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Abstract Quasi steady “external group combustion” of droplet cloud with non-uniform droplet size distributions has been developed to assess the group burning behavior of fuel sprays in industrial and jet engine combustors. The exact solutions for the perturbation equation for power law droplet size distributions are obtained. Numerical analysis pertaining to the initial phase of group combustion with mean droplet size approximation is also presented. The study reveals that current spray burners are operating at high group combustion number regime, wherein the burning mechanism coincides with external group burning mode as previously predicted by Suzuki and Chiu. A spray with a higher group combustion number is also featured by a “sheath vaporization” which is localized in a thin layer located in the outermost region of the cloud. Sprays at lower group combustion number regime cease to burn with external combustion modes when the group combustion number is less than the critical value which is determined by the fuel's properties and combustion environment. Droplet size distribution is also identified as a major parameter that affects the total burning rate of a spray.
Chiu et al. (Thu,) studied this question.