Experimental And Numerical Simulation Of Laminar Combustion Characteristics Of Low Calorific Value Biomass Syngas

With the development of economy,global energy shortage and environmental pollution have gradually become a worldwide problem,and human health is facing round after round of challenges.As a large agricultural country,there are rich biomass raw materials in China,and its own carbon neutrality has attracted wide attention.Biomass gasification technology is the main method of efficient utilization of biomass energy,which can obtain clean syngas.It is mainly composed of CH₄,H₂,CO,N₂and other gases,but the calorific value is low.Due to the change of fuel composition,flame combustion is uncertain.Therefore,studying the combustion characteristics of low calorific value biomass syngas has important practical value.Based on this background,the combustion characteristics of low calorific value biomass syngas with six different fuel components at normal temperature,equivalence ratio 0.6-1.4,initial pressure and oxygen-enriched air coefficient were studied by constant volume combustion bomb experimental system.The CHEMKIN-Pro/Premix module and three detailed chemical reaction mechanisms GRI 3.0,Li-Model and FFCM-1 were used for numerical analysis.The main conclusions are as follows:（1）When the biomass syngas fuel with low calorific value is lean burnt,the effective Lewis number is less than 1,and the thermal diffusion instability makes the flame unstable.When the fuel is rich burnt,the effective Lewis number is greater than 1,and under the effect of thermal diffusion instability,the spherical expansion flame tends to be stable.CH₄ makes spherical flame more unstable than CO.The thermal expansion ratios of different fuel components first increase and then decrease with the equivalence ratio（0.6-1.4）.Compared with CH₄,CO has little effect on the thermal expansion ratio.（2）The Li-Model mechanism tends to predict the laminar burning velocity too low in F1-F3 fuels（mainly CH₄）,and the results in lean combustion of high CH₄ mixtures are more obvious.However,the Li-Model mechanism is more significant in predicting the laminar burning velocity of F4-F6 fuel（mainly CO）,especially at low CO content.The GRI 3.0 and FFCM-1 mechanisms predict the laminar burning velocity of low calorific value biomass syngas with good consistency,and the best match with the linearly derived laminar burning velocity.At high diluent gas ratio,the effect of increasing the ratio of inert gas on the laminar burning velocity is mainly through increasing the heat capacity and reducing the flame temperature,thereby changing the thermal properties of hydrocarbon fuels.（3）The influence of O,H and OH radicals on laminar burning velocity were obtained by GRI 3.0 mechanism.Through the formation of NO_X,CO has a significant inhibitory effect on the formation of NO,and CH₄ has a significant effect on the formation of NO and NO₂.Since the order of magnitude of NO₂ concentration is much lower than that of NO,NO_X in the whole reaction is related to the content of CH₄.（4）With the increase of initial pressure,the laminar burning velocity of fuel decreases,mainly due to the increase of fuel density.The increase of initial pressure increased the number of collisions of active radicals and accelerated the reaction rate.（5）Under oxygen-enriched conditions,the flame radius changes linearly with time,and the combustion speed increases with the increase of the oxygen-enriched coefficient.The three mechanistic models are in good agreement with linear and nonlinear extrapolation.Markstein length is negative in oxygen-enriched air coefficient（0.3-0.5）,and the flame front is more likely to be cellular,resulting in enhanced flame instability.The flame combustion pressure increases with the increase of oxygen-enriched air coefficient.Finally,the experimental and numerical simulation results in this paper provide theoretical guidance for the practical application of low calorific value biomass syngas.