Investigation of the local parameters of a cellular propane/butane/air flame

摘要

A cellular ascending flame is studied in a setup where the fuel/air mixture (volume composition of fuel: propane 75%, butane 25%) outflows through a round hole with a diameter from 10 mm to 40 mm, covered with a brass grid. It is shown that the cells start forming if the mixture composition corresponds to the equivalence ratio of 1.4-1.6, regardless of the initial jet diameter. The flame with a single fixed cell was chosen for contactless measurement of local gas parameters. Gas temperature was measured by CARS (coherent anti-Stokes Raman scattering) with original software for spectra processing. The vertical and horizontal velocity components were measured by PIV (particle image velocimetry) equipment. The data were partially duplicated in experiments using LDA (laser Doppler anemometry). Parameters such as heat release and pressure, which cannot be measured directly, were assessed using the balance ratios in the equations of momentum and energy transfer. It is shown that a zone of increased pressure is formed behind the flame front in the centre of the cell due to the thermal expansion of the combustion products. This causes the curvature of the streamlines of the gas flow through the flame front. The visible contour of the cellular flame complies with an isotherm of ~1000 K, and the heat release surface is shifted about 0.5 mm downstream. High acceleration (2000-3000 m/s~2) and non-uniformity of the gas flow are present near the combustion front.