[liang11]

Hello, everyone. I am at the very beginning of learning Converge, and I have some questions.
1) If some other diluents, like argon, CO2, and H2O, are added to the intake, are there something should be noticed? like the global transport parameters and gas transport data.

2) Similar fixed embedding around spark plug and AMR are actived according to the example in Converge 2.4, but there are still some recovers during the spark ignition and combustion time, with the maximum Num_Recovers of 3. Is this mean non-convergence?

3) Around the exhaust valve open, the time step dt sharply decrease to 1e-07. How can I accrelerate this process?
In addition, if the mimnum time step is set as 4e-06, this proccess is accelerated, but cause no recover. I don't understand how it work.

4)About dynamic mechanism reduction, What is the difference between the species added in the 'main' folder and the species added in the 'species' folder.
If temp is added in the 'main' folder like the 2.4 manual, there is a case issue, but simulation can still be poceeded. How can I add the temp properly?

5)The frequency of band pass filter is 5kHZ-40kHZ, and 40 kHZ correspond to 25 us. Why the maximum Mach CFL need to be lower than 3 to capture pressure oscillation?
If the maximum Mach CFL is set 3 during combusiton, time step in my case is around 1e-07, which is much lower than 25 us. So, I don't understrand.


Thank you very much!

[Kamlesh Patel]

Hello,

Please see my responses below:

1) If some other diluents, like argon, CO2, and H2O, are added to the intake, are there something should be noticed? like the global transport parameters and gas transport data.
--You can use transport.dat if it is available or you can use the gas.dat values for air available with our engine example cases.

2) Similar fixed embedding around spark plug and AMR are actived according to the example in Converge 2.4, but there are still some recovers during the spark ignition and combustion time, with the maximum Num_Recovers of 3. Is this mean non-convergence?
--A few recoveries are okay in the simulation. However, you need to check the inputs if you see recoveries in excess.

3) Around the exhaust valve open, the time step dt sharply decreases to 1e-07. How can I accelerate this process?
In addition, if the minimum time step is set as 4e-06, this process is accelerated, but cause no recover. I don't understand how it work.
--Please check if the minimum valve lift is set properly and if you are using the correct grid setting for exhaust valve angle and intake valve angle. Also try using a region based temporally varying max_cfl_u. Please refer to our SI8 PFI engine example case setup for recommended grid settings and region based temporally varying max_cfl_u profile.

4)About dynamic mechanism reduction, What is the difference between the species added in the 'main' folder and the species added in the 'species' folder.
If temp is added in the 'main' folder like the 2.4 manual, there is a case issue, but simulation can still be poceeded. How can I add the temp properly?
--In main species we typically add fuel, radical and product species. In the Species tab, we select the species to save. Since dynamic mechanism reduction automatically removes species based on local thermo-chemical conditions, you may lose species that are important to your simulation such as soot precursors for emissions modeling. Regarding the inclusion of Temp, could you please share the error/warning message?

5)The frequency of band pass filter is 5kHZ-40kHZ, and 40 kHZ corresponds to 25 ms. Why the maximum Mach CFL need to be lower than 3 to capture pressure oscillation?
If the maximum Mach CFL is set 3 during combustion, time step in my case is around 1e-07, which is much lower than 25 ms. So, I don't understand.
* -- Due to the cell pairing criterion, the cut-cells at the boundaries are a minimum of 30% of the local full cell size. CONVERGE does not need to fully resolve the pressure waves at the boundary cut-cells. So setting the maximum Mach CFL limit to 3 helps us to fully resolve the propagating pressure waves within the domain. For more information, refer AdvancedICE-EngineKnock lecture slide from CONVERGE hub for more details.
*

6)A case have been run by two times, but there is a little difference around the maximum in-cylinder pressure. The difference is similar with that of the case being run with/without map.dat. Why?
--I am sorry that I didn't understand your question well. Could you please elaborate?

[liang11]

Dear Kamlesh,

Thanks for your reply. I really appreciate your help.

1) If the gas transport data need to be modified according to the intake in my case, how can I make it right?
Also, what is the difference between gas transport data and global transport parameters?

2) There are many times of recovers during spark ignition, even with the Num_Recovers of 1.

3)The minimum valve lift is 0.2 mm, and fixed embedding is set around both intake valve angle and exhaust valve angle, which is similar to SI8 PFI engine example.
I will try to use a region based maximum convection CFL later.

4) Does 'Species to save' mean DMR will not affect these species?
The issue is "[trag_species]->DMR: No species name 'TEMP' found within available list"

5) How can I get the lecture slide?

6) Sorry, maybe I make a mistake during the re-calculation on the same case setup.

Thank you again!

[liang11]

Dear Kamlesh,

I have another question. I have run one case twice with different maximum Mach CFL. One corresponds to a maximum Mach CFL of 50, the other is 3.
However, the maximum in-cylinder pressure and combustion phase are totally different, just as the picture in the attachment. The change of TKE of this two calacualtions are similar.
How to keep the mean in-cylinder presure unchange?

Thank you very much!