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Show ' T • • ! - • - 1 - 1 - 1 - ' 1 ' 1 ' 1 • Fuel: C]H,(97vol%>+N2(3vol%) 0.053m3/h, 323K Diluted air 15m'/h, 1223K " - • • Diluted an with N, • Diluted air with C O, A Diluted air with He • Diluted air with flue gas • • • " - i - » - i - • - p - • -i 1 1 i . i . i • 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20 0.22 O Mole Fraction in Diluted Air [-] Figure 12 Influence of oxygen concentration and diluent on N O x emission at furnace exit 1.6 1.5 1.4 8 • s- 1.2 1.1 ' ' - \ \ i 1 1 1 1 - - r - " - i Fuel C,H,(97voI%)+N!(3vol%) 0.053m'/h, 323K Air diluted by N2> 15m Vh, 1223K -1 - \21%02 \ \ \ 10% 02 \ " \ \ \. 4% 02 ^"~\^\^ I . I . I -: 1 r 0 50 100 150 200 250 300 Distance from Air Inlet [mm] Figure 13 Influence of oxygen concentration on temperature uniformity Influence of diluent. In our simulations, nitrogen, carbon dioxide, helium and combustion flue gas were used as diluents respectively. In the case of flue gas, the composition was assumed as 17 % CO2, 79 % N2 and 4 % H 2 O in mole fraction. In a certain oxygen concentration and preheated air temperature, as seen also from Fig 11, the C 0 2 diluted air combustion has the lowest maximum flame temperature, the H e diluted air combustion the highest, while the N 2 and flue gas diluted air combustion the middle. The uniformity of temperature distribution is illustrated in Fig 14 by the Tnax^mcan profiles. The C 0 2 dilution has a better temperature uniformity than the N 2 dilution, while the H e dilution has an almost same temperature uniformity as the C 0 2 dilution even it has a much higher temperature level. The predicted difference between N 2 dilution and C 0 2 dilution is consistent with experimental observations by Kasahara et al [13]. The helium dilution and the flue gas dilution were not tested in their experiments. They inferred that such a difference should result from the difference of heat capacity and/or the difference of mixing processes between fuel and diluted air. According to our simulations, however, the difference of heat capacity might not be the main reason. The specific heat values of N2, C 0 2 and H e are 1.165 kJ/kg- K, 1.259 kJ/kg- K, 5.193 kJ/kg- K, respectively. The big difference of specific heat between H e and C 0 2 could be considered as the reason of the temperature difference, but the little difference of specific heat between N 2 and C 0 2 could hardly explain their temperature difference. The difference of other thermophysical |