a, E-

ame usi res adi twe ore e. ltra le need flame fuels, s such ail in e pro refore, tion and stretch have been studied by using planar and radiative counterflow flames [3–12]. These studies have shown that the flammability limit of stretched flames below a critical Lewis num-ber can be lower than that of unstretched flames. The extended flammable region is found due to the existence of the Near Stagna-tion plane Flame (NSF) and the flammability of the stretched flame below the critical Lewis number is characterized by the limit of the flame cooling on the extinction of the tubular flame, earlier studies focused on the effect of heat loss to the wall [15,20]. The combined effect of radiation heat loss with stretch and curvature, however, has not been addressed in all the previous studies except for the numerical study by Ju et al. [22]. Ju et al. [22] investigated the interaction between radiation heat loss and flame curvature numerically by using premixed tubular CH4/air flames. The results show that the interaction of flame cur-vature and radiation heat loss greatly affects the flame strength and extinction. Unfortunately, the numerical simulations did no