Percolation in Combusting Sprays II. Width of the Percolate Combustion Zone

The recently introduced concept of percolate combustion motivates a refinement of the internal group combustion model analyzed by Chiu and coworkers. The continuous flame sheet separating com busting and non-combusting regions, regarded in the latter model as occupying a zone of negligible thickness, is here regarded as a highly convoluted surface occupying a zone of finite thickness, the "percolate combustion" zone. A simple model is employed to estimate the fraction of the combusting region that is within the percolate combustion zone. This fraction is estimated to be significant for internal group combustion regimes of practical interest. It is proposed that more detailed spray combustion models can incorporate percolation effects by modification of the transport equations and the matching conditions. Possible impacts of such modifications, including practical consequences of percolation effects, are discussed.