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: README.DAT This file GRIMECH12.DAT A reaction mechanism and rate coefficient file, in "Chemkin" format THERMO12.DAT A thermochemical data file to be used with GRIMECH12.DAT, as "NASA polynomial" coefficients The files in this directory are products of computational and experimental research sponsored by the Gas Research Institute. It has been carried out at The University of California at Berkeley, Stanford University, 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 and ignition that we are able to provide as of the date at the head of this file. Our ongoing program comprises the development of extensions to include more chemistry, such as NOx and soot, more robust parameterizations, and additional tools and documentation to make working with GRI-Mech more effective. In order to use the input files directly you need the Sandia National Laboratory "Chemkin-II" programs. (See discussion below.) Ignition profiles 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 are using a flame code other than Chemkin, however, because the transport calculation, the numerical method of solving the partial differential equations, and so on, differs 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 University of California at Berkeley, Stanford University, SRI International and The University of Texas at Austin as a result of work 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. Descriptions of the GRI-Mech current release files 2. Instructions for their use 3. A summary of what we can tell you about the performance of the current release 4. A request for feedback on your experiences with the current release 5. A prognosis of future releases and extensions 6. How to get in touch with us 7. Some cautionary notes. 1. WHAT IS GRI-Mech? What follows is a very brief overview of GRI-Mech. A more detailed account, in the form of a hard-copy document, is forthcoming. Send one of us an e-mail or regular mail request to get on the mailing list for this document. We'll send it to you as soon as it is ready. GRI-Mech is essentially a list of elementary chemical reactions and associated rate constant expressions. Most of the reactions listed have been studied one way or another in the laboratory, and so the rate constant parameters mostly have more or less direct measurements behind them. In order to get successive releases out in a timely manner we have not yet prepared a comprehensive document explaining all of the sources of information that were consulted and evaluated, the rate constant theory that went into constructing the set, and the details of each step of the optimization process. We will provide this documentation in the future. Once we have a starting set of rate constant parameters, we undertake extensive sensitivity tests on a variety of experimental data related to natural gas ignition and flames. These tests tell us which of the rate parameters should be considered closely to "tune" the set so as to get an optimum representation of the data. We then go through a long process of simultaneous parameter optimization, most of it done automatically--- i.e., by a computer adjusting the parameters---to get the parameter set of the current release. This is carried out with very strict constraints to keep the rate parameters being optimized within predetermined bounds that we had set on the basis of evaluations of the uncertainties in measurements of the rates of elementary reactions and by applications of conventional gas reaction rate theory. Once the optimum parameter set is found, it is checked against the literature in an extensive "validation round", as described in Section 3 below. While the mechanism file was specifically formatted for use with the Chemkin modeling programs, it can be reformatted readily to serve as input for any kind of program you may happen to have. In order to do this you only need to know (1) that the rate constant parameters for the bimolecular reactions and the limiting forms of the unimolecular reactions are set up in the form k = A T^m exp(-E/RT), with concentration units mol/cm^3; (2) that the "falloff parameters" for unimolecular reactions are the values of a, T***, T** and T* in the formula F_cent = (1-a)exp(-T/T***) + a exp(-T/T*) + exp(-T**/T) which gives the temperature dependence of F_cent, the factor by which the rate constant of a given unimolecular reaction at temperature T and reduced pressure P_r = k_o[M]/k_infinity of 1.0 is less than the value k_infinity/2 which it would have if unimolecular reactions would behave according to the Lindemann formula k_infinity k = __________________________ F 1 + k_infinity/k_0[M] where the "broadening factor" F, which would be 1 for the idealized case, is computed from log(F_cent) log(F) = -------------------------------------------- 1 + [(log P_r + C)/(N - .14{log P_r + C})]^2 and N = 0.75 - 1.27log(F_cent) and C = -0.4 - 0.67 log F_cent. [For more information about how these formulas work, consult pages 22 and 23 of "Chemkin-II: A Fortran Chemical Kinetics Package for the Analysis of Gas Phase Chemical Kinetics", Sandia Report SAND89-8009B UC-706, Reprinted January 1993, by R.J. Kee, F.M. Rupley and J.A. Miller. The person in charge of Chemkin is Fran Rupley, who can be reached via her Internet address fran@sandia.gov. The theory underlying the use of these formulas in combustion chemistry is described by W.C. Gardiner and J. Troe in Chapter 4 of "Combustion Chemistry", Springer-Verlag, New York, 1984.] The low-pressure limit rate constants, and the rate constants of unimolecular reactions that are always near their low- pressure limits for combustion conditions have been assigned "enhanced efficiencies" in Chemkin format; if your program will not handle different efficiencies for different species automatically, then you will have to account for each of the colliders in separate reactions. In addition to reviewing the literature rate constant data we also examined the thermochemistry of all of the free radicals in the mechanism. Some of the thermochemical parameters in GRI-Mech differ from those in the "Sandia data base". For this reason we include a file with all of our thermochemistry in it, represented as the coefficients of "NASA Polynomials". [To find out about NASA polynomials you can consult the report by A. Burcat "Thermochemical Data for Combustion Calculations", Chapter 8 of Combustion Chemistry, W.C. Gardiner, Ed, Springer-Verlag, New York, 1984; or its more recent incarnations, "1994 Ideal Gas Thermodynamic Data for Combustion and Air- Pollution Use", Technion Report TAE 697, December 1993, by A. Burcat and B. McBride, and "Coefficients for Calculating Thermodynamic and Transport Properties of Individual Species", NASA Report TM-4513, by B.J. McBride, S. Gordon and M.A. Reno, October 1993. A. Burcat can be contacted by Internet at aer0201@technio bitnet.] If you use the Sandia data base usually supplied with Chemkin you may get output that is significantly different. For the flame calculations in the optimization and validation process we used the Sandia transport package and database. (R.J. Kee, J. Warnatz and J.A. Miller, Sandia Report SAND83-8209) We have changed the symbol CH2* used for singlet methylene in the previous version, GRI-Mech 1.1, to the ones labeled CH2(S), as in the original Sandia notation. 2. HOW TO USE GRI-Mech The easiest way to learn how to set up GRI-Mech for combustion modeling is to just do it! If you have Chemkin up and running, and have tested it using the sample files provided with the Chemkin distribution, all you need to do is substitute the GRI-Mech input files for the Chemkin samples. Whatever worked for you to make the Chemkin sample files run will also run the GRI-Mech files. 3. PERFORMANCE THAT WE KNOW ABOUT We have tested the performance of GRI-Mech extensively. In general we found that GRI-Mech 1.2 performs similarly or slightly better than its predecessor, GRI-Mech 1.1, at conditions intended: shock-tube ignition and laminar premixed flames of methane. For some conditions removed from those, we found that GRI-Mech 1.2 has some notable disagreement with experiment; for example: calculated low-temperature high-pressure oxidation rates of methane are faster than experiment by about 20-30 %; calculated low-temperature, high-pressure oxidation rates of CO are faster than experiment; ignition delay for CH2O are underpredicted by a factor 2; and laminar flame speeds of ethane are overpredicted by 10 %. Below is a summary of some of the validation checks that were made, by us and others. A. Ignition Delays Asaba, T., Gardiner, W.C. Jr., and Stubbeman, R.F., 10th Symposium (International) on Combustion, p. 295 (1965). Ignition delays in H2-O2-Ar mixtures. Burcat, A., Crossley, R.W., and Scheller, K. Combust. Flame 18, 115 (1972). Ignition delays in 2% C2H6 - 7% O2 mixtures. Cheng, R.K. and Oppenheim, A.K. CF 58,125-139 (1984). Ignition delays in H2-O2-Ar mixtures. Crossley, R.W., Dorko, E.A., Scheller, K., and Burcat, A., Combust. Flame 19, 373 (1972). Ignition delays in CH4-C2H6 mixtures. Dean, A. M., Johnson, R. L., and Steiner, D. C., Combust. Flame (37), 41, 1980. CH2O-O2-Ar and CH2O-CO-O2-Ar ignition delays. Frenklach, M. and Bornside, D.E., Combust. Flame 56, 1 (1984). Ignition delays in a 9.5% CH4 - 19.0% O2 - Ar mixture. Gardiner, W.C. Jr., McFarland, M., Morinaga, K., Takeyama, T., and Walker, B.F. J. Phys. Chem. 75,1504-1509 (1971). Ignition delays in H2-O2-CO-Ar mixtures. Hidaka, Y., Gardiner, W.C., and Eubank, C.S. J. of Mol. Sci. (China) 2,141-153 (1982). Ignition delays in C2H6-O2-Ar mixtures. Lifshitz, A., Scheller, K., Burcat, A., and Skinner, G.B., Combust. Flame 16, 311 (1971). Ignition delays in several CH4-O2-Ar mixtures. Seery, D.J. and Bowman, C.T., Combust. Flame 14, 37 (1970). Ignition delays in several CH4-O2-Ar mixtures. Slack, M. and Grillo, A., Grumman Research Department Report RE-537, Investigation of Hydrogen-Air Ignition Sensitized by Nitric Oxide and by Nitrogen Dioxide, 1977. H2-Air ignition delays. Snyder, A.D., Robertson, J., Zanders, D.L., and Skinner, G.B., Technical Report AFAPL-TR-65-93, Shock Tube Studies of Fuel-Air Ignition Characteristics, 1965. H2-Air ignition delays. Spadaccini, L.J. and Colket, M.B., III, Prog. Energy Combust. Sci., to be published. Ignition delays in CH4-O2 and CH4-C2H6-O2 mixtures. Takahashi, K., Inomata, T., Moriwaki, T., and Okazaki, S. Bull. Chem. Soc. Jpn. 62,2138-2145 (1989). Ignition delays in C2H6-O2-Ar mixtures. Tsuboi, T. and Wagner, H.Gg., 15th Symposium (International) on Combustion, p.883 (1974). Ignition delays in 0.2% CH4 - 2% O2 shock waves. B. Species Profiles in Shock-Tube Ignition Experiments Chang, A.Y., Davidson, D.F., DiRosa, M., Hanson, R.K., and Bowman, C.T., Shock Tube Experiments for Development and Validation of Kinetic Models of Hydrocarbon Oxidation, Work-in-Progress Poster 3-23, 25th Combustion Symposium. CH3 and OH profiles in CH2-O2-Ar, C2H6-O2-Ar and CH4-C2H6-O2-Ar mixtures Tsuboi, T. and Wagner, H.Gg., 15th Symposium (International) on Combustion, p.883 (1974). CH3 profiles in 0.2% CH4, 2% O2 shock waves. Yu, C.-L., Wang, C., and Frenklach, M., unpublished. OH and CO profiles in a series of CH4-O2 mixtures. C. Laminar Flame Speeds Egolfopoulos, F.N., Zhu, D.L., and Law, C.K., Twenty-third Symposium (International) on Combustion, p.471,1990. Laminar flame speeds at 1 atm in C2H6-air mixtures. Just, Th., personal communication. Laminar flame speeds of methane at 1, 5, and 20 atm, phi=0.75-1.25, at different cold-gas temperatures. Laminar flame speeds of methane at phi=1 and a range of pressures from 0.25 to 20 atm. The sources are: Egolfopoulos F.N., Cho, P., and Law, C.K., Combust. Flame 76, 375 (1989). Garforth, A.M. and Rallis, C.J., Combust. Flame 31, 53 (1978). Babkin, V.S., Kozachenko, L.S., and Kuznetsov, I.L., Zh. Prikl. Mekhan. Tekn. Fiz. 145 (1964); Babkin, V.S. and Kozachenko, L.S., Combust. Explosion and Shock Waves 2(3), 46 (1966); Babkin, V.S., V'yun, A.V. and Kozachenko, L.S., Combust. Explosion and Shock Waves 2(2), 32 (1966). Andrews, G.E. and Bradley, D., Combust. Flame 19, 275 (1972). Lijima, T. and Takeno, T., Combust. Flame 65, 35 (1986). Laminar flame speeds at 1 atm in H2-air mixtures. The sources are: Dowdy, D.R., Smith, D.B., Taylor, S.C., and Williams, A., Twenty-third Symposium (International) on Combustion, 325, 1990. Edmondson, H. and Heap, M.P., Combust. Flame, 16, 161 (1971). Egolfopoulos, F.N. and Law, C.K., Twenty-third Symposium (International) on Combustion, 333, 1990. (corrected in Vagelopouplos et al., 1994) Gunther, R. and Janish, G., Combust. Flame, 19, 49 (1972). Koroll, G.W., Kumar, R.K. and Bowles, E.M., Combust. Flame 94, 330 (1993) Liu, D.S. and MacFarlane, Combust. Flame, 49, 59 (1983). Scholte, T.G. and Vaags, D.B., Combust. Flame, 2, 495 (1959). McLean, I.C., Smith, D.B., and Taylor, S.B., Combust. Flame, in press, 1994. Laminar flame speeds at 1 atm in CO-H2, phi = 1.0 and 1.7. Vagelopoulas C.M., Egolfopoulos F.N., and Law, C.K., Paper 25-303, Presented at the 25th Symposium (International) on Combustion, 1994 Laminar flame speeds of methane at 1 atm, phi=0.4-1.7, with three bath gases: Ar, N2, and CO2. D. Laminar Flame Species Profiles Bernstein, J.S., Fein, A., Choi, J.B., Cool, T.A., Sousa, R.C., Howard, S.L., Locke, R.J., and Miziolek, A.W., Combust. Flame 82, 85 (1993). OH, CH, H, O, CO, CH3, and HCO profiles in a 20 torr CH4-O2-Ar flame. Fleming, J.W., Burton, K.A., and Ladouceur, H.D., Chem. Phys. Lett. 175, 395 (1990). OH and CH profiles in a 10 torr CH4-O2 flame. Heard, D.E., Jeffries, J.B., Smith, G.P., and Crosley, D.R., Combust. Flame 88, 137 (1922). OH, CH, and H profiles in a 30 torr CH4-air flame. Williams, B.A. and Fleming, J.W., Combust. Flame 98, 93 (1994). OH and CH profiles in a 10 torr CH4-O2-Ar flame. E. Flow Reactor Experiments Hunter, T.B, Ph.D. Thesis, Pennsylvania State University, 1994; Hunter, T.B., Wang, H., Litzinger, T.A., and Frenklach, M. Combust. Flame 97:201 (1994). The experimental data on methane combustion were obtained in the Penn State High Pressure Optically Accessible Flow Reactor facility. The calculations were performed by Thomas B. Hunter, Sandia National Laboratories, P.O.Box 969, MS 9052, Livermore, CA 94550-0969. E-mail: hunter@california.sandia.gov Kim, T. J., Yetter, R. A. and Dryer, F. L., Paper 25-240, 25th Combustion Symposium, 1994. A flow reator study of moist CO oxidation at moderate temperatures and pressures from 1-10 atmospheres. Kristensen, P.G., Glarborg, P., and Dam-Johansen, unpublished data. A 9-mm quartz flow reactor study of methane oxidation; the initial conditions are: [CH4]=1473 ppm, [O2]=2996 ppm, [H2O]=0.019, N2 carrier, P=1.07 atm, residence time=127/T (T in K, constant mass flow). The calculations were performed by Peter Glarborg, Department of ChemicalEngineering, Technical University of Denmark, Bldg. 229, DK-2800, Lyngby, Denmark. E-mail: ketpg294@vm.uni-c.dk 4. PLEASE TELL US WHAT YOU LEARN, AND ABOUT YOUR PROBLEMS While the authors are continuing to expand their understanding of how GRI-Mech works in their own labs, 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. It will make us feel good to hear about successful applications of GRI-Mech, but 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 mail to SMITH@MPLVAX.SRI.COM. 5. CURRENT AND FUTURE EXTENSIONS OF GRI-Mech The current release of GRI-Mech is 1.2. This version improves on Release 1.1 in the following ways: --the nominal rate coefficients for two reactions, H + O2 --> OH + O and CH3 + H (+M) --> CH4 (+M), were updated; --the optimization variable for reaction CH3 + H (+M) --> CH4 (+M) was switched from an averall multiplier (used in GRI-Mech 1.1) to a multiplier for the low-pressure limit rate coefficient only; --the list of optimization targets was substantially expanded. We plan to deliver Release 2.1, which will include the basic NOx chemistry pertinent to natural gas flames, in the Spring of 1995. In future releases of GRI-Mech the following extensions will be made. Addition of low-temperature methane oxidation chemistry Addition of soot chemistry In addition, we will be doing our best to improve the modeling accuracy, the robustness of extrapolations to conditions where measurements are difficult, and so on, and to explain, by repeating experiments in our own laboratories, disagreements with the literature that we have found or will find in the future. Thus, we will be doing new optimizations and producing improved GRI-Mech releases periodically. 6. 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 our project, so if you have an official question, he is the person to contact. His 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 Dave Golden golden@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, for the time being please refer to our 1994 Combustion Symposium Poster, "An Optimized Kinetics Model for 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. 7. SOME CAUTIONARY NOTES We want to warn you about several important 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 get it if you want to duplicate its ability to model natural gas combustion on your machine. You will not surpass the performance we obtained for natural gas combustion by adjusting any "sensitive" reaction rate constant expressions. Any substitution of "better" rate constant expressions or removal of species or reactions will put you at risk of getting significantly deteriorated performance of the mechanism when tested against the whole spectrum of natural gas combustion data. We recognize that users will be adjusting rate constants anyhow, or making major changes for specific purposes, like doing sensitivity analyses of one kind or another. But, keep in mind that we are not claiming that GRI-Mech is a starting point for further mechanism building by patchwork means. You can use it that way if you like, but we cannot predict what the consequences may be. b. Numbers of species and reactions. The list of reactions and species in GRI-Mech contains numerous entries that are "unimportant" for natural gas combustion. There are several reasons why we have them there anyway. One is that there are special purposes (like models of flame radiation or ionization) where elementary reactions that are otherwise negligible become very important, and we want to have these reactions on hand for occasions where somebody is checking these aspects. 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 above. [We have NOT checked into the performance of the mechanism for any fuels except methane, ethane, hydrogen and carbon monoxide.] In future releases of GRI-Mech, we will offer some shorter versions that are optimized for natural gas combustion alone. There are techniques for shortening reaction and species lists that you may want to use yourself on GRI-Mech---for example, the "detailed reduction" method described by H. Wang and M. Frenklach, Combust. Flame 87, 365 (1991). We can help you on an individual basis to produce such reduced mechanisms. (Check periodically with our GRI-Mech Mosaic Home Page---http://diesel.fsc.psu.edu/~gri_mech--- for new information on this.) 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, as presented in this directory, will require additional calculations to find out which of them are really needed. Some day we will provide a "reversal tool" for automatic conversion of rate constant expressions to their respective reverse reaction expressions. d. Computer time. The numerous species and reactions in GRI-Mech which really do not need to be included for modeling natural gas combustion 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. If you are using an older PC, then you may encounter longer integration times than you want to live with. We are thinking about ways to deal with this.