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Abstract
This paper presents the formulation and results of numerical simulation of autoignition in gaseous, nonpremixed, turbulent flows. Two specific problems are considered, (a) a homogeneous, isotropic turbulence with chemical reactions and mixing, and (b) an axisymmetric, fuel jet released into an oxidiser environment. For the first problem the fluid mechanics and combustion are decoupled, while the second problem fully incorporates such a coupling. A hybrid computational approach is adopted wherein the governing mean flow and the κ — ϵ equations are solved through a finite-volume, predictor-corrector, pressure implicit code TURBO-2D and the joint scalar pdf-transport equation (pdf= probability density function) is simulated via a Monte Carlo technique. The flow code and the pdf code togelher run in tandem with each other. The fluid dynamics code supplies the mean flow and turbulence quantities to the pdf code. The pdf code, in turn, provides the mean mass density via the mean thermochemical scalars to the fluid dynamics code.
For the homogeneous, isotropic turbulence, computations made over a wide range of Damköhler number reveal at least four different regimes of turbulent autoignition. The results are represented in terms of a regime diagram. For the axisymmetric jet, the computations capture the basic features of autoignition and predict ignition-delay times and flame dimensions. Qualitative comparison of predicted results with experimental data are encouraging. However, a quantitative comparison of mean and fluctuating quantities is an essential future step. The reported work is expected to provide insight into the understanding of chemistry-turbulence interaction during the process of autoignition in nonpremixed combustion
