Autoignition of n-pentane and 1-pentene: Experimental data and kinetic modeling
Autoignitions of n-pentane and 1-pentene are studied by rapid compression between 600 and 900 K at high pressure. Both hydrocarbons show a two-stage ignition and a negative temperature coefficient region (NTC). However, 1-pentene is less reactive. Ignition temperature limit is 50 K higher; cool flames and NTC are weaker and confined to a narrower temperature range. Chemical analyses are performed on the reacting mixture for fuel consumption and cyclic ethers. n-Pentane and 1-pentene give very different distribution patterns for cyclic ethers. 2-Methyltetrahydrofuran dominates the n-pentane pattern, whereas propyloxirane is by far the major cyclic ether formed by 1-pentene. Detailed mechanisms based on a common skeleton scheme are developed and used to simulate the experiments. They are validated for ignition delay times, cool flame intensities, and cyclic ether distributions. Good results are obtained for 1-pentene only if (1) direct addition channels of OH and HO2 to the double bond are included and (2) if a higher rate constant for the decomposition of the hydroperoxyalkyl radicals into cyclic ethers is used when this radical is formed by direct HO2 addition instead of isomerization of alkylperoxy radicals. The sensitivity analysis of the low-temperature scheme for 1-pentene points out that the total ignition delay time is dependent upon the competition between the decomposition channels of hydroperoxyalkyl radical into the branching sequence and into alkenes. The cool flame delay time is less sensitive but depends mainly upon the decomposition rate of unsaturated ketohydroperoxides.
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Cited by (84)
A theoretical calculation and kinetic modeling analysis of H-abstraction from 1-octene for subsequent isomerization and β-dissociation
2024, International Journal of Hydrogen EnergyAs a main component of alkenes, 1-octene is the key important intermediate in the process of oxidation or pyrolysis of n-decane or higher alkanes. In this work, quantum chemistry calculations of the 1-octene combustion and pyrolysis were illustrated for the potential energy surface, including the H-abstraction reactions and subsequent isomerization and -dissociation reactions. The primary -dissociation reactions after the H-abstraction reaction involving H atoms and CH3/NH2/NO2 radicals are detailed description with kinetic calculation. The rate constants of the primary pyrolysis reaction of 1-octene from 300 to 2000K were determined with the RRKM theory combined with CTST. The results indicated the H-abstraction reactions adhere to the Evans-Polanyi principle within the calculation uncertainty 1 kcal/mol. The 3-site exhibited the highest competitiveness in the 1-octene H-abstraction process and dominated, whereas the 1-site is lack of competitiveness due to overcome higher energy barriers (2–4 kcal/mol). The five-membered or six-membered ring in the H atom transfer process served as the most favorable structure for the isomerization reaction of 1-octenyl because of the lowest transition state energy. The dissociation channel for converting 1-octenyl to various octadienes and H atoms consumed the least 1-octenyl in the dissociation process. Following temperatures exceeding 570K, INT6 exhibits a preeminent 1-octenyl consumption ratio, attributed to the synergy between the enthalpy and entropy effects. The modified kinetic data of 1-octene H-abstraction reactions by four radicals and the subsequent isomerization and -dissociation was expanded from 300 to 2000K, 0.01–100 atm. The modified model shows the better experimental prediction capabilities.
Isomeric effects on the reactivity of branched alkenes: An experimental and kinetic modeling study of methylbutenes
2023, Combustion and FlameA detailed experimental study of the low-to-intermediate temperature combustion of methylbutene isomers, i.e., branched C5 alkenes, has been undertaken with multiple experimental facilities. Ignition delay times were measured at equivalence ratios 0.5–2.0, 685–1020 K and up to 45 bar condition from two rapid compression machines and showed slight deviation from an Arrhenius behavior for all three isomers, while their reactivity order differs as temperature changes. Sampled intermediates formed during the oxidation process of mixtures at 900–1150 K and 0.82 bar from a flow reactor and at 730 K and 20 bar from a rapid compression machine were analyzed using gas chromatography techniques. Trends in the formation and consumption of sampled intermediates were modeled using a kinetic model developed in this work for all three isomers. Rate of production and sensitivity analyses emphasize the role of double bond-specific reactions governing the global reactivity of these fuels. Additional studies of the addition reactions of HO2 radicals to the double bond and to allylic radicals may improve the model performance.
Based on the methods of DRGEP, FSSA, reaction path analysis, and sensitivity analysis, the detailed mechanisms of 1-pentene, 2-pentene, and 2-methyl-2-butene are comprehensively reduced and combined with the mechanisms of TRF, methanol, ethanol, and n-butanol. A reduced mechanism of multi-component is proposed to predict gasoline combustion in the engine. It is rare in previous study about mechanisms of surrogate fuels that used pentene to represent unsaturated hydrocarbons, which is the most abundant olefin in actual gasoline in China. JSR experiments were carried out on the mixed fuels of isooctane/methanol/n-butanol and isooctane/1-pentene with different equivalence ratios under the condition of 1.03 atm and temperature range from 500 K∼1000 K, and the component concentration curves were obtained. The accuracy of the multi-component reduced mechanism is verified by JSR experimental data. The results showed that this mechanism could well fit the concentration curve of reactants and final reaction products, and showed the same change trend for intermediate products. The accuracy of the pentene mechanism is verified by the experimental data of ignition delay time and laminar flame velocity. The prediction of the ignition delay time of pentenes is accurate in the middle and high temperature regions, and the prediction in the low temperature region is slightly lower than that of the detailed mechanism, but it can predict the trend of ignition delay time and reflect the low temperature reaction properties of them. The simulated values of 1-pentene can well fit the experimental data of laminar flame velocity under various working conditions, and the difference in laminar flame velocity of three isomerides is also well reflected in this mechanism. The ignition delay time of multi-component mixtures was verified under different pressures by using the mixed fuels of G-A, G-B, and G-C. The results show that this mechanism can predict the ignition delay time of G-A and G-B more accurately under pressure of 20 atm, but the predicted values are lower under 50 atm pressure. Under the pressure of 10 atm, 30 atm, and 50 atm, the ignition delay time of this mechanism can well fit the experimental data of G-C fuel, while the predicted value at low temperature is slightly higher.
A detailed experimental and kinetic modeling study was dedicated to understand the reported octane hyperboosting effect of prenol, by means of the measurement of the ignition delay times of its blends with iso-octane, and measurement of the mole fraction profiles of the fuels and intermediates inside the ULille rapid compression machine. These results show that prenol addition leads to a reduction of the first-stage ignition phenomena and negative temperature coefficient behavior, which is only qualitatively captured by the model and is consistent with knock resistance improvement. It is suggested that this behavior is caused by two different factors. The first originates from gas-phase reactivity of prenol, and spans from the formation of unreactive unsaturated species through resonance-stabilized radicals, thereby constituting a competitive pathway for the radical pool generated by iso-octane. The second is of catalytic nature and cannot be captured by means of gas-phase kinetic modeling, but could also play an important role in the behavior of prenol in internal combustion engines.
Chemical kinetics of cyclic ethers in combustion
2022, Progress in Energy and Combustion ScienceCitation Excerpt :Other CEs are derived from the pentyl radicals that are formed through H-atom addition to the double bond. The model proposed by [411] predicts these experimental results reasonably well. Measurements of IDTs during cyclohexene RCM oxidation indicate a narrow NTC range limited to 20 K.
Cyclic Ethers (CEs) belong to a class of compounds of importance to understand the chemistry of both the engine auto-ignition of hydrocarbon fuels and the combustion of oxygenated biofuels. This article, divided in six parts, aims at systematically analyzing how up-to-date experimental and theoretical methods were applied to unveil the gas-phase oxidation chemistry of these compounds. The first part gives a brief overview on the significance of CEs as intermediates formed during alkane low-temperature oxidation summarizing its generally accepted chemical mechanism. This part also addresses the role of CEs as potential biofuels derived from lignocellulosic biomass and discusses the production methods of these molecules and their combustion performances in engine. The second part presents the different theoretical methods dedicated to calculate the electronic structure, thermochemical and kinetic data of CEs. The third part introduces the experimental methods used in studies related to CEs with a special focus on mass spectrometry and gas chromatography. The fourth part reviews the experimental and modeling studies related to CE formation during the low-temperature oxidation of linear, branched, cyclic alkanes, alkylbenzenes, olefins, and oxygenated fuels. The fifth part analyses the published work concerning the CE degradation chemistry and highlights the dominant involved reactions. To finish, the sixth part concludes and proposes future research directions.
A Shock-Tube and Chemical Kinetics Model Investigation Encompassing all Five Pentene Isomers
2022, FuelKinetic treatment of the full group of C5 olefins is presented with new measurements on 1-pentene (1-C5H10), 2-pentene (2-C5H10), and 3-Methyl-1-Butene (3M1B) combined with recently published data obtained at similar conditions from our group on 2-Methyl-2-Butene (2M2B) and 2-Methyl-1-Butene (2M1B). This extensive experimental database contains carbon monoxide and water time-history profiles, along with their measured CO and H2O induction delay times. The oxidation of the five pentene isomers was carried out at three equivalence ratios (0.5, 1.0, and 2.0) in mixtures highly diluted in 99.5% Helium-Argon. The experiments were performed for temperatures ranging from 1400 to 1900 K at near-atmospheric pressure. A unique comparison of the complete set of pentene isomers permits the understanding of the C=C double bond position and branching impacts on combustion properties, using the chemical kinetics mechanism of both linear and branched structures. The impact of the C = C double bond location – either the 1–2 or 2–3 bond site – is described using the linear molecules 1-C5H10 and 2-C5H10. Species induction delay times were measured for the five isomers for each equivalence ratio investigated. Results showed noticeable differences between isomers, with the induction delay time results for 3M1B being the shortest, closely followed by 2-C5H10, 1-C5H10, and then after a large leap in decreasing reactivity, by 2M2B and 2M1B. Numerical predictions using up to 9 models available in the literature were performed. An error score function was used to evaluate the properties of the pentene isomer models in the current literature.