SHAPES OF NONBUOYANT ROUND LUMINOUS HYDROCARBON AIR LAMINAR JET DIFFUSION FLAMES/

The shapes (luminous flame boundaries) of round luminous nonbuoyant so ot-containing hydrocarbon/air laminar jet diffusion flames at microgra vity were found from color video images obtained on orbit in the Space Shuttle Columbia. Test conditions included ethylene- and propane-fuel ed flames burning in still air at an ambient temperature of 300 K, amb ient 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 la minar smoke point (including flames both emitting and not emitting soo t) with luminous flame lengths of 15-63 mm. The present soot-containin g flames had larger luminous flame lengths than earlier ground-based o bservations having similar burner configurations: 40% larger than the luminous flame lengths of soot-containing low gravity flames observed using an aircraft (KC-135) facility due to reduced effects of accelera tive disturbances and unsteadiness; roughly twice as large as the lumi nous flame lengths of soot-containing normal gravity flames due to the absence of effects of buoyant mixing and roughly twice as large as th e luminous flame lengths of soot-free low gravity flames observed usin g drop tower facilities due to the presence of soot luminosity and pos sible reduced effects of unsteadiness. Simplified expressions to estim ate the luminous flame boundaries of round nonbuoyant laminar jet diff usion flames were obtained from the classical analysis of Spalding (19 79); this approach provided successful correlations of flame shapes fo r both soot-free and soot-containing flames, except when the soot-cont aining flames were in the opened-tip configuration that is reached at fuel flow rates near and greater than the laminar smoke point fuel flo w rate. (C) 1998 by The Combustion Institute.