Abstract:

The lean combustion experiments of natural gas and air mixture were conducted to investigate the influences of electric fields generated by alternating current (AC) at the frequency of 15 kHz and direct current (DC) with the same voltage virtual value on the flame propagation and combustion characteristics of premixed CH₄/air mixtures at room temperature and atmospheric pressure. The results show that the flame shape deforms when the two kinds of voltages are applied to the mesh electrodes. The flame is stretched more severely in the horizontal for AC than for DC at the same excess air ratio, especially when concentration of natural gas is diluted by excess air. When excess air ratios are 1.2, 1.4 and 1.6, average flame propagation speeds increase up to 49.14%, 76.54% and 117.65% for AC, and 41.38%, 58.02% and 62.75% for DC, and peak values of pressure rise up to 9.48%, 11.48% and 14.20% for AC and 4.46%, 5.25% and 8.76% for DC, respectively, compared with those without added voltage. These results indicate that promoting performance for development of combustion flame is better for frequency 15 kHz AC than for DC at the same voltage virtual value.

Key words: natural gas, electrochemistry, ionic wind, numerical analysis, flame propagation characteristics, combustion pressure

摘要：

对常温、常压下定容燃烧弹中的甲烷/空气预混贫燃火焰的传播和燃烧特性进行了研究, 对比了相同电压有效值下15 kHz高频交流电压和直流电压对火焰的影响。结果表明:两种电压加载方式下, 火焰形状均发生变形, 当过量空气系数一定时, 交流电场作用下的火焰在水平方向上的拉伸比直流电场下的剧烈, 且混合气越稀, 两者差异越明显;与未加载电压相比, 当过量空气系数为1.2、1.4和1.6时, 交流电场作用下的平均火焰传播速度分别提高49.14%、76.54%、117.65%, 直流电场下分别提高41.38%、58.02%、62.75%, 交流电场下压力峰值增幅分别为9.48%、11.48%、14.20%, 直流电场下增幅分别为4.46%、5.25%、8.76%。因此, 相同电压有效值下, 15 kHz高频交流电场对火焰的促进作用较直流电场更明显。

关键词: 天然气, 电化学, 离子风, 数值模拟, 火焰传播特性, 燃烧压力