Extinction characteristics of CH₄/CO₂ versus O ₂/CO₂ counterflow non-premixed flames at elevated pressures up to 0.7 MPa

Extinction characteristics of counterflow radiating non-premixed CH ₄/CO₂ versus O₂/CO₂ flames at elevated pressures up to 0.7 MPa were studied both experimentally and computationally. Conventional C-shape extinction curves due to the upstream conduction loss at lower stretch rate were observed at 0.1 and 0.2 MPa. However, at 0.5 and 0.7 MPa, fuel-lean extinction limits were monotonously broadened with the decrease of stretch rate at lower stretch rate region while CH ₄/N₂ versus O₂/N₂ flames showed conventional C-shaped extinction behavior at the same condition. Interpretation of these experimental extinction characteristics was made with one-dimensional computations using optically thin and statistical narrow-band radiation models. The computational results implies the observed phenomena can be attributed to the radiation reabsorption which plays a significant role at high pressure conditions.