SUMMARY

In an aircraft afterburner carrying a very high speed flow flame is stabilized by a high temperature recirculating flow behind bluff body flame holders, such as a V-gutter. In this case, bluff bodies block the high speed flow, and thus, induce a significant total pressure loss. In addition, heating the flame holder by the hot combustion product in the recirculation zone causes a thermal signature, which is a critical issue in a military jet. To reduce these problems, ignition methods using a plasma in the form of high frequency (HF) spark discharge, and using a radical jet generator (RJG) were developed. The electrical power consumption for flame stabilization by HF discharges in a premixed methane-air flow at atmospheric pressure was very small compared to the combustion heat release when the operating velocity is relatively low. However, theoretical study showed that the required electrical power increases rapidly with increasing flow velocity. The operating limits of the flame stabilization by this technique is estimated by the model, and the results were compared to those obtained experimentally. For the flame stabilization in a much higher velocity flow, a radica jet, which is generated by the initialization process by the electrical discharge and then by the cascade process inside the RJG was used. The characteristics of a radical jet obtained Experimentally. The limits of the flame stabilization by this jet was also measured. These results were compared to those of bluff body flame holders. The flame holding performance of the radical jet was also compared to that of thermal jet experimentally. The effect of radicals on the flame stabilization was studied using CHEMKIN. The limit of flame stabilization by the radical jet was estimated using a simplified model. These suggested that the reduction of local ignition delay time by the active species in a radical jet and the longer radical jet than those of the recirculation zone increases the maximum flame stabilization velocity.