Effects of radiative heat loss on the extinction of counterflow premixed H-2-air flames

Radiation heat loss has an important impact on near-limit flames, it has be en shown that radiation heat loss can make stretched CH4-air flames extingu ish at a lower stretch rate. Numerical calculations of counterflow premixed H-2-air dames were conducted using an accurate description of the chemical kinetics and transport properties. Radiation heat loss was considered. The results show that in addition to the stretch extinction limit, radiation h eat loss also allows the lower and middle equivalence ratio counterflow pre mixed H-2-air flames to extinguish at a lower stretch rate. For middle equi valence ratio counterflow H-2-air flames, the closed temperature profiles b ecome distorted O-shaped curves due to the lower Lewis number, being differ ent from those of CH4-air flames. For higher equivalence ratio counterflow premixed H-2-air dames, there are two stable flame branches-a normal dame b ranch and a weak flame branch. When the equivalence ratio is greater than a critical value, the closed temperature profile curve of every equivalence ratio flame opens and the normal dame curve can be extended to zero stretch rate. The calculation of the concentration limit of one-dimensional planar premixed H-2-air dames was also conducted. The results show that the criti cal equivalence ratio corresponds to the concentration limit of the one-dim ensional planar premixed H(2-)air flame. The extension of the flammable reg ion due to the stretch is amplified for the counterflow Ha-air flame becaus e of its much lower Lewis number than that of the counterflow CH4-air flame .