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.