Extinguishment of propane/air co-flowing diffusion flames by fine water droplets
Extinguishment of propane/air co-flowing diffusion flames by fine water droplets
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DOI：
10.1016/j.proci.2012.06.046
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发表时间：
2013
期刊：
影响因子：
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通讯作者：
I. Sakurai;J. Suzuki;Y. Kotani;H. Naito;A. Yoshida
中科院分区：
文献类型：
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作者：
I. Sakurai;J. Suzuki;Y. Kotani;H. Naito;A. Yoshida
在本研究中，通过实验研究了细水滴对丙烷/空气同流扩散火焰的熄灭。水滴由压电雾化器产生，最大液滴流量为1500ml/h。当燃料喷射速度Ufi较低时，底部预混合火焰的附着层流扩散火焰稳定。在距燃烧器边缘一定距离处，发生从层流扩散火焰到湍流扩散火焰的转变，并且在下游区域形成湍流扩散火焰。当喷油器边缘较薄（δ=0.5mm）时，火焰稳定性随着并流气流速度Ua和水滴流量Qm的增加而恶化。稳定机制可以通过底部形成的预混火焰的气体速度和燃烧速度的平衡来解释。然而，当喷油器边缘较厚（δ=5mm）时，会在喷油器边缘下游产生再循环区。淬灭距离 Hqon Uf 和 Qmis 的依赖性相对较弱，稳定性图显示出奇怪的特征。结果表明，Uai 至关重要，因为它决定流动停留时间；如果Ua<0.4m/s，水滴经过再循环区时会蒸发，水蒸气会扩散到再循环区中。然而，如果Ua>0.4m/s，水滴会在没有充分蒸发的情况下通过再循环区，并且不能有效地熄灭火焰。含有水滴的空气的供给速度应足够低，以便水滴能够蒸发，水蒸气能够扩散到底部的预混合区域，以获得足够的水滴灭火效果。
In the present study, extinguishment of propane/air co-flowing diffusion flame by fine water droplets was investigated experimentally. Water droplets are generated by piezoelectric atomizers with the maximum droplets flow rate of 1500ml/h. When the fuel injection velocity Ufis low, an attached laminar diffusion flame with a premixed flame at the base is stabilized. At some distance from the burner rim, a transition from laminar to turbulent diffusion flame occurs, and a turbulent diffusion flame is formed in the downstream region. When the fuel injector rim is thin (δ=0.5mm), the flame stability deteriorates with increase of the co-flowing air stream velocity Uaand the water droplets flow rate Qm. The stability mechanism can be explained by the balance of the gas velocity and the burning velocity of premixed flame formed at the base. However, when the injector rim is thick (δ=5mm), a recirculation zone is produced downstream of the injector rim. The dependence of the quenching distance Hqon Ufand Qmis relatively weak, and the stability diagram shows curious features. It was shown that Uais crucially important since it determines flow residence time; if Ua<0.4m/s, water droplets can evaporate when they go by the recirculation zone, and the water vapor can diffuse into the recirculation zone. However, if Ua>0.4m/s, the water droplets should pass by the recirculation zone without sufficiently evaporated and are not so effective to extinguish the flame. The supply velocity of droplet-laden air should be low enough so that water droplets can evaporate and water vapor can diffuse into the premixed region at the base to obtain sufficient effectiveness of water droplets for fire suppression.