Experimental And Numerical Study On Ignition Delay Characteristics Of Natural Gas

With Energy shortage and environmental pollution becoming increasingly serious,the study of alternative fuels attracted the attention of researchers.Nature gas attracted attention of researchers because of the advantage such as large reserves,high calorific value and low pollutant.Recently,with the advent of natural gas engines,Researchers pay more attention on combustion and emission characteristics of natural gas because of appearance of natural gas engine.To learn about the ignition delay characteristics of natural gas,the ignition delay characteristics of methane,as well as methane/ethane and methane/propane mixtures in a new shock tube were studied in this thesis,the study discussed the effects of temperature,pressure and equivalence ratio on ignition delay time of the fuels.A computational model was established to verify the experimental results.Then the model was used to study the sensitivity analysis and the reaction path of methane,as well as methane/ethane and methane/propane mixtures.The conclusions can be summarized as follows:?1?The effects of shock attenuation,boundary layer and actual gas on the post-wave gas state were obtained in the shock tube.Typical incident shock attenuation rates ranged from 1%to 2.1%/m for the current experiments,which is close to the shock tube facility of Stanford University and King Abdullah University of Science and Technology.With increasing target pressure,the interference of boundary layer to post-wave gas state increases,The rising time of temperature is also in advance.The actual temperature is lower than the theoretical temperature.With the target temperature and target pressure increasing,The difference between actual temperature and theoretical temperature increases.The shock tube was verified via compared with experimental data in the literature.At a temperature of 1500K,the error of the experimental gas's temperature in shock tube is about 20K.With target temperature rising,the error increases.?2?The ignition delay time of methane decreases exponentially with temperature increasing,and increases with pressure decreasing and equivalent ratio increasing.The reaction H+O₂=O+OH is most attributed to ignition of methane,and the reaction2CH₃+M=C₂H₆+M has greatest inhibitory effect on ignition of methane.The reaction path analysis show that:A parallel parallel main path that consumes methyl radicals is CH3 oxidized to CH2O,and another main parallel that consumes methyl radicals is CH₃ combined to C₂H₆.?3?The ignition delay time of methane/ethane and methane/propane mixtures decrease with content of ethane/propane increasing,and its effect gradually decreases at higher levels.The ignition delay time of methane/ethane and methane/propane mixtures increase with dilution increasing,and its effect gradually increases at higher levels.The ignition delay time of methane/ethane and methane/propane mixtures increase with pressure decreasing and equivalent ratio increasing.The equivalent ratio has greater effect on ignition delay time at medium temperature.The reaction H+O₂=O+OH is also most attributed to ignition of methane,and the reaction CH₄+OH=CH₃+H₂O and CH₄+H=CH₃+H₂ have greatest inhibitory effect on ignition of methane.The reaction C₂H₄+H+M=C₂H₅+M of mixed ethane has greatest effect on ignition of methane,and the reaction C₃H₈+M=C₂H₅+CH₃+M of mixed propane has greatest effect on ignition of methane.Mixed ethane and mixed propane both lead to H increasing in dynamic.