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Show 3. Results and Discussion 3.1 Burner eeometry and model The burner consists of a planar enclosure followed by a divergent section in which the flame sits. A long planar duct comes next, ending in a short convergent section from which the hot mixture of air and combustion gases emerge. Only the parts of the burner where the flame develops have been modelled, the remaining sections being of little interest from the point of view of NOx formation. 7 f\) A 3-D finite volume model was used which took advantage of the 12 multiple planes of symmetry of the burner. Since 3-D CFO models are t\' expensive in computing time and restrictive in the number of cells allowed, I\i'(~ the cho ice was made of keep i ng to a mi n i mum the number of ce 11 sin z )\ direction (7 cells) to allow larger numbers in the x and y directions (71 ~~ and 50 cells) which were expected to contain the highest components of the velocity field. The size of the domain in x, y, and z directions respectively is 0.142, 0.05 and 0.00635 m. A sect i on of the burner is shown in Fi g. 1 and the mode 1 used is given as front and enlarged top views in Figs. 2a and 2b. The representation of the circular holes by assemblages of squares was undertaken by preserving the original surface areas of the holes and was dictated by the small number of cells available in z direction. 3.2 Description of the flow The geometry of the burner head plays a cruc i a 1 part in the flow pattern and in the stability of the flame. The burner head is characterized by three areas bu i 1 t up around the central feed duct and hav i ng each an effect on the development of the flow. (i) The first two rows of holes linked at right angle with the feed duct fire the initial flow of gas mixture into the planar enclosure where it mixes smoothly with the secondary air flow due to the slight angle between the enclosure and the plane containing the rows of holes. (ii) The third row of smaller holes, also linked at right angle with the feed duct, fi res the feed gas mi xture at a lower 1 eve 1 than the previous ones. The height drop between the fast incoming mixture of |