Determination On The Shape And Flicker Of Laminar Diffusion Flame Under Oxygen Enriched Condition

The structural shape and flicker characteristics of diffusion flame are two importantaspects in the research of diffusion flame. This paper takes laminar diffusion flame underthe O2/N2and O2/CO2atmosphere with varying oxygen concentrations in the oxidiser asthe study object, and concentrates on the shape and flicker.The theoretical solution of flame shape was solved based on Roper model, there arethree main parts, nondimensionalizing the original equation, solving the dimensionlessequations and solution of cylindrical coordinates. The dimensionless laminar diffusionflame shapes are solved under the O2/N2and O2/CO2atmosphere with varying oxygenconcentrations in the oxidiser. The results show that the dimensionless laminar diffusionflame shapes, under the two kinds of atmosphere, become lower the narrowing whenoxygen concentrations in the oxidiser grow. The oxygen concentrations domaindimensionless laminar diffusion flame shapes if the same fuel was used. Meanwhile, duringthe solving process of cylindrical coordinates, Roper model was extended in view ofdiffusion Flame region’s temperature distribution and velocity distribution, in order toenhance accuracy when flame width is calculated.Ethylene laminar diffusion flame images for two kinds of atmosphere under variousworking conditions, with and without the430nm filter, are obtained though a set of lablaminar diffusion flame test bench. Flame shapes are obtained from recent analyticalmodels are compared with experimental data. The comparison between flame imageobtained though the430nm filter and normal one have revealed that flame image border ismuch closer to diffusion flame boundary with the filter, as the influence of soot emitting isweakened by use of430nm filter. It is observed that the calculating flame shape based ontemperature distribution is better agreement with the experimental data, when compared tothe calculating flame shape based on Constant temperature. What is more, in the calculationof flame shape based on temperature distribution, two assumed conditions have been putforward. Then results under the assumption of uniformly accelerated motion and variableaccelerated motion are Similar, however, there is a little Difference. Overall, the latter ismore appropriate. The results also show that flame calculating and experimental heights under the O2/CO2atmosphere are longer than those under the O2/N2atmosphereconsidering the same oxygen concentrations in the oxidiser, so are the flame widths.With the increasing of oxygen concentrations, The difference between calculation andexpermental value emerges increasing tendency, but the difference under the O2/N2atmosphere is so little, while the other one is relatively obvious.Experimental investigation of co-flow oxidiser effects on the flickering behaviour oflaminar ethylene diffusion flames is taken by using High speed imaging methods. Thereason why the flicker of laminar jet diffusion flames occurs is toroidal vortices outsideflame boundary. It is observed that co-flow oxidiser is able to suppress flame flicker, andwith the increasing of co-flow oxidiser, The dominant flickering frequency become higher,then, maintain a specific value in the end. The flicker frequency was observed to increase indifferent ways with the co-flow rate and the relationship between frequency and co-flowrate is given in this reasearch.