Study On Influences Of Natural Gas Component Variation On Its Laminar Combustion Characteristics

As an alternative gas fuel for engine,natural gas has gotten extensive attention in the industry.Natural gas is a kind of combustible mixture with the primary component of methane,ethane,propane and n-butane,and the components of natural gas mined by different gas fields are largely different.At present,some domestic and foreign scholars have conducted some studies on the premixed laminar combustion characteristics of natural gas with specific components and simulated natural gas,but the researches on the influence of natural gas component variation on its laminar combustion characteristics are quite few.Therefore,this paper,taking the natural gas with different components as the research object,conducts a study on the influence rules of natural gas component variation on the laminar combustion characteristics at the initial conditions of ambient temperature,ambient pressure and different equivalence ratios by employing the method of combining the experiment and numerical simulation.Using constant-volume combustion vessel and high-speed schlieren camera system and CHEMKIN PRO gas-phase chemical kinetics software,this paper employs CH₄–C₂H₆,CH₄–C₂H₆–C₃H₈ and CH₄–C₂H₆–C₃H₈–n-C₄H₁₀ to simulate natural gas,and studies the influence rules of natural gas components variation on the laminar burning velocity and flame instability through changing the components in the natural gas,and analyses the essential reason that the natural gas component variation causes the change of laminar combustion velocities by the flame structure analysis,sensitivity analysis and other chemical kinetics analysis methods.The main conclusions are as follows:?1?When the equivalence ratio remains constant,the laminar burning velocities of natural gas rise with the increasing contents of ethane,propane and n-butane.Compared to propane and n-butane,the influence of ethane content variation on the laminar burning velocity is more obvious.When the natural gas components remain constant,as the equivalence ratio increases,the laminar combustion velocities will increase firstly and then decrease,and reach the maximum value at the equivalent ratio of 1.1.?2?The flame structure analysis shows that there is a strong correlation between the laminar burning velocities of natural gas and the maximum values of the total concentrations of OH radical and H radical in the flames;when the components change,the concentration peak of each main reactive radical will also change and the H radical concentration peak changes most obviously.The change of H radical concentration is the essential reason that causes the change of the natural gas laminar burning velocity.?3?The elementary reactinon sensitivity analysis and the net reaction velocity analysis show that the component variation will affect the important elementary reactions in the natural gas combustion process.The competition between the elementary reactions with positive impacts and the ones with negative impacts changes the concentration peak of H radicals in the flame and the change of ethane contents has the greatest influence on the concentration of H radicals.Therefore,the natural gas laminar burning velocity varies most obviously with the change of ethane contents.?4?The flame instability analysis shows that the transmission of natural gas–air flame is increasingly stable with the increase of ethane contents,propane contents and n-butane contents at the equivalence ratio of 1.0.Natural gas composition variation mainly changes thermal diffusion instability to affect the overall instability of natural gas–air flame.The ability of n-butane is approximately equal to the ability of propane for inhibiting the overall instability of natural gas–gas flame,and is greater than that of ethane.