Sooting Limits of Microgravity Spherical Diffusion Flames in Oxygen-Enriched Air and Diluted Fuel

Effects of C/O Ratio and Temperature on Sooting Limits of Spherical Diffusion Flames

“…1,2,5,7,8 A similar competition can occur in diffusion flames on the fuel side owing to the presence of oxygen in species such as CO 2 and H 2 O. 4,9 Du et al 9 showed that adding CO 2 to the fuel side of diffusion flames can suppress soot formation chemically. Despite the differences between soot inception in premixed and nonpremixed flames, the C/O atom ratio has been shown to be relevant to sooting limits in diffusion flames.…”

“…[1][2][3] One fundamental measure of flame sooting behavior is sooting limits. Sooting limits of spherical microgravity diffusion flames were observed by Sunderland et al 4 The present work is an investigation into those flames with the aid of a detailed computational model.…”

“…Despite the differences between soot inception in premixed and nonpremixed flames, the C/O atom ratio has been shown to be relevant to sooting limits in diffusion flames. 4,10 Past experimental work on spherical diffusion flames in microgravity identified a critical local C/O value of 0.59 for ethylene. 4 Temperature plays a different role in premixed and nonpremixed flames: increasing temperature suppresses soot formation in premixed flames, whereas it enhances soot formation in nonpremixed flames.…”

“…4,10 Past experimental work on spherical diffusion flames in microgravity identified a critical local C/O value of 0.59 for ethylene. 4 Temperature plays a different role in premixed and nonpremixed flames: increasing temperature suppresses soot formation in premixed flames, whereas it enhances soot formation in nonpremixed flames. 2,8 Previous research on diffusion flames has identified an onset temperature at which soot particles are first observed to be in the range of 1250 -1650 K. 2,[11][12][13][14] In addition to C/O ratio and temperature, residence time (or scalar dissipation rate) is the third parameter critical to soot inception limits.…”

“…The flames under consideration are the 17 microgravity flames of Ref. 4, having both normal and inverse convection directions and disparate stoichiometric mixture fraction, adiabatic temperature, and residence time. The model used here is a one-dimensional, time accurate diffusion flame code with detailed chemistry and transport and an optically thick radiation model.…”