The blow-off behaviour of swirling lean methane premixed and heptane spray flames has been examined. The measurements include blow-off limits, visualisation of the blow-off transient with 5 kHz OH~* chemiluminescence, and the quantification of the average duration of the blow-off transient. It was found that correlations based on a Damkohler number collapse the blow-off velocity data for both premixed and spray flames with reasonable accuracy. The blow-off transient for the premixed flames is dependent on the burner geometry and swirl intensity, where progressive disintegration of the reaction zone can occur for a lifted flame, or for an attached flame not at the anchoring region but further downstream. For the spray flames, the last remaining flame fragment tends to lie close to the spray injection cone. It was also found that the average duration of the blow-off event, Text, is strongly dependent on the blow-off behaviour. When normalised with the characteristic flow time d/U_b, values for the methane premixed and heptane spray flames in the same burner configuration are in the range 9-38 and increase with flame power. By changing the burner configuration and swirl intensity, values of T_(ext)/(d/U_b) for methane premixed flames increased to ≈99. The results can help the development of advanced turbulent combustion models.
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