Study of burner geometry effects on non-premixed flame response under acoustic excitation

Abstract

The study of the flame under the acoustic excitation contributes to the study of flame self-excited thermoacoustic instability. Although non-premixed combustion is widely used in industry, research on its combustion instability characteristics is relatively few. This paper experimentally studies the response of a non-premixed swirl flame under excitation. The geometry modifications are the length of the inlet section which is set to be 0.245 m, 0.345 m and 0.445 m and the installation of separation plates. Through the analysis of flame response behavior at different excitation frequencies, combined with the calculation of acoustic mode, we find that for the 0.245 m and 0.345 m inlet length cases, the maximum flame heat release fluctuation responds near 144 Hz. This mode is due to the resonance of the fuel pipe. For the 0.445 m inlet length cases, the maximum flame heat release responds near 134 Hz. This mode is a mixed mode of fuel pipe and combustion chamber. The maximum flame response occurs at the point where the pressure fluctuation reaches the maximum in the inlet section. The image analysis shows the same mode distinction trend between short and long inlet length. Besides, the removing of separation plates leads to a more stable response of the flame in low inlet airflow rate. However, at high airflow rate, the flame tends to be more unstable. Moreover, the higher acoustic forcing frequency than quarter-wave mode will cause the quarter-wave resonant frequency to appear. The results of our work can benefit the implications of thermoacoustic instability in non-premixed flame.

A review on combustion instabilities in energy generating devices utilizing oxyfuel combustion

“…Balasubramanian and Sujith 24 studied the combined effect of non-normality and nonlinearity in combustion systems in triggering thermoacoustic instability mode in non-premixed flames. The effect of burner geometry on thermoacoustic instability under different excitation frequencies has been studied by Zhou et al 105 Baraiya and Chakravarthy 106 studied thermoacoustic instability in three syngas compositions together with H 2 T A B L E 1 Summary of some selected literature on static stability of oxyfuel flames…”

“…Balasubramanian and Sujith 24 studied the combined effect of non‐normality and nonlinearity in combustion systems in triggering thermoacoustic instability mode in non‐premixed flames. The effect of burner geometry on thermoacoustic instability under different excitation frequencies has been studied by Zhou et al 105 Baraiya and Chakravarthy 106 studied thermoacoustic instability in three syngas compositions together with H 2 and H 2 /CH 4 mixtures in a non‐premixed combustor and reported different frequencies of instability with different mixtures and Reynolds numbers. Magri et al 107 showed that in regions of large heat release, hydrodynamics greatly impact the overall thermoacoustic stability.…”

Nonlinear Dynamics of Cross‐Flow Tubes Subjected to Initial Axial Load and Distributed Impacting Constraints

“…e aforementioned investigations related to tube arrays subjected to cross flow have focused on only one or several loose supports on the tube. In heat exchangers, the tubes are multispanned and threaded through the baffle plates through holes [11,27,[32][33][34]. e gap between the tube and the hole could be modeled as loose supports to permit thermal expansion.…”

Thermoacoustic combustion instability of propane‐oxy‐combustion with CO2dilution: Experimental analysis

“…26 The physical mechanism involved in this interaction includes periodic deformation of the vortexes at a certain frequency, vortexes shedding, and instabilities due to precessing vortex core (PVC). The effect of burner geometry on thermoacoustic instability under different excitation frequencies is studied by Zhou et al, 38 where the flame response and heat release fluctuations were reported for each configuration. They found that the shift from the natural acoustics to the vortex shedding modes corresponds to increase in flow velocity.…”

“…Another study by Idahosa et al 37 looked into the response of nonpremixed, swirl-stabilized flames to forced acoustic perturbations and formulated a flame response index analogous to Rayleigh index. The effect of burner geometry on thermoacoustic instability under different excitation frequencies is studied by Zhou et al, 38 where the flame response and heat release fluctuations were reported for each configuration. Three syngas compositions together with hydrogen and hydrogen-methane mixtures were studied in terms of thermoacoustic instability in a non-premixed combustor by Baraiya and Chakravarthy.…”