| Isopentanol is a renewable biomass fuel with better performance than traditional ethanol fuel.Due to the potential application value of isopentanol,the combustion reaction and combustion mechanism of isopentanol have been studied,and a comprehensive combustion model of isopentanol has been established.In-depth analysis of previous research shows that kinetic data in the establishment of isopentanol combustion model are not perfect,and there is also a lack of in-depth exploration of its reaction mechanism from the perspective of quantum chemistry and detailed analysis of the kinetic data of the important reaction mechanism.The full exploration of the combustion mechanism of isopentanol is the beginning of its rational utilization.With the development of experimental techniques and the deepening of theoretical research,research on the combustion reaction of isopentanol needs to be further promoted.Based on previous work,the combustion kinetics of isopentanol were systematically studied from three aspects:experimental measurement,theoretical calculation,and model verification.The pyrolysis and oxidation of isopentanol were investigated by synchrotron radiation vacuum ultraviolet photoionization mass spectrometry(SVUV-PIMS)combined with a jet stirred reactor(JSR)under atmospheric pressure.The pyrolysis of isopentanol under atmospheric pressure was performed at 800-1150 K.Atmospheric oxidation experiments of isopentanol were carried out at 700-1100 K,equivalent ratios of 0.5,1,and 2.The pyrolysis and oxidation experiments were carried out in the JSR.The experiment quantified a large number of products,including alkanes,alkenes,alkynes,alcohols,aromatic hydrocarbons,and other molecules,and distinguished isomers.These experiments laid a foundation for further research on isopentanol kinetics.The unimolecular dissociation reactions of isopentanol are important mechanisms in pyrolysis and oxidation reactions,and the kinetics of these reactions were studied.The barrier reaction and direct bond-breaking reaction of isopentanol are discussed.In the theoretical study of the reaction with a tight transition state,the potential barrier obtained by the CCSD(T)/CBS method is used as the benchmark,and different DFT methods are compared with it.It was found that the M06-2X-D3(0)/def2-TZVP method has the smallest mean unsigned error(MUE),which is most suitable for the current system.The study found that in the reaction with a tight transition state,considering the multi structural torsional anharmonicity effect has a great influence on the result of the rate constant;in the direct bond fission reactions,different multireference methods and the choice of activation space of different reaction pathways also have a great influence on the rate constants.The kinetic study shows that the de-H2O reaction and the C-C bond fission are dominant in all unimolecular reactions.The high-precision quantification study provides reliable thermodynamic and kinetic parameters for the unimolecular dissociation of isopentanol.Then,a kinetic study of isopentanol and OH radicals is introduced in detail.The H-abstraction reaction of OH radicals occupies an important component in both pyrolysis and oxidative combustion reactions,and it is a key radical in the atmospheric troposphere.Therefore,the H-abstraction reaction of OH radicals has been mainly studied.The experimental rate constants of isopentanol and OH at 293-409 K,300-905 K,and 970-1274 K were obtained by using laser photolysis coupled to the laser-induced fluorescence(LIF)method,discharge-flow mass spectrometry(DF-MS)and the low-pressure shock tube(LPST)method.The kinetic parameters of the total and C/O sites of isopentanol+OH were obtained by theoretical calculations.The effects of different C/O sites and molecular structures on the reaction rate constants were considered,such as the ring-forming structure of transition states,steric hindrance,and weak intermolecular interactions,and the kinetic parameters affecting the rate constant were investigated in detail.Both experimental and theoretical studies have found that the H-abstraction reaction of OH radicals has a negative temperature effect below 500 K and a positive temperature effect above 500 K.We also found that the H-abstraction reaction at theα-site is the main reaction channel,but the H-abstraction reaction of the O-site is the most difficult to occur.Next,the H-abstraction reactions of isopentanol by H atoms and CH3 radicals and the product radicals were studied theoretically.The H-abstraction reaction of isopentanol by H atoms and CH3 radicals can be regarded as a one-step reaction,and the influence of reaction complexes and product complexes is ignored in the reaction process.Compared with H-abstraction reactions by CH3 radicals,the reactions by H atoms follow the Evans-Polanyi principle.The isopentanol radicals generated with the H-abstraction reactions are isomerized by intramolecular H transfer.Inβ-dissociation reactions,the radicals undergo bond breaking reactions to generate various olefins,enols,aldehydes,and other substances.Based on exploring the reaction mechanism of isopentanol radicals,we study the reaction kinetics of isopentanol radicals under high-pressure limit(HPL)conditions and the rate constant of the main reaction pathways under pressures of 0.01-100 atm.The isopentanol radical has a short carbon chain and is prone to 1,4-H and 1,5-H shift isomerization reactions.In β-dissociation reactions,the C-C bond fission reaction is more favorable than that of the C-H bond.Among them,the β-dissociation reactions of fuel radicals at the O-site are most likely to occur.Through the comparison of rate constants between different reaction channels,it is found that isopentanol radical isomerization reactions are the main reaction between 300 and 600 K,and C-C bond fission reactions are the main reaction above 600 K.According to the reaction kinetic parameters obtained by theoretical calculation,the isopentanol submechanism in the literature model is updated,and a kinetic model of the isopentanol combustion reaction based on quantum chemical reaction pathways and the rate constant is established.Combined with the experimental study of isopentanol by synchrotron radiation photoionization mass spectrometry,theoretical calculation,and reaction rate measurement experiments,the key reaction kinetic model of the isopentanol combustion reaction was updated.The isopentanol model is verified with the experimental results,and the simulation results can well reproduce the experimental results of SVUV-PIMS.ROP analysis and sensitivity analysis were carried out on the model,and it was found that the H-abstraction reaction dominated both the pyrolysis and oxidation of isopentanol,while the contribution of the unimolecular dissociation reaction was relatively weak.The largest contribution to isopentanol pyrolysis is the H-abstraction reaction by CH3 radicals and H atoms,while the largest contribution during the oxidation process is the H-abstraction reaction of OH radicals.In the conclusion and prospect section,the work of this paper is summarized,using SVUV-PIMS to obtain information on product ionization energy and product concentration,isomers are effectively differentiated,and the concentration curve of pyrolysis and oxidation reaction products with reaction time and temperature is obtained.The high-precision theoretical method provides more accurate kinetic data for the initial and secondary reaction mechanisms of isopentanol.A more accurate and comprehensive reaction rate of isopentanol can be obtained by combining experiments and theory.The ionization energy and concentration information of the products were obtained by synchrotron radiation photoionization mass spectrometry.The isomers were effectively distinguished,and the concentration curves of pyrolysis and oxidation products with reaction time and temperature were obtained.Combined with the theoretical calculation,the combustion reaction mechanism of isopentanol was analyzed in detail and verified effectively,which provided a reliable basis for the optimization and improvement of the isopentanol combustion model in the future. |
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