Experimental study of the effect of internal pressure on oscillating behavior of pool fires.

A series of experiments have been conducted to study the flame behavior of ethanol pool fires in a closed chamber. The effect of internal pressure and the size of the pool burner is considered. Tests include pressure conditions ranging from 50 kPa to 350 kPa and 5 circular pool burners with different diameters (2 cm, 4 cm, 6 cm, 8 cm, and 10 cm). Measurements such as gas temperature, internal pressure, oxygen concentration, and video record for all tests are obtained. Steady-state burning period is identified to facilitate a quantitative analysis of flame behavior. Image processing is carried out to obtain time average appearance of pool fires. The concept of oscillation intensity is introduced. Oscillation behaviors of pool fires in a closed system as a function of internal pressure and pan diameter are correlated with oscillation intensity. Four flame structures are observed: laminar, tip flicking, sinuous meandering, and turbulent flame. Relationships between oscillation intensity to flame structure and Grashof number to flame structure are established. Effect of internal pressure and gravitational force to oscillation frequency is also accessed. Simple theoretical model is developed. An empirical expression using the relationship of Strouhal number and Grashof number is established. Two distinct behaviors on oscillation frequency as a function of pressure are observed. Results obtained from this work will facilitate the understanding of oscillation behavior of ethanol pool fires in different sizes with various internal pressure conditions in a closed chamber.

Large volume scanning laser induced fluorescence measurement of a bluff-body stabilised flame in an annular combustor.

Abstract: This study outlines a variant of three-dimensional OH planar laser-induced fluorescence and its application in characterising a single bluff body stabilised flame inside a 12 burner annular combustor. In this variant of the method a relatively large volume was scanned slowly in order to calculate the full three-dimensional Flame Surface Density (FSD) distribution. The method used a combination of two scanning directions to overcome bias errors associated with laser sheet positions close to the flame edges. The source of this bias error was confirmed numerically through a complimentary synthetic PLIF study, which was also used to refine the experimental setup. The bias error resulted in a reduction of FSD magnitude, although the method was still capable of capturing the flame structure. This was demonstrated by comparing the reconstructions from the two independent scan directions. Combining the data from both directions overcame the bias, and allowed flame asymmetry due to the confinement to be assessed. The FSD was used to determine the heat release rate of the flame with varying local azimuthal angle for different downstream regions. This highlighted the highly asymmetric structure, produced by the asymmetric confinement.

Mechanisms of the Action of Fire-Retardants on Reducing the Flammability of Certain Classes of Polymers and Glass-Reinforced Plastics Based on the Study of Their Combustion.

In the present review, using an integrated approach based on the experimental and theoretical study of the processes of thermal decomposition and combustion of practically important polymers, such as polymethyl methacrylate, polyethylene, and glass-fiber-reinforced epoxy resin, the features of the mechanism for reducing the combustibility of these materials with phosphorus-containing flame-retardants (FR), as well as graphene, are identified. A set of original experimental methods was developed and applied that make it possible to study the kinetics of thermal decomposition and the thermal and chemical structure of the flames of the studied materials, including those with FR additives, as well as to measure the flame propagation velocity, the mass burning rate, and the heat fluxes from the flame on the surface of a material. Numerical models were developed and tested to describe the key parameters of the flames of the studied polymeric materials. An analysis of the experimental and numerical simulation data presented showed that the main effect of phosphorus-containing fire-retardants on reducing the combustibility of these materials is associated with the inhibition of combustion processes in the gas phase, and the effect of adding graphene manifests itself in both gas and condensed phases.

Numerical simulation of the influence of pipe length on explosion flame propagation in open-ended and close-ended pipes.

The pipeline length exerts great influence on flame propagation characteristics, Realizable k-ε model and Premixed combustion model were used to study the influence of pipe length on propane-air explosion flame in open-ended and close-ended pipes. Using the numerical model verified by experiments, the changes of flame structure and flame propagation speed are studied. The result showed that the Realizable model was in good agreement with the experimental results. It also proved that the reflected wave produced a strong interference on the flame front, which promoted the formation of tulip flame. Besides, some obvious vortices were usually generated in the burned gas after the tulip flame formed, which will affect the flow field around the flame front and thus exert influence on the flame structure. The formation mechanism of tulip flame as well as the flame self-acceleration is different in open-ended and close-ended pipes. In close-ended pipes, the reflection wave at the pipe end and the reflection-induced countercurrent both promote the formation of tulip flame. As the flame propagates to the pipe end, the flame propagation is inhibited by the compression wave formed by the rapid expansion of combustion products under high temperature. While, in open-ended pipes, the turbulence induced by the opening at the pipe end is the main cause of tulip flame formation. The flame acceleration depends on the combustion reaction of unburned gas, so the velocity of flame propagation continues to increase. Generally, the maximum flame propagation velocity in the open-ended pipe is larger than that in the close-ended pipe.

H2/CO/air premixed and partially premixed flame structure at different pressures based on reaction limit analysis.

Premixed and partially premixed flames (PPFs) of H2/CO/air syngas are studied numerically to investigate the effect of pressure on syngas PPF structure. Chemical characteristics of the syngas flame at different pressures are investigated based on reaction limit analysis using a one-dimensional configuration. The results show that CO affects the syngas reaction limits through both physical effects that consist mainly in dilution and chemical effects that are related to both R23 (CO + OH = CO2 + H) and HCO pathway. In particular, the HCO pathway weakens the flame at low pressures due to the chain-terminating effect of R25 (HCO + O2 = CO + HO2) and R26 (HCO + H = CO + H2), and enhances the flame at high pressures because of the contribution of R25 to the HO2 chain-branching process. These CO chemical characteristics are also observed in the premixed zone of 50% H2 + 50% CO syngas PPFs whereas only R23 is important in the non-premixed zone.