Effect of confinement ratio on flame structure and blow-off characteristics of swirl flames

•The macrostructure and blow-off characteristics of swirling flame with different confinement rates were studied.•The increase of CR in the confined combustor is helpful to enhance the resistance to stretch-induced extinction.•The ISL vortexes accelerate the flame blow-off near the lean limit.•The downstream ORZ is helpful to stabilize the flame near blow-off with CR = 3.•The transition process from a stable to an unstable flame is extended by increasing the CR of the confined combustor.