A New Simplified Pdf Method For Calculating Major Species Concentrations And Burning In Turbulent Fires

Abstract

A simpl i fied method is presented for calculati ng mean major species concentrations (02' CO 2, CO) in turbulent fires for any fuel given the species distribution of the same fuel in a laminar diffusion flame. This method, verified by extensive measurements, uses a probability d Iat r t bution function (Pdf) for the conserved scalar in turbulent fires together wi th a uniform mi xedness parameter throughout the flames, first proposed in this work.For minor species concentrations (e.g., NO x' soot) that also de pend on the local Kolmogorov straining rates of turbulence, the present method might be extended by including the distribution of turbulent straining rates in a fashion strongly suggested by recent evidence of soot-flame radiation and NO x yield in turbUlent diffusion flames.Finally, based on the present method, an integral model is outlined for turbulent buoyant jet flames. CHEMICAL SPECIES IN TURBULENT FIRESIt is surprising that data obtained by L. Orloff(1) on mean major species concentrations in turbulent pool fires can be correlated with the mean corresponding mixture fraction independently of 1) location inside the f ire plume, 2) the total heat release rate, or 3) the diameter of the fire. Figure 1 (a,b,c) illustrates this result notwithstanding the scatter close to the maximum concentration values. Figure 1 also Incl udea the corresponding data for the opposing laminar flame of Tsuji and Yamaoka(2). Plotting the experimental data in terms of the coordinates of Figure 1 implies 1) equal diffusivities and 2) chemical reactions unaffected by the straining action of the flowfield.The average elemental fraction or mixture fraction used as abscissa in Figure 1 is a conserved quantity in the fire and represents, for example, the ratio of car-bon at om mass at a given place relative to the carbon atom mass at the source l 1 J.If the previous assumptions are accepted, the results of L. Orloff(1) as illustrated in Figure 1 suggest the possibility of predicting the major species concentrations in turbulent fires by using a simple mixing and combustion model.First, we observe that turbulent buoyant flames generate large eddies that move rather lazily inside the fire plume.The visible Kolmogorov micr-oscale is about 1-2 em.The diffusivity is of order of 2 cm 2;sec so that 9,2 the Kolmogorov time scale 'K -D is of the order of a second. This time

Carbon monoxide production during underventilated fires in corridors

“…-The present results as well as some of the previous results can be explained by noting that in general there is a state relationship between CO concentration and mixture fraction (directly related to GER) for laminar flames depending on fuel [43]. If the flames are turbulent, the CO concentration can be calculated from the probability distribution of mixture fraction and the laminar state relations [43]. Depending on the level of fluctuations the CO concentrations in turbulent flows are lower than in laminar flames and can be different for different flow conditions.…”

“…We also note that additional reactions affecting CO may occur if the combustion products pass through areas where high temperatures (over 800 °C) prevail [21,22]. It is possible to use the methodology in [43] to generalize and extend the present data for other fuels.…”

“…These flames may be called "travelling flames". The flame detachment and travel along the enclosure is different from "ghosting flames" reported earlier in the literature because ghosting flames are characterised by burning unsteadily in the volume above the fuel [43][44][45][46]. Fig.…”

Development of a polar direct drive platform for mix and burn experiments on the National Ignition Facility

“…One such model is the BHR model [6] and its revisions [7,8]. Results from this model have been used in burn models that use a probability distribution function [9] (PDF) to describe concentration variations at the sub-grid level to determine the effect on burn [10].…”