Transition Dynamics Between Luminous and Blue Whirling Flames

This paper presents an experimental study to demonstrate transitions between luminous and blue whirling flames. We have designed a fixed-frame four-sided square aluminum test apparatus where liquid fuel is injected vertically upward from the center of the base plate, which reacts with self-entrained tangential air. Our experiments show evidence of the transition of a highly luminous non-premixed fire whirl into a blue whirling flame above the base surface. The formation of a blue whirling flame depends on the enhanced mixing and fuel spread above the metal surface. The smooth surface boundary leads to the formation of Ekman type boundary layer, which is shown to affect the flame. The transition from a fire whirl to a blue whirling flame is found to be dependent on the fuel spread over the metallic surface which depends on the fuel flow rate. This paper also shows the visual observation of flame patterns at different fuel flow rates, gap size (for air entrainment), and surface conditions (to identify the key parameters that are responsible for the formation of a blue whirling flame). The flame images show that a conical whirling flame with a laminar bluish base could be an essential (but not enough) condition to produce the transition to blue whirling flame.