Exploring The Effect Of C=C Bond On Ignition Characteristics Of C₄ Unsaturated Esters

As a potential alternative fuel,biodiesel has attracted great attention due to its repro-ducibility and low pollution.However,due to the complexity of biodiesel,it is quite difficult to study it directly.In this thesis,small molecule fuels with the same functional groups and properties will be studied.In this thesis,the ignition delay time of two C₄unsaturated esters methyl acrylate and vinyl acetate were measured by heating shock tube under different pressures,equivalence ra-tios and temperatures.The ignition delay time of methyl acrylate and vinyl acetate were com-pared to explore the effect of C=C double bond position on the ignition characteristic of C₄unsaturated esters.In addition,the ignition delay time of methyl acrylate and vinyl acetate and their corresponding saturated esters were also compared to explore the effect of C=C double bond on the ignition characteristic of methyl ester and acetate ester.At the same time,the combustion kinetic model of methyl acrylate in the literatures was updated,and based on the combustion model of methyl acrylate,the combustion model of vinyl acetate was constructed by reaction class method,and the influence of C=C double bond on the ignition process was revealed by sensitivity analysis,reaction pathway analysis and rate of production analysis.The thesis content is mainly divided into the following three parts:1)The ignition delay time of methyl acrylate and vinyl acetate were measured in the shock tube.The experimental conditions are temperatures of T=1176–1618 K,pressures of P=4–16 atm,and equivalence ratios ofΦ=0.5–2.0.The experimental results show that the ignition delay time of methyl acrylate and vinyl acetate decrease with the increase of equivalence ratio and the decrease of pressure,but the effect of pressure is negligibly at low temperature,and the effect of high temperature and equivalence ratio are more obvious.The reaction kinetic analyses show that the sensitivity coefficients of the two unsaturated esters are very small,and the each reaction pathway of ester consumption does not change significantly with the change of pressure at low temperature.So the ignition delay time of the two unsaturated esters does not change with the change of pressure at low temperature.The concentration of O₂and HO₂decreases with the increase of equivalence ratio,inhibiting the reaction of HO₂+CH₃=CH₃O+OH,O₂+H=OH+O,and O₂+CH₃=HCHO+OH,It reduces the generation of active radicals so that inhibits the ignition of esters,the ignition changes obviously with the change of equivalence ratio.2)In order to explore the effect of C=C double bond position on the ignition of C₄un-saturated esters,the ignition delay time of methyl acrylate and vinyl acetate were compared,and the sensitivity analysis and reaction path analysis were also carried out.The comparsion of expriment and kinetic analysis show that methyl acrylate is more active than vinyl acetate atΦ=1,the reactivity ofΦ=0.5 andΦ=2 is very close.This is mainly due to the fact that the ignition of methyl acrylate and vinyl acetate is mainly determined by its unimolecular de-composition reaction（MA=CH₂CHC（=O）O+CH₃和VA=CH₂CHOC（=O）+CH₃）and chain branching reaction（O₂+H=OH+O）.3)In order to investigate the effect of C=C double bond on the ignition of methyl es-ter and acetate,the ignition delay time of unsaturated esters methyl acrylate and vinyl acetate and their corresponding saturated esters methyl propanoate and ethyl acetate were compared.The results show that the activities of unsaturated ester methyl acrylate and vinyl acetate are lower than those of saturated ester methyl propanoate and ethyl acetate atΦ=0.5 and 1,while the activities are opposite at high temperature andΦ=2.The sensitivity,reaction pathway and rate of production analysis show that unimolecular decomposition reaction of unsaturated esters were more significant than that of saturated esters during fuel consumption,and its im-portance increase with the increase of temperature.In addition,saturated esters are consumed more quickly than unsaturated esters during ignition,but their consumption produces stable intermediates.These two causes lead to longer ignition delay times for saturated esters,espe-cially under high temperature and rich combustion conditions.