Study Of Flame Propagation Kinetics Of LPG-Hydrogen Fuel Mixture

In order to solve the shortage of non-renewable energy sources and the environmental and safety problems they generate,the search for clean and efficient alternative fuels has become a current hot issue.Studies have shown that hydrogen addition to existing fuels can effectively improve the combustion performance and reduce pollution.However,studies on the safety of conventional gas fuels after hydrogen blending are still in the initial stage,mainly in the field of natural gas blending,and little research has been reported on the blending of liquefied petroleum gas（LPG）,which also has a wide range of applications.In this paper,the flame propagation kinetics of LPG/H₂ blended fuel is investigated.The flame structure,flame tip speed,maximum explosion pressure rise rate and deflagration index of LPG/H₂ blended fuel are obtained by a square glass explosion pipe and a high-speed camera,and the effects of hydrogen addition ratio,equivalent ratio and pipe length on the flame propagation characteristics of LPG are analyzed.The research results provide the basic theoretical basis for the design and optimization of LPG hydrogenation feasibility plan.The main work and conclusions of the paper are as follows:（1）The study of flame propagation characteristics of LPG/H₂ mixture due to variation of mixture components was carried out in a wide range of working conditions.It is found that the equivalent ratio has a greater effect on the LPG/H₂ mixture than hydrogen.When the volume fraction of hydrogen in the fuel mixture is low（Φ≤40%）,the effect of adding hydrogen on increasing the flame propagation speed of the mixture is relatively weak,while when the volume fraction of hydrogen is high（Φ>40%）,the effect of adding hydrogen on increasing the flame propagation speed of the mixture is significantly enhanced.（2）The effect of hydrogen addition on the reaction of LPG/H₂ gas mixture is mainly reflected in the chain reactions O+H₂=H+OH（R2）and OH+H₂=H+H₂O（R3）,which generate a large amount of H and OH key radicals and increase the reaction activity.And with the increase of hydrogen volume fraction,the sensitivity coefficient of the radical reaction promoting the explosion of LPG/H₂ mixture gradually increases.At the same time,the sensitivity coefficient of the radical reaction that inhibits the explosion of LPG/H₂ mixture gradually decreases.The absolute value of the sensitivity coefficient of the promoted reaction is always greater than that of the inhibited reaction,thus ensuring the positive chemical reaction and increasing the laminar combustion rate of the gas mixture.（3）The influence of duct length on the flame propagation structure of LPG/H₂mixture is mainly reflected in the location and time of flame characteristic structure appearance.For the same duct length,hydrogen addition can increase the flame propagation speed of LPG/H₂ mixture,but it does not change the location of the characteristic flame"flat flame".According to the extraction of the position of"flat flame"under different working conditions,it is found that the position of"flat flame"is related to the duct length,and the absolute displacement from the ignition position increases gradually with the increase of the duct length.There is a good non-linear curve relationship between the location of the"flat flame"and the length of the duct.（4）The length of the duct does not change the trend of explosion pressure over time.However,with the increase in duct length to diameter ratio will promote the rate of mixed gas chain reaction,so the flame instability is enhanced,in the flame front and the joint action of the pressure wave,the explosion pressure curve appears obvious oscillation.For the same volume of LPG/H₂ mixture,increasing the duct length within a certain range will increase the explosion hazard of the mixture.