OpenSMOKE++ is a general framework for numerical simulations of reacting systems with detailed kinetic mechanisms, including thousands of chemical species and reactions. The framework is entirely ...written in object-oriented C++ and can be easily extended and customized by the user for specific systems, without having to modify the core functionality of the program. The OpenSMOKE++ framework can handle simulations of ideal chemical reactors (plug-flow, batch, and jet stirred reactors), shock-tubes, rapid compression machines, and can be easily incorporated into multi-dimensional CFD codes for the modeling of reacting flows. OpenSMOKE++ provides useful numerical tools such as the sensitivity and rate of production analyses, needed to recognize the main chemical paths and to interpret the numerical results from a kinetic point of view. Since simulations involving large kinetic mechanisms are very time consuming, OpenSMOKE++ adopts advanced numerical techniques able to reduce the computational cost, without sacrificing the accuracy and the robustness of the calculations.
In the present paper we give a detailed description of the framework features, the numerical models available, and the implementation of the code. The possibility of coupling the OpenSMOKE++ functionality with existing numerical codes is discussed. The computational performances of the framework are presented, and the capabilities of OpenSMOKE++ in terms of integration of stiff ODE systems are discussed and analyzed with special emphasis. Some examples demonstrating the ability of the OpenSMOKE++ framework to successfully manage large kinetic mechanisms are eventually presented.
Program title: OpenSMOKE++
Catalogue identifier: AEVY_v1_0
Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEVY_v1_0.html
Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland
Licensing provisions: GNU General Public License, version 3
No. of lines in distributed program, including test data, etc.: 146353
No. of bytes in distributed program, including test data, etc.: 4890534
Distribution format: tar.gz
Programming language: C++.
Computer: Any computer that can run a C++ Compiler.
Operating system: Tested on Microsoft Windows 7, Ubuntu 14.4.
RAM: From a few Mb to several Gb depending on the size of the system being simulated.
Classification: 22.
External routines: Eigen, Boost C++ Libraries, RapidXML
Nature of problem: Evolution of reacting gas mixtures with detailed description of thermodynamic, kinetic and transport data.
Solution method: Stiff systems of Ordinary differential Equations, whose solution is obtained using methods based on the Backward Differentiation Formulas (BDF) (LU factorization of dense matrices is required).
Additional comments: The code was specifically conceived for managing homogeneous, reacting mixtures including thousands of species and reactions.
Running time: Problem-dependent, from seconds (small kinetics) to hours
The primary objective of the present endeavor is to collect, consolidate, and review the vast amount of experimental data on the laminar flame speeds of hydrocarbon and oxygenated fuels that have ...been reported in recent years, analyze them by using a detailed kinetic mechanism for the pyrolysis and combustion of a large variety of fuels at high temperature conditions, and thereby identify aspects of the mechanism that require further revision. The review and assessment was hierarchically conducted, in the sequence of the foundational C0–C4 species; the reference fuels of alkanes (n-heptane, iso-octane, n-decane, n-dodecane), cyclo-alkanes (cyclohexane and methyl-cyclo-hexane) and the aromatics (benzene, toluene, xylene and ethylbenzene); and the oxygenated fuels of alcohols, C3H6O isomers, ethers (dimethyl ether and ethyl tertiary butyl ether), and methyl esters up to methyl decanoate. Mixtures of some of these fuels, including those with hydrogen, were also considered. The comprehensive nature of the present mechanism and effort is emphasized.
The use of simplifying techniques to obtain skeletal kinetic mechanisms with the required accuracy is often a necessary step when computationally demanding simulations are concerned. In this work, a ...novel approach for an automatic mechanism reduction, aimed at retaining accuracy on specific target species, is proposed. Starting from the consolidated coupling between flux analysis and sensitivity analysis, a methodology based on curve matching and functional data analysis was developed, through which the importance of a species in the target accuracy is assessed via a proper metric. The error associated with the removal of uncertain species from the detailed mechanism is quantified in terms of distance and similarity indices before and after such a removal, within a Species-Targeted Sensitivity Analysis (STSA) framework. A species ranking is then generated, and the original mechanism is progressively reduced. The whole algorithm also implements several improvements to enhance a faster convergence, and adds a novel criterion to remove unimportant reactions, based on sensitivity analysis to kinetic parameters.
The capability of this algorithm was tested through two case studies in this work. A kinetic mechanism for a Toluene Reference Fuel (TRF) was first obtained, with the overall reactivity as reduction target. The numerical procedure allowed to obtain a compact skeletal mechanism (115 species and 856 reactions), able to retain good accuracy in ignition delay time and laminar flame speed predictions of both fuel mixture and pure compounds. More important, two skeletal mechanisms for methane combustion, including chemistry of nitrogen oxides (NOx), were developed, with different degrees of reduction. The agreement between the original and the skeletal mechanisms in terms of NO formation was successfully assessed with satisfactory results. Attention was also dedicated to the choice of the type of reactor where undertaking reduction, which turned out to play a major role in the overall process.
The aim of this kinetic work is to provide a better understanding of the pyrolysis of lignin and biomasses not only in terms of devolatilazation rate but also of the volatile species released. The ...complexity of both lignin structure and its degradation mechanism meant that a lumping approach suitable for handling the huge amount of initial, intermediate and final products had to be used. Despite these simplifications, the proposed semi-detailed kinetic scheme involves about 100 molecular and radical species in 500 elementary and lumped reactions. It has already been proved that this lignin devolatilization model correctly predicts the degradation rates and the detail of the released products. This work constitutes an initial yet significant step towards deriving a complete kinetic scheme of biomass devolatilization.
In this work, we propose a novel data-driven approach for detailed kinetic mechanisms optimization. The approach is founded on a curve matching-based objective function and includes a methodology for ...the optimisation of pressure-dependent reactions via logarithmic interpolation (PLOG format). In order to highlight the advantages of the new formulation of the objective function, a comparison with L1 and L2 norm is performed. The selection of impactful reactions is carried out by introducing a Cumulative Impact Function (CIF), while an Evolutionary Algorithm (EA) is adopted for the optimization. The capabilities of the proposed methodology were demonstrated using a database of ~635 experimental datapoints on ammonia combustion, covering standard targets like ignition delay times, speciation and laminar flame speed. The optimization was carried out starting from a recently published mechanism, describing ammonia pyrolysis and oxidation, largely developed using first-principles calculation of rate constants. After the selection of the 24 most impactful reactions, the related 101 normalized Arrhenius parameters were simultaneously varied, within their uncertainty bounds. Their uncertainty bounds were taken from the literature, when available, or estimated according to the level of theory adopted for the determination of the rate constant. Hence, we also provide guidelines to estimate uncertainty for reaction rate constants derived from first principles calculations using well consolidated computational protocols as a reference. The optimized mechanism was found to improve the nominal one, showing a satisfactory agreement over the entire range of operating conditions. Moreover, the use of ‘curve matching’ indices was found to outperform the adoption of L1 and L2 norms. The comparison between the nominal mechanism and the one optimized via curve matching allowed a clear identification of different critical reaction pathways for different experimental targets. From this perspective, the methodology proposed herein can find further application as a useful design-of-experiments tool for an accurate evaluation of crucial kinetic constants, thus driving further mechanism improvement.
•Biomass origin and structure affect composition and yield of pyrolysis biochar.•Operating conditions of thermal treatment affect composition and yield of pyrolysis biochar.•Further pyrolysis ...reactions modify young biochar structure and release gas products.•A predictive kinetic mechanism of biomass pyrolysis accounts for all these effects.•Large collection of literature experimental data supports the validation of the kinetic mechanism.
Biomass is increasingly being recognized as a promising carrier for both heat, energy and chemicals production. However, several aspects still require intense research activity towards a better design and optimization of industrial combustors, gasifiers and pyrolyzer. The objective of this work is to update the CRECK kinetic mechanism of biomass pyrolysis, allowing a better prediction of both yield and composition of the solid residue (biochar). Moreover, further model modifications allow to better describe the variability of hemicellulose in different biomass. To this end, a large set of literature experimental data is collected and organized into a database, which is used to further tune and validate the proposed kinetic mechanism. Although the kinetic model maintains the previous agreement in respect of the rate of biomass pyrolysis, formation and distribution of gas and tar products, the novelty of this work is the greater attention to the predictions of biochar yield and composition, in a wide range of operative conditions. The model describes the solid residue as a mixture of pure carbon together with lumped metaplastic compounds, which represent the whole range of oxygenated and hydrogenated groups bonded to the carbonaceous matrix. These metaplastic species are released to the gas phase with their own kinetics and describe the change of both mass loss and elemental composition of the biochar. These comprehensive predictions of biochar composition are crucial for an accurate description of the successive oxidation and gasification processes.
The kinetic characterization of the
H
2
/
CO
system is of interest right now due mainly to its role in sustainable combustion processes. The aim of this paper is to revise and validate a detailed ...kinetic model of hydrogen and carbon monoxide mixture combustion with particular focus not only on
NO
x
formation but also on interactions with nitrogen species. Model predictions and experimental measurements are discussed and compared across a wide range of operating conditions. This study moves from the detailed analysis of species profiles in syngas oxidation in flow reactor and laminar premixed flames to global combustion properties (ignition delay times and laminar flame speeds) by referring to a large set of literature data. According to recent literature, the validation of the kinetic scheme confirmed there was a need to slightly modify the kinetic parameters of two relevant
CO
2
formation reactions (
CO
+
OH
=
CO
2
+
H
and
CO
+
O
+
M
=
CO
2
+
M
) and of reaction
HONO
+
OH
=
NO
2
+
H
2
O
.
Aromatase inhibitors are the preferred adjuvant endocrine therapy for the majority of postmenopausal women with hormone-responsive early breast cancer. Although generally more effective than ...tamoxifen, aromatase inhibitor therapy is associated with increased bone loss and fracture risk.
Postmenopausal women receiving adjuvant letrozole (2.5 mg/day for 5 years; N = 1065) were randomly assigned to immediate zoledronic acid (zoledronate) 4 mg every 6 months for 5 years, or delayed zoledronate (initiated for fracture or on-study bone mineral density BMD decrease). The primary end point was the change in lumbar spine BMD at 12 months. Lumbar spine and total hip BMD at subsequent follow-up, disease-free survival (DFS), and overall survival were assessed as secondary end points.
At 60 months (final analysis), the mean change in lumbar spine BMD was +4.3% with immediate zoledronate and -5.4% with delayed intervention (P < 0.0001). Immediate zoledronate reduced the risk of DFS events by 34% (hazard ratio HR = 0.66; P = 0.0375) with fewer local (0.9% versus 2.3%) and distant (5.5% versus 7.7%) recurrences versus delayed zoledronate. In the delayed group, delayed initiation of zoledronate substantially improved DFS versus no zoledronate (HR = 0.46; P = 0.0334).
Immediate zoledronate in postmenopausal women receiving letrozole preserved BMD and is associated with improved DFS compared with letrozole alone.
NCT00171340.
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•A multidimensional CFD model for the evaporation of fuel droplets in convective regime under gravity conditions has been developed and validated.•The model by-passes the well-known ...problem of spurious currents neglecting surface tension and imposing a centripetal force field which is able to hang the droplet against gravity.•The agreement with the experimental data is excellent, both in natural and forced convection regimes in a very wide range of operating conditions.•Non-ideal thermodynamics description is shown to be fundamental to correctly capture the evaporation rate in high pressure conditions, under-predicted in ideal conditions.•A strong internal flow field is captured, providing a nearly isothermal liquid phase.
This paper aims at presenting the DropletSMOKE++ solver, a comprehensive multidimensional computational framework for the evaporation of fuel droplets, under the influence of a gravity field and an external fluid flow. The Volume Of Fluid (VOF) methodology is adopted to dynamically track the interface, coupled with the solution of energy and species equations. The evaporation rate is directly evaluated based on the vapor concentration gradient at the phase boundary, with no need of semi-empirical evaporation sub-models.
The strong surface tension forces often prevent to model small droplets evaporation, because of the presence of parasitic currents. In this work we by-pass the problem, eliminating surface tension and introducing a centripetal force toward the center of the droplet. This expedient represents a major novelty of this work, which allows to numerically hang a droplet on a fiber in normal gravity conditions without modeling surface tension. Parasitic currents are completely suppressed, allowing to accurately model the evaporation process whatever the droplet size.
DropletSMOKE++ shows an excellent agreement with the experimental data in a wide range of operating conditions, for various fuels and initial droplet diameters, both in natural and forced convection. The comparison with the same cases modeled in microgravity conditions highlights the impact of an external fluid flow on the evaporation mechanism, especially at high pressures. Non-ideal thermodynamics for phase-equilibrium is included to correctly capture evaporation rates at high pressures, otherwise not well predicted by an ideal gas assumption. Finally, the presence of flow circulation in the liquid phase is discussed, as well as its influence on the internal temperature field.
DropletSMOKE++ will be released as an open-source code, open to contributions from the scientific community.
An interface-resolved simulation of the combustion of a fuel droplet suspended in normal gravity is presented in this work, followed by an extensive analysis on the physical aspects involved. The ...modeling is based on DropletSMOKE++, a multiphase solver developed for the modeling of droplet vaporization and combustion in convective conditions. A wide range of phenomena can be described by the model, including the interface advection, the phase-change, the combustion chemistry, non-ideal thermodynamics and multicomponent mixtures. To our knowledge, this is the most detailed simulation performed on this configuration, providing a useful theoretical and numerical support for the experimental activity on this field. A recent experimental work is used as a reference, in which a methanol droplet is suspended on a quartz fiber and ignited at different oxygen concentrations. The numerical analysis offers a detailed insight into the physics of the problem and a satisfactory agreement with the experiments in terms of diameter decay, radial temperature profiles and sensitivity to the oxygen concentration. The vaporization rate is affected by the thermal conduction from the fiber, due to the high temperatures involved. Moreover, the fiber perturbs the flame itself, providing quenching at its surface. The combustion physics is compared to the one predicted at zero-gravity, evidencing a lower standoff-ratio, a higher flame temperature and an intense internal circulation. The distribution of the species around the droplet shows (i) a local accumulation of intermediate oxidation products at the fiber surface and (ii) water absorption in the liquid phase, affecting the vaporization rate.
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