Detailed Kinetic Model Research Articles

A revised model of ammonium perchlorate combustion with detailed kinetics

In this study, we propose a revised coupled combustion model for ammonium perchlorate (AP), leveraging recent advances in the modeling of ammonia and NOx chemistry. A coupled combustion model relies on three founding bricks: a detailed gas-phase kinetic model, a condensed-phase decomposition model, and a pyrolysis law describing the relationship between the surface temperature and mass flow. The proposed gas-phase kinetic model, is validated against data on species sampling in jet-stirred reactors, laminar flame speed, and ignition delay time. These test cases, rarely used by the solid propellant community, highlight deficiencies in a reference mechanism from the literature. A new model for AP decomposition in the condensed phase is proposed to be used with the gas-phase mechanism. A suitable pyrolysis law is designed using the Zel’dovich–Novozhilov theory to ensure the stability of the coupled combustion model. The methodology employed is described in detail, for others to replicate. Finally, the overall model is applied to simulate the AP laminar flame in a 1D coupled approach. These calculations provide results on the regression rate, surface temperature, temperature sensitivity and species profiles for prescribed initial temperature of AP and ambient pressure. The behavior of the proposed combustion model is presented in comparison with other reference models. The role of gas-phase kinetics in modeling AP combustion is discussed.

A kinetic modeling study on the effect of alkylbenzenes structure on PAH formation at elevated pressures

Alkylbenzene is one of the significant components of practical transport fuel, which is considered as the main reason leading to serious emissions of polycyclic aromatic hydrocarbon (PAH) from combustion processes. This work reports a kinetic modeling study on the impact of alkylbenzenes structure, i.e., the length and number of the alkyl side chain, on PAH formation at elevated pressures. A detailed kinetic model has been established and a large number of reactions concerning the PAH species formation have been updated according to the latest theoretical studies. The model is then verified by the previous experimental data containing the concentration profiles of PAH species. The fuel decomposition reactivity and the mole fraction curves of monocyclic aromatic hydrocarbon and polycyclic aromatic hydrocarbon can be well predicted by the present model. The kinetic analysis indicates that the dominant formation pathways of PAHs are barely influenced by the alkyl side chain length, especially at the high-temperature window. In the A1_C1-C4 linear alkylbenzenes pyrolysis system, the formation of benzene is mainly affected by the competition between the combination reaction of C5H3 with CH3 and the ipso-substitution reaction of A1CH3 by H. Unlike the A1_C1-C4 linear alkylbenzenes pyrolysis chemistry, fuel-related reactions associated with the formation of PAHs become more usual as the number of alkyl side chain increases, such as the formation pathway of C9 species in the pyrolysis chemistry of o-xylene and the formation pathway of phenanthrene in the oxidation chemistry of 1,3,5-trimethylbenzene.

Three-dimensional coking simulation of endothermic hydrocarbon fuels in rectangular cooling channels

Coking deposition is a critical phenomenon for endothermal hydrocarbon fuel cooling that can significantly affect the performance of a regenerative cooling system. Because of the complicated interactions between fluid flow, heat transfer, fuel cracking, and precursor coking kinetics, previous numerical studies have been limited to simplified two-dimensional circular channels, which cannot reveal the actual spatial distribution with consideration of buoyancy effect in rectangular cooling channels. This work proposes a novel framework for shrinking motion with an O-type hybrid mesh, permitting the direct three-dimensional simulation of coke deposition in complex channels and the visualization of both the axial and circumferential deposition distributions. The concept is tested in a rectangular channel using n-decane as an example, combining a detailed pyrolysis kinetic model with the MC-II coking model, and predictive results have been obtained. Results indicate two locations with heavy deposition rates. The buoyancy effect is weakened due to the acceleration resulting from the reduced cross-sectional area of the channel by the coke layer. The coupling of the flow and pyrolysis is discussed in terms of the dimensionless Damköhler number. The maximum temperature after coking can be 138 K higher than the initial. However, the conversion of n-decane at outlet is decreased due to the reduced flow residence time. The decreased total heat sink per temperature increment and the higher pressure drop are also the penalties from coking. The new framework for the direct three-dimensional simulations of coking is significant for the comprehensive investigation of the efficiency of regenerative cooling.

Omics data for sampling thermodynamically feasible kinetic models

Kinetic models are key to understanding and predicting the dynamic behaviour of metabolic systems. Traditional models require kinetic parameters which are not always available and are often estimated in vitro. Ensemble models overcome this challenge by sampling thermodynamically feasible models around a measured reference point. However, it is unclear if the convenient distributions used to generate the ensemble produce a natural distribution of model parameters and hence if the model predictions are reasonable.In this paper, we produced a detailed kinetic model for the central carbon metabolism of Escherichia coli. The model consists of 82 reactions (including 13 reactions with allosteric regulation) and 79 metabolites. To sample the model, we used metabolomic and fluxomic data from a single steady-state time point for E. coli K-12 MG1655 growing on glucose minimal M9 medium (average sampling time for 1000 models: 11.21 ± 0.14 min). Afterwards, in order to examine whether our sampled models are biologically sound, we calculated Km, Vmax and kcat for the reactions and compared them to previously published values. Finally, we used metabolic control analysis to identify enzymes with high control over the fluxes in the central carbon metabolism.Our analyses demonstrate that our platform samples thermodynamically feasible kinetic models, which are in agreement with previously published experimental results and can be used to investigate metabolic control patterns within cells. This renders it a valuable tool for the study of cellular metabolism and the design of metabolic pathways.

High pressure oxidation of NH[formula omitted]/[formula omitted]-heptane mixtures

Oxidation of NH3/n-heptane mixtures at pressures up to 100 atm and temperatures of 400–900 K was characterized experimentally in a laminar flow reactor and a jet-stirred reactor. A detailed chemical kinetic model was developed, updating the hydrogen and amine subsets and introducing a subset for the chemical coupling with emphasis on the NH2+n-heptane reaction. The kinetic model provided a good prediction of the ignition delay times measured in a rapid compression machine by Yu et al. (Combust. Flame 217 (2020) 2–11) as well as the high pressure experimental data obtained in the present work. The results show that it is important to include updated rate constants for NH2 + HO2 and NH2 + n-C7H16 to obtain reliable predictions for ignition and oxidation of NH3/n-heptane mixtures at high pressure. The effectiveness of implementing analogy rules for determining the rate constant of the key reaction NH2 + n-C7H16 was confirmed by the observed results.

A reliable multi-nutrient model for the rapid production of high-density microalgal biomass over a broad spectrum of mixotrophic conditions

The superior microalgal biomass productivities obtained under mixotrophic conditions have been widely demonstrated. However, to attain the full potential of the method, optimal conditions for biomass production and resource utilization need to be determined and successfully exploited throughout the process operation. Detailed kinetic mathematical models have often proved most efficient tools for predicting process behavior and governing its overall operation. This paper presents an extensive study for obtaining a highly reliable model for mixotrophic production of microalgae covering a wide set and range of nutritional conditions (10-fold the concentration range of Bold’s Basal Medium) and biomass yields up to 6.68 g.L−1 after only 6 days. The final reduced model includes a total of five state variables and nine parameters: model calibration resulted in very small 95% confidence intervals and relative errors below 5% for all parameters. Model validation showed high reliability with R2 correlation values between 0.77 and 0.99.

Impacts of NO on low-temperature oxidation of n-heptane in a jet-stirred reactor

Low-temperature (low-T) oxidation experiments of n-heptane –with and without NO addition– were experimentally and numerically investigated at stoichiometric conditions in a jet-stirred reactor. Experiments were performed at atmospheric pressure over a temperature range of 500–800 K. Reactants, intermediates, and products, were measured using synchrotron vacuum ultraviolet photoionization mass spectrometry. A detailed kinetic model was developed to gain insight into the chemical effect of NO on low-T oxidation chemistry of n-heptane. Taking 650 K as the transition temperature, the results revealed that NO addition exhibited an inhibiting effect on fuel reactivity below 650 K and a promoting effect above 650 K. The reactions of ROO + NO = RO + NO2 and HO2 + NO = OH + NO2 at different temperature regions were responsible for the inhibition and promotion effects, respectively. Evidence gathered from both experimental measurements and kinetic model predictions indicated that NO addition had a significant inhibitory effect on the formation of cool flame species during the low-T oxidation process. NO suppressed low-T oxidation via the reaction of ROO + NO = RO + NO2, which impeded the subsequent isomerization, O2 addition, OH-, and HO2-elimination reaction, and influenced product distribution of the cool flame species. The experimental observations provided detailed information about these reactive intermediates, which offered new insights into low-T oxidation phenomena and clarified the importance of NO reactions which prevent the formation of cool flame products during low-T oxidation.

Applying machine learning techniques to predict laminar burning velocity for ammonia/hydrogen/air mixtures

Ammonia utilisation in internal combustion engines has attracted wide interest due to the current trend toward decarbonisation, as ammonia is a zero-carbon fuel with different combustion properties to hydrocarbons. The laminar burning velocity (LBV) is a fundamental property of fuels with a significant effect on the combustion processes and accurate calculations and measurements of the LBV over a wide range of fuel blends, pressures and flow conditions is a time-consuming, complicated procedure. The main goal of the current study is to predict the LBV of NH3/H2/air mixtures using a hybrid machine learning (ML) approach based on a training dataset consisting of both the experimental LBV values and additional data obtained from numerical simulations with a detailed kinetic model. Initial ML model training data is collected from existing experimental LBV in the literature for NH3/H2/air mixtures. Then, synthetic data is generated using one-dimensional (1D) simulations to reduce data inhomogeneity and increase accuracy of the ML model. In total, 24 different ML algorithms are tested to find the best model both for the experimental and the hybrid dataset. The results suggest that both Gaussian Process Regression (GPR) and Neural Networks (NNs) can be utilised to predict LBV of NH3/H2/air mixtures with reasonable accuracy. The hybrid ML model achieved a coefficient of determination of R2 = 0.998. Finally, hybrid ML model hyperparameters are optimised to achieve a coefficient of determination of R2 = 0.999. It was also found that ML can speed up LBV computation from 9500 to 27000 times compared to 1D simulations with a reduced mechanism.

An experimental and kinetic modeling study on the low-temperature oxidation of oxymethylene ether-2 (OME-2) by means of stabilized cool flames

Oxymethylene ethers have received much attention in recent years as a high-potential alternative for fossil-based fuels. These alternative fuels produced via carbon capture and utilization technologies driven by renewable energy can contribute to the solution of environmental issues in the short term. In this study, the low-temperature oxidation chemistry of oxymethylene ether-2 was investigated by combining experimental and kinetic modeling work. New experimental data were acquired from stabilized, ozone-seeded oxymethylene ether-2/dimethyl ether/oxygen premixed cool flames in a heated stagnation plate burner. Two fuel-lean equivalence ratios were investigated, i.e., ϕ = 0.3 and ϕ = 0.5. The observed and quantified reaction products were methoxymethyl formate, methyl formate, methanol, formaldehyde, CO and CO2. A new detailed kinetic model based on first principles was constructed for the pyrolysis and oxidation of oxymethylene ether-2 with the in-house developed automatic kinetic model generation code Genesys. Compared to an earlier study by De Ras et al. (Combustion and Flame, 2022), additional species and reactions were added to describe the low-temperature oxidation chemistry with more detail, in addition to an update of several thermodynamic and kinetic parameters based on new quantum chemical calculations. The newly developed kinetic model is able to predict the experimental observations of the stabilized cool flames satisfactorily and can reproduce ignition delay times from the literature on average within the experimental uncertainty margin. Rate of production and sensitivity analyses were performed for different reaction conditions to unravel the important decomposition pathways during low-temperature oxidation. It is concluded that oxymethylene ether-2 is a highly reactive fuel, and this without fuel-specific chain branching reactions significantly contributing to the low-temperature oxidation chemistry.

Experimental and Kinetic Study on the Gas-Phase Pyrolysis of Syringol

Syringyl (3,5-dimethoxy-4-hydroxyphenyl) units are abundant in hardwood lignin, which explains the large amount of syringol present in bio-oils derived from these feeds. To improve understanding of the decomposition chemistry of these syringyl units, the gas-phase pyrolysis kinetics of syringol have been studied experimentally and theoretically under typical fast pyrolysis conditions. The experiments were performed at 673–923 K in a micropyrolyzer unit hyphenated with a gas chromatography (GC) × gas chromatography-flame ionization detection/time-of-flight mass spectrometry and a customized gas chromatograph, which allows to detect and quantify products with boiling points up to 823 K next to permanent gases and water. New obtained experimental data show that 2,3-dihydroxybenzaldehyde is the most important phenolic product, and a large amount of pyrolytic water was formed. The proposed decomposition pathways of syringol to these two products show two new features: (1) 2,3-dihydroxybenzaldehyde is formed from a unimolecular decomposition of syringol without any stable intermediates and (2) both pathways leading to 2,3-dihydroxybenzaldehyde and water involve one more H-atom migration step to form the more stable radicals. Potential energy surface calculations at the CBS-QB3 level of theory indicate that the new features are kinetically favorable. Furthermore, a detailed kinetic model for syringol pyrolysis including 361 reactions and 93 species was constructed. Thermodynamic data for important species and kinetics for crucial reactions were determined with ab initio calculations at the CBS-QB3 level of theory. The model predicts well the conversion of syringol and the formation of major products. A rate of production analysis shows that the new proposed pathway is the major decomposition pathway of syringol. These findings shed new light on the pyrolysis and oxidation chemistry of syringyl species.

Multiobjective Optimization of a Metal Complex Catalytic Reaction Based on a Detailed Kinetic Model with Parallelization of Calculations

The solution of the multiobjective optimization problem was performed with the help of the Pareto approximation algorithm. The problem of multiobjective optimization of the reaction process conditions for the olefin hydroalumination catalytic reaction, with the presence of organoaluminum compounds diisobutylaluminiumchloride, diisobutylaluminiumhydrate, and triisobutylaluminum, was solved. The optimality criteria are the yield of the reaction resultants. The largest yield of the high-order organoaluminum compound Bu2AlR was observed for the reactions with diisobutylaluminiumhydrate and triisobutylaluminum. Such results were obtained due to the fact that in the case of diisobutylaluminiumchloride, Bu2AlR was used for the formation of ClBuAlR. The yield of the Schwartz reagent Cp2ZrHCl was higher by a third in the reaction in the presence of diisobutylaluminiumchloride. Unlike the experimental isothermal conditions, the temperature optimal control showed the sufficiency of the gradual growth temperature for achieving the same or higher values of optimality criteria. For computational experiments, the algorithm for solving the multi-criteria optimization problem was parallelized using an island model.

Machine learned compact kinetic models for methane combustion

Chemical kinetic models are an essential component in the development and optimisation of combustion devices through their coupling to multi-dimensional simulations such as computational fluid dynamics (CFD). Due to the significant level of detail contained within, detailed chemical kinetic models are computationally prohibitive for use in CFD. Therefore, low-dimensional kinetic models which retain good fidelity to the reality are needed, the production of which requires considerable human-time cost and expert knowledge.Here, we present a novel automated compute intensification methodology to produce overly-reduced and optimised (“compact”) chemical kinetic models. The Machine Learned Optimisation of Chemical Kinetics (MLOCK) coded algorithm systematically perturbs each of the four chemical kinetic model components to discover what combinations of terms results in a model with high fidelity calculations. A virtual reaction network comprised of n species is first obtained using conventional mechanism reduction procedures. Once n is lower than a threshold value, the model performance is typically of low fidelity.To adjust for this, the weights (virtual reaction rate constants) of important connections (virtual reactions) between each node (species) of the virtual reaction network are numerically optimised across four sequential phases to replicate select calculations.The first version of MLOCK (MLOCK1.0), simultaneously perturbs all three virtual Arrhenius reaction rate constant parameters for important connections and assesses the suitability of the new parameters through objective error functions, which quantify the error in the calculations of each model candidate to a set of optimisation targets, comprised of detailed model calculations.In this study, the MLOCK algorithm is demonstrated by automatic creation of compact models for the archetypal case of methane/air combustion. It is shown that the NUGMECH1.0 detailed model comprised of 2789 species is reliably compacted to 15 species (nodes), whilst retaining an overall fidelity of 79–90% to the detailed model at Industry-defined performance target calculations, outperforming the prior state-of-art.

Experimental and Modeling Investigation on the Pyrolysis of n-Decane Initiated by Nitropropane. Part I: 1-Nitropropane.

Initiators can accelerate the pyrolysis of hydrocarbon fuels, thereby reducing the required reaction temperature in the hypersonic vehicle heat exchanger/reactor. Nitro-alkanes are considered as efficient initiators due to their lower energy barrier of the C-N bond cleavage reaction. To research the mechanism of the initiation effect of nitro-alkanes on the decomposition of hydrocarbon fuel, synchrotron radiation vacuum ultraviolet photoionization-mass spectrometry (SVUV-PIMS) was employed to experimentally study the pyrolysis of n-C10H22, 1-C3H7NO2, and their binary mixtures in a flow tube under pressures of 30 and 760 Torr. The species identified and measured in the experiments included alkanes, alkenes, dialkenes, alkynes, nitrogen oxides, benzene, and free radicals, which revealed the mechanism of n-decane and 1-C3H7NO2 pyrolysis, as well as the interactions of the two fuels. Experiments show that the presence of 1-C3H7NO2 reduces the initial decomposition temperature of n-C10H22, and the increased pressures could achieve a stronger promoting effect on the conversion of n-C10H22. A detailed kinetic model containing 1769 reactions and 278 species was established and validated based on the mole fraction distributions of n-C10H22, major pyrolysis species, and important intermediates measured in pure fuel and initiated pyrolysis. The kinetic model can accurately predict the experimental data, and the mechanism of 1-C3H7NO2-initiated pyrolysis of n-C10H22 is analyzed with the model. The effect of 1-C3H7NO2 on the consumption of n-C10H22 and selectivity of cracked products is highlighted.

Thermal behaviors, thermal decomposition mechanism, kinetic model analysis and thermal hazard prediction of 3,6,7-triamino-7H-[1,2,4]triazolo[4,3-b][1,2,4]triazole (TATOT)

Recently, fused rings compounds have attracted an increasing focus since their outstanding features like high-energy, insensitiveness, high thermal stability, and so on. In order to gain the in-depth understandings of thermal decomposition behavior of them, the thermal decomposition process of TATOT was systematically studied through a series of means, including TG, DSC, TG-DSC-FTIR-MS, condensed-phase thermolysis in ARC and the tubular furnace assisted by SEM, FTIR, and XPS. The results revealed that pyrolysis process of TATOT was most likely to begin with a ring-opening reaction of the fused ring. The detailed mechanism and kinetic model of TATOT were proposed. Two-step consecutive mechanism A→B→C, which was described by f(α)=(1-α)0.868 [1 + 1.364α1.177] and f(α)=(1-α)1.613, represented the kinetic model for TATOT pyrolysis the first stage. The kinetic model for TATOT pyrolysis the second stage was described by three-step consecutive mechanism C→D→E→F, where the first two steps were described by f(α)=(1-α)3.570 and f(α)=(1-α)1.888, and the last step was described by autocatalytic reaction model (KS). The typical safety indicators TMRad of TATOT, such as TD24 and TD8, were calculated to be 182.71 °C and 186.32 °C, respectively.

Isopropylcyclohexane pyrolysis at high pressure and temperature: Part 2. Experiment and simulation

Pyrolysis of isopropylcyclohexane (IPCH), which is part of some transportation fuels, has been investigated at the temperature range of 923–1526 K and pressure of 9.8–20.2 bar. Mole fraction profiles of 27 products were obtained using gas-chromatography (GC) coupled to flame ionization detector (FID). A GC–MS has been used for identification of all the products as well. At high temperature ethene is the most abundant product followed by acetylene. Benzene is the most abundant aromatic product followed by toluene as the 2nd most abundant aromatic. Detailed kinetic model comprising of 426 species and 1354 reactions has been developed which shows a reasonable agreement with the experimental data. This has been aided by detailed ab initio calculations of reaction profiles and TST/VTST calculations of rate parameters reported in Part 1 of this work. Rate of production (ROP) analysis reveals that unimolecular decomposition of IPCH (C3H7 elimination and CH3 elimination) as well as H-abstraction reaction of IPCH are responsible for IPCH consumption. Sensitivity analysis reveals that C3H7 elimination channel is the most sensitive reaction for the consumption of IPCH. On the other hand, cyclohexyl radical (cC6H11) plays a critical role in the formation of aromatic products (as revealed by sensitivity analysis). Its β-C–H scission process (cC6H11 = cC6H10 + H) has positive effect on aromatic formation, while its isomerization via ring-opening (cC6H11 = P6XC6H11–1E) has negative effect on aromatic formation. The overall rate constant for IPCH decomposition has been found to be:(s−1)=108.16±0.25exp(−34.6±1.5/kcalmol−1)RTThese results could aid in our understanding of the unimolecular decomposition of IPCH as well as the aromatic products formation reaction pathways from IPCH and other similar hydrocarbons, which will eventually help us to understand better the combustion process of transportation fuels.

Conformer-Dependent Chemistry: Experimental Product Branching of the Vinyl Alcohol + OH + O2 Reaction

The concentration of formic acid in Earth's troposphere is underestimated by detailed chemical models compared to field observations. Phototautomerization of acetaldehyde to its less stable tautomer vinyl alcohol, followed by the OH-initiated oxidation of vinyl alcohol, has been proposed as a missing source of formic acid that improves the agreement between models and field measurements. Theoretical investigations of the OH + vinyl alcohol reaction in excess O2 conclude that OH addition to the α carbon of vinyl alcohol produces formaldehyde + formic acid + OH, whereas OH addition to the β site leads to glycoaldehyde + HO2. Furthermore, these studies predict that the conformeric structure of vinyl alcohol controls the reaction pathway, with the anti-conformer of vinyl alcohol promoting α OH addition, whereas the syn-conformer promotes β addition. However, the two theoretical studies reach different conclusions regarding which set of products dominate. We studied this reaction using time-resolved multiplexed photoionization mass spectrometry to quantify the product branching fractions. Our results, supported by a detailed kinetic model, conclude that the glycoaldehyde product channel (arising mostly from syn-vinyl alcohol) dominates over formic acid production with a 3.6:1.0 branching ratio. This result supports the conclusion of Lei et al. that conformer-dependent hydrogen bonding at the transition state for OH-addition controls the reaction outcome. As a result, tropospheric oxidation of vinyl alcohol creates less formic acid than recently thought, increasing again the discrepancy between models and field observations of Earth's formic acid budget.

High-fidelity Reaction Kinetic Modeling of Hot-Jupiter Atmospheres Incorporating Thermal and UV Photochemistry Enhanced by Metastable CO(a3Π)

A detailed modeling of simultaneous UV-photochemical and thermochemical processes in exoplanet atmosphere-like conditions is essential for the analysis and interpretation of a vast amount of current and future spectral data from exoplanets. However, a detailed reaction kinetic model that incorporates both UV photochemistry and thermal chemistry is challenging due to the massive size of the chemical system as well as the lack of understanding of photochemistry compared to thermal-only chemistry. Here, we utilize an automatic chemical reaction mechanism generator to build a high-fidelity thermochemical reaction kinetic model later then incorporated with UV photochemistry enhanced by metastable triplet-state carbon monoxide (a3Π). Our model results show that two different photochemical reactions driven by Lyα photons (i.e., H2 + CO(a3Π) → H + HCO and CO(X1Σ+) + CO(a3Π) → C(3P) + CO2) can enhance thermal chemistry resulting in significant increases in the formation of CH4, H2O, and CO2 in H2-dominated systems with trace amounts of CO, which qualitatively matches the observations from previous experimental studies. Our model also suggests that at temperatures above 2000 K, thermal chemistry becomes the dominant process. Finally, the chemistry simulated up to 2500 K does not produce any larger species such as C3 species, benzene, or larger (i.e., PAHs). This might indicate that the photochemistry of C2 species such as C2H2 might play a key role in the formation of organic aerosols observed in a previous experimental study.

Experimental and kinetic modeling studies of N-decane cracking initiated by nitromethane at supercritical pressure

The chemical heat sink of endothermic hydrocarbon fuel has been used to solve the thermal protection problem caused by the high temperature of the scramjet combustion chamber. The fuel is usually in a supercritical state in the cooling channel, so we studied the cracking of n-decane initiated by nitromethane under supercritical pressure in an electrically heated flow reactor. Based on the experimental results, the published low-pressure cracking model and the latest theoretical results, a detailed kinetic reaction model under supercritical conditions of n-decane cracking initiated by nitromethane, including 271 species and 1863 reactions, was established. Through the simulation of the experimental results and the experimental results in the literature, it was proven that this model had good simulation accuracy. The formation rate of n-decane was analyzed to obtain the consumption path of n-decane under supercritical pressure, especially the generation process of C3 above alkanes. The influence of nitromethane on n-decane consumption and product distribution and the cause of its range of action were also analyzed, which provided a theoretical and model basis for the engineering application of fuel.

A wide range experimental and kinetic modeling study of the oxidation of 2,3-dimethyl-2-butene: Part 1

2,3-Dimethyl-2-butene (TME) is a potential fuel additive with high research octane number (RON) and octane sensitivity (S), which can improve internal combustion engine performance and efficiency. However, the combustion characteristics of TME have not been comprehensively investigated. Thus, it is essential to study the combustion characteristics of TME and construct a detailed chemical kinetic model to describe its combustion. In this paper, two high-pressure shock tubes and a constant-volume reactor are used to measure ignition delay times and laminar flame speeds of TME oxidation. The ignition delay times were measured at equivalence ratios of 0.5, 1.0, and 2.0 in “air”, at pressures of 5 and 10 bar, in the temperature range of 950 – 1500 K. Flame speeds of the TME/ “air” mixtures were measured at atmospheric pressure, at a temperature of 325 K, for equivalence ratios ranging from 0.78 to 1.31. Two detailed kinetic mechanisms were constructed independently using different methodologies; the KAUST TME mechanism was constructed based on NUIGMech1.1, and the MIT TME mechanism was built using the Reaction Mechanism Generator (RMG). Both mechanisms were used to simulate the experimental results using Chemkin Pro. In the present work, reaction flux and sensitivity analyses were performed using the KAUST mechanism to determine the critical reactions controlling TME oxidation at the conditions studied.

Atmospheric-pressure shock-tube measurements of high-temperature propane laminar flame speed across multiple equivalence ratios

Laminar flame speeds of premixed propane in 21%O2-79% Ar (so-called ”airgon”) were experimentally measured in a shock tube at atmospheric pressure (1 atm±2%) for a range of equivalence ratios (0.5, 0.75, 1, and 1.2) and unburned-gas temperatures (644–1,044 K). Simultaneous side-wall schlieren and end-wall CH* emission imaging was utilized to track the propagation of outwardly expanding laminar flames initiated by laser-induced spark ignition behind reflected shock waves. The linear curvature model with an area-averaged formulation was used to extrapolate laminar flame speeds to zero-stretch. The high-temperature laminar flame speed results were compared with 1D simulations performed using two detailed kinetic models, NUIG 1.3 and Aramco 3.0, and two skeletal models, USC Mech II and San Diego 2016. The experimental results agree with the NUIG 1.3 model within 3.5%, while the predictions of the models disagree by up to 16%. Sensitivity analyses conducted using the models revealed six chemical reactions that strongly impact the prediction of laminar flame speed. In order for the present data to be compatible with practical combustion systems using air as the oxidizer, the propane/airgon measurements were scaled to obtain laminar flame speeds of propane/air using ratios calculated from 1D simulations. The scaled experimental measurements showed good agreement with literature propane/air results at 650 K. Empirical correlations of laminar flame speed as a function of unburned-gas temperature are then reported for the studied equivalence ratios.