OCR Text |
Show data showed that flame stability was slightly improved, but no significant enhancement was observed. The maximum excess air for this group of tests was 77 %. The contiguration was then moditied by mounting the ten small disks on the water-cooled torus electrode. Tests were performed at the same tiring rate, 1 x 106 Btu/h, and maximum excess air, but with no obvious improvement in flame stability or CO reduction. Next the same torus electrode and disk configuration was tested at the firing rate of 0.5 x 106 Btuth and a nozzle pressure of 6 in. wc. In the base conditions, with the electric field off, a stable flame was achieved at a maximum excess air of 87%. When the electric field was applied, the flame could be stabilized up to 89.1 % of excess air. With the application of an electric field, CO and THe were even lower than at 87% excess air without the electric field, as shown in Fig. 13. NOx emissions as low as 0.6 vppm were achieved. The gas temperature distribution measured at port no. 4 also showed a significant improvement in flame stability using the electric field, as shown in Fig. 14. The fact that the central ring was at a negative voltage is consistent with the picture that an ionic wind is forcing the flame to stay near it. It should be noted that during the testing of the torus electrodes with the applied dc electric field, the consumption of electrical energy was negligible. Over the entire range of the tested firing rates, the values of the electrical consumption did not exceed 5 W, less than 0.002 % of the design firing rate. VI. CONCLUSIONS Experimental results obtained on a cyclonic combustor have demonstrated the feasibility of enhancing flame stability and reducing combustion emissions by the application of a dc electric field. The data obtained show a strong influence of a dc electric field on the flame stability, at a firing rate of 0.5 x 106 Btulh and a smaller influence at 1.0 x 106 Btulh. Based on the experimental results, some preliminary conclusions can be made: 1. A dc electric field can improve flame stability at high excess air operation in the IGT cyclonic combustor. 2. Electrodes can be appropriately located in the combustor based on measured combustion characteristics. 10 |