| At present,polymethyl methacrylate(PMMA)is mainly used in construction,advertising,medicine,transportation,chemical industry and other fields,especially widely used in the construction field.However,due to its poor fire resistance,flammable,explosive and other irritating gases are prone to occur in the combustion process.At the same time,in the process of using PMMA,the width,thickness,angle and other factors are often involved,so the study of the PMMA fire characteristics with different widths,thicknesses and angles is very important,which can enrich PMMA flame spread theory,and provide suggestions for fire prevention design.The experiment material PMMA was used in this paper.the flame spread and combustion characteristics were revealed over PMMA with different widths(2cm,3cm,5cm,8cm and 12cm),thicknesses(2mm,3mm,4mm and 6mm),and incline angles(0°,±15°,±30°,±45°,±60°,±75° and ±90°).The change regulation of flame structure(flame height,flame temperature,flame angle),flame spread speed,and mass loss rate were experimentally analyzed and researched by heat and mass transfer tentatively.Firstly,a series of horizontal flame spread experiments was carried out over PMMA with different widths and thicknesses.The flame spread characteristic parameters such as flame height,average mass loss rate and flame spread speed et al.were revealed.It was found that the flame height was small in the initial phase.With the process of flame spread,it gradually fluctuated to a certain value.Meanwhile,the average flame height increased with the width and then decreased slightly;the flame spread increased with the increase of the width and the mass loss rate increased gradually.At the same time,the horizontal flame spread with thicknesses of 2mm,4mm and 6mm over PMMA was studied.It was found that,for the same width of PMMA samples,the flame spread speed decreased with the increase of the thickness,while the mass loss rate increased gradually.It is mainly due to that,the effect of thickness is greater than the weakening of flame spread speed on combustion.Secondly,this paper carried out a series of small-scale flame spread experiments on PMMA samples,with width 3cm,thick 2mm,and the incline angles(0°,±15°,±30°,±45°?±60°,±75° and ±90°).It was found that,the pyrolysis zone and preheating zone length were largely influenced by incline angle through infrared image analysis.The average flame angle increased greatly when the incline angle changed from 15° to 30° and-60° to-75°.Meanwhile,for upward flame spread(the incline angle is positive),the flame length decreased slowly and then increased with incline angle,however,for downward flame spread(the incline angle is negative),the flame length decreased slightly with the absolute value of the incline angle.As for the upward flame spread speed,when the incline angle changed from 0° to 15°,the average flame spread speed would increase greatly.And for the downward flame spread speed,the average flame spread speed decreased slightly with the absolute value of the incline angle.Finally,in this paper,the coupling effect of width and incline angle was studied over PMMA with widths of 2cm,3cm,5cm and 8cm and incline angles of 0°,15°,30° and 45°.The flame structure and combustion parameters such as: flame spread speed,flame angle,flame height and flame temperature were investigated by image analysis,infrared thermography and thermocouple etc.It was found that,during the flame spread process,the pyrolysis front showd a U shape.With increase of the width,the revolution of U shape would take much more time.Meanwhile,the flame spread speed was greatly influenced by width at the larger incline angle,which means the wider PMMA samples will have larger flame spread speed.It can be attributed to that,with increase of the width and incline angle,the flame angle will become smaller making the flame close to the surface,and therefore promoting the heat transfer.It was also found that,the average flame spread speed was influenced by the average flame height and fluctuation and,the flame temperature doesn't change with width at the same incline angle. |
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