Computation of the Aerothermodynamic Field of Laminar Diffusion Flames

Abstract

This paper describes a theoretical and experimental investigation of laminar diffusion flames leading to their structural characterization. A theoretical model is developed from experimental correlations of major species concentrations and temperature against suitably defined conserved species, otherwise called mixture fraction, using the Shvab Zeldovich similarity principle. These correlations yield a set of similarity equations of stoichiometry which express implicit functional dependence of species concentrations and temperature on mixture fraction. The momentum conservation equation is then solved simultaneously with the conserved species equation to establish the aerothermodynamic field of the flame. In the form defined, the mixture fraction is measured, having well-defined initial and boundary conditions, and allows examination and identification of regions of the flame characterizing either diffusive flow or combined diffusive and chemically reactive flow. Furthermore, it is found experimentally that at a fixed value of mixture fraction Z = 0.059, corresponding to a methane/air equivalence ratio of 1.08, the local temperature maxima occur in the neighbourhood of the visible luminous flame boundary. This observation is used to check the accuracy of calculations of the physical dimensions of the flame. Good comparison is obtained between computed and measured values and distribution of the major species concentrations, temperature and velocities. The model allows investigation of the chemical kinetic structure through its effectiveness in the computation of reaction rates.