OCR Text |
Show the velocity, U, of the fuel/air mixture as it leaves the exit tube, and an increase in the velocity of the combustion products. As h ex:. VO.8 for convective heat transfer to vertical fins, the decrease in the flame temperature difference caused by decreasing ~ is offset by an increase in h. This leads to only a slight dependence of thermal efficiency on ~, and allows this system to maintain the high thermal efficiencies found in current Telstar units. As the previous figures have shown, the thermal efficiencies at powers of 15 kW and above are comparable to that of the Telstar spa heater. More importantly, the WSB delivers these efficiencies in the lean-burning range of ~ < 1.0 where it is expected that the NO emissions would be low. Figure 7 shows the NO concentrations (corrected to 3% O2) of the WSB/Telstar system for 15 and 18 kW. 100 100 90 Average NO level from current Telstar unit (<1> > 1.0) 90 ----- - ----- 80 80 ."..-~.0.-... 70 70 .".~-0. . CJ Future Regulation Level ...... CJ J~,.. 60 60 ~ (below 50 ppm) J,.. J,.. J,.. 0 0 50 0 'C-J ' 50 ------------- - ------------------- - - - - - -- - -- - 'C-J ' e • x 40 e cc.... 40 • 15 kWWSB 0 cc.... 0 30 0 18 kWWSB ., 30 0 Z - - x - - Pulse Comb. ~x Z 20 ~ -x - 20 • _ -x ~ 10 0 - _ -x - 10 ~ - -x. 0 x~ 0 0.6 0.7 0.8 0.9 Equivalence Ratio Figure 7: NO concentrations for the WSB/Telstar unit Also shown in Figure 7 are two references: the proposed 50 ppm regulation and the average NO concentration produced by the unmodified Telstar unit that uses a conventional rack burner. As can be seen, the unmodified Telstar spa heater has NO 12 |