Investigation of Two-Phase Flowfield in Actively Controlled Dump Combustor

Active combustion control experiments were performed in a 53 kW combustor using a secondary pulsed fuel injection that was closed-loop controlled using an adaptive technique. Up to 16% of total fuel was supplied through the controller, which led to 13 dB suppression in instability amplitude compared to the uncontrolled case under identical flow conditions. Particle image velocimetry (PIV) was applied to visualize the fuel droplet dispersion into reacting flow field, and Malvern droplet analyzer was used to characterize the initial size distribution of fuel droplets generated by the actuators. For controlled fuel sprays, the average Sauter-mean diameter was measured to be 59 μm and the initial droplet velocity was up to 6.5 m/sec. Inside the combustor, burning fuel droplets interacted with the carrier Flowfield, reaching axial speed of up to 15 m/sec. Phase-locked characterization of the pulsed sprays revealed that the fuel droplet distribution and the Sauter-mean diameter oscillated at the frequency of fuel actuation. The amount of oscillation was significant as the Sauter-mean diameter varied between 38 μm to 73 μm. Characterization of pulsed fuel sprays and complete evolution of droplet size on oscillation phase are reported in this paper as a function of various operating conditions. It is postulated that such cyclic change in droplet diameter, more than the fuel mass modulation, was mainly responsible for achieving effective combustion control.