Synchronisation behaviour between two candle flame oscillators with similar and dissimilar amplitudes of oscillations

Interactions between a couple of flames often lead to their synchronisation. Flame–flame interaction has recently been linked with thermoacoustic instability in combustors. However, synchronisation caused by the interaction of coupled flames is still not fully understood. Furthermore, the interacting flame oscillators in practical situations often have a slight dissimilarity between them. Here, we systematically study the effects of such dissimilarity on the flame–flame interaction with a simple system consisting of two candle flame oscillators (CFO). The interaction is studied with CFOs having similar and dissimilar amplitudes of oscillations. The distance between the CFOs is parametrically varied. The results indicate that the synchronisation phenomena caused by flame–flame interaction have a complex dependence on the distance between the oscillators. Further, we find the flame–flame interaction to be significantly affected by the dissimilarity of the interacting oscillators. In-phase (IP) synchronisation occurs when the interacting oscillators are separated by a low distance and the oscillators have similar or moderately dissimilar amplitudes of oscillations. On the other hand, for large disparities in the amplitudes of oscillations, lag synchronisation (LS) is observed at a low distance between the CFOs. If the interacting oscillators have similar amplitudes of oscillations, the amplitude death (AD) regime persists throughout the operating range except at a low distance between the CFOs. In contrast, if the interacting oscillators have dissimilar amplitudes of oscillations, different rich dynamical states such as lag synchronisation and partial amplitude death are encountered in addition to amplitude death as the distance between the oscillators is varied. This study might be useful to understand synchronisation due to flame–flame interaction in modern multi-burner turbulent combustors where the constituent burners often have inherent dissimilarities.