Diffusion flame

About: Diffusion flame is a research topic. Over the lifetime, 9266 publications have been published within this topic receiving 233522 citations.

Flamelet models of turbulent non-premixed combustion

Abstract: A flamelet model for thermodynamic state in turbulent non-premixed flames is described in which the microscopic element in the turbulent ensemble has the structure of an undisturbed laminar diffusion flame. The profiles of scalar properties through this flame uniquely define instantaneous mixture state and hence provide an alternative thermochemical relationship to that of chemical equilibrium, commonly employed in flowfield calculations. The need for a flowfield model is avoided by using published measurements of mean temperature and RMS temperature fluctuation in a turbulent flame to determine the necessary mixture fraction statistics, so that the instantaneous laminar flamelet composition profiles can be appropriately averaged.Comparison is made between species prediction using the alternative thermochemical assumptions, and experiments as reported in the literature. Substantial improvements in prediction are achieved in the fuel-rich regions of an open turbulent flame, notably in the sensitiv...

Non-normality and nonlinearity in combustion-acoustic interaction in diffusion flames

Abstract: The role of non-normality and nonlinearity in flame–acoustic interaction in a ducted diffusion flame is investigated in this paper. The infinite rate chemistry model is employed to study unsteady diffusion flames in a Burke–Schumann type geometry. It has been observed that even in this simplified case, the combustion response to perturbations of velocity is non-normal and nonlinear. This flame model is then coupled with a linear model of the duct acoustic field to study the temporal evolution of acoustic perturbations. The one-dimensional acoustic field is simulated in the time domain using the Galerkin technique, treating the fluctuating heat release from the combustion zone as a compact acoustic source. It is shown that the coupled combustion–acoustic system is non-normal and nonlinear. Further, calculations showed the occurrence of triggering; i.e. the thermoacoustic oscillations decay for some initial conditions whereas they grow for some other initial conditions. It is shown that triggering occurs because of the combined effect of non-normality and nonlinearity. For such a non-normal system, resonance or ‘pseudoresonance’ may occur at frequencies far from its natural frequencies. Non-normal systems can be studied using pseudospectra, as eigenvalues alone are not sufficient to predict the behaviour of the system. Further, both necessary and sufficient conditions for the stability of a thermoacoustic system are presented in this paper.

A flat flame burner as calibration source for combustion research: Temperatures and species concentrations of premixed H2/air flames

Abstract: A commercially available flat flame burner with a sintered porous bronze disk was used to stabilize premixed H2/air flames at atmospheric pressure. Temperatures for various stoichiometries, flow rates, and heights above the burner disk have been measured by coherent anti‐Stokes Raman scattering with an accuracy of ≊2.5%. The corresponding exhaust gas compositions have been derived from equilibrium calculations. This burner together with the data presented in this article can be used for the verification or calibration of a variety of measuring techniques in combustion research.