Bis(2,2,2-trifluoroethyl) carbonate (BtFEC) is a fire suppressant candidate for the use of lithium-ion batteries (LIBs). It is known that the electrolyte components in LIBs are highly flammable, making them susceptible to igniting, whether this is due to a manufacturing fault or an abuse of the LIB itself. To address this risk, the efficiency of BtFEC as a fire suppressant was investigated experimentally in a high-temperature combustion environment, allowing for further refinement and validation of the model. Using a shock tube, BtFEC combustion properties were measured experimentally behind a reflected shock wave, capturing OH* chemiluminescence to assess ignition delay times (IDT) as well as CO time-history profiles through the implementation of laser absorption spectroscopy. Both pyrolysis and oxidation conditions were captured with three equivalence ratios (phi = 0.5, 1.0, and 1.5) for a temperature range of similar to 1200-1650 K at near-atmospheric pressures. In addition, key species measurements were taken using a microflow reactor (MFR) with a controlled temperature profile associated with Fourier transform infrared spectroscopy (FTIR). Key species investigated were BtFEC, CO, CO2, CHF3, CF2O, C2F6, and HF for the temperatures range of 800-1300 K. MFR measurements allowed for a new set of measurements by which to validate the model compared to the previous study [Mathieu et al. Proc. Combust. Inst. 2023, 39, 499] where the first assembly of the model used CO time-history, IDT, and laminar flame speed measurements. Refinement of the model was carried out with new high-level calculations as well as sensitivity, rate-of-production, and reaction pathway analyses using recent reaction rate updates from the literature. The modifications led to improvements in the level of agreement between the kinetic modeling and the new experimental data.

Recent investigations of diethyl ether (DEE) high-temperature pyrolysis and fuel-rich oxidation have highlighted the failure of existing kinetic models to describe experimental CO production. The DEE high-temperature pyrolysis and oxidation chemistry is thus investigated through ab initio calculations. Geometries, frequencies, and hindered-rotor potentials of reactants, products, and transition states of key reactions (fuel decomposition radical decomposition and H-abstraction reactions) are calculated with the B2PLYP-D3/def2-TZVPD method, whereas final energies are refined using CCSD(T)/aug-cc-pV(D,T)Z. Temperature- and pressure-dependent rate constants are then derived from either canonical transition state theory (CTST) or ME/RRKM analysis with the inclusion of tunneling effect and hindered-rotor corrections and compared to experimental measurements when available as well as to previously suggested values. This new information is then merged with a C0-C3 core chemistry model and a low-temperature chemistry DEE subset from the literature to propose a new kinetic model for the combustion of DEE. This model is tested successfully against a large database related to the high-temperature oxidation and pyrolysis chemistry of DEE, including ignition delay times, shock tube speciation data, time-resolved CO profiles, laminar flame speeds, flame structures, and jet-stirred reactor data.

Bis(2,2,2-trifluoroethyl) carbonate (BtFEC) is a candidate fire suppressant for lithium-ion batteries (LIBs). The high flammability of the electrolyte is the reason behind the frequent fire incidents reported with LIBs. These incidents are due to various factors, such as a default in the conception of the battery or operational abuse. The flame-retardant effectiveness of BtFEC was investigated by measuring its effect on the oxidation of ethyl methyl carbonate (EMC), a common LIB electrolyte component. Laminar flame speed (LFS) measurements for EMCBtFEC in air mixtures were carried out at 403 K, 1 atm, for equivalence ratios (phi) between 0.8 and 1.4, and with 0.5 % vol. BtFEC. Additional measurements were made at phi = 1.1 with BtFEC addition ranging from 0.1 up to 1.4 % vol. To further understand the combustion chemistry of the EMC-BtFEC system, ignition delay times (time at the maximum peak production of the excited radical OH*) and CO time histories were measured in a shock tube with temperatures ranging from 1217 to 1732 K, at near-atmospheric pressure (1.24-1.42 atm), and for three equivalence ratios (phi= = 0.5, 1.0, and 2.0). These new results constitute an experimental database that was used to evaluate the performance of a model assembled for both BtFEC and EMC using previous work from our group. The updated, detailed chemical kinetics mechanism presented in this study consists of 237 species and 1630 reactions. Sensitivity, rate-of-production, and reaction pathway analyses permitted the oxidation of the BtFEC-EMC system to be described. A flame sensitivity analysis exhibited the significant effect from the reactions H + CF2O 2 O reversible arrow HF + CFO and CF3 3 + H reversible arrow CF2 2 + HF, which consume H radicals that are involved in the branching reaction H + O2 2 reversible arrow OH + O, ultimately reducing the LFS. This study shows that improvements in the base fluorine chemistry are still necessary to obtain better agreement with the experiments, especially at the speciation level.

In this work, the propene oxidation is experimentally studied by using a supercritical pressure jet-stirred reactor (SP-JSR) at 10 and 100 atm, over a temperature range of 600-950 K, at fuel lean and rich conditions. A negative temperature coefficient (NTC) region is found under 100 atm at fuel rich condition, which doesn't exist in atmospheric pressure condition. Furthermore, OH addition to propene is found to be the dominant pathway under 100 atm. However, the following O-2 addition reactions are not complete in previous propene models. Thus, theoretical calculations are performed to determine the rate constants of two hydroxypropyl radicals related reactions. The updated model shows improvement but still fails to capture the NTC behavior. The possible reasons might be the uncertainties of the initiation reactions and the missing pathways of important intermediates under 100 atm. Reaction pathway analysis is performed under 10 atm, 925 K and 100 atm 725 K. It is found that under 100 atm, the main consumption pathway is OH addition to form hydroxypropyl radicals and they will go through O-2 addition to give ROO radicals. The ROO radical is not stable and will decompose to acetaldehyde and formaldehyde and OH, also, it will form three-membered ring species. However, under 10 atm, H-abstraction of propene to form allyl radical dominants propene oxidation.

The growing utilization of alternative fuels has sparked an interest in understanding the combustion characteristics of oxygenated fuels at low temperature. Cool flame extinction limits provide direct measures of the low-temperature reactivity of fuels and critical information for advanced low-temperature combustion engine design. This paper investigates the effects of fuel and oxygen concentrations on the extinction limits of diffusion cool flames for oxygenated fuels, including dimethyl ether, methyl decanoate, and 1-dodecanol in an atmospheric counterflow burner. The cool flame radical indexes of these oxygenated fuels are developed by isolating the thermal and transport effects from the chemical contribution to diffusion cool flame extinction. The results show that the ranking of low-temperature reactivities of long carbon chain oxygenated fuels, compared with n-alkane, is ether > n-alkane > alcohol > ester for a similar carbon number. Furthermore, due to the critical role of multiple oxygen addition reactions in the low-temperature chemistry, the relationship between the cool flame extinction limit and the oxygen concentration is also explored. The results show that the cool flame extinction limits of the oxygenated fuels are proportional to a nth power of the oxygen concentration, [O2]n, due to the combined effects of multiple oxygen addition reactions and the negative temperature coefficient in low-temperature chemistry. Additionally, the measured n number of 1-dodecanol is found to be larger than 2, which suggests the existence of the third oxygen addition reactions in low-temperature chemistry for large alcohols.

To reduce the flammability of lithium-ion battery electrolytes, the fire suppressant effect of di(2,2,2trifluoroethyl) carbonate (DtFEC) was investigated experimentally and numerically using a new detailed kinetics model. DtFEC has a structure similar to diethyl carbonate (DEC), which is a very common component of battery electrolytes. This similar structure should allow for an integration of the fire suppressant without excessive degradation of the battery performance. To validate the model and assess the fire suppressant potential of DtFEC, several kinds of experiments were performed around atmospheric pressure. The high-temperature chemistry of DtFEC was investigated in shock tubes by measuring ignition delay times for a DtFEC/O2/Ar mixture and by measuring the CO formation during its pyrolysis using a laser absorption diagnostic. DtFEC's fire suppressant potential was assessed by measuring the effects of a small DtFEC addition on the ignition delay times and laminar flame speeds of well-known fuels, namely H2 and CH4. A model was assembled using a well-validated and modern base mechanism (NUIGMech1.1) coupled with existing chemistry for fluoroalkanes. Using ab-initio calculations, the DtFEC module and corresponding thermodynamics data were implemented. The resulting model performs well at predicting the global kinetics data (ignition delay time, laminar flame speed), but improvements on CO time-history profiles are still necessary.

In order to comply with present and future stringent environmental policies, engine manufacturers have to improve engine design and control to achieve combustion with high dilution ratios. The use of CFD simulations with complex combustion chemistry remains prohibitive, and alternatives to assess quickly the laminar flame speeds at local grid cell conditions (temperature, pressure, equivalence ratio, and dilution ratio) are desired, such as empirical correlations. Whereas these correlations should ideally be obtained from experimental measurements, comprehensively validated kinetic models can help extend databases to conditions that cannot be achieved practically. Hence, the present study proposed a reduced kinetic mechanism, containing 593 species and 3698 reactions, for one gasoline surrogate, namely Toluene Reference Fuel with Ethanol addition (TRFE). It is obtained by first compiling sub-mechanisms from the literature for the four components (isooctane, n-heptane, toluene, and ethanol) with updates of some key rate constants, and then is reduced for 1-D flame speed computations. The model was first validated against recent experimental laminar flame speed measurements of TRFE/air/diluent mixtures for various temperatures, pressures, equivalence ratios, and dilution ratios and then employed to extend the experimental database for the TRFE surrogate to higher dilution ratios and temperatures. A new formalism, including new mathematical expressions for the reference and dilution terms, and the temperature exponent are proposed. This new formalism exhibits improved abilities in fitting the laminar flame speeds, especially at high dilution ratios and in very fuel-lean and fuel-rich conditions. A new mathematical correlation based on these formulas was developed, whose correlation parameters were obtained by fitting both experimental data and mechanism predictions. Regardless of the conditions, the present correlation is observed to show overall good agreements with available experimental data in the literature for laminar flame speeds and their dependence on equivalence ratio, temperature, pressure, and dilution. Results show that the effect of dilution in reducing flame speeds is not linear and depends on the equivalence ratio. A parameter μ is defined in the correlation formulas to evaluate the dilution effectiveness of the diluent, which is found to be composition-specific and possibly follows a linear mixing rule for diluent mixtures.

The increasing demand for silicon-based materials requires the optimization of silicon deposit manufacturing processes and therefore a better understanding of the gas-phase reactivity of silicon precursors such as silicon tetrachloride (SiCl4). In the present work, hydrogen atom resonance absorption spectroscopy (H-ARAS) has been used to investigate the high-temperature reactivity of SiCl4 behind reflected shock waves at ∼1.5 atm in the presence of either ethyl iodide or molecular hydrogen, used as H atom precursors. Several key reactions of SiCl4 and its main gas-phase decomposition products (SiCl3, Cl, SiHCl3, SiHCl2) have been determined theoretically. The structures and vibrational frequencies of reactants, products, and tight transition states were determined at the B2PLYP-D3/aug-cc-pVTZ level and final single-point energies refined from extrapolated RCCSD(T)/aug-cc-pVnZ (n = D, T, and Q) calculations. The minimum-energy paths of barrierless reactions were calculated at the NEVPT2 level. Final rate constants were then derived from the transition-state theory (TST) and the variational TST/master equation analysis within the rigid rotor harmonic oscillation framework. A kinetic mechanism was assembled, based on the present ab initio calculations, to successfully model and interpret the experimental absorption profiles. Sensitivity analysis unambiguously highlighted the need to account for pressure dependence in the SiCl4 decomposition (SiCl4 ⇄ SiCl3 + Cl) while discarding previous theoretical and experimental determinations of this rate constant.

Experimental, numerical, and theoretical studies are performed to understand the explosive thermal decomposition of monomethylhydrazine/argon mixtures. Ignition delays of concentrated MMH/Ar mixtures (20-30%) have been measured behind a reflected shock wave around 1000 K and 1 atm. Although several detailed chemical kinetic models have predictive abilities for diluted and highly diluted mixtures, none of them showed predictive for concentrated mixtures. A new kinetic model is proposed, in which numerous rate constants and thermochemical data are reassessed based on theoretical calculations, with the purpose to determine whether, or to what extent, trends derived from diluted or highly diluted MMH/Ar mixtures can explain observations in concentrated MMH mixtures. The present kinetic model is found to predict speciation experimental profiles in diluted MMH/Ar mixtures and is a significant improvement in predicting the induction delays of concentrated MMH/Ar mixtures.

Studies on combustion of synthetic jet fuels is of growing importance because of their potential for addressing security of supply and air transportation sustainability. The oxidation of a 100% naphthenic cut (NC) that fits with typical chemical composition of biomass or coal liquefaction products, gas-toliquid fuel (GtL), and a GtL–NC mixture were studied in a jetstirred reactor under the same conditions (550-1150 K; 10 bar; equivalence ratio of 0.5, 1, and 2; initial fuel concentration of 1000 ppm). Surrogate model-fuels were designed based on fuel composition and chemical properties for simulating the kinetics of oxidation of these fuels. We used model-fuels consisting of mixtures of n-decane, decalin, tetralin, 2-methylheptane, 3methylheptane, n-propyl cyclohexane, and n-propylbenzene. The proposed detailed chemical kinetic reaction mechanism was validated using the full experimental database obtained for the oxidation of pure GtL, GtL–NC mixture, and pure NC. Kinetic reaction pathway analyses and sensitivity analyses were used for interpreting the results.

There is increasing interest for utilizing synthetic biofuels in blends with conventional oil-derived liquid fuels. In this contest, research on the combustion of synthetic jet fuels has lately gained significance because they could help addressing sustainability and security of supply for air transportation. Improving the kinetic modeling of the oxidation of synthetic fuels requires further investigations under well-controlled conditions. The combustion of a 100% naphthenic cut fitting typical chemical composition of biomass or coal liquefaction products and a 50%vol. mixture with Gas to Liquid fuel were studied in a jet-stirred reactor (JSR) under the same conditions (550–1150K, 10bar, equivalence ratio of 0.5, 1, and 2, and 1000ppm of fuel). For simulating the kinetics of oxidation of these fuels, model-fuels were designed to fit fuels chemical composition and properties. They consisted of mixtures of n-decane, 2-methylheptane, 3-methylheptane, n-propylcyclohexane, decahydronaphtalene, and tetrahydronaphtalene. The proposed detailed chemical kinetic reaction scheme was validated using the whole experimental data set acquired in the present work; for the oxidation of pure GtL, we used previous obtained data. For interpreting the results, reaction pathways and sensitivity analyses were used.

Research on the production and combustion of synthetic jet fuels has recently gained importance because of their potential for addressing security of supply and sustainable air transportation challenges. The combustion of a 100% naphtenic cut that fits with typical chemical composition of products coming from biomass or coal liquefaction (C12.64H23.64; M=175.32 g.mol(-1); H/C=1.87; DCN=39; density=863.1 g.L-1) and a 50% vol. mixture with Gas to Liquid from Shell (mixture: C11.54H23.35; M=161.83 g.mol(-1); H/C=2.02; DCN=46; density=800.3 g.L-1) were studied in a jet stirred reactor under the same conditions (temperature, 550-1150 K; pressure, 10 bar; equivalence ratio, 0.5, 1, and 2; initial fuel concentration, 1000 ppm). Surrogate model-fuels were designed based on fuel composition and properties for simulating the kinetics of oxidation of these fuels. We used new model-fuels consisting of mixtures of n-decane, decalin, tetralin, 2-methylheptane, 3-methylheptane, n-propyl cyclohexane, and n-propylbenzene. The detailed chemical kinetic reaction mechanism proposed was validated using the entire experimental database obtained in the present work and for the oxidation of pure GtL, we used previous results. Kinetic computations involving reaction paths analyses and sensitivity analyses were used to interpret the results.

The first speciation data regarding the oxidation of methyl ethyl ketone (MEK) are presented. Fuel-lean, stoichiometric and fuel-rich mixtures were studied at constant fuel concentration (1000ppm) in a jet stirred reactor at atmospheric and high pressure (10atm). A detailed kinetic mechanism is proposed based on theoretical calculations at the G3//MP2/aug-cc-pVDZ level of theory. The new rate constants differ substantially from the estimations employed in the previous MEK submechanism available in the literature, and impact MEK oxidation pathways. The model was tested successfully against these new speciation data and other available data (ignition delay times, flame speeds, pyrolysis species profile). However, some deficiencies in the model were identified concerning methyl ketene and methyl vinyl ketone. Reaction path analyses are used to interpret the results.

Author(s): Moshammer, K; Jasper, AW; Popolan-Vaida, DM; Lucassen, A; Dievart, P; Selim, H; Eskola, AJ; Taatjes, CA; Leone, SR; Sarathy, SM; Ju, Y; Dagaut, P; Kohse-Hoinghaus, K; Hansen, N

A novel method to establish self-sustaining cool diffusion flames with well-defined boundary conditions is experimentally demonstrated by adding ozone to the oxidizer stream in counterflow configuration. It is found that the atomic oxygen produced through the decomposition of ozone dramatically shortens the induction timescale of the low temperature chemistry, extending the flammable region of cool flames. Thus, it enables the establishment of self-sustaining cool flames at the pressure and timescales at which normal cool flames may not be observable. The present method, for the first time, provides an opportunity to study cool flame dynamics, structure, and chemistry simultaneously in well-known flame geometry. Extinction limits of n-heptane/oxygen cool diffusion flames are measured and a cool diffusion flame diagram is experimentally determined. Numerical simulations reveal that the extinction limits of cool diffusion flames are strongly governed by species transport and low temperature chemistry activated by ozone decomposition. The structure of cool diffusion flame is further investigated by measuring the temperature and species distributions with a micro-probe sampling technique. The kinetic model over-predicts the rate of n-heptane oxidation, the heat release rate, and the flame temperature. Measurements of intermediate species, such as CH2O, acetaldehyde, C2H4, and CH4, suggest that the model over-predicts the QOOH thermal decomposition reactions to form olefins, resulting in substantial over-estimation of C2H4, and CH4 concentrations. The new method and data of the present study will contribute to promote understandings of cool flame chemistry.

Author(s): Moshammer, K; Jasper, AW; Popolan-Vaida, DM; Lucassen, A; Dievart, P; Selim, H; Eskola, AJ; Taatjes, CA; Leone, SR; Sarathy, SM; Ju, Y; Dagaut, P; Kohse-Hoinghaus, K; Hansen, N

As two of the most important species that characterize hydrocarbon low temperature ignition, HO2 and H2O2 formation during dimethyl ether (DME) oxidation was quantified using the same experimental conditions, for the first time, in an atmospheric flow reactor at low and intermediate temperature range. Dual-Modulation Faraday Rotation Spectroscopy (DM-FRS) and Molecular Beam Mass Spectrometry (MBMS) were used to measure HO2 and H2O2 respectively. DME and other important intermediate species such as CH2O and CO are also measured by MBMS between 400 and 1150 K at different fuel concentrations. Species profiles in the reactor were calculated by using both zero- and two-dimensional computations with different detailed kinetics for cross-validation and comparison with experimental results. The models predict adequately the low and intermediate oxidation temperature windows near 600 and 1000 K, respectively. However, both models over-predicted the DME consumption as well as CO, HO2 and H2O2 formations at the low temperature oxidation window by more than a factor of four. Moreover, although the model predicted reasonably well the formation of CH2O and CO/CO2 at the intermediate temperature oxidation window, the concentration of H2O2 was also over-predicted, suggesting the large uncertainties existing in the DME low temperature chemistry and in H2O2 chemistry at intermediate temperature. Furthermore, to analyze the uncertainty of the low temperature chemistry, a branching ratio of QOOH decomposition to CH2O was derived using measured DME, CH2O and CO concentrations. The large difference between the modeled and measured branching ratios of QOOH decomposition suggests an underestimated QOOH decomposition rate to form CH2O in the current DME models.