Combustion characteristics in a three-dimensional gas-fired combustion chamber with radiation effect

Abstract

The finite-volume method for radiative heat transfer is extended to general three-dimensional coordinates and applied to solve a pure radiative transfer problem of three-dimensional kidney-shaped combustion chamber of which shape is curvilinear after validating present formulation by comparison with published results in various enclosures. To capture anisotropic scattering, the scattering phase function is approximated by a finite series of Legendre polynomials. The geometric relations, which transform the Cartesian coordinate into a general body-fitted coordinate, can be obtained in the same way as in the field of computational fluid dynamics. Thereby, the directional weights analogous to the multiplication of direction cosine by quadrature weights in the conventional discrete-ordinates method are calculated analytically. The finite-volume method has also been used to analyze the radiative heat transfer in axisymmetric and nonaxisymmetric three-dimensional cylindrical enclosures containing a radiatively participating media. The intrinsic difficulty in computing the angular derivative term in the conventional discrete-ordinates method does not arise, since the unit direction vectors are based on the Cartesian base vectors. For the problem of axisymmetric radiation, a mapping which transforms the dependence of intensity on two-spatial and two-angular variables to three-spatial and one-angular variables is adopted. For nonaxisymmetric computations, the treatment of control angle overlaps at the boundary is studied. A modified discrete-ordinates method has been proposed to solve the radiative transfer equation in the axisymmetric cylindrical combustor with an absorbing, emitting and scattering medium. Different from the conventional discrete-ordinates method, the main feature of this method includes a flexibility in specifying control angles like in the finite-volume method, while keeping the same simplicity in the solution procedure as in the conventional discret...