Trajectory and incineration of rogue droplets in a turbulent diffusion flame

The trajectory and incineration efficiency of individual droplet streams of a fuel mixture injected into a swirling gas turbulent diffusion flame were measured as a function of droplet size, droplet velocity, interdroplet spacing, and droplet injection angle. Additional experiments were performed in a laminar flow flat flame burner to evaluate the predictive capabilities of a droplet stream burning model, simplified by assuming infinitely fast flame chemistry and by utilizing measured temperature and velocity fields. It was found that use of a measured burning rate parameter significantly improved model predictions. Calculations of turbulent flame droplet trajectories compare well with mean experimental observations. However, turbulence effects, which were surprisingly large, could not be predicted due to inadequate measurement of turbulence intensity and frequency. It was found that large “rogue” droplets (>200 μm diameter) pass through the flame zone and burn as isolated droplets in the postflame gases. Destruction of these droplets appears to limit overall incineration efficiency.