Detailed Chemical Kinetic Mechanism Research Articles

Heterogeneous CPU-GPU parallelization for modeling supersonic reacting flows with detailed chemical kinetics

Accurate simulations of complex combustion phenomena associated with supersonic reacting flows require the use of detailed chemical kinetic mechanisms. However, detailed chemical mechanisms may consist of a large number of species and reactions resulting in extremely high computation cost. In order to accelerate the simulations of supersonic reacting flows with detailed chemical mechanisms, a heterogeneous CPU-GPU parallel algorithm and its portable software implementation are presented. The parallel algorithm was broken down into two parts: the CPU handled the computation of fluid dynamics while the GPU evaluated the chemical source terms and gas physical properties. The use of overlapping computations of chemical source terms on GPU and calculations of viscous flux on CPU is also presented. A study of performance tests was conducted. The performance results show that evaluating chemical source terms and gas physical properties on 2 GPUs are about 157.8× and 78.5× faster than running on the 16-core CPU when using the most complex mechanism on a grid of 3.3 million cells, respectively, resulting in an excellent speedup of the whole iteration up to 47. The significant performance improvement provided by the parallel algorithm can provide a significant perspective for designing heterogeneous CPU-GPU algorithms for applications in simulating supersonic reacting flows with detailed chemical kinetics. Program summaryProgram Title: OpenHurricaneCPC Library link to program files:https://doi.org/10.17632/m9pphg9cjj.1Licensing provisions: GPLv3Programming language: C++, CUDANature of problem: The computation cost in evaluating chemical source terms and theirs diagonal Jacobian matrices, and in calculating gas physical properties dominates the simulations of supersonic reacting flows with detailed chemical kinetic models. And the parallelization of these computations can yield great benefits from GPU acceleration.Solution method: The parallel implementation of evaluating the chemical source terms and theirs diagonal Jacobian matrices, and calculating gas physical properties were conducted on GPU to speed up the computation.

Intrinsic instability of lean hydrogen/ammonia premixed flames: Influence of Soret effect and pressure

The addition of hydrogen in ammonia/air mixtures can lead to the onset of intrinsic flame instabilities at conditions of technical relevance. The length and time scales of intrinsic instabilities can be estimated by means of linear stability analysis of planar premixed flames by evaluating the dispersion relation. In this work, we perform such linear stability analysis for hydrogen-enriched ammonia/air flames (50%H2-50%NH3 by volume) using direct numerical simulation with a detailed chemical kinetic mechanism. The impact of pressure and the inclusion of the Soret effect in the governing equations is assessed by comparing the resulting dispersion relation at atmospheric pressure and 10 atm. Our data indicate that both pressure and the Soret effects promote the onset of intrinsic instabilities. Comparisons with available numerical literature data as well as theoretical models are also discussed.

Reduced Chemical Kinetic Models of DME Based on Variance Filtering Method

Based on the variance value of each species concentration during the combustion process, a new chemical mechanism reduction method is proposed. The data sets which are the molar concentration of each species are generated based on numerical results of zero-dimensional homogeneous ignition process using detailed chemical kinetic mechanisms under various operating conditions. By calculating and analyzing the variance value of each species concentration during the combustion process to determine the contribution of each species to the combustion process, and by selecting a suitable threshold value to determine whether the species and elementary reactions are removed or not. The skeletal mechanisms of DME generated by using the present VFM method are compared to those generated by the path flux analysis (PFA) method and the detailed mechanism. The comparisons of the temperature and the concentration of important species showed that with either the same or significantly smaller number of species, the skeletal mechanisms generated by the present VFM method are more accurate than that of PFA in a broad range of initial pressures, temperatures and equivalence ratios. In addition, the reduction speed of VFM is one orders of magnitude faster than that of PFA.

Advanced numerical simulation of hydrogen/air turbulent non-premixed flame on model burner

A numerical investigation of hydrogen (H2)/air turbulent non-premixed flame on the model burner was conducted. A large eddy simulation of reacting flow with partial and detailed chemical kinetic mechanisms was employed to obtain a high-resolution and accurate prediction of thermochemical states inside the combustion chamber, including pollutant NO, which have not been adequately predicted until now. This study employed temperature and species mass fraction data from two combustion cases of fully developed turbulent and transition regimes with a fuel composition of 50 % H2 and 50 % N2, experimentally measured by the German Aerospace Center (DLR) and TU Darmstadt. A reactor-based partially-stirred reactor (PaSR) model was used to handle the turbulence chemistry interaction. The employed chemical mechanisms included GRI-Mech 3.0 and partial Mevel mechanism. The effects of chemical mechanism and inlet jet velocity on simulation accuracy were discussed. The more elaborative nitrogen reactions in GRI-Mech 3.0 result in a better NO prediction compared to the partial Mevel mechanism. The implementation of finite rate chemistry in a PaSR model yields a significantly improved prediction of NO from the flamelet probability density function approach with less than 1 % root mean square deviation from experimental data. The performed simulation successfully captured the thermochemical profile of a fully developed turbulent flame; however, further improvement on boundary condition modeling is still required for a flame undergoing a transition from laminar to turbulent regimes. Finally, using the partial Mevel mechanism leads to a computational cost reduction of 32.66 % compared to the GRI-Mech 3.0 mechanism, which confirms the proportional relation between the size of the mechanism and computational cost.

Understanding the Nonlinear Reactivity Promoting Effect of n-Heptane Addition on the Binary Mixture From Low to Intermediate Temperature: A Case of Methane/n-Heptane Mixtures

Abstract To understand the effect of n-heptane (NC7H16) addition on the auto-ignition of methane (CH4) at low to intermediate temperatures, the ignition delay times (IDTs) of stoichiometric CH4/NC7H16 blends with varying NC7H16 concentrations were measured at temperatures from 600 to 1000 K, pressures of 20 and 40 bar. Detailed chemical kinetic mechanisms were validated against the newly measured IDTs. Adding NC7H16 in the binary mixture shows a nonlinear promoting effect on the IDTs: micro-addition of NC7H16 can significantly reduce the IDTs of the binary mixture when the NC7H16 is lower than 20%. However, the decrease of the IDTs becomes much slower when further increasing the NC7H16 addition. Affected by the negative temperature coefficient (NTC) behavior of NC7H16, this nonlinear effect is particularly notable at around 795 K, the low boundary of the NTC region. To reveal the nonlinear reactivity-promoting effect of NC7H16 addition on the binary mixture, reaction flux, ignition sensitivity, rate of production of the key radicals along heat production analyses were conducted. Apart from contributing more O˙H production through the low-temperature chain-branching reaction pathways of NC7H16, adding NC7H16 also promotes the pre-ignition heat release of the binary mixture. The heat release raises the system temperature and further promotes the mixture ignition, enhancing the nonlinear effect at low temperatures.

Experimental and Modeling High-Pressure Study of Ammonia-Methane Oxidation in a Flow Reactor.

The present work deals with an experimental and modeling analysis of the oxidation of ammonia-methane mixtures at high pressure (up to 40 bar) in the 550-1250 K temperature range using a quartz tubular reactor and argon as a diluent. The impact of temperature, pressure, oxygen stoichiometry, and CH4/NH3 ratio has been analyzed on the concentrations of NH3, NO2, N2O, NO, N2, HCN, CH4, CO, and CO2 obtained as main products of the ammonia-methane mixture oxidation. The main results obtained indicate that increasing either the pressure, CH4/NH3 ratio, or stoichiometry results in a shift of NH3 and CH4 conversion to lower temperatures. The effect of pressure is particularly significant in the low range of pressures studied. The main products of ammonia oxidation are N2, NO, and N2O while NO2 concentrations are below the detection limit for all of the conditions considered. The N2O formation is favored by increasing the CH4/NH3 ratio and stoichiometry. The experimental results are simulated and interpreted in terms of an updated detailed chemical kinetic mechanism, which, in general, is able to describe well the conversion of both NH3 and CH4 under almost all of the studied conditions. Nevertheless, some discrepancies are found between the experimental results and model calculations.

An experimental and chemical kinetic simulation study of the high-temperature pyrolysis of linear C1–C5 alcohols

The high-temperature pyrolysis characteristics of C1–C5 linear alcohols, including methanol, ethanol, 1-propanol, 1-butanol, and 1-pentanol, systematically studied experimentally and the results interpreted using a detailed kinetic model. Specifically, a single-pulse shock tube coupled to a gas chromatography-mass spectrometry (GC-MS) system and a gas chromatograph (GC) is used to conduct a comprehensive experimental study on the high-temperature pyrolysis of the five alcohols, at pressures of 5 and 10 bar, in the temperature range 1000–1800 K at 1% fuel diluted by argon. Qualitative and quantitative analyses are conducted on the reactant, intermediate, and product species involved to determine species distributions as a function of temperature. A detailed chemical kinetic mechanism, NUIGMech1.3, is used to simulate the experimental data under the working conditions. The simulation results are compared with the experimental results, and it is shown that the overall trends between experiments and model predictions are relatively ideal in the comparison of all product and reactant concentrations, even though there is still a phenomenon of inaccurate prediction. Reaction pathway analysis is then conducted on the five alcohols. The present work not only provides additional experimental data for alcohols, but also provides insights into the high-temperature pyrolysis characteristics of the five fuels, which will be valuable for further development and optimization of detailed kinetic mechanisms of these alcohols and promote their practical application.

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.

A wide ranging experimental and kinetic modeling study of TMEDA pyrolysis and oxidation

Traditional liquid propellants like unsymmetrical dimethylhydrazine include several issues, such as toxicity, short storage time and preservation difficulty at low temperatures. For this reason, exploring green and stable propellant fuels is imperative in the development of propellants. Tetramethyl ethylenediamine (TMEDA) is considered to be a promising green propellant fuel with high specific impulse, non-toxicity, and long-term storage stability. Thus, investigating the combustion characteristics of TMEDA and constructing a detailed chemical kinetic mechanism are of fundamental importance in describing its combustion in computational fluid simulation. For this work, ignition delay times of TMEDA were measured in a shock tube at equivalent ratios of 0.5, 1.0 and 2.0, at pressures of 2, 10, and 20 bar, and in the temperature range of 870–1500 K with fixed fuel concentration at 2 %. After the reflected shock at 990–1500 K, the pyrolysis products of 2000 and 5000 ppm TMEDA in Argon were also measured at 5 and 10 bar conditions in a single pulse shock tube. In addition, laminar flame speeds of TMEDA were measured at initial pressures of 1 bar, initial temperatures of 333 and 353 K, and equivalence ratios ranging from 0.8 to 1.5 in a constant volume reactor. The experimental results were simulated using a detailed TMEDA kinetic mechanism. Reaction path analysis and sensitivity analysis were provided to clarify the chemical kinetics of TMEDA oxidation and pyrolysis. The current work provides new experimental data and fundamental analyses for understanding the oxidation and pyrolysis characteristics of TMEDA, and sheds light on optimal directions for future models.

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.

Local sensitivity informed anisotropic sparse grid method for uncertainty quantification of chemical kinetics

The determination of rate coefficient parameters in detailed chemical kinetic mechanisms through experiments often suffers from avoidable aleatory uncertainty, while the use of reduced mechanisms, based on various reduction methods, introduces epistemic uncertainty. Both sources of uncertainty pose significant challenges for modeling and numerical simulation, highlighting the need for calibrating these uncertain parameters to achieve robust chemical mechanisms in the next generation. However, the high-dimensional parameter space of chemical kinetic mechanisms remains a significant obstacle in uncertainty computing. The Anisotropic Sparse Grid (ASG) technique has been successful in dealing with high-dimensional uncertainty problems, but it lacks prior knowledge of anisotropy. To address this issue, we propose the Local Sensitivity-Informed Anisotropic Sparse Grid (LSIASG) method, which utilizes local sensitivity as prior information for the ASG method, thereby accelerating the entire uncertainty quantification process. We test the LSIASG method on a theoretical model, a detailed hydrogen kinetic mechanism, and a methane mechanism and demonstrate that it can capture high-dimensional uncertainty characteristics, including expectation and deviation.

Mechanism study on the auto-ignition and reaction kinetic characteristics of hydrogen/n-dodecane mixture under mid and high temperature conditions

To acquire the ignition promotion methods for scramjet engine, the auto-ignition and reaction kinetic characteristics of hydrogen/n-dodecane mixture under mid and high temperatures were revealed by detailed chemical kinetic mechanism and experimental data. The results illuminated that the increases of n-dodecane's content and ϕ significantly declined the ignition delay time (IDT) of hydrogen mixture (by two orders of magnitude at most) at mid-temperature high-pressure (T = 950 K&p = 40 bar). The addition of n-dodecane induced the OH radical formation in initial stage and the advance of fuel's H-abstraction reactions (hydrogen: R3, n-dodecane: R2741/R2742/R2743/R2746). Whereas, the corresponding reduction in hydrogen content inhibited the establishment of active radical pool in dual-fuel reaction system before ignition time point. The ignition promoting effect of advanced initial reaction stage overweighted the ignition inhibiting effect of weakened rapid reaction stage in mid-temperature low-reactivity dual-fuel reaction system. Interestingly, at high-temperature high-pressure (T = 1300 K&p = 40 bar), the IDT firstly decreased (by 18.8%), and then continuously increased (by 105.3% at most) with the elevating n-dodecane's content. The minor addition of n-dodecane (1% of mole fraction) at high-temperature had a similar ignition promoting effect as that at mid-temperature. Whereas, the further reduction in hydrogen content dramatically suppressed the formation of active radical pool (H/OH/HO2/H2O2), which overweighted the ignition promoting effect of slightly advanced initial reaction stage. In other words, the hydrogen played a more critical role than the n-dodecane in high-temperature reaction system due to the originally high reactivity of hydrogen. The auto-ignition properties of hydrogen/n-dodecane mixture relied on the competition relationship of initial and rapid reaction stages under specific thermodynamic conditions and blending ratios. This investigation not only reveals internal interaction mechanism between fuels and active radicals in hydrogen/n-dodecane reaction system, but also provides fundamental insights for the precisely ignition promition methods of hydrogen/aviation-kerosene dual-fuel scramjet engine.

A detailed chemical kinetic mechanism of 1,1-diamino-2,2-dinitroethylene (FOX-7) initial decomposition in the gas phase

1,1-Diamino-2,2-dinitroethylene (FOX-7 or DADNE) is a promising ingredient of the low-vulnerability propellants. However, one of the major concerns in its further development and applications is the lack of detailed kinetic mechanism for its initial decomposition in the gas phase. In this study, a detailed chemical kinetic mechanism consisting of 38 species and 131 reactions was developed to describe the initial decomposition process of FOX-7. At first, a comprehensive reaction network was established with the aid of reactive molecular dynamics (MD) simulation. Then, the potential energy surfaces (PES) for both unimolecular and bimolecular reactions were identified at the QCISD(T)/CBS//M062X/6-311++G(d,p) level of theory. The rate coefficients were obtained by solving RRKM/ME, and the thermochemical properties of relevant species were calculated at CBS-APNO/G3/G4 levels with the atomization method. Finally, these kinetic and thermochemistry data were processed into a kinetic mechanism and used to simulate the initial decomposition process of FOX-7. The results demonstrated that the H-atom transfer to the beta carbon atom (enamino-imino isomerization) followed by the nitro group elimination dominates the initial decomposition, and the reaction FOX-7 = R3a + NO2 becomes the most significant one under high temperatures (Channel C3). Besides, bimolecular reactions also play a role as the decomposition goes on. Overall, this work provides quantitative predictions of the reaction pathways of gas-phase FOX-7 initial decomposition, and it would serve as a solid foundation for the development of a fully detailed combustion kinetic mechanism for FOX-7.

Numerical study of hydrogen blending on the laminar combustion characteristics of n-decane/air mixtures

In this work, the effects of n-decane/hydrogen on the laminar burning velocity (LBV), adiabatic flame temperature (AFT) and net heat release rate (NHRR) of n-decane were analysed and determined based on calculations using CHEMKIN/PREMIX with a detailed chemical kinetics mechanism. The results show that LBV may be divided into three phases according to the proportion of hydrogen in the C10H22/H2/air mixtures. The chemical effect of H2 promoted the LBV and AFT of n-decane. In addition, the physical effect of H2 inhibited the chemical reaction of n-decane, resulting in the decrease of NHRRs. The sensitivity analysis shows that the key reaction to promote LBV is R1: H + O2 = OH + O. Hydrogen reduced the emissions of NO, NO2 and CO, especially the NO production rate decreased by 24%. Our results demonstrate that adding hydrogen to n-decane can improve the laminar combustion characteristics, especially LBV and pollutant emissions.

High pressure ammonia oxidation in a flow reactor

The present work deals with an experimental and modeling analysis of ammonia oxidation at high pressure (up to 40 bar), in the 600–1275 K temperature range using a quartz tubular reactor and argon as diluent. The impact of temperature, pressure, oxygen stoichiometry and presence of NO has been analyzed on the concentrations of NH3 and N2 obtained as main products of ammonia oxidation. The main results obtained indicate that increasing either pressure or stoichiometry results in a shift of NH3 conversion to lower temperatures. The effect of pressure is particularly significant in the low range of pressures studied. The main product of ammonia oxidation is N2, while NO, NO2 and N2O concentrations are below the detection limit for all the conditions considered. The experimental results are simulated and interpreted in terms of a literature detailed chemical kinetic mechanism, which, in general, predicts satisfactorily the experimental results.

Oxidation study of small hydrocarbons at elevated pressure. Part I: Neat 1,3-butadiene

To study the formation pathways of aromatic compounds in the oxidation process of soot precursors under different equivalent ratios (φ), two parts of work were carried out. The present work was the part I: the oxidation of 1,3-butadiene (1,3-C4H6) was studied in a jet-stirred reactor at high-pressure (12 atm) within a temperature range covering 575–1075 K, at fuel equivalence ratios (φ) of 0.5 and 3.0. Part II focused on the study of oxidation of a two-compound mixture of acetylene and 1,3-butadiene. Mole fraction profiles of 20 species obtained by GC/MS analysis were identified and quantified. The measured species profiles serve as a data base for the further development of a detailed chemical kinetic reaction mechanism AramcoMech 3.0 generated by Zhou et al. previously for describing the ignition delay time and laminar flame speed of 1,3-butadien. The resulting reaction mechanism comprising 625 species and 3188 reactions was found to be able to describe credibly the experimental species profiles. Rate-of-production (ROP) analysis reveals that addition reactions of H and OH radicals to 1,3-C4H6 are the major channels governing 1,3-C4H6 consumption under both fuel-lean and fuel-rich conditions. Acetylene (C2H2), vinyl acetylene (C4H4), and propargyl radicals (C3H3) are playing important roles within the formation of mono-aromatics. Here, benzene is mainly formed via the C2 + C4 pathways instead of the C1 + C5 routes. Furthermore, C3H3 radicals were found to play a key role within C6H5CH3 formation. Naphthalene are formed by the reactions of C6H6 and 1,3-C4H6 or C4H5N/I radicals. These results will enrich the understanding of elevated pressure chemistry of 1,3-C4H6 and facilitate to further model development and validation focusing on a more detailed description of the formation network of aromatic compounds.

Reactivity enhancement of natural gas/diesel RCCI engine by adding ozone species

Reactivity controlled compression ignition (RCCI) is an alternative combustion strategy with the potential of significant advantages in terms of increasing thermal efficiency together with reduction of NOx and soot emissions. The RCCI engines have been encountered not to be applicable broadly since they suffer from some difficulties mainly contributed to the controllability of combustion and limited operating ranges. The difficulties become even worse where low-reactivity fuels like natural gas (NG) are applied. Ozone gas, a chemical species with an extreme level of reactivity, can improve the combustion efficiency along with the advancement of combustion phasing in the RCCI engine. In this study a multidimensional computational fluid dynamic (CFD) which is coupled with proper detailed chemical kinetic mechanisms is employed to investigate the influence of ozone addition (i.e., 10, 100 and 1000 ppm) to air-fuel mixture with different initial conditions (e.g., intake temperature and equivalence ratio), on the performance and emissions characteristics of the RCCI engine. The results imply that the addition of even low concentrations of ozone (10 ppm) have considerable influences on the RCCI combustion characteristics. Addition of ozone by a distinct quantity not only can enhance the combustion phasing controllability, but also can extend the operating range of the RCCI engine in both lower intake air temperature and the lower fraction of the high-reactive fuel. From the results it is conceived that by adding 1000 ppm ozone into the air-fuel mixture, it is possible to reduce the diesel fuel fraction from 20% to 10% and intake air temperature from 355 K to 335 K, respectively.

A novel object-oriented directed path screening method for reduction of detailed chemical kinetic mechanism

Numerical simulation is widely recognized as an efficient means of developing high-performance combustors. However, its efficiency is limited by the growing size of chemical kinetic mechanisms, which increases computation costs. To substantially reduce the size of mechanism while retaining the accuracy, an object-oriented directed path screening (OoDPS) method is proposed in this study. In this methodology, species are ranked according to the order in which they are generated in flame, then reactions are ranked according to the generation of the species in the left hand side of each reaction. A set of important species codetermining the accurate prediction of concerned combustion characteristics are predefined as the "Object". Calibration databases are extracted from laminar premixed flames simulated using the detailed mechanism with equivalence ratio varying from 0.7 to 1.5. The contributions of each reaction in the detailed mechanism to the production/consumption of each species in the Object are evaluated. The size of the reduced mechanism depends on the user-defined contribution coefficient threshold. In this study, a detailed mechanism for methane-ammonia oxidation, consisted of 84 species and 703 reactions, is applied to demonstrate the reliability of the OoDPS method. Several derived skeletal mechanisms are validated against the detailed mechanism. OoDPS method shows a better performance than DRGEP in predicting the laminar burning velocity and ignition delay time at the same level of reaction number. For diffusion flames, OoDPS remains superior to DRGEP in predicting the concentration profiles of H, O and OH, and this superiority becomes more significant for reduced mechanism with less reactions. Unfortunately, as the size of reaction decreases from 703 to 109, the accuracy of OoDPS-generated skeletal mechanism decreases as the increase of ammonia in the fuel, which can be restrained by extending the calibration databases.

Theory-Based Mechanism for Fluoromethane Combustion I: Thermochemistry and Abstraction Reactions

A new detailed chemical kinetic mechanism is presented for small fluorinated hydrocarbons. Ab initio electronic structure theory is used to provide heats of formation with subchemical accuracy. The ANL0 method is extended to include fluorine. The resulting heats of formation at 0 K are in excellent agreement with 36 benchmark species in the Active Thermochemical Tables, with a mean error of μ = -0.02 kJ/mol and a standard deviation of σ = 0.91 kJ/mol. The thermophysical properties for 92 small-molecule H/C/O/F species are computed. The rate coefficients for 40+ H-abstraction reactions involving H, O, F, OH, OF, HO2, and various methyl radicals with CH4, CH3F, CH2F2, CHF3, CH2O, and CHFO are discussed. The computed rate constants are in excellent agreement with the available literature. Additionally, 30+ rate constants are provided for F abstraction, which are several orders of magnitude smaller than H abstraction. The thermophysical properties and rate constants are provided in a mechanism. This mechanism is the first in a series of theory-based investigations into the thermal destruction of per- and polyfluorinated species.

Development of a Reduced Gasoline/Hydrogenated Catalytic Biodiesel Blends Mechanism for Engine Applications

ABSTRACT Gasoline/hydrogenated catalytic biodiesel blending fuel has been proposed to improve gasoline ignitability and combustion stability in gasoline compression ignition (GCI) engines. Comprehensive numerical simulation in GCI engine models provides useful information that can be used for efficient utilization of this promising fuel. However, the use of detailed chemical kinetic mechanisms is unfeasible. In this work, a reduced mechanism was developed for a blended fuel of gasoline/hydrogenated catalytic biodiesel (HCB). Based on the fuel composition and physicochemical properties, n-hexadecane was proposed as a surrogate fuel for HCB. Three reduction methods with error propagation extension to directed relation graph, full species sensitivity analysis and quasi steady state approximation were utilized to reduce the detailed mechanism of n-hexadecane. The reduced mechanism was coupled with a gasoline surrogate mechanism to construct gasoline/HCB surrogate mechanism. Reaction path analysis and sensitivity analyses were performed to optimize the reaction kinetic constants of several reactions. The final reduced mechanism included 82 species and 370 reactions, and was able to accurately predict various combustion characteristics such as ignition delay times, laminar flame speed and species concentrations. The reduced mechanism is also applied to 3D computational fluid dynamics to validate the prediction ability of the direct injection compression ignition engine, and the predicted results show good agreement with experimental data. The overall results suggest that the current reduced mechanism could be applied for predicting gasoline/HCB mixture in practical engine simulations.