Investigation of ignition behavior of dimethyl and ethyl isomers of cycloalkanes and furans (original) (raw)
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Ignition delay studies on hydrocarbon fuel with and without additives
Shock Waves, 2009
Single pulse shock tube facility has been developed in the High Temperature Chemical Kinetics Lab, Aerospace Engineering Department, to carry out ignition delay studies and spectroscopic investigations of hydrocarbon fuels. Our main emphasis is on measuring ignition delay through pressure rise and by monitoring CH emission for various jet fuels and finding suitable additives for reducing the delay. Initially the shock tube was tested and calibrated by measuring the ignition delay of C2H6 − O2 mixture. The results are in good agreement with earlier published works. Ignition times of exo-tetrahdyrodicyclopentadiene (C10H16), which is a leading candidate fuel for scramjet propulsion has been studied in the reflected shock region in the temperature range 1250-1750 K with and without adding Triethylamine (TEA). Addition of TEA results in substantial reduction of ignition delay of C10H16.
combustion.org.uk
Dimethyl ether (DME) is a potential biofuel of interest due to its low sooting potential as well as its high cetane number (~55) which makes it a potential ignition enhancer for compression ignition engines. It has been shown that the addition of even a small amount of DME to methane increases the reactivity of the system significantly [1, 2]. In this study, ignition delay times for mixtures of DME and methane in air were measured behind reflected shock waves at pressures varying from 1.3 atm to 35 atm over the temperature range 900 K to 1650 K. Eight sets of mixtures have been investigated with equivalence ratios of 0.3, 0.5, 1.0 and 2.0. The rate constant for the unimolecular decomposition reaction CH 3 OCH 3 (+M) = CH 3 O + CH 3 (+M) has been re-estimated and a nineparameter Troe fit generated to describe the reaction as a function of temperature and pressure. The resulting rate expression agrees well with that recently reported by Cook et al. [3] in the temperature range 1300-1700 K at 1.5 atm. A mechanism consisting of 118 species and 667 reactions was used to simulate the experimental data. Overall agreement between the model and experiments is found to be good.
Shock tube measurements of ignition delay times for the butanol isomers
Combustion and Flame, 2012
Ignition delay times of the four isomers of butanol were measured behind reflected shock waves over a range of experimental conditions: 1050-1600 K, 1.5-43 atm, and equivalence ratios of 1.0 and 0.5 in mixtures containing 4% O 2 diluted in argon. Additional data were also collected at 1.0-1.5 atm in order to replicate conditions used by previous researchers. Good agreement is seen with past work for 1-butanol ignition delay times, though our measured data for the other isomers were shorter than those found in some previous studies, especially at high temperatures. At most conditions, the ignition delay time increases for each isomer in the following order: 1-butanol, 2-butanol and i-butanol nearly equal, and t-butanol. In addition, t-butanol has a higher activation energy than the other three isomers. In a separate series of high-pressure experiments, ignition delay times of 1-butanol in stoichiometric air were measured at temperatures as low as 800 K. At temperatures below 1000 K, pre-ignition pressure rises as well as significant rollover of ignition delay times were observed. Modeling of all collected data using several different chemical kinetic mechanisms shows partial agreement with the experimental data depending on the mechanism, isomer, and conditions. Only the mechanism developed by Vranckx et al.
Ignition delay times of methyl oleate and methyl linoleate behind reflected shock waves
Proceedings of the Combustion Institute, 2013
Ignition delay times for methyl oleate (C 19 H 36 O 2 , CAS: 112-62-9) and methyl linoleate (C 19 H 34 O 2 , CAS: 112-63-0) were measured for the first time behind reflected shock waves, using an aerosol shock tube. The aerosol shock tube enabled study of these very-low-vapor-pressure fuels by introducing a spatiallyuniform fuel aerosol/4% oxygen/argon mixture into the shock tube and employing the incident shock wave to produce complete fuel evaporation, diffusion, and mixing. Reflected shock conditions covered temperatures from 1100 to 1400 K, pressures of 3.5 and 7.0 atm, and equivalence ratios from 0.6 to 2.4. Ignition delay times for both fuels were found to be similar over a wide range of conditions. The most notable trend in the observed ignition delay times was that the pressure and equivalence ratio scaling were a strong function of temperature, and exhibited cross-over temperatures at which there was no sensitivity to either parameter. Data were also compared to the biodiesel kinetic mechanism of Westbrook et al. [10], which underpredicts ignition delay times by about 50%. Differences between experimental and computed ignition delay times were strongly related to existing errors and uncertainties in the thermochemistry of the large methyl ester species, and when these were corrected, the kinetic simulations agreed significantly better with the experimental measurements.
Cyclopentane combustion. Part II. Ignition delay measurements and mechanism validation
Combustion and Flame, 2017
Cycloalkanes are significant constituents of conventional fossil fuels, in which they are one of the main contributors to soot formation, but also significantly influence the ignition characteristics below ~900 K. This paper discusses the development of a detailed high-and low-temperature oxidation mechanism for cyclopentane, which is an important archetypical cycloalkane. The differences between cyclic and non-cyclic alkane chemistry, and thus the inapplicability of acyclic alkane analogies, required the detailed theoretical investigation of the kinetics of important cyclopentane oxidation reactions as part of the mechanism development. The cyclopentyl + O2 reaction was investigated at the UCCSD(T)-F12a/cc-pVTZ-F12//M06-2X/6-311++G(d,p) level of theory in a timedependent master equation framework. Comparisons with analogous cyclohexane or noncyclic alkane reactions are presented. Our study suggests that beyond accurate quantum chemistry the inclusion of pressure dependence and especially that of formally direct kinetics is crucial even at pressures relevant for practical application.
Proceedings of the Combustion Institute, 2020
We report the first shock tube measurements of formaldehyde (CH 2 O) during the first stage ignition of n-heptane, 2-methylhexane and 3,3-dimethylpentane, in highly diluted fuel/oxygen mixtures in the pressure range of 7-10 atm and temperature range of 700-880 K. Combined time histories of all carbonyl (-C = O) species, CO and fuel were also measured simultaneously in an effort to study the impact of fuel structure on the concentration and the rate of evolution of first stage ignition products. Of the three isomers studied in this work, n-heptane was found to be the fastest, while 3,3-dimethylpentane was found to be the slowest. The differences in the time scale of formation, and plateau concentration of the intermediates between the isomers across the entire range of test conditions suggests a strong dependency of the measured time histories to fuel structure. These species therefore act as markers of the Negative Temperature Coefficient (NTC) behavior of fuels and can be used as targets for developing semi-empirical, hybrid chemistry models of complex, multicomponent petroleum derived gasoline and jet fuels. The time histories reported in this work should prove very useful in the refinement of detailed kinetic models of n-heptane, and development of rate rules for branched alkane isomers.
Paper # 070RK-0008 Topic: Reaction Kinetics 8 th U. S. National Combustion Meeting
2016
Ignition delay times for five low-vapor-pressure biodiesel surrogates were measured behind reflected shock waves, using an aerosol shock tube. These fuels included methyl decanoate (C 11 H 22 O 2 , CAS: 110-42-9), methyl laurate (C 13 H 26 O 2 , CAS: 111-82-0), methyl myristate (C 15 H 30 O 2 , CAS: 124-10-7), and methyl palmitate (C 17 H 34 O 2 , CAS: 112-39-0), all of which have a fully saturated alkane chemical structure. This study also examined a methyl oleate (C 19 H 36 O 2 , CAS: 112-62-9) / Fatty Acid Methyl Ester (FAME) blend. Experiments were conducted in 4% oxygen/argon mixtures with the exception of methyl decanoate which was studied in 1% and 21% oxygen/argon blends. Reflected shock conditions covered temperatures from 1026 to 1388 K, at pressures of 3.5 and 7.0 atm, and equivalence ratios from 0.3 to 1.4. Arrhenius expressions describing the experimental ignition delay time data are given and compared to those derived from applicable mechanisms available in the literature. Graphical comparisons between experimental data and mechanism predictions are also provided. Experiments of methyl laurate, methyl myristate, and methyl palmitate represent the first shock tube ignition delay time measurements for these fuels. Finally, experiments with methyl palmitate represent, to the authors' knowledge, the first neat fuel/oxidizer/diluent gas-phase experiments involving a fuel which is a waxy solid at room temperature.
A shock tube study of ignition delay in the combustion of ethylene
Combustion and Flame, 2011
Ethylene combustion was investigated behind reflected shock waves. The experimental conditions covered a temperature range of 1000-1650 K, at pressures of 2, 10 and 18 atm, equivalence ratios of 3 and 1, for several mixture compositions using argon as the diluent (93%, 96% and 98% (vol)). In all experiments, dwell times were kept in the range of 7.55-7.85 ms by using a suitable argon-helium mixture as the driver gas. Ignition delay times were determined from the onset of visible broadband emission observed at the end plate of the shock tube. In selected experiments ignition delay times were also determined by simultaneous measurement of chemiluminescence emissions of CH Ã and OH Ã . In relatively concentrated ethylene/oxygen mixtures with 93% argon (vol), the results show an indiscernible difference between ignition delay times over the ranges of pressure and equivalence ratio tested. In more dilute mixtures (with 98% and 96% argon), longer ignition delay times were observed and there was a noticeable variation of delay times as a function of pressure; with an increase in pressure having the effect of shortening the delay time and an increase in the apparent activation energy. Modeling results using USC Mech II (Wang et al., 2007 [31]) based kinetic model, SERDP PAH model 0.1, developed by Wang and Colket, show good agreement with experiments under stoichiometric and fuel-rich conditions at low pressures. At high pressures for fuel-rich mixtures, optimized version of USC Mech II model (Wang et al., 2009 [36]) had to be used to produce good agreement between calculated ignition delay times and the experimental results. The results of this study are consistent with literature data. The present work extends the existing ethylene ignition delay experimental data set to high pressure and fuel-rich domain, the conditions that are critical for soot and polycyclic aromatic hydrocarbons (PAHs) formation.
Combustion and Flame, 2019
1,3-cyclohexadiene (1,3-CHD) can be transformed into cis-1,3,5-hexatriene (1,3,5-HT) upon light irradiation, which makes it a potential additive able to change the reactivity of a conventional fuel. This paper presents the development of a detailed chemical kinetic model for the low-temperature (50 0-120 0 K) combustion of 1,3-cyclohexadiene and 1,3,5-hexatriene. Theoretical calculations were performed to compute the thermochemistry of a large number of intermediates involved in the reaction mechanism, and for several kinetic parameters. In particular, the pericyclic reactions of 1,3-cyclohexadiene, linking it to cis-1,3,5-hexatriene, were studied theoretically. It was shown that 1,3,5-HT is inherently a secondary molecule of the 1,3-CHD mechanism and a comprehensive set of its oxidation reactions were included. Simulation of literature data (ignition delays and products speciation) measured in rapid compression machines for 1,3-CHD were performed using the newly developed kinetic model. A good agreement with experiments was found, and kinetic analyses highlighted the decomposition mechanism of 1,3-CHD and the most sensitive reactions affecting the auto-ignition delay times. Simulations of cis-1,3,5-HT auto-ignition in an RCM were also performed and compared to the ignition behaviour of 1,3-CHD. The simulation results showed that 1,3,5-HT combustion involves an induction period characterized by the predominant formation of 1,3-CHD, whose decomposition starts the radical chain mechanism.