Shock Tube and Kinetic Modeling Study of Cyclopentane and Methylcyclopentane

Abstract

Ignition delay times for 1% cyclopentane/O 2 and 0.833% methylcyclopentane/O 2 mixtures diluted by argon were measured behind reflected shock waves at pressures of 1.1 and 10 atm, with equivalence ratios of 0.577, 1.0, and 2.0, and in the temperature range from 1150 to 1850 K. Submechanisms for cyclopentane and methylcyclopentane were developed and added to the JetSurF2.0 mechanism for the kinetic interpretation of cyclopentane and methylcyclopentane oxidation chemistry at the high temperature region. Simulations with the model exhibit fairly good agreements with the measured ignition delay times of both cyclopentane and methylcyclopentane under all tested conditions. Cyclopentane shows longer ignition delay time than methylcyclopentane, especially for the fuel-lean mixture. Reaction pathways and sensitivity analyses were conducted to get insights into the oxidation process of cyclopentane and methylcyclopentane. Then, three factors are given for the effect of a cyclic ring and substitution of a methyl group. Substitution of a methyl group weakens the C−C bond to motivate fuel unimolecular decomposition. The shape of the cyclic ring determines the chain alkyl radicals, affecting regeneration and accumulation of H radical. The presence of a methyl group also leads to different alkyl radicals.

Cyclopentane combustion chemistry. Part I: Mechanism development and computational kinetics

“…Due to their simplicity and abundance, particularly in shale-and oil sand-derived fuels [10], cyclohexane and cyclopentane are often used to represent the naphthenic fraction in surrogate fuels. While models for cyclohexane [11][12][13][14] cover a wide temperature range, the cyclopentane models currently available in the literature are limited to high-temperature [15,16]. The rate coefficients of elementary reactions in these mechanisms are mostly based on analogies with cyclohexane due to the lack of cyclopentane-relevant kinetic data.…”

“…The ring strain energy changes the oxidation kinetics, particularly for the ring-opening reactions, which also involve significant change in entropy [8].Furthermore, unlike in n-alkanes, methyl substitution in cycloalkanes increases lowtemperature reactivity [9] for reasons that are not well known on the molecular level.Therefore, more detailed kinetic research is needed to better explain the observed trends, and to enable accurate predictive modeling of cycloalkane-containing fuels.Due to their simplicity and abundance, particularly in shale-and oil sand-derived fuels [10], cyclohexane and cyclopentane are often used to represent the naphthenic fraction in surrogate fuels. While models for cyclohexane [11][12][13][14] cover a wide temperature range, the cyclopentane models currently available in the literature are limited to high-temperature [15,16]. The rate coefficients of elementary reactions in these mechanisms are mostly based on analogies with cyclohexane due to the lack of cyclopentane-relevant kinetic data.Kinetic determinations pertaining to cyclopentane reactivity are mostly concerned with high-temperature pathways such as unimolecular decomposition [17], H-abstraction by OH [18][19][20], and the β-scission of C-C and C-H bonds in cyclopentyl radicals [21][22][23][24].Only Sirjean et al [25] provide kinetic data of low-temperature cyclopentane reactivity.Specifically, they report high-pressure limit rate constants of cyclopentylperoxy (ROO) reactions, including alkylperoxyhydroperoxyalkyl isomerization (ROOQOOH) and cyclic ether formation, calculated at the CBS-QB3 level of theory.…”

Elucidating reactivity regimes in cyclopentane oxidation: Jet stirred reactor experiments, computational chemistry, and kinetic modeling

“…Studies have shown that cycloalkanes are less reactive, as evidenced by their longer ignition delay times [3] and higher octane numbers [4]. Moreover, methyl substitution, which is known to reduce reactivity of normal alkanes, has the opposite effect on cycloalkanes [5] since the addition of a methyl group promotes alkylperoxy isomerizations resulting in low-temperature chain branching [6]. Data currently available is not enough to explain the differences in ignition properties and reactivity trends of these compounds.…”

“…Only a few studies provide kinetic models for cyclopentane combustion. These include high-temperature oxidation mechanisms developed by Tian et al [5] based on the JetSurF2.0 mechanism and by Sirjean et al [11] using EXGAS software. These mechanisms have been validated against shocktube ignition data measured under relatively dilute conditions (0.5 and 1% fuel/oxidant mixtures) in Argon for the temperature range of 1100-1800 K, at pressures up to 8.4 atm, and equivalence ratios between 0.5 and 2.0 [5,11].…”

“…These include high-temperature oxidation mechanisms developed by Tian et al [5] based on the JetSurF2.0 mechanism and by Sirjean et al [11] using EXGAS software. These mechanisms have been validated against shocktube ignition data measured under relatively dilute conditions (0.5 and 1% fuel/oxidant mixtures) in Argon for the temperature range of 1100-1800 K, at pressures up to 8.4 atm, and equivalence ratios between 0.5 and 2.0 [5,11]. Daley et al [12] provided high-temperature ignition data for cyclopentane and cyclohexane fuel/air mixtures at lean/stoichiometric conditions and relatively high pressures (13 and 45 atm).…”