Direct measurement of laminar flame quenching distance in a closed vessel

The study of flame-wall interactions is of crucial importance for the understanding of near wall combustion. One of the parameters directly responsible for heat exchange near the wall is the quenching distance. The results of direct measurements of the quenching distance during side-wall quenching and head-on quenching of premixed methane/air flame are presented. A laminar flame is produced at the centre of a rectangular combustion chamber. The experiments are performed using different wall materials: polished steel, steel covered with soot and ceramics. Flame interacts with a rectangular obstacle placed at the bottom of the combustion chamber. The quenching distance near the top of the obstacle and in the vicinity of its side-wall is measured using direct photography of the flame position near the quenching surface. The quenching phenomenon depends on the wall material. These circumstances must be taken into account during heat flux measurements. For ceramics, the side-wall quenching distance is less than for polished steel by a factor of 1.1-1.8 in the pressure range of 0.05-0.15 MPa. The coating of polished steel by a 15-20 mum thick soot layer decreases the quenching distance by a factor of 1.1-1.5. The head-on quenching distance for polished steel is 1.4-2.5 times less than side-wall quenching in the pressure range of 0.08-0.19 MPa. An evaluated value of the maximum heat flux to the wall during quenching is obtained from the value of quenching distance using a simple relationship. For atmospheric pressure and cold wall conditions, the peak heat flux to the polished steel surface is found to be 0.46 and 0.26 MW/m(2) for the head-on and side-wall quenching, respectively. Near the ceramic surface these values are 0.8 and 0.39 MW/m(2) for head-on and side-wall quenching, respectively. (C) 2002 Elsevier Science Inc. All rights reserved.