Flame Patterns and Combustion Intensity Behind Rifled Bluff-Body Frustums

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, inner-rifled, outer-rifled, and two-faced rifled. The flame patterns and flame lengths were observed and measured by direct-color photography. The temperature profiles and (total) combustion intensity were detected and calculated with an R-type thermocouple. Three flame patterns (jet, flickering, and lifted flames) were defined behind the pure-jet nozzle. Four flame patterns (jet, flickering, bubble, and turbulent flames) were observed behind the unrifled frustum. The bluff-body frustum changes the lifted flame to turbulent flame due to a high T. I at high central-fuel velocity (u(c)). The experimental data showed that the grooved rifles improved the air-propane mixing, which then improved the combustion intensity. The rifled mechanism intensified the swirling effect and then the flame-temperature profiles were more uniform than those behind the pure-jet nozzle. The increased TI also resulted in the shortest flame length behind the two-faced rifled frustum and increased the total combustion intensity.