非平衡等离子体对甲烷——氧扩散火焰影响的实验研究

利用自主设计的等离子喷注器采用介质阻挡放电方式产生非平衡等离子体,首先利用纹影技术、热电偶、单点红外测温等多种诊断方法实验研究了纯氧放电等离子体的电学特性、热效应及气动效应,然后通过可见光和化学自发辐射成像技术获得了火焰形态及特征参数,详细分析了等离子体对甲烷--纯氧扩散火焰形态和释热的影响,并计算了放电功率及费效比. 结果表明, 燃烧导致放电电流显著增大,其中电压幅值与氧气流速对放电电流大小的影响规律正好相反;与空气等离子体相比, 相同流量与电压条件下氧等离子体放电功率较高,但其发光强度明显较弱; 氧等离子体热效应微弱, 对燃烧的影响可以忽略,放电反应中释热过程主要由含氧组分决定;放电产生了具有3个速度分量的诱导射流, 增大了氧射流角,且电压越大越显著.等离子体主要通过气动效应改变了燃料与氧化剂的掺混,使得一定条件下火焰变得更稳定、释热更强.在所研究的范围内等离子体作用的费效比最低仅为2.2％,大流量、小混合比更有利. 

EXPERIMENT STUDY OF EFFECT OF NONEQUILIBRIUM PLASMA ON METHANE-OXYGEN DIFFUSIVE FLAME 1)

Based on the self-designed plasma injector, a nonequilibrium oxygen plasma is generated by dielectric barrier discharge to study the effect of pure oxygen plasma on methane-oxygen diffusive flame. The discharge characteristics, thermal and gas dynamic effects of the plasma, together with the flame characteristic parameters, the discharge power, and the cost-benefit ratio are all experimentally analyzed by utilizing various diagnostic methods, such as schlieren imaging, thermocouple, infrared thermometer, broadband and CH* chemiluminescence imaging. Results show that the discharge current increases notably due to combustion. The current increases with the discharge voltage rises, yet it decreases with the flow rate of oxygen increases. The discharge power of oxygen plasma is higher than that of air plasma, yet the light emission intensity is obviously weaker under a certain flow rate and voltage. The heating of discharge plasma is mainly restricted within the injector. Since the maximum temperature increment led by the plasma is only 30.6 K, it is assumed that the thermal effect of oxygen plasma is too weak to influence the flame combustion. Moreover, according to the experimental results of air discharge plasma, the heat release process of the discharge reactions should mainly be determined by species, which contain oxygen. An induced jet, which has three velocity components, is generated by the discharge. The angle of the original oxygen jet is enlarged due to this induced jet, especially for a higher voltage. The relative capability of the plasma on enlarging the jet angle is stronger under a lower flow rate. The flame becomes more stable and its heat release enhances under certain conditions mainly due to the plasma gas dynamic effect, which changes the mixing between fuel and oxidizer. The lowest cost-benefit ratio of the plasma is only 2.2％ in this study, and the plasma performs better under a high flow rate or a small mixing ratio.