| Plasma-assisted combustion is a promising approach to achieve fast ignition and highly efficient combustion.The decomposition and conversion of fuel and the purification and reduction of gas can be achieved to help ignite and stabilize the flame.The main enhancement effects of discharge plasma-assisted combustion are thermal enhancement,kinetic enhancement and transport enhancement.The nanosecond pulsed power supply has higher electron density and average electron energy than the conventional AC driven discharge plasma.The parameters of pulse power supply have important influence on plasma assisted combustion.In this work,the methane-air nanosecond pulsed dielectric barrier discharge plasma-assisted combustion is numerically investigated by combining a home-made plasma model with the combustion model of software CHEMKIN-PRO.A one-dimensional plasma fluid model and a two-dimensional plate shear flow combustion model based on CHEMKIN-PRO were established to solve the plasma assisted combustion process.The plasma fluid model takes into account the local field approximation,the current generated by the flow of ions under the electric field and the space-time evolution of particle density,which can be used to analyze the mechanism of particle consumption and generation path.Effects of pulse parameters on characteristic parameters of the plasma-assisted planar shear flow combustion as well as the reaction pathway maps of not only the nanosecond pulsed dielectric barrier discharge plasma but also the combustions without and with plasma assistance are systematically illustrated and analyzed.The characteristics of plasma discharge include discharge current density,electron density,average dissipated power density,average electron temperature,spatial distribution of electric field and average particle density.(1)The simulation results indicate that under the combined action of increasing electric field intensity and increasing charged particle densities,the peak value of the discharge current density increases and the peak time of the discharge current density brings forward with the increase of the applied voltage amplitude.The temperature reaches its peak value earlier in the methane-air combustion with plasma assisted than in that without plasma assisted.With the increase of pulse voltage peak value,the methane-air combustion time appears earlier,but the auxiliary combustion effect is close when the pulse voltage amplitude is greater than 11 k V.There are emerging pathways to generate hydrocarbons C2H4 and C2H2in the plasma-assisted combustion,the reactions of CH4 on CH and C2H on H2,respectively.The reactions involving active species such as H play a significant role in the plasma-assisted combustion,which causes an obvious decrease in the densities of these active species with plasma assistance.(2)With the increase of pulse frequency the discharge current density,average electron temperature and average dissipated power density have little change in a single cycle.The average active particle density increased with the increase of the average pulse.With the increase of pulse width,the discharge current,average electron temperature and average dissipated power density change differently.In nanosecond pulse dielectric barrier plasma-assisted combustion,the long-lived particles of O3,O2(a)and O accelerate the chain reactions.The mole fraction of O2(a)changes rapidly within0.5 cm and then decreases slowly after passage,and is consumed at about 3 cm away from the gas inlet.The O3 mole fraction increases briefly after penetration and then decreases rapidly and is consumed at about 2 cm from the gas inlet.Analysis of methane-air mixed gas energy change,the backward reaction of O3+M?O2+O+M is the reaction with the highest heat release after plasma penetration.The reaction of plasma particles with methane,nitrogen and oxygen can release heat to heat the gas and generate O,H and OH,and other important active particles of methane combustion.Nanosecond pulsed dielectric barrier discharge plasma makes the combustion happen earlier through kinetics and thermodynamics. |
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