Entropy and flame transfer function analysis of a hydrogen-fueled diffusion flame in a longitudinal combustor

Abstract

In this work, entropy generation and flame transfer function investigations are conducted on a hydrogenburnt diffusion flame in a longitudinal combustor with acoustic waves present. For this, a time-domain 2D numerical model of a jet diffusion flame is developed to gain insights on its dynamic response to acoustic disturbances at either resonant or non-resonant frequencies. The model is validated first by comparing the numerical results such as turbulence intensities, pressure and velocity mode shape and flame shapes with the experimental data available in the literature. The model is then applied to evaluate the effects of the frequencies and amplitudes of the forcing acoustic waves, and the flame-holder/nozzle axial positions on entropy generation of both hydrogen-and propane-fueled flames. It is found that the entropy generation rate is sensitive to acoustic forcing frequencies, amplitudes and the nozzle axial positons. Furthermore, entropy produced from the heat conduction and the chemical reaction processes is shown to be dominant and secondary respectively. However, the mass diffusion is found to play a negligible role on entropy generation. As the acoustic forcing frequency is set to 385 Hz near resonance, the total entropy generation rates are minimized, and the mass diffusion contribution is maximized with the flame being placed at velocity node locations in comparison with other flame-holding locations. Finally, flame transfer function (FTF) analysis is performed by using two different methods. It is shown that the flame responds strongly to low-frequency acoustic disturbances, acting like a band-pass filter. Increasing the acoustic intensity leads to the flame being more sensitive to the acoustic disturbances over more frequency bands.

Linear and nonlinear entropy-wave response of technically-premixed jet-flames-array and swirled flame to acoustic forcing

“…Studies that focus on the conversion of entropy waves to entropy noise [12][13][14] usually rely on synthetically generated temperature waves, using, for instance, electric heaters. Recently, several numerical and exper- imental studies dealing with the production of entropy waves, were conducted [15][16][17][18][19][20]. However, there is still a compelling need for further experimental data, especially with turbulent technically premixed flames under technical premixing of fuel and air, for which temperature fluctuation measurements are very challenging.…”

Characterization of Nonlinear Responses of Non-Premixed Flames to Low-Frequency Acoustic Excitations

“…The flame pinch-off was observed with strong low-frequency perturbations and the flame exhibited a low-pass filter characteristic. The dynamics of the jet diffusion flame in a standing wave were studied [32][33][34][35][36]. The low-pass characteristic of the response of the jet diffusion flame was also observed in this geometry.…”

Multi-physics coupling in thermoacoustic devices: A review

“…In 1896, Rayleigh [1] first gave a qualitative explanation of the thermoacoustic effect: thermoacoustic oscillations are maintained when the phase between pressure oscillations and heat release is appropriate. Ra leigh s criterion still holds as the basic principle of self-excited thermoacoustic oscillations in engine and combustion systems [34][35][36]. In the 1970s, Rott conducted a series of pioneering works on the stability limit of thermally-induced acoustic oscillations by quantifying the energy flows within the boundary layers [37][38][39][40][41][42].…”