Shapes of nonbuoyant round luminous hydrocarbon/air laminar jet diffusion flames

Abstract

The shapes (luminous flame boundaries) of round luminous nonbuoyant soot-containing hydrocarbon/air laminar jet diffusion flames at microgravity were found from color video images obtained on orbit in the Space Shuttle Columbia. Test conditions included ethylene-and propane-fueled flames burning in still air at an ambient temperature of 300 K, ambient pressures of 35-130 kPa, initial jet diameters of 1.6 and 2.7 mm, and jet exit Reynolds numbers of 45-170. Present test times were 100-200 s and yielded steady axisymmetric flames that were close to the laminar smoke point (including flames both emitting and not emitting soot) with luminous flame lengths of 15-63 mm. The present soot-containing flames had larger luminous flame lengths than earlier ground-based observations having similar burner configurations: 40% larger than the luminous flame lengths of soot-containing low gravity flames observed using an aircraft (K.C-135) facility due to reduced effects of accelerative disturbances and unsteadiness; roughly twice as large as the luminous flame lengths of sootcontaining normal gravity flames due to the absence of effects of buoyant mixing and roughly twice as large as the luminous flame lengths of soot-free low gravity flames observed using drop tower facilities due to the presence of soot luminosity and possible reduced effects of unsteadiness. Simplified expressions to estimate the luminous flame boundaries of round nonbuoyant laminar jet diffusion flames were obtained from the classical analysis of Spalding (1979); this approach provided successful correlations of flame shapes for both soot-free and soot-containing flames, except when the soot-containing flames were in the opened-tip configuration that is reached at fuel flow rates near and greater than the laminar smoke point fuel flow rate.

Smoke-point properties of non-buoyant round laminar jet diffusion flames

“…Experimental methods ,,viii be described only briefly, see Urban et al [25] for details about the apparatus and instrumentation and Linet al [28] for a tabulation of test conditions. Monitoring measurements included the fuel flow rate, the fuel inlet temperature, the chamber pressure, and the chamber gas temperature [25,28].…”

“…Monitoring measurements included the fuel flow rate, the fuel inlet temperature, the chamber pressure, and the chamber gas temperature [25,28]. The flames were observed using a color CCD video camera …”

Soot Formation and Oxidation in Fires from Laminar Smoke Point Measurements

“…This behaviour is consistent with the similarity behaviour of non-sooting laminar flames. However, in reality [20], this ratio increases slightly as the flame height increases because the temperatures in the oxidation regime decrease (due to higher radiation losses) and thus, the oxidation time will increase (more than the soot formation time) until oxidation stops at about 1300 K.…”

Effects of Gravity on Soot Formation in a Coflow Laminar Methane/Air Diffusion Flame

“…Thus soot research has received considerable attention in both normal gravity and microgravity (Haynes and Wagner 1981;Glassman 1988;K ue ta l .1995;Haggard and Cochran 1972;Greenberg and Ku 1997a, b;Megaridis et al 1996;Sunderland et al 1994;Urban et al 2000;Konsur and Megaridis 1999;Lin et al 1999;Aalburg et al 2005;Walsh et al 2000;Kaplan et al 1996a). In microgravity, the elimination of buoyancyinduced flows increases the residence time and decreases the fresh air supply.…”

“…Most studies have focused on experimental investigations on the soot field structures at microgravity (Greenberg and Ku 1997a, b;Megaridis et al 1996;Sunderland et al 1994;Urban et al 2000;Konsur and Megaridis 1999;Lin et al 1999;Aalburg et al 2005) to elucidate the effects of buoyancy on soot formation. However, it is difficult to investigate all the aspects that influence soot formation because of the cost and the limited number of experiments that can be conducted in microgravity.…”