The Effect of Fuel Rotation on Different Characteristics of Fire Whirls: An Experimental Analysis

Fire whirls are frequently spotted during forest fires in which unburnt or half burnt fuel around the fire can be seen rotating along with the whirl. The fuel rotation inside the whirl affects the fire characteristics compared to the stationary burning condition. In this work such variation in Mass Burning Rate (MBR), centerline field temperature, radiative heat flux, flame length, flame width, flame wandering and emission of laboratory-scale fire whirl are studied. For a constant pool diameter (d), the MBR (\({\dot{m}}^{\prime\prime}\)) of fire whirls depends on the imposed rotations/circulation (Γ). A correlation \({\dot{m}}^{\prime\prime}\) = 0.05Γ^0.94 is proposed to relate the mass loss flux with imposed circulation. Whereas, with fuel rotation, mass loss flux decreased up to 20% due to the change in bottom boundary conditions. As fire whirl height (H_f) is a function of MBR and imposed circulation, the correlation \(H_{f}^{*} = K.(\mathop {Q^{*} }\limits^{ \bullet } .\Gamma^{*2} )^{m}\) has been modified with the help of experimental data, where constants K and m closely resemble the literature data. To quantify flame wandering a parameter Appearance Probability (AP) was introduced and calculated. The AP—time plot indicate that the imposed rotation caused the flame to wander, eventually increasing the centerline field temperature by 20%. Finally, the measurement of fire effluents suggests that CO and CO₂ concentration increases with imposed circulation in the fire whirls and instantly reaches the Threshold Level Values for a short time exposure limit (TLV-STEL).