of soot formation and evolution in turbulent swirling flames. First, the physicochemical processes involved in soot formation and evolution are introduced, including the formation of gas-phase soot precursors, soot nucleation, coagulation and condensation, surface growth, and oxidation and fragmentation. These processes are discussed in the context of the features of soot formation and evolution in turbulent swirling flames. A detailed review is then made of the experimental measurements and diagnostic methods related to soot. Through the classification of the burner configurations, a comprehensive review of the experimental progress of sooting swirl flames is given. The parameter studies, including pressure, equivalence ratio, and thermal power, among others, are summarized, resulting in a detailed overview. Subsequently, numerical simulation methodologies of sooting swirl flames are introduced, including the numerical construction of chemical kinetics, turbulent combustion, and soot models. A comprehensive review of numerical studies is made in terms of burner configurations, modeling methods, and mechanism analysis. This review concludes by summarizing the challenges faced in turbulent swirl flames and anticipating future research on soot.