Flame Patterns and Combustion Intensity Behind Rifled Bluff Body Frustums

Abstract

Rifled fillisters were milled on cannular frustums to modulate flow behavior and to increase the turbulence intensity (TI). The TI and combustion intensity were compared in four configurations of frustums—unrifled, innerrifled, outerrifled, and twofaced rifled. The flame patterns and flame lengths were observed and measured by directcolor photography. The temperature profiles and (total) combustion intensity were detected and calculated with an Rtype thermocouple. Three flame patterns (jet, flickering, and lifted flames) were defined behind the purejet nozzle. Four flame patterns (jet, flickering, bubble, and turbulent flames) were observed behind the unrifled frustum. The bluffbody frustum changes the lifted flame to turbulent flame due to a high T.I at high centralfuel velocity (uc). The experimental data showed that the grooved rifles improved the airpropane mixing, which then improved the combustion intensity. The rifled mechanism intensified the swirling effect and then the flametemperature profiles were more uniform than those behind the purejet nozzle. The increased TI also resulted in the shortest flame length behind the twofaced rifled frustum and increased the total combustion intensity.