The Effect of Lateral Spacing on the Combustion Dynamics and Thermal Structure of an Array of Burning Droplet Streams

Abstract

The effect of lateral stream separation distance on the dynamics of flame propagation and thermal structure of a simplified spray flame has been studied. The flame was made up of 300µm average diameter hexane droplets injected through ten droplet streams in a plane, horizontally separated by a distance varying from 1 to 6 mm. Sequential photography was used to document the flame front motion and micro-thermocouples were used to perform measurements of gas-phase temperatures. The reactive flow was characterized by an inlet pre-ignition zone, followed by a bluish partially-premixed flame which acted as the ignition source of the fuel streams. Further downstream, a pattern of yellowish diffusion flames surrounding individual streams or groups of them was established, depending on the lateral separation of the streams. As the lateral spacing of the streams was increased, the vertical region swept by the flame front increased due to an augmentation in the flame propagation unsteadiness associated with larger variations in the local fuel-vapor concentration. Increased lateral spacing resulted in higher temperature fluctuations and lower average temperature gradients across the flame front.