Structures and extinction limits of counterflow diffusion flame were numerically investigated. Especially, methane-hydrogen mixed fuel flame structure and their extinction mechanism were carefully analyzed. The reactive flow equations are solved numerically by employing Newton iteration. The chemical model includes detailed transport properties and complex kinetics. The Jacobian of the system becomes singular in the vicinity of the extinction point. To avoid the computational difficulties, a flame controlling continuation method is formulated.
It is shown that the diffusion flame of methane-hydrogen mixed fuel has two layers of the fuel consumption. Methane is depleted in the fuel side of the reaction zone and hydrogen is consumed in the oxidant side after depletion of methane. Very high affinity of methane to H, O, OH radicals causes the fast exhaustion of methane. Thus the methane leakage from the reaction zone is not observed. As the strain rate increases, the leakage of hydrogen and oxygen increases. The increasing leakage of hydrogen and oxygen is the mechanism of extinction in methane-hydrogen mixed fuel flame
