Nitrogen oxides (NOx) emission control in a liquid fuel diffusion flame using acoustic excitation.

Nitrogen oxides (NOx) emission control will be a major issue in the upcoming years in the development of domestic boilers as well as automotive or aircraft engines. Pulsed combustion offers an alternative, low-energy solution. In this paper, we demonstrate the efficiency of this pollutant reduction technique when applied to a 20 kW boiler burning domestic fuel oil. An actuator is located on the air duct. Two kinds of actuators have been successfully tested: a loudspeaker and a rotary valve. Both produce frequencies ranging from 100 Hz to 1000 Hz. Nitrogen oxide emissions can be reduced up to 20%, The feasibility of this concept has been proven on a larger-scale device (840 kW, operating with liquid fuel). The mechanisms involved under excitation are examined using optical diagnostics. Results show a strong reorganization of the flow configuration and flame structure. An annular vortex is formed at each cycle at the trailing edge of the flame holder. This analysis provides guidelines for a new, more effective NOx emission control using acoustic excitation.