Synchrotron Radiation Experiments And Kinetic Modeling Of Low-temperature Oxidation Of N-pentane

Nowadays,the increasingly serious problems of fossil energy depletion and ecological environment deterioration drive the development of advanced combustion technologies.Low-temperature combustion is a clean and efficient combustion technology that can improve the combustion efficiency of fuels and reduce the emission of pollutants,which is one of the important directions of engine research.Low-temperature combustion is mainly controlled by the chemical kinetics of the fuel,and a comprehensive understanding of the low-temperature oxidation chemistry of the fuel is required for further development of low-temperature combustion technology.In addition,the design and evaluation of advanced low-temperature combustion engines depend on accurate combustion kinetic models,and the elucidation of the low-temperature oxidation reaction mechanism of fuels is essential for the development of universal and accurate combustion kinetic models.Straight-chain alkanes are important components of fossil fuels such as gasoline,kerosene,and diesel.Detailed combustion reaction kinetics studies on straight-chain alkanes can help promote the development and application of advanced low-temperature combustion engines.Among these alkanes,n-pentane(C5H12)is a typical representative of straight-chain alkanes,which has a moderate molecular backbone size and is an ideal model fuel for studying combustion reaction kinetics.Although the low-temperature oxidation kinetics of n-pentane have been extensively studied in the past few decades,there are still large inconsistencies in the model predicted results and experimental measurements.Further carrying out n-pentane low-temperature oxidation experiments and clarifying the reaction network of intermediates are of great significance for understanding the low-temperature oxidation chemistry of alkane fuels and developing a detailed combustion kinetics model.Hence,n-pentane was chosen as the target in this paper,and the low-temperature oxidation of n-pentane was studied.In this work,synchrotron vacuum ultraviolet photoionization mass spectrometry(SVUV-PIMS),gas chromatography(GC)and Fourier transform infrared spectroscopy(FTIR)were used to study the low-temperature oxidation of n-pentane in a jet-stirred reactor(JSR)in the temperature range of 500-825 K.By these analytical methods,numerous intermediates were measured,including aldehydes,ketones,olefins,alkanes,carboxylic acids,hydrogen peroxide,alkyl hydroperoxides and carbonyl hydroperoxides,which were detected and identified during the low-temperature oxidation of n-pentane.These speciation profiles were used to clarify the low-temperature oxidation reaction pathway of n-pentane and to validate its kinetic model.The current experimental measurements of carbonyl hydroperoxides,carboxylic acids,and acetone are significantly different from the predictions of previous models,and these inconsistencies drove further model updates in this paper,including the rate constants for the decomposition of C5 carbonyl hydroperoxides and hydroperoxy cyclic ethers,as well as the rate constant for the Korcek reaction of C5 carbonyl hydroperoxides.For key reaction classes(QOOH+O2,QOOH decomposition,concerted elimination reaction of RO2,decomposition of C5 carbonyl hydroperoxide,decomposition of C5 hydroperoxy cyclic ether,and the Korcek reaction of C5 carbonyl hydroperoxide),the pressure-dependent rate constant was also considered;in addition,detailed sub-mechanisms for C5 carbonyl hydroperoxides and hydroperoxy cyclic ethers were added.In this paper,the updated model predicts the speciation profiles and ignition delay times well,especially for the speciation profiles.This indicated that the decomposition rate of peroxides and the pressure-dependent effect of the above key reaction paths play an important role in the low-temperature oxidation of n-pentane.Peroxides are an important class of intermediates in the low-temperature oxidation and autoxidation of organic compounds,which control the ignition process of engines and play a key role in the formation of secondary organic aerosols.At present,it is difficult to realize the quantitative analysis of peroxides in the low-temperature oxidation and autoxidation of organic components due to the lack of standards of peroxides,which leads to the reaction kinetics of peroxides being unclear.Therefore,exploring quantitative methods for peroxides is of great significance for developing detailed kinetic models of peroxides and further understanding low-temperature oxidation and autoxidation processes.In this paper,a new method for the enrichment and quantification of organic peroxides is developed for the n-pentane system as an example.A self-designed and constructed enrichment device was used to enrich organic peroxides in the low-temperature oxidation of n-pentane,and qualitative and quantitative measurements of organic peroxides in the n-pentane system were achieved based on a standard iodine titration chemical analysis method combined with a low-pressure spray injection and synchrotron radiation vacuum ultraviolet photoionization mass spectrometry experimental platform.The proposed method for the enrichment and quantification of peroxides is expected to provide an important reference for subsequent kinetic studies of peroxides.