CHARACTERISTIC RESIDENCE TIMES OF LAMINAR NONPREMIXED FLAMES AT EXTINCTION

The relationships between the inverse of the characteristic residence time a(q) which is a measure of the strain rate at extinction, the ''s calar dissipation rate'' at extinction chi(q), the adiabatic dame temp erature T-st, and the stoichiometric mixture fraction Z(st) in diffusi on flames are examined. Numerical calculations are performed to determ ine the structure and critical conditions of extinction of diffusion d ames stabilized between counterflowing streams, one containing methene and the other containing oxygen. These reactant streams are diluted w ith nitrogen or with nitrogen and argon. In the flame the value of the scalar dissipation rate is found to vary over a wide range and its va lue evaluated at Z(st) is used to characterize the system. At constant values of T-st the values of a(q) and chi(q) are found to decrease wi th decreasing values of Z(st). The value of chi(q) decreases at a fast er rate than that of a(st). At constant Values of Z(st) the values of a(q) and chi(q) are found to decrease at the same rate with decreasing values of T-st. At constant values of both T-st and Z(st) the values of a(q) and chi(q) are found to be constant for various concentrations of reactants and inert species in the counterflowing streams.