Experimental Study On Flashback Of Lean Premixed Swirl-stablized Combustor

With the improvement of individual’s environmental protection awareness, clean and efficient low-pollution combustion technology has been developed widely. Because the lean premixed combustion technology is low-pollution, low-energy consumption and high-efficiency, therefore, it has become an international hot issue. However, when the experiment conditions are far away from the stoichiometric ratio, lean premixed combustion flame easily leads to some problems, such as blow out and flashback. These problems lead to the combustion proceeding in unstable conditions, which lags the progress of lean premixed combustion technology greatly.To analyze the flashback instability rule in the process of lean premixed combustion, and acquired the limits of corner recirculation zone flashback under different experimental conditions. The cold-flow and hot-flow characteristics of the combustor and flashback behavior of the combustion flames are studied by using the PIV system and the High Speed Photography in this paper. The main research work and conclusions are as followed:(1) The lean premixed swirl-stabilized combustor is constructed, which includes the combustor, the fluidized bed tracer particle generators, the data acquisition system and the adjusting and control system of experiment. The flow structure of combustor is obtained by PIV and the combustion flame is acquired by High Speed Photography, which is the basis for researching the flashback behavior of lean premixed swirl-stabilized combustor.(2) The characteristics of cold-flow filed under swirling are researched on experimental platform. Results show that the cold-flow structure includes corner recirculation zone, central recirculation zone and shear layer, and the Precessing Vortex Core is formed in the cold-flow filed. The cold-flow structure of the swirl-stabilized combustor is stable under different experiment conditions. The recirculation zone length and width decreased with increasing the inlet pressure. The central position of the recirculation zone moves to the upstream of the combustor and the maximum reverse flow velocity of the recirculation zone is enhanced as inlet pressure is increased. But the influence of combustor equivalence ratio on cold-flow distribution rule is opposite with inlet pressure.(3) The characteristics of hot-flow filed of lean premixed swirl combustor are researched on combustor platform. Results reveal that the hot-flow structure includes corner recirculation zone, central recirculation zone and shear layer, and the Precessing Vortex Core can be observed clearly in the cold-flow filed. The hot-flow structure of the combustor is stable under different experiment conditions. The recirculation zone length decreased with increasing inlet velocity. The maximum reverse flow velocity of the recirculation zone is enhanced as inlet velocity is increased. The central position of the recirculation zone moves to the upstream of the combustor as inlet velocity increased.(4) The characteristics of cold-flow and hot-flow in combustor are compared, and there are two different points:① Corner recirculation zone is more indistinct compared to that in cold-flow and the distribution of combustor flow field is more irregular under the hot conditions.② The central position of the recirculation zone is different in cold-flow and hot-flow. The central position of the recirculation zone moves to the downstream of the combustor and the recirculation zone length is increased under hot conditions. Compared to the cold-flow, the maximum reverse flow velocity is smaller in the hot-flow.(5) The effects of combustor equivalence ratio and air flow on the limits of lean blow out flame were analyzed. It is found that the limit of blow out is enhanced as dump ratio is increased when the air flow is constant. In addition, the limit of blow out decreased with the increase of air flow when the dump ratio is constant, and the decreased scope of blow out limit is increased as dump ratio is increased when the range of air flow increased is constant.(6) Flashback in corner recirculation zone can be observed and the flame color becomes from pale blue to bright blue with the increase of equivalence ratio. The premixed section flashback appears when the flame is propagating to upstream of the combustor and it can be prevented effectively if bluff body is installed on the premixed pipe. In addition, the inlet velocity has little effect on the characteristics of flashback flame, but the influence of the swirler height and the dump ratio on the flashback flame is distinct. The studies show that the limit of flame flashback is around 0.65 in different inlet velocity and the phenomenon of flashback is especially obvious when the swirler height is forty millimeter or the dump ratio is 3.1.