Dual-stage lean premixed combustion is proposed to improve the stability of premixed flame. It is organized by dividing premixed gas into radial stages with different equivalence ratio for the purpose of stable combustion under lower global equivalence ratio. The minimum equivalence ratio of primary gas in jet flame or dual-stage lean premixed flame is defined as extinction limit and measured experimentally

and the effect of flame manner and coflow parameters on extinction limit is investigated. The result shows that the outer coflow affects the distribution of concentration and velocity near flame root. The secondary premixed coflow in dual-stage lean premixed flame can reduce the dilution effect of outside atmosphere on the premixed gas

so the flame has a wider extinction limit. The secondary equivalence ratio is key parameter affecting extinction limit of dual-stage lean premixed flame. Comparing with uniform jet flame

the dual-stage lean premixed flame can combust under lower equivalence ratio

which is important for industrial controlling of NOx emission.