GTI and ERC Senkin Quick Reference

1. GTI and ERC Senkin Quick Reference Version 04-08-04 This document contains instructions for using Senkin to analyze natural gas combustion in a constant volume combustion facility. Sponsors and Contributors Chol-Bum Kweon and John PratapasGas Technology Institute Randy Hessel and Amar PatelUniversity of Wisconsin-Madison, Engine Research Center

2. Introductory Comments This document is intended to provide a brief description for new users on how to run senkin on a UNIX platform and also to serve as a quick reference for those with experience. senkin is primarily used to perform sensitivity analysis on reactions. Sensitivities to initial pressure, temperature and species concentrations can be done. Reducing complex mechanisms is an important application of senkin. Three main steps are covered in this document. They are running chemkin, running senkin and running senkin’s post-processor, senkin_post. chemkin is run to provide reaction and species information to senkin. senkin, in this application, is run to perform the reaction in a constant volume combustion chamber over the time specified. senkin_post is run to analyze the results from senkin. Having performed all the steps listed, the user can analyze what species are formed and when in a given fuel and oxidizer reaction. Pressure, temperature and time sensitivities on species formed can be investigated and ignition delays can also be estimated.

3. Outline to Setup for chemkin, senkin and senkin_post THESE STEPS SHOULD ONLY HAVE TO BE DONE ONCE. On the following slides, you will be instructed on how to: • Acquire executables of chemkin, senkin and senkin_post for UNIX. • Set up the Environmental Variables for chemkin, senkin and senkin_post. • Locate the senkin-home directory as a sub-directory of your home directory.

4. Acquire executables of chemkin, senkin and senkin_post THIS STEP SHOULD ONLY HAVE TO BE DONE ONCE. • Assuming you have proper permission, the chemkin, senkin and senkin_post executables can be downloaded by clicking on their links. • Place the executables somewhere in your UNIX search path. In this example, we will put them in a sub-directory of your home directory called BIN. • To create the BIN directory, open a UNIX window and from your home directory, entermkdir BIN • Download the executables to the BIN directory (chemkin is called chem). • Make sure the BIN directory is in your path by adding the following line to the .cshrc file, which is located in your home directory.set path = (/pathToYourHomeDirectory/BIN $path)where:pathToYourHomeDirectory must be edited to go from the topmost directory (root directory) to your home directory (ex: /usr/people1/hessel/).$path retains all previous defined paths defined by you, or your system administrator.

5. Set up the Environmental Variables for chemkin, senkin and senkin_post THIS STEP SHOULD ONLY HAVE TO BE DONE ONCE. • The executables have to be able to find certain files. To facilitate this, edit the .cshrc file in your home directory to contain the following lines,setenv CHEMKIN_DIR /usr/erc/people/username/senkin-home/setenv REACTION_DIR /usr/erc/people/username/senkin-home/setenv CHEMKINHOME /usr/erc/people/username/senkin-home/setenv REACTION_LICENSE_FILE/usr/apps1/chemkin36/licenses/chemkin.licsetenv LM_LICENSE_FILE /usr/apps1/chemkin36/licenses/chemkin.licsetenv LM_LICENSE_PATH /usr/apps1/chemkin36/licenses/chemkin.lic • In the above lines, replace username with your log in name. • enter the UNIX command source .cshrcin order to activate the new settings.

6. Locate the senkin-home directory as a sub-directory of your home directory THIS STEP SHOULD ONLY HAVE TO BE DONE ONCE. • The “senkin-home” directory, which was referred to in the ‘setenv’ statements on the previous slide, contains include and license files required for the executables to run. • Please request the “senkin-home.zip” file and extract it from your home directory. • This concludes the general setup for the executables. What remains is learning how to construct input files and run each executable.

7. Outline for Running Senkin for Constant Volume Combustion • Acquire a mechanism file that contains the reactions for your fuel and oxidizer and the thermodynamics data file that contains thermodynamic data for the species involved in the reactions. • Using the above files as inputs to chemkin, run chemkin to generate a chem.asc file, which is used by senkin. • Besides the chem.asc file generated above, you must also provide senkin with things like initial conditions, maximum time step, etc. These are provided through the senkin.inp file, which must be edited for each case. • Run senkin using the chem.asc and senkin.inp files mentioned above. • senkin will produce a file called save.bin, which is used by senkin’s post-processor, senkin_post. senkin_post also requires additional information, which is provided via the input file, senkin_post.inp. • Results from senkin_post can be viewed with a text editor, or pasted into a spreadsheet program for further analysis.

8. Acquiring Mechanism and Thermodynamic Data Files At the ERC, contact Song-Charng Kong for these files for a variety of fuels. For natural gas, follow these instructions: Point your browser to http://me.berkeley.edu/gri_mech/releases.html Click the link for the ‘Current release of GRI_Mech’. Click on the “Getting the Files” link. Click on the grimech(version#).dat and thermo(version#).dat files and download them to the location where you will be running chemkin. Rename grimech(version#).dat to chem.inp and thermo(version#).dat to therm.dat.

9. chemkin I/O and Execution Summary • input files • chem.inpis called the mechanism file and it contains information about the species and reactions being studied. • therm.datcontains thermodynamic data for each species. At a minimum, it must contain data for each specie that takes part in the reaction. • execution • chem < chem.inp > chem.outchem is the executable< tells chemkin to read a file called chem.inp> tells chemkin to write output to a file called chem.out • output files • chem.asccombines chem.inp and therm.dat data and will be read by senkin. It is an ascii version of the cklink files used by chemkin. • chem.outcontains three sections of information, species in the mechanism are listed as are the mechanisms used along with their Arrhenius parameters, and most important, errors are listed at the end of the file.

10. senkin I/O and Execution Summary • input files • chem.ascwas created by chemkin. See previous slide. • senkin.inpcontains initial conditions, problem definition and time specifications. Click on the link to download a sample senkin.inp file. Put the file in the directory where you will be running from. This can be the same directory that you ran chemkin in. Edit the file as needed. Click on the links to see keywords for the sensitivity and problem selection, initial conditions and integration control sections of senkin.inp. • execution (note: currently senkin must be run from erc2000, so ssh to erc2000) • senkin < senkin.inp > senkin.outsenkin is the executable< tells senkin to read a file called senkin.inp> tells senkin to write output to a file called senkin.out • output files • save.binis a file used by the post-processor, senkin_post. • senkin.outcontains a list of all inputs, gives all species mole (or mass) fractions, pressure and temperature at each time step. From this file, species, pressure and temperature histories can be extracted, as well as ignition time.

11. senkin_post I/O and Execution Summary • input files • save.binwas created by senkin. See previous slide. • senkin_post.inpspecifies what information is to be extracted from save.bin. Click on the links to download a sample senkin_post.inp file, or a senkin_post keywords list. • execution • senkin_post < senkin_post.inp > senkin_post.outsenkin_post is the executable< tells senkin_post to read a file called senkin_post.inp> tells senkin_post to write output to a file called senkin_post.out • output files • senkin_post.outoutputs variable values that have been input. • *.csvone .csv file is created for each species. Each file contains information about the specie production and destruction for each reaction in which the specie is involved. Net production/destruction is also recorded. These data can be read into a spreadsheet program to analyze what reactions are contributing to species production/destruction and at what time in the reaction history. Refer to file chem.out for a list of reaction numbers. • senk_sol.csvcontains tabular data that can also be read into a spreadsheet and temperature, pressure and mole (or mass) fractions can be plotted vs. time.

12. Sample senkin_post results from senk_sol.csv Temperature vs Time Pressure vs Time Results are for a specified initial temperature, pressure and species concentration. Mole Fraction vs Time

13. Sample senkin_post results from senk_H2_rate.csv H2 Production Rates vs. Time Results are for a specified initial temperature, pressure and species concentration.

14. Summary Having gone through this document, you should now be able to • specify a reaction of interest and run chemkin to create the reaction and thermodynamic data necessary to solve the problem, • run senkin to solve the reaction, • analyze the reaction results with senkin_post. From this and similar exercises, reaction sensitivities to pressure, temperature, time and even the number of reactions used can be analyzed. This information is of particular importance to better understand how particular species are created and destroyed, and perhaps provide direction on how to increase, or decrease the amount of a particular species by manipulating the environment and time undergone by a reaction.