OCR Text |
Show in V. Similar effect of V on N O x was also observed with the FDI oxy-fuel burner combustion shown in Figure 13. Higher V promotes self-induce E G R , reducing peak flame temperature and NOx . Enhancement of self-induced E G R appears to play a major role to reduce N O x . The effect of V on N O x for the FDI flat flame burner shown in Figure 20, however, is less significant than that for the FDI burner shown in Figure 13. For the FDI burner that injects oxygen parallel to the central fuel jet, the effect of V on N O x is relatively straightforward. Higher V simply enhances the self-induced E G R , reducing flame temperature and N O x . For the FDI flat flame burner, on the other hand, the effect of V appears to be rather complex possibly due to the formation of flat flame by the inclined injection of oxygen towards the center fuel jet. Higher V not only enhances self-induced E G R , but also generates more wide-spread flame with more flame radiation. Higher V may have two positive effects to lower flame temperature and N O x . There appears to be a negative effect of higher V on the N O x reduction. The effect of V on the heat flux distribution shown in Figure 17 gives more insight on the effect of V on the flame temperature and NOx . The heat flux distribution for V = 7 0 m/s is larger than that for V=50 m/s, suggesting that flame temperature may be higher for V = 7 0 m/s than for V = 5 0 m/s. While it generates more wide-spread flame with higher degree radiation and self-induced E G R to reduce NOx , higher V may result in higher flame temperature which favors N O x formation. For the FDI flat flame burner the effect of V may generate two competing impacts, one positive and the other negative, on the reduction of N O x. Figure 21 shows the effect of L on NOx emission. Three levels of L (100, 200 and 300 m m ) were tested with 0 set at 10 degrees. For all the three levels of V tested, N O x emission clearly increased with the increase in L from 50 to 100 m m . N O x emission maintained nearly constant with the increase in L from 100 to 200 m m . The effect of L shows little consistency with that for the FDI burner shown in Figure 14. The FDI burner in Figure 14 suggests that larger L, thus more segregation between the fuel gas and the air, promotes the self-induced E G R to reduce N O x . For the F DI flat flame burner, on the other hand, the effect of L appears to be rather complex possibly due to the formation of a flat flame. Eye observation of the FDI flat flames suggests that smaller L leads to higher degree of flatness of flames. The effect of L on the formation of flat flame was by most significant when L was reduced from 100 to 50 m m . The flame for L=50 m m was much flatter and more wide-spread than that for L=100 m m . Flatter flame is believed to promote radiation from the flame while enhancing the self-induced E G R . W h e n L was increased from 100 to 200 m m , less change in the flatness of flame was observed, suggesting the effect of L to be marginal. 11 |