Experimental Investigation of Combustion Dynamics in a High-Pressure Liquid-Fueled Swirl Combustor

In this paper, we present combustor acoustics in a high-pressure liquid-fueled Rich burn - Quick quench - Lean burn (RQL) styled swirl combustor with two separate fuel circuits. The fuel circuits are the primary fuel (which has a pressure atomizer nozzle) and secondary fuel (which has an air blast type nozzle) circuits. The data were acquired during two dynamical regimes — combustion noise, where there is an absence of large amplitude oscillations during the unsteady combustion process, and intermittency, where there are intermittent bursts of high amplitude oscillations that appear in a near-random fashion amidst regions of aperiodic low amplitude fluctuations. This dynamic transition from combustion noise to combustion intermittency is investigated experimentally by systematically varying the fuel equivalence ratio and primary-secondary fuel splits. Typical measures such as the amplitude of oscillations cannot serve as a measure of change in the dynamics from combustion noise to intermittency due to the highly turbulent nature. Hence, recurrence plots and complex networks are used to understand the differences in the combustor acoustics and velocity data during the two different regimes. We observe that the combustor transitions from stable operation to intermittency when the equivalence ratio is increased for a given primary fuel flow rate and conversely, when the percentage secondary fuel flow rate is increased for a given equivalence ratio. The contribution of this work is to demonstrate methodologies to detect combustion instability boundaries when approaching them from the stable side in highly turbulent, noisy combustors.