Abstract
The structure of an edge flame in a mixing layer of two uniformly flowing pure CH
4
and pure O
2
streams has been investigated numerically by employing a detailed methane-oxidation mechanism in order to investigate the influence of using pure oxygen, instead of air, as the oxidizing agent. The results exhibited similar behaviour to the CH
4
-air counterpart in the premixed-flame front, through which the carbon-containing compound leaked mainly in the form of CO and H
2
instead of HC compounds. However, while passing through the rich premixed-flame region, the most pronounced distinction of using pure oxygen was that the major route for CO production, in addition to the direct CH
4
decomposition, is C
2
H
m
compound formation followed by their decomposition into CO, thereby giving continuous CO production, contrary to the rich CH
4
-air premixed-flame region in which CO consumption existed.
In the downstream region from the rich premixed flame front, CO is further oxidized into CO
2
in a broad diffusion-flame-like reaction zone located around the moderately fuel-rich side of the stoichiometric mixture by the OH radical produced from the oxygen leakage from the fuel-lean premixed-flame front. Since the secondary CO production through C
2
H
m
decomposition has a relatively strong reaction intensity, an additional heat-release branch appears and the resulting heat-release profile can no longer be treated as a tribrachial structure.