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Abstract
In the current research, experimental work is investigated for vertically and horizontally downward propagating flames in an open-ended tube. The objective was to study and compare the influence of flammability limits, gravity, and the flame speed in the different tube configuration for two different fuels. The experimental facility included a 20 mm inner diameter tube, 1200 mm in length and an optical access quartz tube made centrally of 700 mm in length. Methane-air and propane-air fuel were compared for both vertically and horizontally downward propagating flames. The flame speed at each equivalence ratios for both fuels was lower for the flame that propagates downward compared to the flame that propagates horizontally. For both fuels, the flammability limits tend to rise for the vertically downward flame. The influence of gravity was seen as the flames become leaner and richer in methane-air and propane-air flames that propagate vertically downwards, causing a transformation in the contour of the flame from a steady curved flame to a vibrating corrugated flame.
Highlights
Experiments have shown that the ratio of fuel and oxygen which can support a flame varies with each combustible gas or vapour and determines the propagation of the flame
Though from literature, the maximum laminar burning velocity for both methane and propane lies around φ = 1.0 and φ = 1.1, but our result shows a shift in the peak flame speed into the rich region for horizontally propagating propane/air flame
The effect of gravity, flammability limits and laminar burning speed for a propagating flame was studied with orifice plate placed at the tube ends
Summary
Experiments have shown that the ratio of fuel and oxygen which can support a flame varies with each combustible gas or vapour and determines the propagation of the flame. The minimum amount of fuel required to support the formation of a flame in air is the Lower Flammability limits (LFL). The maximum amount of fuel required to support the formation of a flame in air is the Upper Flammability limits (UFL), and above this amount, the mixture is considered too rich to burn. Jarosinski [1] has shown that as the deviation from stoichiometric mixture increases, the differences between the downward and upward flammability limits increase He opined that this difference arose from the difference in the time taken for the flame extinction. Burning at the LFL decreases the temperature of the burned gas, increasing the specific heat ratio
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