IMPROVEMENT OF IGNITION SYSTEM OF DETONATION ENGINES WITH AN INITIATED MICROWAVE SUBCRITICAL STREAMER DISCHARGE

Pulsed detonation engines are considered to be the promising e¨ective propulsion systems for future space missions. The ignition system has always posed problems in commercial applications. Many experimental, theoretical, and numerical studies have been performed for the past years and various ignition systems (e. g., electric discharge, microwave discharge, laser radiation) have been tested. The propulsive performance of air-breathing pulsed detonation engines (PDEs) has been theoretically and numerically studied over a wide range of system con¦gurations, operating parameters, and §ight conditions. It has been suggested that discharges which create the quickest expanding high-temperature region or discharges which occupy a large volume are optimal for ignition because they can most rapidly and reliably bring the radius of the ignition kernel to its critical value for transition into a self-propagating §ame. Signi¦cant e¨orts are being spent on acceleration of fuel combustion and rising its e©ciency. Existing studies have mainly focused on optimizing fuel injection and mixing, repetitive initiation of detonation, and integration of detonation tubes with fuel inlets. Understanding of streamer propagation mechanism is of essential importance for the studies of electrical breakdown phenomena and their related applications. In this study, a subcritical microwave streamer discharge is used to initiate ignition of air fuel mixtures. The study focuses on investigation of possibilities of the use of microwave radiation to initiate combustion and detonation of air fuel mixtures. The results of experimental and computational studies related combustion and detonation of air propane mixture are presented. To initiate the combustion and detonation, the deep subcritical streamer discharge is used. The discharge is formed by a ¦eld with the intensity smaller than the minimum pulse intensity leading to the gas breakdown. An acceleration of combustion and a uniform temperature front are obtained and the possibility of combustion of fuel-lean mixture is con¦rmed. An increase in combustion e©ciency is also observed. Streamer discharge ignition of particularly lean air fuel mixture with air-to-fuel ratio greater than the §ammability limit has been demonstrated under normal conditions. The indirect evidence suggests that the ignition by the microwave discharge is of the nonthermal nature. The advantages of igniting the fuel mixture by streamer discharge is attributed to the ultraviolet radiation emitted by oxygen atoms subjected to the discharge. The ultraviolet radiation generation causes formation of the nonequilibrium cold plasma with avalanche increase in the number of free electrons. The microwave streamer ignition can be considered for the application in internal combustion engines to replace the conventional spark ignition.