Abstract
The premixed combustion under the fuel-lean condition is effective in reducing the NO_x quantity. Furthermore, a multi-port type premix burner can distribute the premixed fuel and air to each small port and shorten the flame, and the heat load is increased easily. In this kind of combustion systems, supplying homogeneous mixture is essential for the equalization and the reduction of the combustion temperature all the burner surface over. With the previous methods that estimate the degree of mixing, it is impossible to get the detailed and quantitative information about the flowing mixture simultaneously. In this paper, a convenient method to estimate the degree of mixing on the gaseous mixture is proposed. Dry-ice mist, that is fed into the mixer instead of the gaseous fuel, is visualized with the He-Ne Laser Light Sheet as the fuel distribution in the mixture. The density of the mist in the mixture is measured by an image of the scattering light intensity taken with a TV camera and the degree of mixing is calculated. The multiple scattering characteristics on the mist are investigated on the experiment with the homogeneous mixture. The following knowledge, that enables to get the proportional image to the density distribution, is composed based on these characteristics. 1) The quantity of the fed mist should be kept as lean as possible, to reject the weakening of the incident light. 2) The forward scattering light should be detected, to strengthen the image intensity. 3) The non-linear relation between the image intensity and the density, that is made by the spatial error of the scattering angle and by the geometrical arrangement of the optical devices, should be compensated under the multiple scattering characteristics. As applications of this method, this paper shows some results of the tests on a mixer that is composed of a multi-blade fan and a sub mixing chamber. The mist is visualized on the outlet of the mixer, which is 60mm by 80mm. The mixer without the sub mixing chamber mixes the fuel to the air partially and the arrangement of the fuel supply nozzle influences the density distribution. On the other hand, the sub mixing chamber improves the mixing characteristics of the mixer with the extension of the path and the enforcement of mixing with the impeller. At the end, this method can be successfully applied to the measurement of the mixing characteristics on the wide burner surface, which is 260mm by 80mm.
