Coupled radiation and soot kinetics calculations in laminar acetylene/air diffusion flames

Abstract

Radiation heat transfer from flames depends on the instantaneous soot volume fractions and temperatures. A coupled radiation and soot kinetics calculation in laminar acetylene/air and acetylenemethane/air diffusion flames is described. Transport equations for mass, momentum, gas-phase mixture fraction, enthalpy (sensible + chemical), soot mass fraction, and soot number density are solved. A simplified soot kinetics model incorporating nucleation, growth, oxidation, and agglomeration processes is used. The reaction rates in the simplified kinetics model depend on the temperature and the local concentrations of acetylene and oxygen. The major gas species concentrations are obtained from state relationships. The local temperature is obtained by solving the energy equation, taking radiation loss and gain and the energy exchanges associated with soot formation and oxidation into consideration. The radiative source/sink term in the energy equation is obtained using a multiray method. Since these flames radiate a substantial part of their energy, the kinetic rates associated with soot processes are strongly coupled to the energy equation. This strong coupling between radiation, and soot formation and oxidation processes is modeled for the first time. The results of the soot kinetics model are compared with measurements of soot volume fractions obtained using laser tomography. The agreement between measurements and predictions of soot volume fractions supports the present method. The predicted temperature profiles support the structure of strongly radiating flames discovered earlier.