Quantitative comparison of detailed numerical computations and experiments in counterflow spray diffusion flames

A comprehensive numerical model of counterflow spray diffusion flames was developed using detailed chemical kinetics and transport. The liquid phase was modeled by assuming that droplets were surrounded by a quasi-steady spherically symmetric film and that the temperature within each droplet was spatially uniform but time varying, as it traveled toward the flame. The evolution of the droplet size distribution was followed by using sectional conservation equations. The model was tested on a methanol flame under conditions of small velocity: slip between the droplets and the gas at the fuel boundary. The latter constraint was dictated by the need to use similarity solutions and to treat the problem as one-dimensional. Input conditions were such that the droplet vaporization region was well separated from the flame; that is, droplets did not interact directly with the flame. Consequently, the flame structure was found to be relatively insensitive to vaporization details, such as the number of sections used to describe the droplet size distribution. Quantitative agreement was found between model predictions and experimental measurements of gas-phase temperature, velocity, droplet size, and velocity distributions, provided that the measured gas-phase velocity gradients at the boundaries were used in the model, as opposed to common modeling assumptions, such as plug or potential flow.