Simulation Models for High Temperature Air Combustion - High Temperature Air Combustion: From Energy Conservation to Pollution Reduction - page 189

the lower edge of flame, not on the center line, even though the H 2 O concentration
becomes 0.4%. By Jones' model the lifted height does not change much in terms
of oxygen concentration, and it is predicted to be as small as 20 mm when oxygen
is 5%. In contrast, by Srivatsa's four-step reaction model the flame lifted height is
predicted to be comparatively large. The H 2 O concentration of 0.4% was adopted
here as the definition of the flame lift for the convenience of a comparison with that
for the one-step reaction model.

0.6 0.6 0.6

3000

2500

0.4 0.4 0.4

2000

1500

1000

0.2 0.2 0.2

500

0

0. -0.04 0. -0.04 0. -0.04

0.0 0.04 0.0 0.04 0.0 0.04

Y m Y m Y m

(a) One-step global
reaction model

(b) Jones' 4-step
reaction model

(c) Srivatsa's 4-step
reaction model

FIGURE 3.6 Comparison of temperature distributions by different combustion models.

3.2.5.2 Comparison of Maximum Flame Temperature by
Different Reaction Models

Figure 3.8 shows a comparison of the maximum flame temperature predicted by
each model. If we do not take thermal dissociation into account, Coffee's one-step
global reaction model based on the theoretical complete reaction predicts a flame
temperature over 2800 K for preheated air of 1400 K reacting with methane (using
normal oxidant). The temperature corresponding to this condition was 2292 K by
Jones' model, and 1834 K by Srivatsa's model, which seems more realistic. Exam-
ining the change of maximum flame temperature in terms of oxygen concentration,
a flame temperature over 2000 K was predicted even when oxygen concentration is
10.5% by Coffee's model and Jones' model, if the influence of thermal dissociation
was not taken into account.