| In recent years,plasma shows outstanding advantages in enhancing low temperature ignition and combustion at extinction limit.As numerous active species are produced by non-equilibrium excitation in a plasma,the application of non-equilibrium plasma to ignition and combustion can change combustion reaction pathways,and therefore improve flame stability,increase ignition volume,reduce ignition delay time,extend flammability limitation and reduce emissions.The researches of plasma assisted ignition,combustion,pyrolysis and oxidation,as well as fuel reforming have been conducted by fundamental and applied studies.Many innovative results have been achieved.However,there still lack of researches about the kinetic studies of plasma assisted low temperature ignition,pyrolysis and oxidation by non-equilibrium excitation and the design of optimized discharge types for plasma assisted ignition.In this work,the kinetic enhancement of non-equilibrium excitation on low temperature H2,CH4 and C5H12 pyrolysis,oxidation and ignition is studied both by experimental measurements and numerical modeling.A plasma assisted low temperature fuel pyrolysis and oxidation experimental system is set up.Time-dependent TDLAS measurements are conducted to quantify gas temperature and intermediate species density evolutions in a plasma.Mole fractions of steady species are measured by the Gas Chromatography.The kinetic mechanisms of plasma assisted low temperature fuel pyrolysis,oxidation and ignition are developed and validated by the experimental measurement.A new zero-dimensional plasma assisted combustion code is developed to study the effects of non-equilibrium excitation on low temperature ignition and combustion.The effects of vibration excitation on CH4/air ignition in a nanosecond discharge（NSD）are studied.The main pathways of N2（v）are investigated by path flux analysis and sensitivity analysis.The low temperature ignition enhancement of CH4/O2/He mixtures by non-equilibrium excitation using a hybrid repetitive nanosecond and DC discharge（NSD-DC）is studied.This discharge type shows an improvement of active species selectivity by adding a DC discharge.In addition,the optimum discharge condition to achieve the maximum ignition enhancement is studied by analyzing the effects of vibrationally excited species,O2（a1?g）,O（1D）and O on ignition enhancement.The low temperature ignition enhancement of H2/O2/He mixtures in a hybrid repetitive NSD and DC discharge is studied.The results show that the optimized ignition enhancement is achieved when the dissociation of H2 and O2 and the exication of vibrationally excited species and O2（a1?g）both occur efficiently at an appropriate DC electric field strength.Meanwhile,the uncertainties of the plasma reactions involving H2（v）and O2（a1?g）on ignition delay time calculation indicate that the selection of accurate rate constants is important for plasma assisted combustion modeling.The kinetic pathways of plasma assisted low temperature C5H12 pyrolysis and oxidation are studied.The importance of the multi-bonds break reactions of C5H12 in the plasma are revealed.The effects of N2/Ar/He on low temperature CH4 pyrolysis in a repetitively-pulsed nanosecond discharge are studied.The effects of plasma generated species by non-equilibrium excitation on CH4 pyrolysis are demonstrated.This study provides a theoretical insight for plasma assisted low temperature pyrolysis and oxidation,plasma assisted low temperature ignition as well as optimization design of discharge types. |
