Effect of injection location on the effectiveness of an active control system using secondary fuel injection

The effect of secondary fuel injection location on the effectiveness of active combustion control was studied in an atmospheric pressure, laboratory-scale dump combustor operating on natural gas with a nominal heat release rate of 75 kW The combustor provided For secondary fuel injection from three different locations. The effectiveness of both open- and closed-loop control was found to be strongly dependent on the secondary fuel injection location. To understand this behavior, CO2 chemiluminescence imaging measurements were made of the spatial and temporal heat release distribution in the combustor, both to characterize the evolution of the heat release distribution during unstable combustion and to characterize the heat release produced by the injection of secondary fuel. The results indicate that the most effective approach to preventing unstable combustion is not necessarily to add heat in a manner which is out of phase with the instability but that effective control tan also be achieved by disrupting the mechanism that is driving the instability These results serve to illustrate that gaining an understanding of the phenomenology of the instability is a critical step in designing and optimizing an active combustion control system.