Interference effects during burning of tandem porous spheres in mixed convective environment

The interference effects during the burning of a binary tandem droplet array in a mixed convective environment have been studied both theoretically and experimentally for the upward airflow configuration. In the theoretical model, the flow and transport equations have been solved subject to the assumptions of constant properties (except for density) and infinite rate kinetics, by the use of the finite element method. The gas density has been treated as a variable, only for evaluating the buoyancy force contribution, and it has been determined through the ideal gas mixture assumption. A porous-sphere facility has been employed for simulating experimentally the burning characteristics of a fuel droplet array with fixed separation distance. The measured mass burning rates for both the spheres and the observed flame shapes are in excellent agreement with the corresponding theoretical predictions. The burning rate of the rear droplet is considerably less than that of the front droplet or an isolated droplet, for smaller separation distances. For larger separation distances, the burning rate of the rear droplet is of the same order as the front droplet, and it is sometimes even larger than that of the isolated droplet. The rate of burning of the front droplet mildly varies with separation distance, and it is approximately equal to that of an isolated droplet. The flame of a tandem binary droplet system is observed to be pushed away from the axis due to the presence of the second droplet.