Non-premixed flame characteristics and exhaust gas concentrations behind rifled bluff-body cones

Four bluff-body cones with/without rifled v-grooves were installed behind a non-premixed traditional combustion nozzle to intensify the bluff-body effects and swirl flow. The spiral rifles transformed axial momentum (or axial velocity) into tangential momentum (or tangential velocity). The interaction between the fuel tangential component and axial air flow increased turbulence intensity (T.I.). The Schlieren photography was utilized to visualize the flame structures and classify three flame patterns—jet flame, recirculation flame, and turbulence flame. The jet flame occurs when fuel-jet velocity is high and air-jet velocity (u_a) is low. However, the turbulence flame exists at the high air-jet velocity. The flame lengths were measured using the direct photography scheme. The flame length at high u_a is significantly shorter than that at low u_a. Furthermore, the increase of rifle number (i.e., increasing T.I.) induces the high maximum temperature and low nitric-oxide concentration.