EXPERIMENTAL-STUDY OF EXTINCTION OF NONADIABATIC COUNTERFLOW PREMIXEDFLAMES

The effects of the velocity gradient and nonadiabaticity on the extinc tion of premixed counterflow low-pressure flames were studied using sa turated laser-induced fluorescence of OH radicals. The temperature and OH concentration were determined at a stagnation point for different opposed flow velocities in nonadiabatic and near-adiabatic methane-oxy gen-nitrogen flames in the range of equivalence ratio 0.6-1.2. The tem perature and OH concentration profiles were measured in twin flames fa r from and close to extinction. Temperatures at the stagnation point v ary with heat losses and velocity gradient, while OH concentrations de pend mainly on velocity gradient. Spatial gradients of temperature or OH concentration profiles in twin flames are insensitive to velocity g radient and heat losses. The implication of these results for the corr ectness of probe sampling and mass-spectrometric analysis in low-press ure flat flames is discussed.