Radiation characteristics and turbulence–radiation interactions in sooting turbulent jet flames

Abstract

A comprehensive modeling strategy including detailed chemistry, soot and radiation models coupled with state-of-the-art closures for turbulence–chemistry interactions and turbulence–radiation interactions is applied to various luminous turbulent jet flames. Six turbulent jet flames are simulated with Reynolds numbers varying from 6700 to 15,000, two fuel types (pure ethylene, 90% methane–10% ethylene blend) and different oxygen concentrations in the oxidizer stream (from 21% O2 to 55% O2). All simulations are carried out with a single set of physical and numerical parameters (model constants). A Lagrangian particle Monte Carlo method is used to solve a modeled joint probability density function (PDF) transport equation, which allows accurate closure for turbulence–chemistry interactions including nonlinear soot subprocesses. Radiation is calculated using a particle-based photon Monte Carlo method that is coupled with the PDF method to accurately account for both emission and absorption turbulence–radiation interactions (TRI). Line-by-line databases are used for accurate spectral radiative properties of CO2 and H2O; soot radiative properties also are modeled as nongray. For the flames that have been investigated, soot emission can be almost 45% of the total emission, even when the peak soot volume fraction is of the order of a few parts-per-million (ppm) and up to 99% of soot emission can escape the domain without re-absorption. Turbulence–radiation interactions have a strong effect on the net radiative heat loss from these sooting flames. For a given temperature, species and soot distribution, TRI increases emission from the flames by 30–60%, and the net heat loss from the flame increases by 45–90% when accounting for TRI. This is higher than the corresponding increase in radiative heat loss due to TRI in nonsooting flames. Absorption TRI was found to be negligible in these laboratory-scale sooting flames with soot levels on the order of a few ppm, but may be important in larger industrial-scale flames and in higher-pressure systems.