Study On The Combustion Reaction Kinetics Characteristics Of Air-light Hydrocarbon Mixing Gas

With the rapid growth of the global economy and the increasing demand for heating and cooling from human activities and industrial production,profound changes have taken place in the energy supply and demand and governance methods of major countries and regions in the world.China is actively building a new energy structure and seeking comprehensive utilization of traditional energy.Light hydrocarbons,the main component of which is pentane,is a by-product produced in the process of oilfield exploitation.It can be used as fuel after being gasified and mixed with air in an appropriate ratio.This mixed gas is called as air-light hydrocarbon mixing gas,which has the characteristics of high heating value,high utilization efficiency and being used as an independent gas source,and is very suitable as city gas.This paper firstly analyzes the sensitivity of the ignition of n-pentane,as well as the composition changes and combustion characteristic parameters during the oxidation process.Secondly,the detailed mechanism of n-pentane is used to study the combustion characteristics and emission index of air-light hydrocarbon mixing gas with different mixing degrees.Finally,during the explosion of pentane caused by leakage,the changes of reactants,products and free radicals are studied,and suggestions are provided for preventing the explosion from proceeding and preventing secondary disasters caused by the explosion.The main study work includes the following three parts:The first part,the pentane isomer model is used to study the important elementary reactions of n-pentane that affect ignition delay,the changes of key components and free radicals in the oxidative cracking process,and the combustion characteristic parameters.The results show that,firstly,the normalized sensitivity coefficient of ignition delay time is calculated and it is found that the elementary reactions 2HO₂=H₂O₂+O₂（-1）and2HO₂=H₂O₂+O₂（-2）only inhibit ignition at a temperature of 1000 K.Therefore,to study the ignition delay time of n-pentane at this temperature,these two key reactions must be considered.Secondly,at the distance of 0.04 cm from the exit,the concentrations of the four key components are zero or close to zero,while the concentrations of three free radicals are in the rising stage,but the concentration of CO is in the falling stage,and finally the concentrations of these four oxides tend to stabilize.Finally,the ignition delay time of all equivalence ratios of n-pentane has a temperature intersection point,and the ignition delay time of this temperature intersection point is the same.When the equivalence ratio is 1.0,the laminar flame speed of n-pentane reaches the maximum value of 39.88 cm/s,the extinction residence time is 0.0718 ms,which is the inflection point of the C-curve,and when the equivalence ratio is 1.4,the extinction temperature reaches the maximum value of 1796 K.The second part,the detailed chemical mechanism of n-pentane is used at atmospheric pressure and room temperature to study the combustion characteristics and emission index of air-light hydrocarbon mixing gas with different mixing degrees at the critical equivalence ratios,including ignition delay time,laminar flame speed,extinction residence time and CO emission.The results show that,firstly,at temperatures of1000-1118 K,the ignition delay time of air-light hydrocarbon mixing gas is greater than that of n-pentane,while the opposite at temperatures of 1118–1600 K.Secondly,through comprehensive analysis of laminar flame speed and ignition delay time,it is found that the essence of air-light hydrocarbon mixing gas is that its characteristic parameters are determined by the ratio of n-pentane to total air during combustion.Thirdly,the extinction residence time of air-light hydrocarbon mixing gas is not synchronized with the change of CO emission index.That is,for air-light hydrocarbon mixing gas with excellent extinction residence time,the CO emission index is not necessarily small.Finally,CO sensitivity analysis and CO rate of production（ROP）identified key species and reactions that are primarily responsible for CO formation and annihilation.The mixing degree plays a key role in the CO emission index of air-light hydrocarbon mixing gas.The third part,the changes of reactants,products and free radicals in the process of pentane explosion from the perspective of chemical kinetics are studied,especially the influence of the concentration of oxygen and carbon monoxide on the human body in this environment.The results show that,firstly,in all cases of pentane leakage,an explosion situation where the proportion of pentane in the environment is equal to 4.90%is the most dangerous,because in this case not only an explosion occurs but also a large amount of toxic gas carbon monoxide is generated.Even if it is not affected by the explosion,people may suffer serious injuries or even die within a short time due to the consumption of oxygen and the high concentration of carbon monoxide.Secondly,the reaction H+O₂<=>O+OH is the most important reaction in the pentane explosion process.It plays a key role not only in the formation of carbon monoxide but also in the formation of free radicals and the chain reaction.In practice,compounds containing CO₃^2-and HCO₃^-can be used to neutralize and extinguish the fire.Finally,under the stoichiometric condition,the research on the key reactions of the production and annihilation of free radicals indicates that the reaction that contributed the most to the suppression of the three major free radicals is CH₃+HO₂<=>CH₄+O₂.