Research On The Flame Stability And Propagation Characteristics Of Syngas Premixed Flame

In view of the increasingly serious environmental problems and energy shortages caused by the use of fossil fuels,exploring clean alternative energy fuels and investigating combustion mechanisms to achieve high efficiency combustion are two important solutions.Syngas mainly consists of carbon monoxide and hydrogen,which has a wide range of raw materials and various preparation methods.At present,syngas has been widely used in integrated gasification combined cycle(IGCC)power generation.However,due to the differences in the preparation methods,the concentration of different components in syngas varies greatly,which leads to the differences in physical and chemical properties of fuels.The research on the laminar and turbulent premixed combustion of syngas/air can establish the basic database of the turbulent premixed combustion of syngas/air,and provide the necessary basic data for the development of the turbulent combustion model.In addition,with the further understanding of the mechanism of syngas/air turbulent premixed combustion,it is possible to improve the efficiency of syngas/air turbulent combustion.A turbulent constant volume combustion bomb experimental system was built.The experimental system consisted of constant volume combustion bomb,turbulence generation system,ignition system,synchronized trigger system,intake and exhaust system and image acquisition system.The turbulence generation system was designed based on the combination of swirl and jet of airflow,and the turbulence intensity was controlled by the combination of the fan rotation and the orifice plate.The combination of the schlieren system and the high-speed camera realizes the visualization of combustion.Based on the experimental system,the experimental data laminar and turbulent premixed flame of syngas/air mixtures were obtained.The evolution of crack was studied by extracting the cellular structure information of the flame front.The influence of equivalent ratio,hydrogen fraction and initial pressure on the evolution of crack was obtained.It was clear that the imbalance between the expansion speed of flame and the cell splitting speed influenced by the local flame stretch rate leading to the oscillating growth of the dimensionless crack propagation speed.The mechanism of the influence of flame inherent instabilities on the cellular structure process of flame front was revealed.The non-linear propagation characteristics of syngas/air laminar premixed flame were studied.The effects of equivalence ratio and hydrogen fraction on laminar combustion velocity at various initial pressure were studied.The accuracy of GRI 3.0 mechanism and USC II mechanism in predicting laminar burning velocity was verified and the predicted values of USC II mechanism were closer to the experimental values.The effects of elementary reactions on the laminar burning velocity were analyzed.The influences of equivalence ratio,hydrogen fraction and initial pressure on the two stage self-acceleration characteristics of syngas/air laminar premixed flame were studied.It was clear that the enhancement of flame inherent instabilities could reduce the proportion of transition stage and increase the proportion of saturation stage.The correlation between flame inherent instabilities and acceleration exponent and fractal excess of two stage self-acceleration were studied.The mechanism of flame stretch on the flame self-acceleration characteristics was discussed.The flame front characteristics of syngas/air turbulent premixed flame were studied.The evolution of the average area and uniformity of the large-scale wrinkle area of the flame front were studied by extracting the large-scale wrinkle information of the flame front.It was clear that the enhancement of turbulence and flame inherent instabilities increased the average area of the large-scale wrinkle area of flame front,and the difference of different large-scale areas became larger.The influence of turbulence intensity,equivalence ratio and hydrogen fraction on the curvature distribution of flame front was discussed.It was clarified that the enhancement of turbulence and flame inherent instabilities could increase the distribution range of flame front curvature and the proportion of components with relatively small curvature decreased gradually.Wavelet analysis was used to decompose the flame front structure in multi-scale.The disturbance energy and the correlation of different disturbances of different scale were obtained.It was found that turbulence could enhance the fluctuation degree and disturbance energy of different scale disturbances.The influence of turbulence on the flame front structural characteristics was analyzed.It was clear that there is no obvious correlation between the disturbances of different scales on the flame front.The propagation characteristics of syngas/air turbulent premixed flame were studied.The regimec diagram of syngas/air turbulent premixed combustion was investigated.The influence of turbulence intensity on the regimec diagram of turbulent premixed combustion and the influence of regimec diagram on the flame front structure were analyzed.The self-similar propagation of syngas turbulent premixed flame was investigated.The influence of hydrogen fractions and equivalence ratios on the self-similar propagation of syngas turbulent premixed flame was found.It was clear that the effects of Ma number reduction caused by the increase of hydrogen ratio or decrease of equivalence ratio on the self-similar propagation of syngas/air turbulent premixed flame were completely opposite.The effects of turbulence intensity,hydrogen fraction and equivalence ratio on the turbulent burning velocity of syngas/air were studied.It was found that Re and Da were positively and negatively correlated with uT/uL,respectively.The influence of turbulence on correlation of the flame local stracture and local propagation was analyzed.