Research On Dynamic Propagation Characteristics Of Tulip Flame In Tube Under Preheating And Variable Diameter Conditions

From daily life to engineering applications,biomass syngas which has a certain alternative to traditional non-renewable energy,can relieve energy pressure,and it is more friendly to the environment.Tulip flame is a very important phenomenon in syngas combustion and explosion.The appearance of tulip flame will be accompanied by a series of physical changes such as flame propagation speed and overpressure.Its formation process is complex and there are many influencing factors,which have brought certain limitations for the study of tulip flame.Therefore,in order to understand the change rule and influence mechanism of tulip flame,in this paper,the experimental platform designed and built independently is used to study the tulip flame in different initial temperatures and variable diameter pipes,which have positive reference significance for promoting or suppressing the combustion and explosion of combustible gas.Firstly,the experimental study on combustion and explosion of methane gas with three equivalence ratios of 0.7,0.8 and 0.9 was carried out in pipes with three different initial temperatures of 300 K,400 K and 500 K.From the analysis of the front characteristics of the flame propagation process and the pressure changes in the combustion chamber,it is found that when the equivalence ratios were 0.7,0.8,and 0.9,the tulip flames appeared at normal temperature at 84 ms,70 ms,and 38.75 ms,respectively.With the increase of initial temperature of the premixed gas,the time of the appearance of the tulip flame gradually advanced,and the peak overpressure in the combustion chamber also gradually increased.It is caused by the increase of the activity of the gas molecules due to the increase of the initial temperature.In order to further explore the influencing factors of tulip flame,a variable-diameter combustion chamber was designed for experimental research.It can be seen from the study that with the decrease of the flaring rate of the combustion chamber,the shape of the tulip flame became more obvious and appeared twice in a row.This is because the change of the inner diameter of the pipe affects the interaction of the reflected wave in the pipe and the flame front,which further affects the change of the overpressure in the pipe and the flame propagation speed,which led to the second appearance of the tulip flame.This paper mainly studied the dynamic propagation characteristics of tulip flame from the aspects of flame front structure,flame front position and overpressure change in the combustion chamber based on the factors such as gas composition,initial temperature of premixed gas and change of pipe inner diameter.Some experimental conditions are analyzed.Numerical simulation was carried out to deepen the understanding of tulip flame propagation characteristics from the mathematical level.The research show that the calculation results are in good agreement with the experimental results,and the influence of the change of the inner diameter of the pipe on the flame propagation characteristics of tulips is obtained.