Simulation Study On Laminar-premixed Combustion Characteristics Of Nature Gas Components

As an alternative transportation fuel,natural gas has drawn much attention for its potential in relieving the dependence on the petroleum-based fuels and reducing the environmental pollutants.Natural gas is a complex mixture,which mainly consists of methane,ethane,propane and butane.With respect to the premixed laminar combustion characteristics of natural gas and its components,some studies have been conducted.However,among these studies,the compositions of the natural gas used are dependent upon the origins.Detailed comparisons and analysis are also absent.Therefore the objective of the present thesis is to investigate numerically the premixed combustion characteristics of natural gas and its components based on the chemical kinetic mechanism.With the chemical dynamic software CEHMKIN,this paper first made a research under the different initial conditions of premixed laminar combustion characteristics for the main components of natural gas and its components,and the structure of the flames,the sensitivity of some important elemental reactions as well as the reaction path of natural gas and its components were analyzed.Then,a surrogate fuel of natural gas was conducted based on the premixed laminar combustion characteristics.Finally,the unstability about natural gas and its components and surrogate fuel were calculated in this study.The main conclusions of this study are summaried as follows:?1?.The laminar burning velocity of methane is the lowest and ethane is the highest respectively,propane and butane laminar burning velocity between the methane and ethane;the maximum values of the sum of the major active radicals more fractions?Max{O+OH+H}?present the same trend as the laminar burning velocities.Through the reaction path analysis,this study was found that low carbon alkane combustion process with higher the number of carbon atoms than itself of alkanes generated.?2?.Based on the laminar combustion characteristics of natural gas and its components,this study constructed an alternative natural gas components including 90%CH₄,4.5%C₂H₆,3%C₃H₈ and 2.5%C₄H₁₀??3?.Under the same initial conditions,the fluid dynamics instability of methane is the lowest,the highest fluid dynamic instability is thane;through the comparison of thermal diffusion instability evaluation parameters can be found that the thermal diffusion unstable of methane with the increase of equivalent ratio,the thermal diffusion instability of ethan?propane and butane decreased with the increase of equivalent ratio;Markstein length trend is also proved this phenomenon.