Xuehui Wang

On the behavior of flame expansion in pool fire extinguishment with steam jet

Theoretical analysis and quantitative methodology are proposed to predict the behavior of flame expansion in pool fire extinguishment with an impinging steam jet. The theoretical analysis contains the following three standpoints: (1) a fuel vapor-rich core exists in the base of the pool fire while oxygen is lacking. The existence of a fuel vapor-rich core is the prerequisite for flame expansion phenomenon. (2) The root cause responsible for the flame expansion is the fuel vapor convection by the impinging steam jet. An expanded fire ball is formed due to the burning of the convected fuel vapor, resulting in flame expansion phenomenon. (3) The flame expansion phenomenon could be divided to three typical stages: the flame height-decreasing stage, the fire-expanding stage, and the burn-out stage. The flame height-decreasing stage is the stage in which the steam jet impacts the flame and reaches the fuel vapor-rich core. The fire-expanding stage is the stage in which the fuel vapor is convected and burnt as a fire ball after the steam impacts the fuel vapor-rich core. The fire is then suppressed in the burn-out stage. Three quantitative features of the flame expansion phenomenon, the expansion ratio of the flame width ϕl, the expansion ratio of the flame volume ϕv, and the expansion ratio of the flame radiation ϕr, are defined to characterize the level of the expansion. A series of extinguishment tests using medium-size pool fires with an impinging steam jet were conducted to validate the theoretical analysis. The experimental results reveal that the theoretical analysis describes the flame expansion phenomenon quite well. Based on the experimental data, the height of the fuel vapor-rich core was calculated for each test case, and it was found that the height of the fuel vapor-rich core was about 0.2 times the visible flame height. The durations of the three stages and the flame shapes calculated using the proposed theoretical analysis compare favorably with the experimental measurements. The calculation shows that the expansion ratio of the flame width is about 2.0 in each test case of the medium size pool fire; the expansion ratio of the flame volume approximately matches the calculated value, and the calculated values of the expansion ratio of the flame radiation are close to the experimental values.

Thermal behavior of nitrocellulose with different aging periods

To further understand the aging process of energetic materials such as nitrocellulose (NC), aging treatment of NC samples was performed by a constant temperature chamber and non-isothermal experiments were performed by a TG-DSC analyzer. Also, scanning electron microscope was utilized to detect the morphological changes of NC in different forms. The results revealed that, with the increasing aging time, the decomposition properties including mass loss, decomposition temperature, heat production rate and heat of decomposition exhibit significantly different trends for the two forms of NC. Furthermore, the thermal kinetic parameters of pure NC were calculated based on Kissinger method. It is found that pure NC has the highest thermal instability at the aging time of 24xa0days under the aging temperature of 90xa0°C, and the stability of NC will increase when the aging time exceeds 32xa0days.

Pyrolysis and Combustion of Polyvinyl Chloride (PVC) Sheath for New and Aged Cables via Thermogravimetric Analysis-Fourier Transform Infrared (TG-FTIR) and Calorimeter

To fill the shortages in the knowledge of the pyrolysis and combustion properties of new and aged polyvinyl chloride (PVC) sheaths, several experiments were performed by thermogravimetric analysis (TG), Fourier transform infrared (FTIR), microscale combustion calorimetry (MCC), and cone calorimetry. The results show that the onset temperature of pyrolysis for an aged sheath shifts to higher temperatures. The value of the main derivative thermogravimetric analysis (DTG) peak of an aged sheath is greater than that of a new one. The mass of the final remaining residue for an aged sheath is also greater than that of a new one. The gas that is released by an aged sheath is later but faster than that of a new one. The results also show that, when compared with a new sheath, the heat release rate (HRR) is lower for an aged one. The total heat release (THR) of aged sheath is reduced by 16.9–18.5% compared to a new one. In addition, the cone calorimetry experiments illustrate that the ignition occurrence of an aged sheath is later than that of a new one under different incident heat fluxes. This work indicates that an aged sheath generally pyrolyzes and it combusts more weakly and incompletely.

Investigation on the fire hazard characteristics of ethanol–water mixture and Chinese liquor by a cone calorimeter

In this study, a series of ethanol–water mixture and Chinese liquor combustion experiments were conducted using an ISO5660-1 cone calorimeter and an automatic flash point tester. The main purpose was to obtain key fire parameter data, including the burning duration, mass loss rate, mass loss rate per unit area, heat release rate per unit area, CO and CO2 volume fraction, CO2/CO ratio and closed-cup flash point. At the same time, the experimental differences between Chinese liquor and ethanol–water mixture were analyzed. Also, the fire risk classification was discussed based on the code of GB 50016-2014. When the ethanol volume fraction of Chinese liquor is greater than 34.8xa0vol%, the fire risk is the most dangerous level, Class I. While the critical ethanol volume fraction of ethanol–water mixture is 38.9xa0vol%, it needs to pay more attention to the fire safety of Chinese liquor storage and usage when the ethanol volume fraction is generally from 30 to 65xa0vol%.