Effects of velocity and fuel concentration oscillations on premixed flames

Abstract

Effects of velocity and fuel concentration oscillations on premixed flames are discussed. Methane/air premixed flame is formed in a wall stagnating flow. The velocity oscillation is imposed to the flow with 𝛷=0.7 by an oscillator with single cylinder-piston unit. The equivalence ratio oscillation is imposed by an oscillator with two cylinder-piston units. The methane/air mixture with the equivalence ratio 𝛷=1.0 is supplied to one unit and that 𝛷=0.4 is supplied to the other unit. Pistons move with 180 degree phase difference which creates a sinusoidal equivalence ratio oscillation keeping the volume flow rate constant. Two oscillators are driven by a single DC motor to ensure complete synchronization. Phase difference between velocity oscillation and equivalence ratio oscillation is set by changing the relative position of pulley teeth of two oscillators. The oscillator frequency varies between 2 Hz and 20 Hz, which means that the oscillation wavelengths are much longer than the flame thickness. The flame motion was recorded by a high-speed video camera. Results showed that the amplitude of the flame motion was a linear superposition of the flame motion by the velocity oscillation and the equivalence ratio oscillation, indicating that each oscillation affects the flame motion independently.Effects of velocity and fuel concentration oscillations on premixed flames are discussed. Methane/air premixed flame is formed in a wall stagnating flow. The velocity oscillation is imposed to the flow with 𝛷=0.7 by an oscillator with single cylinder-piston unit. The equivalence ratio oscillation is imposed by an oscillator with two cylinder-piston units. The methane/air mixture with the equivalence ratio 𝛷=1.0 is supplied to one unit and that 𝛷=0.4 is supplied to the other unit. Pistons move with 180 degree phase difference which creates a sinusoidal equivalence ratio oscillation keeping the volume flow rate constant. Two oscillators are driven by a single DC motor to ensure complete synchronization. Phase difference between velocity oscillation and equivalence ratio oscillation is set by changing the relative position of pulley teeth of two oscillators. The oscillator frequency varies between 2 Hz and 20 Hz, which means that the oscillation wavelengths are much longer than the flame thickness. The flame...