Influence of Chamber Length and Equivalence Ratio on Flame Propagation in a Constant-Volume Duct

摘要

An investigation of flames propagating in a constant volume duct of square cross-section (38 mm by 38 mm) is reported. Two borosilicate glass windows provide full optical access to the combustion process. A line ignition source creates an approximately two-dimensional flame front. The relations among pressure, flame shape, flame speed, and mass consumption rate are examined. The investigation of flame characteristics is made for 1) stoichiometric methane-air flame propagation in ducts of lenghts from 30 mm to 150 mm and 2) ethylene-air flames with equivalence ratios from 0.6 to 1.1 propagating in a 150 mm duct. Uncertainties in the experimental approach are investigated and traced to deviations in the flame from its assumed two-dimensional shape and to the sensitivity of the flame speed calculation during the flame initiation period to noise in the pressure data. Results point to distinct regions of flame development, labeled cylindrical, planar, and folded. A correlation between flame shape development and flame speed is noted. The time to peak pressure for the methane experiments is a linear function of duct length. This indicates that despite the distinct flame development regions, the mean mass consumption rate is not sensitive to flame shape variations. Ethylene flames are found to demonstrate the same general characteristics as the methane flames. The ethylene flame propagation rates are found to be about twice as fast as methane flame propagation rates. The folded ethylene flames exhibit a greater amount of turbulence than comparable methane flames. At low equivalence ratios buoyancy alters the ethylene flame shape. 20 figures. (ERA citation 08:004199)