Experimental And Numerical Research On The Laminar Combustion Characteristic Of Biogas

In our daily life,the city produces a large amount of municipal solid waste?life garbage?.The general treatment for municipal solid waste is through landfill.Given the high perishability and moisture content,these municipal solid wastes will be rapidly degraded,thereby generating a large number of landfill gases?biogas?,which results in high resource potential of the landfill.Biogas is a combustible mixture containing gaseous combustible components,such as CH₄,H₂,and CO,with a calorific value of 4600 kcal/m³.When biogas is used as fuel to generate electricity,it can not only recycle the resources,but it can also reduce the emission of polluted gas,resulting in significant economic and social benefits.At present,the design fuel of the gas turbine for power generation is basically natural gas or light diesel.When the fuel gas turbine is converted from natural gas to biomass gas,the fuel composition changes and the calorific value decreases.Moreover,the requirements of environmental protection,as well as the reliability and economy of the gas turbine have to be met.At the same time,due to the influence of many factors,the content of each component in biogas varies significantly,which will have a significant effect on its calorific value,ignition characteristics,and combustion characteristics.Therefore,adjusting and improving the combustion chamber structure and operating parameters of the gas turbine based on the full understanding of the combustion characteristics of biogas,as well as the combustion stability and laminar combustion characteristics is necessary.In this paper,the flame propagation characteristics of biogas are tested in the constant volume bomb under the following conditions:equivalence ratios of 0.7 to 1.4,initial pressures of 0.1 MPa to 0.5 MPa,initial temperatures of 290 K to 380 K,and methane contents of 47%,55.5%,and 59%.The effects of equivalence ratio,initial pressure,initial temperature and methane content on the flame propagation characteristics,flame stability,and laminar combustion velocity of biogas are analyzed.The results show that:?1?The effects of equivalence ratio,initial pressure,and methane content on the flame propagation characteristics of biogas are obvious,but the effect of initial temperature is not obvious.The flame front is smooth,and it always develops outward in a quasi-spherical shape under most conditions.However,the preferential diffusion or buoyancy instability will appear in the flame propagation process and flame front presents irregular cellular structure and protuberances or the flame core will fly upward at certain conditions.?2?The flame radius increases linearly with time at each condition.With increased equivalence ratio,the growth rate of the flame radius increases initially and then decreases gradually,and reach the maximum value at the condition of the equivalence ratio is 1.1.Meanwhile,with decreased initial pressure and increased methane content in biogas,the growth rate of the flame radius shows an accelerating trend.However,the influence of initial temperature on the flame propagation velocity is not significant.Under the different initial operating conditions,the stretched flame velocity shows a rising trend with increased flame radius.At the same time,the variations of stretched flame velocity versus flame stretch rate show a linear relation,and with increased flame stretch rate,the stretched flame velocity decreases.?3?Increasing the equivalence ratio and the methane contents or decreasing the initial pressure increases the Markstein length and the stability of the flame front is increased.However,the effect of the initial temperature on the Markstein length is not obvious.With the equivalence ratio increasing,the unstretched flame velocity and the laminar combustion velocity illustrate an increase initially and then decreases gradually,and the maximum values are measured at the condition of the equivalence ratio is 1.1.Furthermore,the unstretched flame velocity and laminar combustion velocity of biogas decrease with increased initial pressure or decreased initial temperature and the methane contents.?4?In most working conditions,the combustion rate of biomass gas laminar flow calculated by Gri_Mech 3.0 combustion reaction matches well to the experimental values in the corresponding working conditions.