This paper presents an experimental study of the influence of heat losses on the onset of thermoacoustic instabilities in flames propagating in a horizontal tube of diameter, D = 10 mm. Flames are ignited at the open end of the tube and propagate towards the closed end undergoing strong oscillations of different features owing to the interaction with acoustic waves. The frequency of oscillation and its axial location are controlled through the tube length L and the intensity of heat losses. In addition to the experimental measurements, a quasi-one-dimensional analysis of the burnt gases is provided, which introduces the effect of heat losses at the wall of the tube on the interplay between the acoustic field and the reaction sheet. As a result, this analysis provides an improved description of the interaction and accurately predicts the excited flame-oscillation harmonics through the eigenvalues of the non-adiabatic acoustics model.  This confirms the importance of heat losses in the modulation of the instabilities and the transition between different flame oscillation regimes.  

Title: Non-adiabatic modulation of premixed-flame thermoacoustic frequencies in slender tubes
Authors: E Flores-Montoya, V Muntean, M Sánchez-Sanz, D Martínez-Ruiz
Journal: Journal of Fluid Mechanics 933
Publication date: January 2022.
You can read an excerpt here