Experiments on the incendivity of radio-frequency, breakflash discharges (1.8ߝ21 MHz c.w.)

The incendive properties of radio-frequency, breakflash discharges have been investigated experimentally in the 1.8ߝ21 MHz frequency range, using a continuous wave source. Minimum powers and voltages for ignition have been measured. For ethylene/air and methane/ air mixtures, matched load powers of 7 W and 12 W, respectively, must be exceeded for ignition. However, the precise form of the impedance of the radio-frequency source has an important effect, and for some sources much higher powers are required to produce an incendive discharge. The electrode material is also significant: a minimum voltage of about 300 V (peak) is required between clean metal electrodes to produce an incendive discharge, but no voltage criterion has been detected with rusty steel electrodes. The shape of the electrode is important: some shapes promote flame quenching. Neither the rate of separation of the electrodes nor the excitation frequency were found to have a significant effect on ignition. Many of the combustion aspects of the problem can be explained by a simple ignition model.