Lean laminar premixed propane and methane flames which were anchored by a hydrogen-pilot flame in a tube were investigated experimentally. Different flame shapes were observed by varying mean velocity from 10 to 200cm/s and equivalence ratio from 0.45 to 0.7. It was possible to draw a stability diagram for propane and methane flames. The stability diagram consists of flashback region, tail-out region, stable region and vibrating region. The stability diagram in this paper is valid for pilot flow rate of 11.9ml/min and glass tube of 20cm length.
Only a pilot flame exists in the tail-out region and the anchored flame flashes back along the surface of pilot nozzle in the flashback region. The anchored flame vibrates from the pilot flame emitting audible sound in the vibrating region and the flame exists stably in the stable region.
Thermo-diffusive flame instability was investigated in the stability diagram for propane and methane flames. First, there was oscillation in both propane and methane flames between the stable region and the tail-out region, but there was a difference between propane and methane flame shape while propagating. The curvature in the methane flame becomes more steeper while propagating, but the one in the propane flame remains unchanged. Such is due to Lewis number effect. Second, there was difference of flame intensity in the propane and methane flame in the vibrating region which is also due to Lewis number effect.