Shouxiang Lu

Initial fuel temperature effects on burning rate of pool fire

The influence of the initial fuel temperature on the burning behavior of n-heptane pool fire was experimentally studied at the State Key Laboratory of Fire Science (SKLFS) large test hall. Circular pool fires with diameters of 100mm, 141 mm, and 200 mm were considered with initial fuel temperatures ranging from 290 K to 363 K. Burning rate and temperature distributions in fuel and vessel wall were recorded during the combustion. The burning rate exhibited five typical stages: initial development, steady burning, transition, bulk boiling burning, and decay. The burning rate during the steady burning stage was observed to be relatively independent of the initial fuel temperature. In contrast, the burning rate of the bulk boiling burning stage increases with increased initial fuel temperature. It was also observed that increased initial fuel temperature decreases the duration of steady burning stage. When the initial temperature approaches the boiling point, the steady burning stage nearly disappears and the burning rate moves directly from the initial development stage to the transition stage. The fuel surface temperature increases to its boiling point at the steady burning stage, shortly after ignition, and the bulk liquid reaches boiling temperature at the bulk boiling burning stage. No distinguished cold zone is formed in the fuel bed. However, boiling zone is observed and the thickness increases to its maximum value when the bulk boiling phenomena occurs.

Impacts of elevation on pool fire behavior in a closed compartment: A study based upon a distinct stratification phenomenon

The impacts of elevation on pool fire behavior in a closed compartment were investigated based upon a distinctive stratification phenomenon. The parameters including the mass loss rate, the combustion efficiency, and the heat release rate were measured. The results indicated that the mass loss rate maintained a steady stage for fires whose flame did not impinge the ceiling. The boiling burning occurred soon after the ignition, the mass loss rate increased sharply and the value was much larger than that in the open space if the flame impinged the ceiling. The combustion efficiency and carbon conversion ratio tended to be smaller if the fire was elevated higher. The combustion efficiency of fires whose flame impinged the ceiling was much smaller than that of fires whose flame did not impinge the ceiling. From the perspective of the heat release rate, elevated fires whose flame impinged the ceiling were more hazardous at the early stage.

Unsteady burning of thin-layer pool fires

The burning behavior of circular, thin-layer n-heptane pool fires having a diameter of 0.2 m and initial fuel thicknesses of 6.5 mm and 13 mm were experimentally studied. Fire parameters and temperature distribution in fuel were recorded during the experiments. Results show that flame height and burning rate exhibited different stages for fires with different thickness of fuel layer, while flame temperature was independent of the fuel layer and was almost constant. The fuel surface temperature increased to its boiling point, with the temperature of fuel below the surface starting to rise shortly after ignition. A boiling zone was formed that increased with time for the thicker fuel layer. A theoretical analysis based on a heat-transfer model is proposed to explain the differences in heat transfer between the liquid and environment during the different burning phases. Reasons for the increase of burning rate are introduced.

Burning rate of merged pool fire on the hollow square tray

In order to characterize fire merging, pool fires on hollow trays with varying side lengths were burned under quasi-quiescent condition and in a wind tunnel with the wind speed ranging from 0m/s to 7.5m/s. Burning rate and flame images were recorded in the whole combustion process. The results show that even though the pool surface area was kept identical for hollow trays of different sizes, the measured burning rates and fire evolutions were found to be significantly different. Besides the five stages identified by previous studies, an extra stage, fire merging, was observed. Fire merging appeared possibly at any of the first four stages and moreover resulted in 50-100% increases of the fire burning rates and heights in the present tests. The tests in wind tunnel suggested that, as the wind speed ranges from 0 m/s to 2 m/s, the burning rates decrease. However with further increase of the wind speed from 2 m/s to 7.5 m/s, the burning rate was found to increase for smaller hollow trays while it remains almost constant for larger hollow trays. Two empirical correlations are presented to predict critical burning rate of fire merging on the hollow tray. The predictions were found to be in reasonably good agreement with the measurements.

The effect of azeotropism on combustion characteristics of blended fuel pool fire

The effect of azeotropism on combustion characteristics of blended fuel pool fire was experimentally studied in an open fire test space of State Key Laboratory of Fire Science. A 30 cm × 30 cm square pool filled with n-heptane and ethanol blended fuel was employed. Flame images, burning rate and temperature distribution were collected and recorded in the whole combustion process. Results show that azeotropism obviously dominates the combustion behavior of n-heptane/ethanol blended fuel pool fire. The combustion process after ignition exhibits four typical stages: initial development, azeotropic burning, single-component burning and decay stage. Azeotropism appears when temperature of fuel surface reaches azeotropic point and blended fuel burns at azeotropic ratio. Compared with individual pure fuel, the effect of azeotropism on main fire parameters, such as flame height, burning rate, flame puffing frequency and centerline temperature were analyzed. Burning rate and centerline temperature of blended fuel are higher than that of individual pure fuel respectively at azeotropic burning stage, and flame puffing frequency follows the empirical formula between Strouhal and Froude number for pure fuel.

The effect of uncertain parameters on evacuation time in commercial buildings

To quantify the impact of uncertain parameters on evacuation time in commercial buildings, Monte Carlo simulation with FDS + Evac is presented in this article. In addition, the partial correlation coefficients and partial rank correlation coefficients are adopted to determine the sensitivity of evacuation time to uncertain input parameters. To illustrate the effectiveness of research procedures, a hypothetical commercial building is described as a fire compartment and the data of evacuation time are obtained from the simulation results of the FDS+Evac, which is based on the social force model, developed by the VTT Technical Research Centre of Finland and fully embedded in Fire Dynamics Simulator (FDS). And the results indicate that Monte Carlo simulation with FDS + Evac can effectively quantify the uncertainty of evacuation time caused by the uncertainties associated with input parameters. Evacuation time value corresponding to the most likely occurrence scenario may be inappropriate to be selected as the typical value used in commercial building design. In addition, safety factors can be employed to deal with the uncertainties associated with input parameters of evacuation models, but it is obvious that the safety factor should be selected prudently in performance-based fire protection design. Moreover, the most significant factor is pre-movement time among uncertain input parameters considered, which is much more important than occupant density and occupant type. When the pre-movement time or effective width distributions are large enough, occupant density and occupant type can be regarded as constant at their nominal values. However, when the occupant density or occupant type distributions are large, their impact on evacuation time cannot be ignored and should be examined carefully.

Uncertainty and sensitivity analyses of heat fire detector model based on Monte Carlo simulation

Estimating activation time for heat fire detectors is essential in fire safety engineering. Due to the complexity of the heat detector model, many uncertainties are associated with the input parameters. It is necessary to consider the influence of the uncertainties associated with the input parameters on predicted activation time. For this purpose, uncertainty and sensitivity analyses method for the heat fire detection model based on Latin hypercube sampling are introduced. The uncertainty analysis results indicate that the predicted activation time would be a variable approximating to a unimodal, positively skewed distribution rather than the strictly normal distribution, with the consideration of uncertainties associated with the input parameters. Various statistical coefficients and the result of stepwise regression, both confirm that location of the heat detectors and fire growth rate have the most significant influence on the predicted activation time.Estimating activation time for heat fire detectors is essential in fire safety engineering. Due to the complexity of the heat detector model, many uncertainties are associated with the input parameters. It is necessary to consider the influence of the uncertainties associated with the input parameters on predicted activation time. For this purpose, uncertainty and sensitivity analyses method for the heat fire detection model based on Latin hypercube sampling are introduced. The uncertainty analysis results indicate that the predicted activation time would be a variable approximating to a unimodal, positively skewed distribution rather than the strictly normal distribution, with the consideration of uncertainties associated with the input parameters. Various statistical coefficients and the result of stepwise regression, both confirm that location of the heat detectors and fire growth rate have the most significant influence on the predicted activation time.

Low temperature CO catalytic oxidation and kinetic performances of KOH–Hopcalite in the presence of CO2

Catalytic removal of CO from fire smoke is critical to ensure human safety and post-fire atmospheric recovery in typical confined spaces. Copper manganese oxide compounds show promise as highly efficient catalysts for low temperature CO oxidation. However, the CO oxidation activity will be affected when the catalyst is applied in fire smoke containing high-concentration CO2. In this work, a bi-functional catalyst of KOH–Hopcalite is synthesized by impregnation of KOH on Hopcalite (copper manganese oxides mixture) precursor. The catalyst is characterized by N2 adsorption–desorption, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). CO oxidation activity and long-term working stability of the precursor and catalyst in the presence of CO2 are investigated. CO oxidation activity of the precursor would decrease when CO2 is present. KOH modification can mitigate the inhibiting effect of CO2 on CO oxidation activity of the precursor. Reaction mechanisms and kinetic performances of the catalyst in the presence of CO2 are also demonstrated. The catalyst could be potentially utilized as a scavenging agent for post-fire cleanup and atmospheric recovery in confined spaces.

A Monte Carlo analysis of the effect of heat release rate uncertainty on available safe egress time

Available safe egress time is an important criterion to determine occupant safety in performance-based fire protection design of buildings. There are many factors affecting the calculation of available safe egress time, such as heat release rate, smoke toxicity and the geometry of the building. Heat release rate is the most critical factor. Due to the variation of fuel layout, initial ignition location and many other factors, significant uncertainties are associated with heat release rate. Traditionally, fire safety engineers prefer to ignore these uncertainties, and a fixed value of heat release rate is assigned based on experience. This makes the available safe egress time results subjective. To quantify the effect of uncertainties in heat release rate on available safe egress time, a Monte Carlo simulation approach is implemented for a case study of a single hypothetical fire compartment in a commercial building. First, the effect of deterministic peak heat release rate and fire growth rate on the predicted available safe egress time is studied. Then, the effect of uncertainties in peak heat release rate and fire growth rate are analyzed separately. Normal and log-normal distributions are employed to characterize peak heat release rate and fire growth rate, respectively. Finally, the effect of uncertainties in both peak heat release rate and fire growth rate on available safe egress time are analyzed. Illustrations are also provided on how to utilize probabilistic functions, such as the cumulative density function and complementary cumulative distribution function, to help fire safety engineers develop proper design fires. (Less)

Effect of Xanthan Gum on the Performance of Aqueous Film-Forming Foam

Solution properties of aqueous film-forming foam (AFFF) formulations containing different xanthan gum contents were investigated first by varying the mass fraction of xanthan gum in the range of 0.1–0.5%. Foam properties and fire-extinguishing performance of the AFFF formulations were then evaluated. Results indicated that xanthan gum content slightly affected surface tension of foam solutions. However, xanthan gum significantly affected viscosity of AFFF concentrates. Foaming of the AFFF formulations was hardly affected by xanthan gum, but foam stability of the compounds was obviously enhanced with the addition of xanthan gum. Optimal xanthan gum content was determined as 0.3%, which resulted in the shortest 90% control time and fire extinguishment time. Burnback time of foams increased with the addition of xanthan gum because of the enhanced foam stability. GRAPHICAL ABSTRACT