Study On Ignition Characteristics Of Three Typical C5 Unsaturated Methyl Esters At High Temperatures

Biodiesel is a new type of fuel,which belongs to renewable energy and is also a clean energy.It has attracted much attention because of its advantages of easy to burn,low loss and good safety.Biodiesel is a mixture of saturated methyl（or ethyl）ester and unsaturated methyl（or ethyl）ester composed of long-chain fatty acids such as oleic acid and linoleic acid.Due to the complex composition of biodiesel,it is difficult to carry out experimental and computational research on the combustion of biodiesel.Therefore,it is more practical to select alternative fuels with simple composition and similar chemical functional groups and properties for engine modeling.In this thesis,MB was selected as the substitute molecule of larger saturated methyl ester.MC is an unsaturated ester corresponding to MB,which is used as an alternative molecule of unsaturated methyl ester.In addition,due to the different positions of C=C double bond,MC also has isomers MB3D and MMA.In this thesis,the ignition delay times of three typical C5 unsaturated methyl esters MMA,MC and MB3D were measured and compared with a heated shock tube under different pressure,equivalence ratio and temperature conditions,so as to explore the influence of the position of C=C double bond on the ignition characteristics of C5unsaturated methyl ester.In addition,the ignition delay of C=C unsaturated methyl ester is compared with that of C=C unsaturated methyl ester.At the same time,the mechanism models of three C5 unsaturated methyl esters in the literature are selected to reveal the influence of C=C double bond on ignition characteristics through sensitivity analysis,reaction path analysis and species concentration analysis.The research content of this thesis is mainly divided into the following three parts:（1）The ignition delay time of methyl crotonate,methyl 3-butenoate and methyl methacrylate was measured under the conditions of temperature range of T=1108-1783 K,pressure range of P=4-16 atm and equivalent ratio of 0.25-2 under the precondition of shock tube heating and keeping temperature at 50℃.The experimental results show that the ignition delay time of methyl crotonate,methyl 3-butenoate and methyl methacrylate all decrease with the increase of equivalence ratio and the decrease of pressure,but the pressure has little effect on the ignition at low temperature,it has obvious effect on the ignition at high temperature,and the change of equivalence ratio has more obvious effect on the ignition.According to the selected chemical kinetic models,the ignition delay time of methyl crotonate,methyl 3-butenoate and methyl methacrylate is simulated,and the mechanism simulation results are basically consistent with the experimental results.（2）In order to explore the influence of the position of C=C double bond on the ignition characteristics of C5 unsaturated methyl ester,the ignition delay time of methyl crotonate,methyl 3-butenoate and methyl methacrylate was compared,and the sensitivity analysis and reaction path analysis were also carried out.Kinetic analysis shows that the reaction H+O₂=O+OH has the strongest promoting effect on the reaction system of three C5 unsaturated methyl esters.The reaction HO₂+CH₃=O₂+CH₄has the strongest inhibitory effect on the reaction system of methyl crotonate.The reaction CH₃+HO₂=CH₄+O₂has the strongest inhibitory effect on the reaction system of methyl methacrylate,followed by the self-recombination reaction of methyl C₂H₆（+M）=2CH₃（+M）.MB3D+H=MB3J,followed by MB3J=CH₃OCO+C₃H₆,CH₃+CH₃（+M）=C₂H₆（+M）and CH₃+HO₂=CH₄+O₂,has a strong inhibitory effect on the reaction system of methyl3-butenoate.With the change of pressure,the sensitivity coefficients of these reactions have little change,and the increase of pressure has little effect on the ignition characteristics of three C5 unsaturated methyl esters at low temperature.（3）In order to explore the influence of C=C double bond on the ignition characteristics of C5 methyl ester,the ignition delay time of methyl crotonate,methyl 3-butenoate and its corresponding saturated ester methyl butanoate and that of methyl methacrylate and its corresponding saturated ester methyl Isobutanoate were compared.The comparison results show that there is no obvious difference between the ignition delay time of C5 unsaturated methyl ester and C5 saturated methyl ester,which indicates that the existence of C=C double bond has little effect on the ignition characteristics of C5 methyl ester.