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March 26, 2021, 02:52 |
Knock Prediction with G-equation and SAGE
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#1 |
New Member
Join Date: Sep 2019
Posts: 9
Rep Power: 7 |
Hello, everyone!
I ran two cases: 1) Normal combustion case: flame propagation modelled by G-equation 2) Knocking combustion case: G-equation for flame propagation while SAGE for the unburn region with Mach CFL = 3.0 as recommended by CONVERGE training. The pressure rise in the knocking case is vertical. This behaviour cannot be physical. Does anyone have an idea what is the cause of the error? Thank you |
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March 26, 2021, 07:12 |
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#2 | |
Senior Member
Nitesh Attal
Join Date: Sep 2017
Location: Convergent Science, Northville MI
Posts: 113
Rep Power: 9 |
Quote:
1) What does the mean max and min temperatues look like before spark. Check if the ignition dealy at these conditions is so small that it leads to autoignition for the mechanism that you have used. 2) Take a look at the 3D data before and after spark to see if the pressure rise is comming from autoignition of the unburnt charge. Thanks, Nitesh |
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March 26, 2021, 22:01 |
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#3 | |
New Member
Join Date: Sep 2019
Posts: 9
Rep Power: 7 |
Quote:
Thank you for quick reply. 1) Mean and Maximum temperature are same in both cases before spark. 2) Looking at 3D data, there is no autoignition in the unburnt region. The pressure rise due to very fast flame propagation |
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March 29, 2021, 08:14 |
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#4 | |
Senior Member
Nitesh Attal
Join Date: Sep 2017
Location: Convergent Science, Northville MI
Posts: 113
Rep Power: 9 |
Quote:
1) What is the value of the temperature before spark? What is the ignition delay at conditions just prior to spark? 2) Do you have sufficent frequency of 3D data to visualize the sharp pressure rise (to conclude this is not from autoignition in the unburnt region)? 3) Add monitor points around the circumfrence near the head to see if you are experiencing end gas autoignition. Thanks, |
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March 31, 2021, 03:00 |
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#5 | |
New Member
Join Date: Sep 2019
Posts: 9
Rep Power: 7 |
Quote:
1) Temperature before spark is 850K. Ignition delay is 30ms prior to spark 2) I generate 3d data at 0.02CAD. 3) Monitor points do not show any autoignition in end gas |
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March 31, 2021, 10:20 |
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#6 | |
Senior Member
Nitesh Attal
Join Date: Sep 2017
Location: Convergent Science, Northville MI
Posts: 113
Rep Power: 9 |
Quote:
For your engine speed how much does 30ms correspond to in crank angles? From the post files, do you see the flame moving so fast to engulf the charge in the cylinder? If so, can you share the images/movies? If you do not want to post the results here you can write to support@convergecfd.com Best, |
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Tags |
knock, knocking |
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