LDA measurements in a pulverized coal flame at three swirl ratios

A two-color Laser Doppler Anemometer (LDA) was used to obtain axial and tan gential velocity information in a 0.2 MW pulverized coal flame. In addition to the reacting flow data, a study on the accuracy of using coal as a seed particle to measure gas phase velocity using LDA was performed. Non reacti ng flow velocity measurements were also obtained near the fuel inlet and in the quart region of a geometrically identical burner to identify the veloc ity profile at several burner settings and to assist in establishing modeli ng inlet conditions. Both the reacting and non reacting velocity data were obtained at three or more swirl settings and various axial positions allowi ng a study of the affect of swirl on inlet turbulence and flame structure. The velocity results were compared with effluent NOx measurements. At the f low rates and accelerations experienced in this study, the coal particles w ere shown to be useful as seed particles for LDA gas phase velocity measure ments. The coal-name Velocity indicated a centerline flame at 0 swirl trans itioning to a radially directed flame with a central recirculation zone at swirl settings of 0.5 and 1.5. The transition of the flame structure to a c entral recirculation zone was also seen at the fuel inlet plane in the non reacting flow studies and was found to correlate with a decrease in measure d effluent NOx. Measured axial velocity profiles 5 mm below the fuel inlet showed negetive axial velocities tin the opposite direction of the average flow velocity) were produced along the primary tube as swirl was increased from 0 to 1.5 with the transition occuring between 0.5 and 0.75 swirl. Tran sition in the now near the fuel inlet correlated well with a drop in efflue nt NOx and with transitions in the recirculation zones measured further dow nstream. The strong interaction with burner velocity profiles and NOx sugge st velocity profile, in addition to swirl number, is an important measured boundary condition for modeling. The velocity data shown here in combinatio n with a companion paper showing temperature and species data should provid e important information needed to develop better models of pulverized coal combustion.