Software CHEMKIN

The task of the problem-independent chemistry software is to make evaluating the terms in Equations (6-10) as straightforward as possible. In this case subroutine calls to the Chemkin software are made to return values of p, Cp, and the and hk vectors. Also, subroutine calls are made to a Transport package to return the ordinary multicomponent diffusion matrices Dkj, the mixture viscosities p, the thermal conductivities A, and the thermal diffusion coefficients D. Once this is done, finite difference representations of the equations are evaluated, and the residuals returned to the boundary value solver. 

CHEMKIN is now maintained and distributed by Reaction Design, Inc., which is a software company licensed by Sandia National Laboratories. CHEMKIN 4.1 is the latest commercial version of the CHEMKIN software suite from Reaction Design. The software suite has all the application modules of CHEMKIN II and III (such as SURFACE CHEMKIN, EQUIL, SENKIN, PSR, and PREMIX), and has been extended to include many more. Refer to the website http //www.reactiondesign.com/lobby/open/index.html for more information. 

For homogeneous gas-phase kinetics one may incorporate arbitrarily complex reaction mechanisms into the mass and energy conservation equations. Aside from questions of units, there is almost no disagreement in the formulation of the elementary rate law the rate of progress of each reaction proceeds according to the law of mass action. The CHEMKIN software [217] is widely used in the kinetics community to aid in the formulation and solution of gas-phase kinetics and transport problems. 

Problems like plug flow can be posed as standard-form ODEs, but it is much more convenient to pose them as DAEs. Other situations, such as boundary-layer flow (Chapters 7 and 17) are difficult to pose as standard-form ODEs, but a DAE formulation works well. The Dassl family of software [46] is designed for solving DAEs and is used extensively in the Chemkin software. 

There are a great many applications that have been build using the CHEMKIN software, including the solution of two- and three-dimensional chemically reacting flow problems. 

With this book we seek to document the experience we have gained over some 20 years of research and application chemically reacting fluid flow. An important aspect of the experience has been the development and application of the Chemkin software that implements much of the theory discussed in this text. 

Finally, there are a great many researchers worldwide who work with the Chemkin software. We appreciate the many interactions that the sharing of this software has stimulated. While the individuals are far too numerous to mention by name, their feedback has had an important influence on the development of the modeling tools that are documented herein. 

A microkinetic reaction model was constructed to elucidate the intrinsic reaction mechanism and to provide insight into the processes occurring in the reactor. CHEMKiN software [50] was used to accommodate this model. The PrOx reaction mechanism describing the detailed gas-phase and surface chemical kinetics was constmcted from previously published work [51] and adapting the rate parameters to our experimental results. The model is composed of eight adsorption reactions, eight desorption reactions and 12 surface reactions with nine gas-phase species (N2, O, O2, CO2, H, OH, CO, H2, H2O) and eight surface species [Pt(s), 0(s), H(s), OH(s), H20(s), C(s), CO(s), CO2 (s)]. 

Upon completion of the reaction model, the CHEMKIN software provides information on rates of production of various species from each reaction, along with measures of the sensitivity of the solution to each reaction rate. Such an analysis fadhtated the assessment of reaction importance and resulted in the reaction network in Figure 27.19, which shows the nine major forward and reverse reactions that comprise the overall reaction pathways for consumption of CO and formation of H 2O and CO2 for the conditions of interest. The reaction model was thus verified with established PrOx mechanisms in the literature and compared with our experimental data. 

Numerical simulations of the reaction system for preferential oxidation of carbon monoxide was performed by Ouyang et cd. who applied CHEMKIN software and a network of 8 species in the gas phase, 8 surface species and 28 elementary reaction steps, not provided here in detail [117]. The simulation described the experimental performance of the reactor of Ouyang et al. very well. It revealed that the oxidation of carbon monoxide occurred by reaction between adsorbed CO and O H species and not by the reaction between adsorbed CO and O species, because the latter reaction rate was ten orders of magnitude lower. Thus a simplified mechanism of the reaction network could be formulated according to Ouyang et al. as follows ... 

Due to its modularity, the software comes in many parts (shown in Fig. 9). The Chemkin package is composed of four important pieces the Interpreter, the Thermodynamic Data Base, the Linking File, and the Gas-Phase Subroutine Library. The Interpreter is a program that first reads the user s symbolic description of the reaction mechanism. It then extracts thermodynamic information for the species involved from the Thermodynamic Data Base. The user may add to or modify the information in the data base by input to the Interpreter. In addition to printed output, the Interpreter writes a Linking File, which contains all the pertinent information on the elements, species, and reactions in the mechanism. 

Figure 9. Schematic representation of the relationship of the Chemkin and Transport software packages with an application code.

The Chemkin package deals with problems that can be stated in terms of equation of state, thermodynamic properties, and chemical kinetics, but it does not consider the effects of fluid transport. Once fluid transport is introduced it is usually necessary to model diffusive fluxes of mass, momentum, and energy, which requires knowledge of transport coefficients such as viscosity, thermal conductivity, species diffusion coefficients, and thermal diffusion coefficients. Therefore, in a software package analogous to Chemkin, we provide the capabilities for evaluating these coefficients. ... 

CHEMClean and CHEMDiffs The Comparison of Detailed Chemical Kinetic Mechanisms Application to the Combustion of Methane, Rolland, S. and Simmie, J. M. Int. J. Chem. Kinet. 36(9), 467 471, (2004). These programs may be used with CHEMKIN to (1) clean up an input mechanism file and (2) to compare two clean mechanisms. Refer to the website http //www. nuigalway.ie/chem/c3/software.htm for more information. 

MECHMOD A utility program written by Turanyi, T. (Eotvos University, Budapest, Hungary) that manipulates reaction mechanisms to convert rate parameters from one unit to another, to calculate reverse rate parameters from the forward rate constant parameters and thermodynamic data, or to systematically eliminate select species from the mechanism. Thermodynamic data can be printed at the beginning of the mechanism, and the room-temperature heat of formation and entropy data may be modified in the NASA polynomials. MECHMOD requires the usage of either CHEMK1N-TT or CHEMKIN-III software. Details of the software may be obtained at either of two websites http //www.chem.leeds.ac.uk/Combustion/Combustion.html or http //garfield. chem.elte.hu/Combustion/Combustion. html. 

Using these methods, the elementary reaction steps that define a fuel s overall combustion can be compiled, generating an overall combustion mechanism. Combustion simulation software, like CHEMKIN, takes as input a fuel s combustion mechanism and other system parameters, along with a reactor model, and simulates a complex combustion environment (Fig. 4). For instance, one of CHEMKIN s applications can simulate the behavior of a flame in a given fuel, providing a wealth of information about flame speed, key intermediates, and dominant reactions. Computational fluid dynamics can be combined with detailed chemical kinetic models to also be able to simulate turbulent flames and macroscopic combustion environments. 

With the possibility that dozens or even thousands of elementary chemical reactions may have to be included in a complex reaction mechanism, the need for a general and compact formalism to describe detailed reaction kinetics becomes apparent. Chemkin [217] is a widely used chemical kinetics software package designed to aid in such complex reaction kinetics calculations. 

Chemkin is a large body of software designed to facilitate the computational modeling of chemical kinetics in flowing systems. An application program (e.g., a combustion-analysis code) can draw on any of three major software packages ... 

The software is highly structured and modular, which provides great flexibility in applying it to a wide variety of problems. However, this modularity also compels the user to manipulate a number of programs and files. The flow of information from the first input to the Chemkin Interpreter to the inclusion of a library subroutine in an application program is shown in Fig. E.2. 

A third software package, which handles gas-phase molecular transport, may or may not be needed in a particular application. If it is used, the Transport Property Fitting Code reads the Chemkin Linking File and identifies all the gas-phase species that are present in the gas-phase reaction mechanism. Then, drawing on a database of molecular parameters,... 

Once the basic Chemkin philosophy and software were established in 1980, we had a framework into which new models could be integrated. Thus we could expand the integrated modeling tools efficiently to meet the needs of increasingly challenging applications. Over the years, more than 20 individuals have contributed to aspects of Chemkin. Major contributors include Fran Rupley (Reaction Design, Inc.), Ellen Meeks (Reaction Design, Inc.), Rich Larson (Sandia National Laboratories), and Andy Lutz (Sandia National Laboratories). 

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