An experimental study of well-defined turbulent nonpremixed spray flames

An experiment system was designed for the study of well-defined turbulent n onpremixed spray flames. Particular emphasis was placed on minimizing the i nfluence of the injector design and on maximizing turbulence within the spr ay flames. A comprehensive description of the structure of such flames was obtained by applying a variety of complementary diagnostic techniques, incl uding: broadband chemiluminescence imaging, CH* emission-imaging, phase Dop pler interferometric techniques, and spontaneous Raman spectroscopy. Two me thanol spray flames were examined in detail, with Reynolds number ranging f rom 2.1 x 10(4) to 2.8 x 10(4). Flame appearance and detailed measurements confirmed the occurrence of group combustion. Near the burner mouth, a dens e column of drops enveloped by a common flame was observed. Further up, lar ge corrugated structures were visualized which eventually developed into se parate "islands." A significant fraction of the spray escaped unburned, whi ch implies that droplet evaporation is slow in this configuration. Detailed scanning of the flames provided an extensive database of average and fluct uating components of gas velocity and temperature, as well as spray and dro plet size-classified properties. Key conclusions from such measurements inc lude: the evidence of two-way coupling between the two phases along the cen terline near the burner mouth; a velocity acceleration in the densest areas of the spray flames, as a result of momentum addition through vaporization , followed by deceleration farther downstream as the jet spreading predomin ates; and the droplet inertial behavior, especially for the large size clas ses, as confirmed by estimates of some relevant Stokes numbers. The average flame height was found to correlate with an overall equivalence ratio and with the initial concentration of droplets at the burner mouth. (C) 2000 by The Combustion Institute.