Studies On Fire Spill Plume From A Compartment Opening Under No Wind And Cross Wind

Spill fire plume is a common and very important combustion phenomenon in compartment fire. Ventilation condition plays an important role in the formation and spread of spill fire plume. The previous studies mainly focused on the single opening compartment fire scenario in still air, while few works touch on the conditions with more complex openings under no wind and the scenario with wind. This work performs a systematic theoretical investigation on the formation and combustion dynamics of fire spill plume from a single opening and dual opening with no wind and the dual openings with cross wind. The influence of dual openings and cross wind on the spill fire plume is focused on. A combustion wind tunnel and a reduced-scale compartment are used for experiments of fire spill plume from dual symmetric openings under different wind speeds.Results show that, for the spill fire plume from single opening compartment under no wind, the increase of fuel supply rate and compartment air temperature results in the decrease of neutral plane height. A Gaussian function normalized by full width at half maximum (FWHM) successfully describes the symmetrical self-similar profile of radial temperature, and is successful to correlate the experimental data of the present work and that of the literature. The self-similar profiles of axial temperature and flame height of spill fire plume from single opening under no wind are revealed based on a modified Zukoski number and a length scale. It is found that at the continuous flame region, the intermittent region and the buoyant plume region, the self-similar axial temperature profile of spill fire plume fits the coincident power law of the normal plume. With the increase of excess heat release rate, the spill fire plume gradually turns from a wall fire to a symmetric fire. The power law of the self-similar flame height profile of the plume in the wall region is different from that of a normal plume. This is inferred to be mainly caused by the restriction of air entrainment due to the plume attachment.When cross wind is absent, a compartment with dual openings has a higher neutral plane height with respect to single-opening case. This in turn affects the air temperature inside the compartment. The neutral plane height model of spill fire plume from unsymmetrical dual openings under no wind is established by theoretical derivation, which agrees well with the data in literature.When cross wind is present, the wind has two competitive effects on the burning intensity and air temperature inside:promoting combustion by supplying more oxygen, while cooling the combustible gas. The theoretical derivation indicates that the wind has threefold effects on the pressure profile of fire spill plume:1) directly exerting wind pressure along the windward and leeward compartment openings; 2) causing the variation of the inside pressure; and 3) causing the variation of hydrostatic pressure. The cross wind also causes the rise and drop of neutral plane along the windward and leeward openings of the reduced-scale spill fire plume from compartment with dual symmetric openings, and affects the flow pattern and direction of fire spill plume. These results by theoretical derivation agree with the experimental data.The experimental radial temperature data under different cross wind speeds are successfully correlated by the Gaussian function normalized by full width at half maximum (FWHM), and the self-similar symmetric Gaussian profile will not be affected by varied with different cross wind caused axial trajectory curvature. Under the cross wind, the axial trajectory of fire spill plume consists of a first detached region and a subsequent attached region. The FWHM has a weak linear profile along the plume height.Experimental data under the cross wind speed of 1.5 m/s and 3 m/s indicate that, the dimensionless model and the length scale are successful to correlate the axial temperature and total heat flux to the facade under different wind speeds, opening dimensions and internal combustion intensities. It is found that at the three regions of the spill fire plume (continuous flame region, intermittent flame region and buoyant plume region), the self-similar axial temperature profile has the coincident power law with that of a normal plume. The increase of wind speed leads to a faster transition of the three flame regions, mainly due to the enhanced air entrainment. The decrease of neutral plane height due to the cross wind will enhance the near and far field air entrainment of fire spill plume. The restricted air entrainment owing to the existence of facade has a significant effect on the temperature profile and axial trajectory of fire spill plume. The experimental data under different wind speeds indicate that the cross wind has two competitive effects on the total heat flux and temperature of facade, as evidenced by the nonlinear increase of the total heat flux and temperature with wind speed.