Abstract: R. Hernandez-Rivera, G. Troiani, T. Pagliaroli, A. Hernandez-Guerrero (2019)

This paper presents a nonlinear time-series analysis of the thermoacoustic instabilities of an experimental slot burner. The main objective was the calculation of indexes capable of detecting in advance the combustion instabilities by gradually increasing the flow Reynolds number of the pilot burner. A chaotic analysis based on diagonalwise measurements of the recurrence plots was performed on the basis of which the following indexes were calculated: the Ï„-recurrence rate index RRÏ„, the Ï„-determinism index DETÏ„, the Ï„-average diagonal line length index LÏ„, and the Ï„-entropy index sÏ„. A quantification carried out by means of the standard deviation Ïƒ and mean values Î¼ of the diagonalwise measurements showed that the aforementioned indexes were successfully able to sort all cases under analysis mainly into two groups: the first three cases that correspond to the stable regime named "Combustion Noise" and the remaining cases that were associated with the unstable regime called "Combustion Instability." Additionally, the particle image velocimetry optical method was applied in order to compute a new index based on the velocity fields. The results showed that the index Vh, based on the local heights of the velocity profiles of the central flame, was also capable of detecting the same two groups previously identified by the nonlinear analysis. Nevertheless, the most sensitive indexes were the indexes RRÏ„Î¼, DETÏ„Ïƒ, and sÏ„Ïƒ since these indexes were able to detect the transition between the combustion noise and combustion instability regimes. Therefore, the present results proved that the proposed five indexes were effective precursors in order to detect in advance the combustion instabilities.

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Detection of the thermoacoustic combustion instabilities of a slot burner based on a diagonal-wise recurrence quantification