| Facing the problem of low efficiency of energy utilization in current energy crisis and the difficulty of stable combustion in the development of scramjet in aerospace dynamics, the combustion rate and efficiency need a higher requirement. According to these problems, this paper proposes a method of using femtosecond laser induced plasma to assist combustion. There exist plenty of free radicals, excited components in the plasma induced by femtosecond laser. And the existence of these active particles increases the rate of chian reactions of combustion and flame propagating, achieving the effect of assisting combustion.The paper first analyzes the feasibility of combustion enhancement by femtosecond activation gas reactive molecules. Then we set up the combustion model using the flame propagation speed calculator module in CHEMKIN combined with methane burning mechanism with the action femtosecond laser. With this model, we analyze the influence of several active compents in plasma to the laminar pre-mixed flame. Using the methods of sentivity analysis and product generation rate analysis, we analyze the mechanism of combustion enhancement by O and O2(a1Δg) in laminar pre-mixed flame.Through the simulation analysis, we found that O and O3 can improve flame propagation speed and concentrations of H, O, OH compenents through the whole range of equivalence, achiving the effect of combustion enhancement. CH3 and CH2 can improve flame propagation speed for poor fuel flame when the equivalent is lower than a certain boundry. Excited components O2(a1Δg) and O2(b1Σg+) can obviously increase the flame propagation speed and concentrations of H, O, OH compents. The effects of combustion enhancement by O2(b1Σg+) are more apparent than O2(a1Δg). We found that when acting with O2, N2(A3Σu+) can realize combustion enhancement by stimulating O2 to O2(a1Δg) and O2(b1Σg+) or disintegrate O2 into O. At the same time, through disintegrating H2 into H, N2(A3Σu+) can also realize combustion enhancement by increasing the concentration of H component in laminar pre-mixed flame.Based on the mechanism analysis, we found that the reaction of H+O2(?)O+OH is the most important one to control flame propagation speed and the concentration of H, O, OH in laminar pre-mixed flame. The existence of O and O2(a1Δg)in pre-mixed flame increase the forward reaction rate of the reactions with positive sensitivity to flame propagation speed and the reverse reaction rate of the reactions with negative sentivity to flame propagation speed. This phenomenon explains the reason of combustion enhancement by O and O2(a1Δg). |
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