Numerical study of characteristics of liquefied petroleum gas flames in coflow air

Liquefied Petroleum Gas (LPG) is a fossil fuel mixture, widely used in domestic and industrial burners for several applications. Non-premixed flames are commonly preferred in these burners owing to their stability and controllability. However, based on operating conditions, non-premixed flames emit emissions such as CO and soot. Several techniques, including supply of coflow air and partial premixing of air with fuel, are used to abate these emissions. Due to multicomponent nature of LPG and its complex oxidation pathway, numerical studies on LPG flames are scarce in literature. However, such studies are helpful in the analysis of flames in several burners. With this motivation, systematic numerical simulations of canonical non-premixed coflow flames of LPG and air, without and with partial premixing of air in the fuel stream, have been presented. A two-dimensional axisymmetric domain is used to represent coflow burner. The numerical model includes sub-models to account for soot formation and its oxidation, and radiation energy loss due to participating species and soot. A short kinetic mechanism with 43 species and 392 elementary reactions is used. Results from the numerical model have been validated for flames of propane, n-butane and LPG. Coflow air is varied as proportions of stoichiometric air. Partial premixing of air to the fuel stream results in a reactant mixture that is not flammable. Characteristics of flames in all these cases are presented systematically using the fields of temperature, flow and species mass fractions. A relative comparison of soot production between all these cases is made. Results reveal that in coflow flames, the net soot emissions increase initially, reach a local maximum and then decrease. In partially premixed flames, soot emissions continuously decrease with an increase in the primary air and become almost negligible after a specified air addition to the fuel stream.