Control of flames by tangential jet actuators in oxy-fuel burners

The active control of oxy-fuel flames from burners with separated jets is investigated. The control system consists of four small jet actuators, placed tangential to the exit of the main jets to generate a swirling flow. These actuators are able to modify the flow structure and to act on mixing between the reactants and consequently on the flame behavior. The burner (25 kW) is composed of separated jets, one jet of natural gas and one or two jets of pure oxygen. Experiments are conducted with three burner configurations, according to the number of jets, the jet exit velocities, and the separation distance between the jets. OH chemiluminescence measurements, particle image velocimetry, and measurements of NOx emissions are used to characterize the flow and the flame structure. Results show that the small jet actuators have a significant influence on the behavior of jets and the flame characteristics, particularly in the stabilization zone. It is shown that the control leads to a decrease in lift-off heights and to better stability of the flame. The use of jet actuators induces high jet spreading and an increase in turbulence intensity, which improves the mixing between the reactants and the surrounding fluid. Pollutant measurements show important results in terms of NOx reductions (up to 60%), in particular for low swirl intensity. The burner parameters, such as the number of jets and the spacing between the jets, also impact the flame behavior and NOx formation.