CO Time-histories Research Articles

Enhancing lithium-ion battery safety: Investigating the flame-retardant efficacy of bis(2,2,2-trifluoroethyl) carbonate during ethyl methyl carbonate combustion

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 EMC-BtFEC in air mixtures were carried out at 403 K, 1 atm, for equivalence ratios (ϕ) between 0.8 and 1.4, and with 0.5 % vol. BtFEC. Additional measurements were made at ϕ = 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 (ϕ = 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 ⇆ HF + CFO and CF3 + H ⇆ CF2 + HF, which consume H radicals that are involved in the branching reaction H + O2⇆ 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.

Experimental and modeling study of the combustion of ethyl methyl carbonate, a battery electrolyte

Ethyl methyl carbonate (EMC) is one of the main constituents of the electrolyte in lithium-ion batteries (LIBs). To understand better fire events involving LIBs and try to prevent them, the combustion of EMC was studied experimentally, and the results were analyzed using modern detailed kinetics models. Shock tubes were used to collect ignition delay times (IDTs) and CO time histories, while laminar flame speeds were measured in a closed vessel. All experiments were carried out near atmospheric pressure. The shock tube experiments were performed for three equivalence ratios (0.5, 1.0, and 2.0) with the IDTs measured with “fuel-air” mixtures and the CO spectroscopic laser measurements in mixtures highly diluted in 99.25% He/Ar. Comparisons with results obtained for other linear carbonates typically found in LIBs, such as dimethyl carbonate and diethyl carbonate, are also presented. Numerical predictions from recent detailed chemical kinetics mechanisms (Takahashi et al., 2022, Grégoire et al., 2023) did not capture well the combustion behavior of EMC in some of our conditions. Sensitivity analyses suggest that EMC decomposition reactions and subsequent combustion chemistry of the formed intermediates, i.e. methanol and ethylene, still need improvement.

CO Laser Absorption Measurements During Syngas Combustion at High Pressure

Abstract Syngas is a desirable fuel for combustion in the Allam-Fetvedt cycle, which involves combustion under supercritical-CO2 conditions. While some work has been conducted in collecting ignition delay times (IDT) at the extreme pressures required by these systems, significant model deficiencies remain. Additionally, considerable barriers in terms of nonideal gas dynamic effects have been shown for these experiments in shock tubes. Further investigation into the fundamental combustion kinetics of H2/CO/CO2 mixtures is required. Time-resolved speciation measurements for target species have been shown to better aid in improving the understanding of underlying chemical kinetics than global ignition delay time measurements. Therefore, laser absorption measurements of CO were measured behind reflected shock waves during combustion of syngas at 5 and 10 bar and temperatures between 1080 and 2100 K. The mixtures investigated utilized H2-to-CO ratios of 1:1 and 1:4, respectively, each at stoichiometric conditions, allowing for discussions of the effect of initial fuel composition. A ratio of fuel to CO2 of 1:2 was also utilized to represent commercially available syngas. The mixtures were diluted in helium and argon (20% He, 76.5% Ar) to minimize thermal effects and to expedite CO thermal relaxation during the experiment. The resulting CO time histories were then compared to modern chemical kinetics mechanisms, and disagreement is seen for this system, which is assumed to be fairly well known. This study elucidates particular chemistry that needs improvement in moving toward a better understanding of syngas combustion at elevated pressures.

Mid-infrared absorption spectroscopy measurements and model improvements during the oxidation of ammonia/ethanol and ammonia/diethyl ether blends in a shock tube

Blending ammonia with highly active fuels (hydrogen, hydrocarbons, oxygenated hydrocarbons, etc.) has been identified as an efficient way to improve the mixture's reactivity. In this study, the temperature, CO, CO2, H2O, NH3, and NO time-histories were measured simultaneously during the oxidation of ammonia/ethanol and ammonia/diethyl ether (DEE) blends (equivalence ratio ϕ ∼ 1.2) using mid-infrared laser absorption spectroscopy behind reflected shock waves. Various models (ten for ammonia/ethanol and three for ammonia/DEE) were selected to perform the simulation and compared with the measurements. The predictions are very different for both mixtures, among which the CRECK model was selected to perform discussion and kinetics analyses for the ammonia/ethanol mixture and the Shrestha 2022 model was selected for the ammonia/DEE mixture. The CRECK model performs well in predicting the temperature rise/plateau, H2O formation rate/plateau, CO consumption rate/plateau, and CO2 formation rate. However, it underpredicts the CO formation rate and slightly overpredicts the CO2 plateau and NH3 consumption rate; for the NO time-history, the CRECK model well captures the rapid NO formation but underpredicts the near-equilibrium NO concentration and gives an unnormal initial NO production. The Shrestha 2022 model accurately predicts the plateaus of temperature and H2O, but significantly underpredicts the reactivity of the ammonia/DEE mixture and overpredicts the near-equilibrium NO concentration. According to the kinetics analyses, key reactions affecting the species' time-histories were selected. Fourteen reactions in the CRECK model and eight reactions in the Shrestha 2022 model were updated by the reported data or estimations to improve the predictions. However, discrepancies still exist, which are mainly located in the CO formation and NH3 consumption rates. Further effort should mainly focus on these two aspects, as well as the interactions between oxygenated hydrocarbons and ammonia at high temperatures.

Shock-tube CO measurements during the pyrolysis of ethylene carbonate

Ethylene carbonate (EC) is a key component of the flammable electrolyte in lithium-ion batteries. In this study, the pyrolysis of ethylene carbonate was investigated by measuring CO time histories near atmospheric pressure and in highly diluted conditions (0.999 He/Ar). The performance of a recent detailed chemical kinetics mechanism from Kanayama et al., 2022, was evaluated, and noticeable discrepancies were found, possibly indicating missing reaction pathways. A tentative model was proposed by merging the EC sub-mechanism from the Kanayama study with a recent model for linear carbonate pyrolysis from the authors (Grégoire et al., 2023). This tentative model includes the addition of several missing reactions for oxirane pyrolysis, and a couple of reactions for acetaldehyde and EC thermal decomposition were modified within their error uncertainties. The resulting model presents better predictions overall, but room for improvement remains. This study highlights the need to further study the pyrolysis chemistry of EC as well as acetaldehyde, which is a major intermediate component from EC pyrolysis under our conditions.

Experimental and chemical kinetic modeling study of high-temperature oxidation of diisopropyl methylphosphonate (DIMP) - A sarin simulant

Chemical warfare (CW) agent simulants are used in laboratory experiments to study the combustion characteristics of CW agents due to their high toxicity. A crucial CW agent simulant with a chemical structure similar to the deadly nerve agent Sarin (GB) is diisopropyl methylphosphonate (DIMP), an organophosphate compound (OPC). In this study, the high-temperature oxidation of DIMP is investigated in a shock tube at temperatures between 1440 K and 1710 K and a pressure of 1–2 atm. The carbon monoxide mole fraction time histories near 4.9 µm were obtained using laser absorption spectroscopy. The rate parameters for DIMP's H-abstraction reactions with O, and OH radicals were determined using molecular simulations. The rates of reactions involving smaller phosphorous species were also calculated at the CBS-QB3 level. These reactions along with the isopropanol sub-mechanism from the literature were added to the LLNL model to obtain an improved chemical kinetic mechanism for DIMP. Since isopropanol was a major intermediate in DIMP decomposition, validations were conducted with CO time histories during the oxidation of isopropanol. The new model predicted CO during isopropanol oxidation reasonably well. Both the LLNL model and the model developed in this work could predict CO time histories during DIMP oxidation satisfactorily. To comprehend the CO formation pathways and sensitive reactions during DIMP oxidation, reaction path analysis and sensitivity analysis were also carried out. The reaction mechanism developed here will help in the design, development, and optimization of efficient, effective and secure CW destruction techniques.

Experimental Kinetics Study on Diethyl Carbonate Oxidation

Diethyl carbonate (DEC) is a common component of the liquid electrolyte in lithium ion batteries (LIBs). As such, understanding DEC combustion chemistry is imperative to improving chemical kinetic modeling of LIB fires. To this end, a comprehensive experimental study was conducted to collect ignition delay times, CO time histories, and laminar flame speeds during DEC combustion. Ignition delay times were collected using a heated shock tube at real fuel–air conditions for three equivalence ratios (ϕ = 0.5, 1.0, and 2.0) near atmospheric pressure and for temperatures between 1182 and 1406 K. Another shock tube was used to collect CO time histories using a laser absorption diagnostic. These experiments were conducted for the same equivalence ratios, but highly diluted in argon and helium (79.25% Ar + 20% He) at an average pressure of 1.27 atm and a temperature range of 1236–1669 K. Finally, a heated constant-volume vessel was used to collect laminar flame speeds of DEC at an initial temperature and pressure of 403 K and 1 atm, respectively, for equivalence ratios between 0.79 and 1.38. The results are compared with different mechanisms from the literature. Good agreement is seen for the ignition delay time and flame speed measurements. However, significant deviations are observed for the CO time histories. A detailed discussion of the chemical kinetics is presented to elucidate the important reactions and direct future modeling efforts.

Experimental study of the methane/hydrogen/ammonia and ethylene/ammonia oxidation: Multi-parameter measurements using a shock tube combined with laser absorption spectroscopy

Ammonia (NH3) is a promising hydrogen carrier and carbon-free fuel, which can be synthesized using renewable energy and has attracted increasing attention from both academic and industrial communities. This study selected six absorption lines and developed a laser absorption diagnostics system that can simultaneously measure the temperature, CO, CO2, H2O, NH3, and NO time-histories during the oxidation of CH4/H2/NH3 and C2H4/NH3 mixtures (equivalence ratio ϕ ≈ 1.2) behind reflected shock waves. Since the fuels were highly diluted to reduce the nonideal effects and heat release behind reflected shock waves, the maximum NO mole fraction was only ∼0.2% and led to a small absorption (< 2.0%). Therefore. the wavelength modulation spectroscopy (WMS-2f/1f) was used for the NO time-history measurements while the other species were measured using fixed-wavelength absorption spectroscopy. A total of thirteen kinetics models were used to interpret the measurements. The main differences between the model predictions and measured data lie in two aspects: the mixture reactivities and the NO production. Generally speaking, for both CH4/H2/NH3 and C2H4/NH3 mixtures, the Glarborg model performs the best in predicting the temperature and species time-histories but the differences still exist. The high-quality experimental data support further analyses and improvements. Detailed kinetics analyses based on the Glarborg 2018 model were performed. It indicates that H + O2 = O + OH is the most sensitive and promoting reaction for both mixtures, followed by the H-abstraction reactions of H2 and C2H4. Conversely, the H-abstraction reactions of CH4 and NH3 impede oxidation due to competition with promoting reactions for reactants (H, OH, or O). Moreover, subsequent reactions involving the produced CH3 or C2H3 radicals also have significant effects on oxidation. The reactions affecting the NO plateau were also selected as the basis to optimize the predicted NO plateau. Although updating the rate constants of some key reactions improved model performance for both mixtures, discrepancies still exist, particularly for the C2H4/NH3 mixture.

Low-temperature oxidation of n-octane and n-decane in shock tubes: Differences in time histories of key intermediates

The impact of chain length on the time histories of key intermediate species that form upon first-stage ignition was studied experimentally in a shock tube using multi-color laser absorption diagnostics. CO, CH2O, OH, and composite time histories of heavier carbonyls were measured simultaneously during the low temperature oxidation of n-octane & n-decane in the temperature range of 720–860 K, and pressure range of 4.1–5.8 atm. The test mixtures were 0.64% & 0.6% fuel in oxygen, respectively. A two-color diagnostic was also developed and used in tandem with other diagnostics to quantify the evolution of temperature during oxidation. To our knowledge, this work reports the first measurement of CH2O, OH, and temperature during oxidation of C8 or heavier hydrocarbon fuels at low temperatures. The measured time histories were also compared against the predictions of two recent detailed kinetic models. Significant differences in the measured and predicted first-stage ignition delay times, absolute concentration of species post-ignition and the maximum rate of formation of species were observed. Our measurements will serve as targets for further refinement of these detailed kinetic models and in the development of rate rules for similar classes of fuels. The measurements also revealed significant differences in the relative reactivity of n-octane and n-decane. Taken together with previous speciation studies conducted in n-heptane, we observe a strong correlation between the species time histories, reactivity, and chain length of straight chain alkanes. This observation lends further support to the selection of CO and CH2O as target species for development of Low-Temperature Hybrid Chemistry (HyChem) models for real transportation and aviation fuels in future.

Nitromethane as a nitric oxide precursor for studying high-temperature interactions between ammonia and nitric oxide in a shock tube

Ammonia (NH3) is a promising carbon-free fuel for carbon neutrality that has recently received increasing attention. However, NOx emissions are one of the main problems for NH3 or NH3-blended combustion. This study used nitromethane (CH3NO2) as a nitric oxide precursor to study NH3/NO interactions at high temperatures. The temperature, CO, CO2, NO, and NH3 time-histories were measured simultaneously during the pyrolysis and oxidation (equivalence ratios ϕ = 2.0 and 1.0) of CH3NO2 and CH3NO2/NH3 mixtures behind reflected shock waves using mid-infrared laser absorption spectroscopy to analyze the NH3/NO interactions. The measurements were used to validate and evaluate seven kinetic models which gave very different predictions for the different mixtures, among which the Glarborg et al. (2018) and Shang et al. (2020) models agreed best with the temperature, NO, and NH3 measurements. The measured CO and CO2 time-histories are shown in the Supplementary Material. Both mechanisms accurately capture the temperature plateau while the main difference is the temperature increase during oxidation. The NO formation rate and plateau concentrations during CH3NO2 pyrolysis are better predicted by the Shang model than by the Glarborg model. Both mechanisms capture the NO formation rate for CH3NO2 oxidation with ϕ = 2.0 but underestimate it for ϕ = 1.0. With NH3, the Glarborg model better predicts the NO removal during CH3NO2/NH3 pyrolysis. However, both mechanisms underestimate the NO formation rate and maximum but overestimate the NO removal rate and NH3 consumption for CH3NO2/NH3 oxidation. Rate-of-production and sensitivity analyses show that: for the NO formation, CH3 + NO2 = CH3O + NO and NO2 + H = NO + OH are the primary pathways and CH3NO2 (+ M) = CH3 + NO2 (+ M) is the most sensitive reaction. NH3 + OH = NH2 + H2O contributes the most to the NH3 consumption during CH3NO2/NH3 pyrolysis, while NH3 + H = NH2 + H2 and NH3 + O = NH2 + OH are increasingly important at oxidation condition. NH2 + NO = N2 + H2O and NH2 + NO = NNH + OH are the most important reactions for the NO reduction with NH3 existing. The rate constants of some key reactions were revised to improve the predictions.

Laminar Flame Speed, Ignition Delay Time, and CO Laser Absorption Measurements of a Gasoline-like Blend of Pentene Isomers.

The combustion properties of a gasoline-like blend of pentene isomers were determined using multiple types of experimental measurements. The representative mixture (Mix A) is composed of 5.7% 1-pentene (1-C5H10), 39.4% 2-pentene (2-C5H10), 12.5% 2-methyl-1-butene (2M1B), and 42.4% 2-methyl-2-butene (2M2B) (% mol). Laminar flame speeds were measured at equivalence ratios of 0.7-1.5 in a constant-volume combustion chamber, and ignition delay times (including both OH* and CH* diagnostics) as well as CO time-history profiles were performed in shock tubes, in highly diluted mixtures (0.995 He/Ar), at a stoichiometric condition for temperatures ranging from 1350 to 1750 K, and at near-atmospheric pressure. Two additional unbalanced mixtures removing either 2M2B (Mix B) or 2-C5H10 (Mix C) were studied in a shock tube to collect CO time histories, representing the most stringent validation constraints, as these two pentenes constitute the biggest proportions in Mix A and exhibit opposite behaviors in terms of reactivity due to their chemical structure differences. Numerical predictions using a recent validated chemical kinetics mechanism encompassing all pentene isomers from Grégoire et al. ( Fuel2022, 323, 124223) are presented. The use of a complex blend of four pentene isomers in the present paper provided a capstone test of the current mechanism's ability to model pentene-isomer combustion chemistry, with very good results that reflect positively on the current state of the art in pentene isomer kinetics modeling.

Shock tube and multi-species laser absorption measurements of rate constants for methanol pyrolysis

Quantitative and high-accuracy measurements of multiple rate constants regarding the reaction kinetics of methanol pyrolysis were performed in shock tube experiments over 1200 - 1610 K, 0.72 - 4.50 atm. The key reactions investigated include both the thermal dissociation of methanol and its major fragments (for example, CH2OH and CH3O), and their H-abstraction by H and CH3 radicals. Laser absorption time-histories of CH2O, CO and H2O were measured and analyzed with a Bayesian approach for systematic determination of the joint posterior distribution of their rate constants, using FFCM-1 as the base mechanism. Various types of uncertainty sources in the current measurements, including both the non-ideal effects in the shock tube and uncertainties in the mixture composition and the absorption model, were thoroughly analyzed. A comparative analysis using other reaction models was also briefly discussed.

Simultaneous measurements of temperature, CO, and CO2 time-history in reacting n-heptane/O2/argon mixtures blended with diethyl ether behind reflected shock waves

The temperature, CO, and CO2 time-histories for the fuel-rich (equivalence ratio ϕ = 1.2 and 2.0) oxidation of n-heptane/diethyl ether/O2/argon mixtures were measured simultaneously in a shock tube using laser absorption spectroscopy. Two transition lines (v" = 0, P8, 4.73 μm and v" = 1, R21, 4.56 μm) in the CO fundamental band were selected to simultaneously measure the temperature and CO time-histories. One transition line in the CO2 fundamental band (v3“= 0, R88, 4.18 μm) was used for the CO2 time-history measurements, with its absorption cross-section measured at 1240 – 2600 K and 0.7 – 3.8 bar. A kinetic model was then developed that combined the NUI Galway 1.1 mechanism and the DEE sub-mechanism (Sakai et al. 2017). All the measured data were compared with predictions based on the proposed mechanism and the Zeng et al. (2017) mechanism.Both mechanisms accurately predicted the near-equilibrium/plateau temperatures for ϕ = 2.0 and CO for ϕ = 1.2. However, for ϕ = 1.2, both mechanisms slightly overpredict the near-equilibrium temperature and CO2. For ϕ = 2.0, the presented mechanism better predicts the CO plateau concentrations while the Zeng et al. (2017) mechanisms are better in predicting CO2 plateau concentrations. The predictions were less accurate for the temperature rise and CO/CO2-evolution processes. The predictions were also less accurate for specific equivalence ratios and blending ratios of n-heptane and diethyl ether. Rate-of-production analyses showed that HCO + M = H + CO + M is the primary pathway for producing CO and CO + OH = CO2 + H is the primary pathway for producing CO2 for the conditions in this manuscript. Sensitivity analyses show that the most sensitive reaction is H + O2 = OH + O, with some reactions related to AXC3H5 and CH3CHO also influencing the CO and CO2 time-histories. Modifying the rate constants of the specific reactions reduces the differences between the predicted and measured results, but discrepancies still exist and the mechanisms need to be further improved.

Assessing NO2-Hydrocarbon Interactions during Combustion of NO2/Alkane/Ar Mixtures in a Shock Tube Using CO Time Histories

Modern gas turbines use combustion chemistry during the design phase to optimize their efficiency and reduce emissions of regulated pollutants such as NOx. The detailed understanding of the interactions during NOx and natural gas during combustion is therefore necessary for this optimization step. To better assess such interactions, NO2 was used as a sole oxidant during the oxidation of CH4 and C2H6 (the main components of natural gas) in a shock tube. The evolution of the CO mole fraction was followed by laser-absorption spectroscopy from dilute mixtures at around 1.2 atm. The experimental CO profiles were compared to several modern detailed kinetics mechanisms from the literature: models tuned to characterize NOx-hydrocarbons interactions, base-chemistry models (C0–C4) that contain a NOx sub-mechanism, and a nitromethane model. The comparison between the models and the experimental profiles showed that most modern NOx-hydrocarbon detailed kinetics mechanisms are not very accurate, while the base chemistry models were lacking accuracy overall as well. The nitromethane model and one hydrocarbon/NOx model were in relatively good agreement with the data over the entire range of conditions investigated, although there is still room for improvement. The numerical analysis of the results showed that while the models considered predict the same reaction pathways from the fuels to CO, they can be very inconsistent in the selection of the reaction rate coefficients. This variation is especially true for ethane, for which a larger disagreement with the data was generally observed.

Shock-tube spectroscopic CO and H2O measurements during 2-methyl-1-butene combustion and chemical kinetics modeling

New CO and H2O time histories were measured for 2-Methyl-1-Butene (2M1B) behind reflected shock waves. The experimental setup was developed to simultaneously obtain carbon monoxide and water time histories from the oxidation of 2M1B in 99.5% He/Ar (20% He and 79.5% Ar). The experiments were carried out at three different equivalence ratios (ɸ = 0.5, 1.0, and 2.0) at pressures and temperatures ranging from 1.15 atm to 1.32 atm and 1414 K to 1894 K, respectively. A very limited number of studies focusing on 2M1B are available in the literature, and no model is designed specifically for this C5 alkene, as opposed to its other isomers: 1-pentene (1-C5H10), 2-pentene (2-C5H10), 3-Methyl-1-Butene (3M1B), and 2-Methyl-2-Butene (2M2B). Experimental profiles were compared to recent literature models containing a 2M1B sub-mechanism. Numerical predictions using the AramcoMech 3.0 and Ruwe et al. mechanisms show that the combustion behavior of 2M1B is not well captured by these recent detailed kinetics models. More importantly, Cheng et al. proposed a modified version of AramcoMech 3.0 with improvements on the 1-C5H10 and 2M2B sub-mechanisms, which deteriorates the mechanism's performance for 2M1B. Similarly, Power et al. had modified AramcoMech 3.0 on the sub-mechanisms for 1-C5H10 and 2-C5H10, but it does not reproduce H2O and CO time histories any better. The Dong et al. model is accurate within 10% when considering only the induction delay times, but it shows discrepancies for the concentration levels. The present study used an updated, detailed chemical kinetics model, and this mechanism was able to capture the experimental results with suitable precision, giving the best predictions.

Shock tube study of ethanol pyrolysis II: Rate constant measurements and modeling

The rate constants of two unimolecular decomposition channels of ethanol, C2H5OH(+Ar) = CH3 + CH2OH(+Ar), and C2H5OH(+Ar) = C2H4 + H2O(+Ar) were measured near 1 atm and 10 atm behind reflected shock waves between 1190 and 1550 K by tracking the evolution of CO and C2H4, respectively. Use of sensitive laser diagnostics in conjunction with carefully selected test mixtures enabled the suppression of sensitivity of CO and C2H4 time-histories to secondary reactions, resulting in a significant reduction of uncertainty in the measured rate constants. Additionally, CH3CHO time-histories measured during the pyrolysis of 2% C2H5OH/Argon mixtures were used to determine the rate constant of the most dominant H-abstraction channel, C2H5OH + H = sC2H4OH + H2 between 1290 and 1530 K. The low temperature CH3CHO time-histories were also used to infer the rate constant of sC2H4OH = CH3CHO+H. The measured rate constants were used to generate an updated kinetic model, whose performance was evaluated against the species time-history data reported in recent shock tube pyrolysis studies. The performance of the updated model was also evaluated against ignition delay times (IDTs) of stochiometric C2H5OH/Oxygen/Nitrogen mixtures, measured between 1000 and 1500 K near 20 atm in this study. The updated kinetic model was found to show excellent agreement with both shock tube pyrolysis and IDT studies. Additionally, the reduction in the uncertainty of the rate constants studied in this work resulted in a significant reduction in the uncertainty of the model predictions. The rate constant expressions listed below were derived from the measurements in this work, and are valid in the temperature range of 1200–1600 K.kC2H5OH(+Ar)↔CH3+CH2OH(+Ar),1atm=2.125×1013e−34070Ts−1(±21%)kC2H5OH(+Ar)↔CH3+CH2OH(+Ar),10atm=3.079×1014T0.23e−38030Ts−1(±28%)kC2H5OH(+Ar)↔C2H4+H2O(+Ar),10atm=6.062×1036T−6.45e−42180Ts−1(±31%)ksC2H4OH↔CH3CHO+H,1atm=5.817×109e−11372Ts−1(±55%)kC2H5OH+H↔sC2H4OH+H2=1.780×107T1.94e−1835Ts−1(±28%)

Speciation measurements in shock tubes for validation of complex chemical kinetics mechanisms: Application to 2-Methyl-2-Butene oxidation

Abstract Shock-tube species time histories can be used to generate multiple validation targets to develop and validate detailed chemical kinetics mechanisms. In this study, new shock-tube species time-history data are provided to further validate the detailed mechanisms for 2-methyl-2-butene (2M2B). Experiments were conducted in mixtures of 2M2B/O2 diluted in 99.5% inert gas at three equivalence ratios of ϕ = 0.5, 1.0, and 2.0 over a temperature range of 1396 to 1752 K near atmospheric pressure. Time histories of CO and H2O were measured using laser absorption diagnostics near 4.6 and 1.4 µm, respectively. Chemiluminescence from OH* was also collected near 307 nm to allow ignition delay time determination. Detailed procedures and considerations for the data processing of the laser absorption experiments are provided. The results from the OH* profiles showed two distinct peaks: one near time-zero and the other later in the experiment corresponding to the main ignition. The predictions from three 2M2B kinetics mechanisms were compared with the experimental results. A quantitative comparison is also presented using the multiple characteristic times extracted from the species time history profiles to quantify the performance of the mechanisms. A reaction pathway analysis was performed on the decomposition of 2M2B, revealing clear discrepancies in the major reaction pathways of these mechanisms. A sensitivity analysis was also performed, leading to similar conclusions regarding the differences among the mechanisms. The sensitivity analysis also showed that the OH* peak near time-zero is mainly due to the rapid 2M2B fuel decomposition reactions, indicating that these reactions can be independently validated using the OH* peak near time-zero as a target. This paper provides not only the first detailed species time-history measurements for 2M2B in a shock tube, but it also documents the proper collection and interpretation of such data, which is useful for future studies.

Nitromethane pyrolysis in shock tubes and a micro flow reactor with a controlled temperature profile

Nitromethane has many applications, such as in racing, as a gasoline fuel additive, and as a monopropellant. Despite a large number of studies and the small size of the molecule, the combustion chemistry of nitromethane is still not well understood. To improve models, the pyrolysis of nitromethane (CH3NO2) was investigated experimentally in shock tubes and in a micro flow reactor with a controlled temperature profile (MFR), under dilute conditions. Several spectroscopic diagnostics were used in the shock tubes to follow the concentration time histories of CO, H2O (both using IR laser absorption), and CH3NO2 (UV light absorption). A quadrupole mass spectrometer was used to measure CH3NO2, NO2, CH4, C2H4, and C2H2 at various temperatures with the MFR. These unique experimental results were compared to modern, detailed kinetics models from the literature, and no mechanism was able to reproduce these data over the wide range of conditions investigated. Predictions for the CO and H2O levels were generally inaccurate, and the CH4, C2H4, and C2H2 predictions were poor in most cases for the MFR data. Importantly, all models largely differ in their predictions. A numerical analysis was performed to identify ways to improve the next generation of nitromethane models. Results indicate that nitromethane decomposition needs to be improved below 1050 K, and that hydrocarbon-NOx interactions still need to be further investigated.

Laminar flame speed and shock-tube multi-species laser absorption measurements of Dimethyl Carbonate oxidation and pyrolysis near 1 atm

Dimethyl Carbonate (DMC) is a carbonate ester that can be produced in an environment-friendly way from methanol and CO2. DMC is one of the main components of the flammable electrolyte used in Li-ion batteries, and it can also be used as a diesel fuel additive. Studying the combustion chemistry of DMC can therefore improve the use of biofuels and help developing safer Li-ion batteries. The combustion chemistry of DMC has been investigated in a limited number of studies. The aim of this study was to complement the scarce data available for DMC combustion in the literature. Laminar flame speeds at 318 K, 363 K, and 463 K were measured for various equivalence ratios (ranging from 0.7 to 1.5) in a spherical vessel, greatly extending the range of conditions investigated. Shock tubes were used to measure time histories of CO and H2O using tunable laser absorption for the first time for DMC. Characteristic reaction times were also measured through OH* emission. Shock-tube spectroscopic measurements were performed under dilute conditions, at three equivalence ratios (fuel-lean, stoichiometric, and fuel-rich) between 1260 and 1660 K near 1.3 ± 0.2 atm, and under pyrolysis conditions (98%+dilution) ranging from 1230 to 2500 K near 1.3 ± 0.2 atm. Laminar flame speed experiments were performed around atmospheric pressure. Detailed kinetics models from the literature were compared to the data, and it was found that none are capable of predicting the data over the entire range of conditions investigated. A numerical analysis was performed with the most accurate model, underlining the need to revisit at least 3 key reactions involving DMC.

Shock-Tube Laser Absorption Measurements of CO and H2O during Iso-Octane Combustion

The oxidation of iso-octane was studied in two different shock tubes by recording mole fraction time histories of CO and H2O at various equivalence ratios (0.5, 1.0, and 2.0) at around 1.5 atm, bet...