Dynamics of Premixed Flames in Tube

Experimental work is reported for premixed flames propagating in tubes. The flames were ignited with a pilot flame and the flame propagation captured with high-speed cameras. Initial measurements were performed characterising the rig. These included investigations of the end configuration (open, closed, orifice plate) and whether the tube was horizontal or vertical. For horizontal tube open at both ends, the pressure signal of the propagating flame was recorded and the flame temperature distribution along the tube length was found by observation of a thin silicon carbide filament. The flame propagated steadily immediately after ignition with a curved front, then was subjected to oscillations at the middle of the tube. At the end of the tube, it regained its stability. The pressure and temperature of the propagating flame were highest at the middle point where the flame oscillated. Methane-air flames enriched with hydrogen were studied. As the hydrogen concentration was increased the acoustic pressure initially increased and then decreased this was found to be associated with the presence of Rayleigh-Taylor instabilities. For downwardly propagating flames to a closed end, methane and propane were studied. The flames initially propagated steadily, then at approximately a third of the way down the tube, the primary acoustic oscillation sets in resulting to change in the flame shape. This was then followed by a plateau of variable length before a more violent secondary acoustic oscillation. In some circumstances, flames were observed to rotate due to the primary acoustic instability. Some of the flames were subjected to Rayleigh Taylor instabilities associated with large pressure oscillations. The flame front position growth rate for both methane and propane were similar despite the differences in the fuels. There was a strong correlation between the flame oscillations and changes in CH* and C2* as well as the flame surface area.