Experimental And Simulation Study On Premixed Combustion Characteristics Of Natural Gas

Natural gas equivalent combustion combined with EGR can reduce pollutant emissions,and the engine does not need a major modify,so the technology has a good application prospect.Laminar combustion is an important research field,and it has important guiding significance for the study of turbulent combustion and the practical application of the fuel.In this research,natural gas-diluted gas premixed combustion experiments was conducted based on a constant volume bomb with a Schlieren system.The laminar burning velocity was calculated using Schlieren method,and the flame stability was investigated.In addition,Chemkin-Pro was used to calculate the laminar burning velocity,the concentration of reactants and products,and the concentration of important active radicals.The equivalent effect of coupling the initial conditions on laminar burning velocity were analyzed based on the data from Chemkin-Pro.Besides,the regulation of flame stability,concentration of important active radicals,and the difference in the whole combustion process of test conditions with very close laminar burning velocities were analyzed.First,the effects of initial conditions on flame speed,burning velocity,flame stability,flame structure and active radical concentration were analyzed.The results are shown below: both flame propagation speed(stretched and un-stretched)and the laminar burning velocity increase first and then decrease with an increasing equivalence ratio.The peak burning velocity occurs at the equivalence ratio of 1.1~1.2.Markstein length increases with equivalence ratio,and decreases with initial pressure.Markstein length decreases with initial temperature at lean side,while the effect of initial temperature on Markstein length is not significant at rich side.When the equivalence ratio is less than 0.9,Markstein length decreases with dilution rate;when the equivalence ratio is greater than 0.9,Markstein length increases with dilution rate.The preferential diffusion instability of the flame decreases with equivalence ratio,decreases with initial temperature,increases with the dilution rate,and hardly changes with the initial pressure.The hydrodynamic instability of the flame increases with initial pressure and decreases with initial temperature and dilution rate.The concentration distribution of the reactants and products does not change significantly with any initial condition(except for carbon dioxide,which increased as the dilution rate increased).Active radicals OH,H,and O mainly affect the laminar burning velocity,and the maximum concentration increases with initial temperature,and decreases with initial pressure and dilution rate.The maximum concentration of OH+H is highly correlated with the laminar burning velocity.Besides,the distribution of laminar burning velocity and the equivalent effect of coupling initial conditions on laminar burning velocity were analyzed.The results are shown below: laminar burning velocity shows a certain distribution with the coupling of initial temperature,initial pressure and dilution rate.In area with higher laminar burning velocity(high temperature,low pressure and low dilution rate),laminar burning velocity is more sensitive to the change of initial conditions which has been coupled.Regard to couple initial conditions for equivalent laminar burning velocity,when the coupling conditions are initial temperature and dilution rate,the variation of the coupled initial conditions is almost constant(i.e.when one initial condition changes by Δa,the other initial condition changes by Δb,and these two values do not change with laminar burning velocity).When coupling initial temperature and initial pressure with a constant change in initial pressure,the change in initial temperature is smaller in the area where laminar burning velocity is smaller,while the change in initial temperature is greater in the area where laminar burning velocity is greater.When coupling initial pressure and dilution rate with a constant change in initial pressure,the change in dilution rate is smaller in the area where laminar burning velocity is smaller.Test conditions with very close laminar burning velocities still show differences in combustion pressure,combustion temperature,heat release and combustion duration.