Nonlinear Dynamics Of A Laminar V-Flame In A Combustor

This study investigates a laboratory-scale combustor consisting of a tube (a quarter-wavelength resonator with an open end at the top, and a closed end at the bottom) with a laminar V-flame inside it. The parameter of interest is the axial position of the flame relative to the tube. This position was varied in a step-by-step manner by moving the flame in small steps from the top end towards the bottom end of the tube. In each step, the pressure-time history was recorded and its frequency content was analysed. Nonlinear time series analysis was performed on the recorded pressure-time history to identify the dynamic states. As the flame got lowered, a range of dynamic states were observed. These include limit cycles at low and high amplitudes, but also highly irregular oscillations. The instability frequencies showed a continuously decreasing trend, as well. A set of thermal imaging with a large wavelength infra-red camera, was performed to understand the reason of this behaviour. Finally, the flame was filmed with a high-speed camera, and the images were used to explain the oscillation pattern during the limit cycle.