Study On The Effects Of Laser Induced Plasma On The Methane Flame Stability

In recent years, High Supersonic Aircraft Technology has developed rapidly inaerospace filed. Scramjet Engine has currently been considered as the best powersystem for supersonic aircraft and become the hot research spot all over the world. It isone of the most difficult technologies to achieve highly efficient ignition and stablecombustion in the combustion chamber of scramjet. Due to the disability of traditionalmethods to achieve good combustion stability in scramjet, plasma flameholding methodhas gradually attracted people’s attention. Compared with the discharge plasma, laserinduced plasma is very suitable for scramjet because of its non invasion character, highrepetition frequency, capacity to generate plasma in any position and many otheradvantages.After analyzing the shortcomings of current research work, the research content ofthis paper was determined. According to the laser induced plasma principle and laserinduced plasma flameholding theoretical model, the experimental program was come upwith.On the self designed laser induced plasma flameholding experimental platform,the effects of stoichiometric ratio, oxygen volume percentage, laser pulse energy andlaser focal position on the flame extinct limit were studied. It was found that when thestoichiometric ratio ranged from0.7to1.0, the flame blowoff limit was increased by9.3%25%. When the oxygen volume percentage and laser pulse energy reached22.2%and1.82mJ, the blowoff limit was increased by87.4%and53.8%respectively. Besides,the flame could still stay stable even when the laser was lifted up three times of theburner diameter. The above had perfectly proved the feasibility and the effect of thismethod.Based on the spontaneous emission fluorescence spectra observed in theexperiments, O, CH, H, CH₃and other active radicals were found out in the plasma. Bycoupling the combustion reactions with gas flow in FLUENT software, the influence ofO, CH₃and laser focal position on the flame blowoff limit were investigated, which washelpful to get a better understanding of the mechanism of the plasma flameholdingmethod and proved its feasibility.