Effects of oxidizer preheating and dilution on the extinction and structure of CH₄-O₂-Ar counterflowing diffusion flames

The effects of oxidizer preheating and dilution levels of fuel and oxygen by inert gas on the extinction and structure of counterflow CH₄-O₂-Ar diffusion flame were studied experimentally and numerically. The OPPDIF code and the GRI-Mech 2.11 database were used for the calculation. The experimental results agreed well with the numerical calculation results. The detailed measurement and calculation of the flame structure revealed that a flame location was in the oxidizer flow side at smaller stoichiometric mixture fraction (F_st). The region of F_st from 0.2 to 0.6 approximately corresponded to the transition region. In this region, the extinction limit depended on the oxidizer and fuel side conditions. The flame location was quite important factor to understand the effects of dilution levels and oxidizer preheating on the extinction phenomena and of the present study.