Flamelet modeling of lifted turbulent methane/air and propane/air jet diffusion flames

Abstract

The stabilization mechanism of lifted turbulent jet diffusion flames is a test problem for models of partially premixed turbulent combustion. In these flames, combustion processes occur in both the nonpremixed and the premixed mode. For the flame stabilization process, however, flame propagation of the premixed branches seems to play a crucial role. In this paper, a flamelet model for partially premixed turbulent combustion is presented that combines flamelet models for non-premixed and premixed combustion. A new model for the turbulent burning velocity in partially premixed flows is proposed. It is based on a formulation for a conditional turbulent burning velocity which depends on mixture fraction. The effect of partially premixing is taken into account by using the presumed probability density function (pdf) approach in terms of the mixture fraction. Mean scalar quantities on both sides of the premixed flame front are calculated in the same way. From a computational point of view, the model has the advantage that the calculation of the chemical processes can be decoupled from the flow calculation, allowing for simulations of realistic configurations, yet retaining detailed chemistry. The model is used to simulate the stabilization process of turbulent methane/air and propane/air jet diffusion flames. The calculated lift-off heights compare favorably with experimental data from various authors.

Large eddy simulation of spark ignition in a turbulent methane jet

“…Few numerical studies address the problem of ignition of turbulent diffusion flames in complex configurations. Such simulations require treatment of both premixed and non-premixed combustion modes [27][28][29][30]. Richardson [31] and Richardson and Mastorakos [32] have discussed ignition of turbulent diffusion flames using a Reynolds Averaged Navier-Stokes (RANS) -Conditional Moment Closure (CMC) modeling: results suggest that the first order CMC reaction rate closure seems inadequate for such configurations.…”

Benchmarking of Improved DPAC Transient Deflagration Analysis Code

“…The burning velocity prior to the expansion of the burned gas is estimated by combining an analysis conducted by Chen et al [8], which gives the turbulent burning velocity as a function of the turbulence strength for the flame, with an estimate of the turbulence strength at the flame front. The Chen et al correlation is an asymptotic combination of a turbulent diffusion model, originally proposed by Damköhler [9], and a limiting value for the turbulent flame speed obtained from experiments.…”

Level‐set based flamelet approach for simulating turbulent lifted jet flame

“…Thus, a formulation for both premixed and nonpremixed combustion has to be used. In order to properly account for the turbulence-chemistry interaction in the partially premixed turbulent lifted jet flames, the present study has adopted the level-set-based flamelet approach suggested by Chen et al [12]. In this approach, the flamelet model of non-premixed combustion is combined with the level-set approach for premixed combustion.…”

“…The mixing of fuel and oxidizer in the turbulent flow field is described by transport equation of mean mixture fraction and its variance [5]. For the convenience of presentation, the important part of the level-set-based flamelet formulations proposed by Chen et al [12] is described here.…”

“…The mean turbulent burning velocity [12] of a partially premixed flame can be formulated by employing the presumed PDF approach…”