Against the backdrop of a low-carbon economy, the control of soot emissions from combustion processes is of paramount importance. In this study, the effects of CO2 dilution on soot formation in ethylene laminar diffusion flames are investigated through a combination of experimental measurements and numerical simulations. In addition, a virtual species, denoted as FxCO2, is introduced to progressively decouple the individual mechanisms by which different effects suppress soot formation. The results indicate that increasing the CO2/N2 dilution ratio leads to reductions in both the peak flame temperature and the soot volume fraction, with CO2 exhibiting a more pronounced inhibitory effect than N2. The decoupling analysis reveals that the dilution effect and the chemical effect are the dominant contributors to flame temperature reduction. The soot-inhibiting effectiveness of the individual effects follows the order: dilution effect > thermal effect > chemical effect > density effect > transport effect. With respect to their influence on C2H2 concentration, the effects are ranked as: dilution effect > chemical effect > transport effect > thermal effect > density effect. The chemical effect suppresses the formation of OH radicals, thereby reducing the flame temperature and H radical concentration. In contrast, the dilution effect enhances soot oxidation by increasing the OH radical concentration, effectively inhibiting soot particle formation.
Liu et al. (Tue,) studied this question.