The information in this document can also be accessed on the World Wide Web at http://www.gri.org point to the 'Basic Research' button, and then to 'GRI-Mech' At this Web location you can also view results of validation tests, directly load the GRI_Mech files, and check on any late-breaking news available. Files in this directory: README211.DAT This file. GRIMECH211.DAT A reaction mechanism and rate coefficient file, in Chemkin format, describing 276 reactions of 49 species. It includes reactions of nitrogen-containing species relevant to the NOx chemistry of natural gas combustion and reburning. A corrected version of the mechanism was posted 11/4/95. THERMO211.DAT A thermochemical data file to be used with GRIMECH21.DAT, as sets of "NASA polynomial" coefficients. TRANSPORT.DAT A file containing the parameters needed for calculating transport coefficients to be used in the Sandia flame code. BUGFIX.DAT A file containing information on bugs found in using GRI-Mech in various computer codes. Dr. Vladimir Zamansky of Energy and Environmental Research has brought to our attention the following error in the initial release of GRI-Mech 2.1. The 'E' terms in the rate constant expressions for reactions (277) NH3 + H = NH2 + H2 and (278) NH3 + OH = NH2 + H2O should be positive rather than negative as originally given. The mechanism file has been corrected as of November 4, 1995, and the corrected version is referred to as GRI-Mech 2.11. This change does not affect our results because the mechanism was not designed for ammonia or deNOx kinetics, and none of the targets chosen for the 2.1 version or validation experiments tested afterwards show measurable sensitivity to these reactions. Recalculation of all targets and validation experiments has been done with GRI-Mech 2.11 (completed November 21, 1995). No significant changes from the results obtained using GRI-Mech 2.1 were found. The files in this directory are products of computational and experimental research sponsored by the Gas Research Institute. Previous mechanism and readme files are available. In particular, you can consult the README12.DAT file for a description of the hydrocarbon oxidation mechanism, GRI-Mech 1.2, and its performance in validation tests. The hydrocarbon part of GRI-Mech 1.2, with the single exception mentioned below, has been retained intact in GRI-Mech 2.11. The research was carried out at The Pennsylvania State University, Stanford University, The University of California, Berkeley, The University of Texas at Austin, and SRI International. GRI-Mech is an optimized (see below) detailed chemical reaction mechanism capable of the best representation of natural gas flames, ignition, and NOx formation and reburning in natural gas combustion that we are able to provide as of the date at the head of this file. In order to use the input files directly you need the Sandia National Laboratory "Chemkin-II" programs. (See discussion below.) Ignition and flow reactor profiles and well-stirred reactor outputs calculated with this mechanism and thermochemical data should be independent of the program used to compute them; noticeable small differences in flame profiles should be expected if you use a flame code other than Premix, however, because the transport calculation, the numerical method of solving the partial differential equations, and so on, differ from program to program. Before telling you more we are obliged to say: ******************* GRI DISCLAIMER ******************** LEGAL NOTICE These files, both the ones intended for use as computer input as well as those comprising documentation, were prepared by The Pennsylvania State University, Stanford University, SRI International, The University of California, Berkeley, and The University of Texas at Austin as a result of research sponsored by the Gas Research Institute (GRI). Neither GRI, members of GRI, nor any person acting on behalf of either: a. Makes any warranty or representation, express or implied, with respect to the accuracy, completeness, or usefulness of the information contained in these files, or that the use of any data, method, or process disclosed in these files may not infringe privately owned rights; or b. Assumes any liability with respect to the use of, or for damages resulting from the use of, any information, data, method or process disclosed in these files. ************************************************************ Now that you have read our disclaimer, here is what you can find in this README file: 1. A description of the version 2.11 GRI-Mech release files. 2. A summary of what we can tell you about its performance. 3. A request for feedback on your experience with it. 4. How to get in touch with us. 5. Some cautionary notes. 1. WHAT IS GRI-Mech 2.11? What follows is a brief overview of the GRI-Mech 2.11 enhancement to the version 1.2 release. Consult the README file for GRI-Mech 1.2 for general information about GRI-Mech. GRI-Mech 2.11 is a compilation of 276 elementary chemical reactions and associated rate coefficient expressions and thermochemical parameters for the 49 species involved in them. It differs from the version 1.2 release in that it includes nitrogen chemistry relevant to natural gas chemistry and reburning. The version 2.11 data files serve the same purposes as those of the version 1.2 release and they serve them in exactly the same way. If you have the Chemkin programs, all you need to do is substitute the GRI-Mech 2.11 input files for whatever files you have working with Chemkin before and you will be ready to go. 2. VERSION 2.11 PERFORMANCE THAT WE KNOW ABOUT We test the performance of GRI-Mech extensively. The performance of version 1.2, containing the C-H-O parts of natural gas ignition and flame chemistry, is described in the README12.DAT file. Version 2.11 contains the identical chemistry as in version 1.2 plus 99 reactions of 17 additional nitrogen-containing species. The parameters of the 177 reactions in version 1.2 were not varied in the course of the Version 2.11 optimization process except for the rate coefficient of the CH + H2O --> H + CH2O reaction, which was found to play an important role in prompt NO formation but to have no effect on the course of the carbon-hydrogen- oxygen chemistry of methane combustion. Version 2.11 is therefore identical to version 1.2 with respect to the carbon-hydrogen-oxygen chemistry of natural gas ignition and flames. Version 2.11 was not optimized for modeling pure nitrogen- hydrogen-oxygen chemistry or any form of NOx removal process except for reburning. In the course of developing GRI-Mech 2.11 we learned quite early that optimizing the nitrogen chemistry relevant to natural gas flames and reburning is qualitatively a very different challenge than optimizing the carbon- hydrogen-oxygen chemistry. In the first place, we were able to locate only a much smaller data base of experimental information from which to draw optimization targets. Then, once the modeling process had proceeded far enough that we could examine matches between computed and observed behavior, we found a far higher degree of discord among the matches to targets and other data than we had seen in working with our earlier optimizations of carbon-hydrogen-oxygen chemistry. We therefore have to caution users of GRI-Mech 2.11 to regard it only a preliminary starting point that can not be applied with anything like the degree of confidence that can be attached to the version 1.2 carbon-hydrogen-oxygen chemistry. We do believe that GRI-Mech 2.11 is a signficant improvement over previous attempts to describe NOx formation and reburning for example the 1989 Miller and Bowman mechanism, and are therefore releasing it at this time in the spirit of "beta testing" our first optimized result and stimulating further experimental study of NOx formation and removal in natural gas flames. Here is a list of the validation checks of Version 2.11 that we have made. Examining the comparisons between prediction and observation, provided in graphical form on our World Wide Web site, will show you pretty quickly how well GRI-Mech 2.11 performs. A. Flow Reactors Glarborg, P. and Miller, J.A., "Mechanism and Modeling of Hydrogen Cyanide Oxidation in a Flow Reactor," Combustion and Flame 99, 475 (1994). HCN, NO, and N2O mole fractions at the exit of a laminar isothermal flow reactor for temperatures between 900 and 1400 K. B. Low-Pressure Flames Miller, J.A., Branch, M.C., McLean, W.J., Chandler, D.W., Smooke, M.D. and Kee, R.J., "The Conversion of HCN to NO and N2 in H2-O2-HCN-Ar Flames at Low Pressure," Twentieth Symposium (International) on Combustion, The Combustion Institute, pp. 673-684, 1984. HCN, NO, N2 and relative CN profiles in rich and lean flames at 25 Torr. Heard, D.E., Jeffries, J.B., Smith, G.P. and Crosley, D.R., "LIF Measurements in Methane/Air Flames of Radicals Important in Prompt-NO Formation," Combustion and Flame 88, 137 (1992). NO and relative CH profiles in a slightly rich CH4-air flame at 30 Torr. Williams, B.A. and Fleming, J.W., "Comparative Species Concentrations in CH4/O2/Ar Flames Doped with N2O, NO and NO2," Combustion and Flame 98, 93 (1994). Relative CH and CN concentration profiles in 10 Torr stoichiometric CH4-O2-Ar flames doped with NO and N2O. Etzkorn, T., Muris, S., Wolfrum, J., Dembny, C., Bockhorn, H., Nelson, P.F., Attia-Shahin, A. and Warnatz, J., "Destruction and Formation of NO in Low Pressure Stoichiometric CH4/O2 Flames," Twenty-fourth Symposium (International) on Combustion, The Combustion Institute, pp. 925-932, 1992. NO concentration profile in a stoichiometric 10 Torr CH4-O2 flame with added NO. Zabielski, M.F. and Seery, D.J. "Mechanisms and Reaction Dynamics Related to Methane Combustion," GRI Report 84/0126, 1984. CH, CN and NO mole fraction profiles in a 35 Torr slightly rich CH4-O2-Ar flame with added NO. C. Stirred Reactors Bartok, W., Engleman, V. S., Goldstein, and del Valle, E.G., "Basic Kinetic Studies and Modeling of Nitrogen Oxide Formation in Combustion Processes," AIChE Symposium Series No. 126, Vol. 68, pp. 30-38, 1972. NO mole fraction in reactor products for CH4-Air and CH4-Air-NO for fuel-air equivalence ratios from 0.6 to 1.6. Steele, R.C., Malte, P.C., Nichol, D.G. and Kramlich, J.C., "NOx and N2O in Lean-Premixed Jet-Stirred Flames," Combustion and Flame 100, 440 (1995). NO and N2O mole fractions in reactor products for CH4-Air. 3. PLEASE TELL US WHAT YOU LEARN, AND ABOUT YOUR PROBLEMS While the authors are continuing to expand their understanding of how GRI-Mech works, it is only natural that others will see things that should be done with quite different perspectives. We would very much like to hear from you. We want to hear about your experiences with GRI-Mech, both successes and failures. It will help us more in our development work, and consequently all users of our later releases, to hear about failures. We welcome suggestions of any kind. Please be as specific as you can in telling us about your results and your problems. We will be happy to include the results of your "validation runs", with appropriate citation to you, in our printed materials. We are especially interested in maintaining a list of users, so that we can quickly communicate changes, problems, and updates. Since our ftp daemon does not record actual usernames, we request that those who are considering use of the mechanism send us their e-mail addresses. Please address them to SMITH@MPLVAX.SRI.COM. 4. HOW TO CONTACT THE AUTHORS We can be reached at any of the addresses given below. Bob Serauskas at GRI is the Program Manager of this project. If you have an official question, he is the person to contact. Bob's phone number is 312-399-8208, his mailing address is c/o Gas Research Institute, 8600 West Bryn Mawr Avenue, Chicago, Illinois 60631-3562, his Internet address is rserausk@gri.org, and his fax number is 312-399-8170. For scientific questions please contact Greg Smith or one of the other authors listed below: University of California, Berkeley: Michael Frenklach (myf@euler.berkeley.edu) Mikhail Goldenberg (mgold@euler.berkeley.edu) Stanford University: Tom Bowman (bowman@navier.stanford.edu) SRI International: Greg Smith (smith@mplvax.sri.com) University of Texas at Austin: Bill Gardiner (bill@lioness.cm.utexas.edu) Vitaly Lissianski (vitaly@lioness.cm.utexas.edu) To cite GRI-Mech, please refer to our World Wide Web location or to our 1994 Combustion Symposium Poster, "An Optimized Kinetics Model for Natural Gas Combustion", by M. Frenklach, H. Wang, C.T. Bowman, R.K. Hanson, G.P. Smith, D.M. Golden, W.C. Gardiner and V. Lissianski, 25th International Symposium on Combustion, Irvine, California, Work-In-Progress Poster Session 3, Number 26. The poster does not describe the nitrogen chemistry in Version 2.11; the World Wide Web location does. 5. SOME CAUTIONARY NOTES First we want to warn you about several general aspects of GRI-Mech. a. PLEASE DO NOT MAKE ANY SUBSTITUTIONS! Or if you MUST so, be very careful. GRI-Mech has been optimized as a whole, and should be used just as you receive it if you want to duplicate its ability to model natural gas combustion and NO formation and removal. You likely will not surpass the performance we obtained for natural gas combustion and NO formation and removal by the independent adjustment of any "sensitive" reaction rate parameters. Any substitution of "better" rate coefficient expressions or removal of species or reactions may lead to your getting significantly deteriorated performance of the mechanism when tested against the whole spectrum of natural gas combustion and NO data. We recognize that GRI-Mech users are human and will adjust rate coefficients or make major changes for specific purposes, such as doing sensitivity analyses. When doing this please keep in mind that we do not claim that GRI-Mech is suitable as a starting point for mechanism development by patchwork means. We cannot predict what the consequences may be. b. NUMBERS OF SPECIES AND REACTIONS. The list of reactions and species in GRI-Mech 2.11 contains entries that are "unimportant" for natural gas combustion and NO formation and removal for the conditions investigated to date. There are several reasons why we have them there. One is that there are special purposes (like models of flame radiation or pollutant emissions) where elementary reactions that are otherwise negligible become important, and we want to have these reactions on hand for such occasions. A second reason is that the combustion of some other fuels (methanol, acetylene, ...) can be modeled using GRI-Mech as a subset, with the knowledge that the part of the mechanism relevant to natural gas has been optimized in the manner described in the documentation for GRI-Mech 1.2. [We have not looked into the performance of the GRI-Mech for any fuels except methane, ethane, hydrogen and carbon monoxide.] There are techniques for reducing reaction and species lists that you may want to use yourself on GRI-Mech 2.11; please see the relevant comments in the version 1.2 documentation. c. Back reactions. We consider all reactions to be reversible, even though it is clear on thermochemical grounds that negligible reverse flux will occur in many reactions. If your modeling program requires explicit inclusion of reverse reactions, GRI-Mech 2.11, as presented in this directory, will require additional calculations to find out which of them are really needed. d. Computer time. The numerous species and reactions in GRI-Mech, some of which really do not need to be included for modeling natural gas combustion and NO formation and removal, increase the demand on computer resources for doing the chemical part of the model by a large factor. We accept this in order to avoid coping with the numerous problems that arise in streamlining such computations. Computer time has not been a problem for us even when using GRI-Mech on small workstations and fast PCs.