介质阻挡体放电对甲烷扩散火焰特性的影响

The Influence of Volume Dielectric Barrier Discharge on Methane Diffusion Flame Characteristics

本文在高频交流激励模式下,采用同轴圆柱构型激励器,开展了介质阻挡体放电对空气/甲烷同轴剪切扩散火焰燃烧特性影响实验研究。激励器敷设在外喷嘴环缝以电离空气,采用纹影系统和B型热电偶分别获取流场形态和火焰温度,激励频率为8 kHz,通过改变气体流量和放电电压,分析了不同工况下射流流场、火焰结构和火焰温度在等离子体作用下的变化规律。结果表明:等离子体气动效应能有效增强射流湍流强度,强化空气/甲烷掺混,增大射流角,并随激励电压提高作用效果逐渐增强,实验中未形成明显扩张流动的初始射流在放电电压30 kV时其射流角最大为23.5°。贫燃条件下等离子体激励会改善火焰形态,增强燃烧稳定性,并在流量较低时缩短火焰长度。此外,富燃火焰下游温度会随着激励强度增大不断升高,而贫燃火焰下游温度变化受上游燃烧强度影响存在升高和降低两种情况。

With high-frequency AC actuation,the effect of volume dielectric barrier discharge on combustion characteristics of shear-coaxial air/methane diffusion flames has been experimentally studied by adopting coaxial-cylinder actuator in this paper.The actuator is arranged in the external annular tube to ionize the air.The schlieren system and B-type thermocouple are used to obtain the flow field morphology of coflow jet and flame temperature respectively.By changing the gas flow and discharge voltage with actuating frequency of 8 kHz,the variations of shear-coaxial jet flow field,flame structure and flame temperature under the plasma control are analyzed.The results show that,based on the aerodynamic effect,the plasma actuation can effectively enhance the jet turbulence intensity,strengthen air/methane mixing and enlarge jet expansion angle,and this phenomenon becomes more obvious with increasing discharge voltage.The maximum jet expansion angle of the jet that initially seems no obvious expanding flow will reach to 23.5°with discharge voltage of 30 kV in the experiment.As the combustion in fuel-lean situation with plasma discharge,the flame morphology is significantly improved,which reveals that the flame stability is also enhanced,and the flame length is shortened corresponding low flow rate.Moreover,there is an increasement in the flame downstream temperature with plasma discharge in fuel-rich situation,and it becomes more pronounced with higher voltage.For fuel-lean condition,as flame downstream temperature is greatly affected by the combustion intensity in the upstream part of flame,there exists both of increasement and decreasement in the variation of temperature.