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Show 3.3 Effect of air injection velocity on NOx emission The study varied the combustion air velocity (air injection velocity) to investigate the effect of self-induced EGR. The study tested two levels of air injection velocity. Compared to 15 m/s of the original burner, a higher velocity of 30 rn/s was tested by halving the number of air injection ports from six to three. Only the primary gas was supplied to the burner. Figure 4 shows the effect of excess air ratio on NOx for the two levels of air injection velocity. Compared with the original burner with Vair=15 rn/s that showed 56 ppm, the burner with higher velocity (30 m/s) demonstrated 27 ppm (0% 0) of NOx at the excess air ratio of 1.1. As much as 50% NOx reduction was thus achieved. With the high air injection velocity increased by reducing the number of the injection ports, self-induced exhaust gas recirculation appeared to be enhanced, leading to a substantial reduction of NOx. VlSual observations confinned a remarkable difference in flame characteristics. At the high injection velocity, the flames looked slightly lifted, which presumably maximized the effect of selfinduced EGR combustion. The self-induced EGR was thus superior to the forc~ EGR combustion. 4. Lifted Flame Combustion Based on a New Concept Since the simple modification of the TPM burner showed a substantial reduction of NOx emission as described previously, the study then focused on the enhanced effect of selfinduced EGR and low NOx combustion characteristics of lifted flames. A generic burner of lifted flames was designed and tested to maximize the self-induced EGR. 4.1 Test burner Figure 5 shows a schematic of the test burner. The test burner has front and rear plates, the rear plate is attached around the fuel pipe while in contact with the inside surface of the air pipe. Combustion air is supplied through three slot-like air injection ports arranged around the rear plate. The front plate, larger in diameter than the fuel pipe, is attached to the tip of |