************************************** Instruction for Princeton-ChemRC ***************************

Transcription

1 ************************************** Instruction for Princeton-ChemRC *************************** Any questions, please contact with Wenting Sun or Yiguang Ju at Princeton University ), Feedbacks and questions are appreciated. A: Function: Princeton-ChemRC is an open software developed originally at Princeton in for generating a comprehensively reduced mechanism automatically by using the multi-generation Path Flux Analysis (PFA) method. B: Software strucutre: Princeton-ChemRC has the functions of Senkin, PSR, PFA, ARRC, and tools to remove selected species from a chemical kinetic mechanism and to generate a reduced mechanism. C: References: To use this code, the users need to refer the following website and three pulbications: Wenting Sun, Zheng Chen, Xiaolong Gou, Yiguang Ju, A Path Flux Analysis Method for the Reduction of Detailed Chemical Kinetic Mechanisms, 157(2010), No.7, Xiaolong Gou, Wenting Sun, Zheng Chen, Yiguang Ju, A Dynamic Multi-Timescale Method for Combustion Modeling with Detailed and Reduced Chemical Kinetic Mechanisms, Combustion and flames, 157(2010), No.6, Tianfeng Lu, Yiguang Ju, C.K. Law, Complex CSP for chemistry reduction and analysis, Combustion and flames, 126(2001), No.1-2, (if ACRC is used) D: Instruction: Step 1: download Princeton-ChemRC at and unzip it. Step 2: prepare your mechanism which needs to be reduced. 1. You need to interpret the mechanism (generate the binary file of chem.inp). If you know how to do it, you can skip this step and go to step 3 directly. 2. If you don t know how to do this, follow the following instruction 3. Copy your mechanism files (chem.inp, and/or therm.dat) to folder \Princeton-ChemRC\test 4. Download mechanism interpreter from and unzip it. Run Chemtran.exe

2 Input files Output files Select the path of related input and output files as \Princeton-ChemRC\test. Notes for Chemtran.exe: please be sure to choose the right path for your mechanism files. Then press ChemBin button to generate the binary files. (The capability of the software to generate binary files is around 1000 species, no limitations for other software. Mechanism reduction doesn t require transport properties.) 5. Check the chem.out file to make sure there is no error message. Step 3: generate your own reduced mechanism 1. Run Princeton-ChemRC.exe at \Princeton-ChemRC\Bin\ and set the working folder as \Princeton-ChemRC\test, and open the chem.inp in that folder. 2. Generate the database for mechanism reduction. (database are generated by using Senkin and PSR, the conditions are the conditions at which the reduced mechanism will be applied, such as pressure, temperature, equivalence ratios.)

3 a. Set the mixture.inp as the example, the input numbers are mole fractions (which will determine the equivalence ratio). The species names must be identical as the name used in chem.out. See the example at \Princeton-ChemRC\test\mixture.inp. You can have several mixture.inp files, which may be fuel lean, fuel rich and stoichiometric case. b. Run Senkin. Save the file as test1.asc. You will see as Useless part Input file for compositions Input pressures, and temperatures for Senkin (ignitions) Then, press make button. Senkin is done. Notes: each time, you can only run one equivalence ratio which is determined in the mixture.inp, but several pressures and

4 initial temperatures. Save all the data (test1.asc, test2.asc, test3.asc ) you generated for later use. c. Run PSR. PSR is very similar to Senkin. Set mixture.inp, pressures and temperatures, then press the make button. d. Combine all the data you generated. Combine test1.asc, test2.asc, test3.asc and rename to libdata.asc. When you combine the two files, please delete the title part from one file (see the following pictures), then copy all the rest content to the other files. Please add a letter E at the end of the file (see the example in the folder \Princeton-ChemRC\test\libdata.ASC). Delete before combination e. Run PFA Set Selection.dat. The first lines shows the important species numbers in chem.out you already know (generally, just fuel and air, 1, 2 and 71 are N2, O2 and C10H22 in the chem.out). The second number (0.3) is the threshold value or interaction coefficient. Check the PFA paper for the definition if you are interested. The larger the threshold value, the smaller the reduced mechanism.

5 Then, run PFA under the menu CutSp. After finished, run New Mechanism under the menu CutSp. Open chem.inp at folder \Princeton-ChemRC\test\. Then, go to operation - Delete Species # list. Open FORTRIM.TXT. Then go to the button Creat New inp file. Then press the button New inp file. Save the new.inp file. That s the reduced mechanism you generated. It s done!

6 Step 4: Before you use the reduced mechanism, be sure to validate the reduced mechanism. The way to do that is to run Senkin and PSR for the reduced mechanism and compare the results with the detailed mechanism, such as ignition delay times. Some notes: if the detailed mechanism is huge, it takes long time to run Senkin and PSR. Be patient. You may also need to run PFA (only first generation).exe at the folder \Princeton-ChemRC\test\ to generate a smaller mechanism and then do the same thing for the smaller mechanism by considering more generations.

7 Selected Q&A Q ( ): Generally speaking, you don t need to change any values. Because both SENKIN and PSR problems are homogeneous problems, the only parameter is the time step to do integration and the parameters are already set for the software. In some extreme case, the parameters in SENKIN or PSR need to be changed, for example, a case with extreme long ignition delay (e.g, 2 hours), you have to adjust the integration time to be longer than 2 hours. Otherwise, you don t need to worry the parameter in senikn.tpl and psr.tpl. Q( ): Q: So, can I conclude that all settings (in senkin.tpl and psr.tpl ), except from the time step, have no effect in the calculations? You are right. No effects. Q: I use n-decane (C10H22) as a fuel. Consequently, I changed everything to C10H22. In senkin.tpl for instance, there was a REAC C6H5CH , which seems to be wrong in my case. Was the change to C10H22 correct or was it still unnecessary? This is an acute question. It s unnecessary. That part REAC C6H5CH doesn t affect anything (I have to say sorry about this confusion. Q: In psr.tpl no fuel is included at all (!/REAC h2 4.0 is uncommented). Is this done on purpose? Shouldn t there be C10H22 in psr.tpl, too? The answer of this question is the same as the above one. It s unnecessary to change this part because it doesn t affect anything. You already specified your mixture (fuel and oxidizer) in mixture.inp. Q: What is the meaning of TAU in psr.tpl and in psr.inp? It looks like TAU would be the (absolute) time or the end time; it continuously increases, when I check the file PSRLIB.ASC (third column). I am really confused about TAU and TIME in the TPLs and about Tau (third column) in the two ASCs. There seems to be an inconsistency with the naming or the meaning of TAU/Tau. TAU in psr.tpl is the end time (or the longest possible residence time), and the Tau in PSRLIB.ASC is the residence time (from 0 to TAU you defined in psr.tpl ). These definitions of parameters are exactly the same with the CHEMKIN -SENKIN and PSR. And the software ACRC2001a.exe is just integration of the two codes (SENKIN and PSR in FORTRAN version) with modified output.

8 Q: I assume that the settings (values) in the two routines Make Senkin Lib and Make PSR Lib need to be identical. E.g. in Make Senkin Lib the Initial Temperature is set by default to 1000., 1200., 1500., ; in Make PSR Lib the Initial Temperature is set by default to only As I understand the context, the values should be identical (considering that the two generated files are copied together into one single file). - So, is the assumption correct that the settings ( Phi Value, Initial Pressure, Initial Temperature, etc.) in both routines need to be identical? Wouldn't the combination of SENLIB.ASC and PSRLIB.ASC in libdata.asc lead to nonsense if the settings are not absolutely identical? - In this context, I noticed that it is tricky to change the Initial Temperature in Make PSR Lib. The program wants to keep the pre-set (i.e. uses only 300 when running), regardless if I change the value. Is this done on purpose? What would be the reason for it? They don t need to be the same. SENKIN and PSR are two different problems, one for ignition and one for extinction. For SENKIN, the initial temperature must be high (such as 1000 K) to introduce the ignition. For PSR, 300 K is just the inlet flow temperature which doesn t affect the results much, then the inlet flow mixed with the productions of the combustion (based on the model of Perfect Stirred Reactor). Combination of the two data base is just for considering the two problems together simply. Of course you can use different Phi values for the two cases, and combine the results at the end. When we do mechanism reduction, we have to be a little conservative to allow the reduced mechanism having wider working conditions than you really need. We consider both ignition and extinction which allow us to capture the major chemistry in the whole combustion process. If you need to mechanism to simulate a extinction phenomena, you can pick up more species by lower the threshold value in the PSR problem. Q: What combustion modeling do you use in Senkin? As I see it, you basically use a Perfectly Stirred Reactor (constant volume) in the first step with Senkin, too. Is this correct? In Senkin, the mode is homogeneous mixture with constant pressure. Given the initial temperature, the temperature of the mixture will increase gradually until ignition happened (it s also a adiabatic problem, so ignition always happens). (there are several ways to define ignition, we use 400 K temperature increase here.) PSR is used for the extinction at e.g. 300K. Is the extinction generated solely by lowering the temperature or in addition by decreasing the Phi value? By lowering the temperature. Phi is specified in the mixture.inp and will not change.

9 Let s assume an example: I choose a Phi of 0.5, 1.0, 1.5 for the Senkin step. Shouldn t I choose the same for the PSR step? Looking at the settings in psr.tpl (no fuel at all), it seems to me that the Phi value is without any meaning for the PSR. In this case, extinction would be caused by lower temperature and decreasing Phi at the same time. Is this assumption correct? The Phi values you chosen on the GUI don t work because you already specified the Phi in the mixture.inp. This part doesn t work if you use Custom mixture Q: Looking at the ASC files SENLIB.ASC and PSR.ASC, I do not understand the meaning of the species. What is it? (Net) Production rate, mass fraction, molar fraction? Is it summed over all reactions a particular species is part of? I my case, C10H22 stays almost constant. Nothing happens to it. Can that be correct? The unit of the species is moles/cm 3 (the same units used in Senkin - a popular fortran code in combustion society) C10H22 couldn t be constant, please make sure in the mixture.inp, n-decane should be expressed as C10H22 which must be the same with the name in chem.out, other than NC10H22. I just checked, when I upload the software, the input files are all NC10H22 which was used in other mechanisms, please change it back to C10H22.

10 Q: When using the option Custom Mixture, what values need to be set in the file mixture.inp? Are the values to be set for a stoichiometric mixture? If so, how can I make sure that the parameter Phi is varied according to my specifications? Can you confirm that Phi is really varied, when using the option Custom Mixture? I use Custom Mixture in order to include relative humidity. It should be possible to proceed this way, shouldn't it? In the mixture.inp, you can set any compositions for your use. Generally, I use 3 mixture.inp, one fuel lean, one fuel rich and one stoichiometric. When you change the composition in the mixture.inp, the Phi value will change automatically even though the output file didn t show that change. Q: What happens with the values specified in the GUI. There I also can set Phi values. Which Phi values are taken for the calculation? As I mentioned above, this part on GUI doesn t work. Q: What is the meaning of the option Include Middle Branch? It is not really clear to me. What are the effects of activating or not activating this option? Middle Branch is the middle branch in S curve in combustion. It s physically non-stable and can t be observed experimentally, but numerically, you can calculate it. By considering the middle branch, which allow us to reproduce the extinction phenomena more adequately. Q: If I select e.g. C10H22 in the GUI, all the other fuel species remain in senkin.inp. Is this correct? I deleted those species manually. If you use Custom Mixture, the selection on GUI doesn t work. When you run the code, the senkin.inp will be updated automatically. So you don t need to delete those species. Q: Is my understanding correct that senin.inp is a temporary file that keeps the actual settings for every time step? The settings themselves are taken from the GUI. Yes, it s right.