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Knock Prediction with G-equation and SAGE

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Old   March 26, 2021, 01:52
Default Knock Prediction with G-equation and SAGE
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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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Old   March 26, 2021, 06:12
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Quote:
Originally Posted by man1 View Post
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

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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Old   March 26, 2021, 21:01
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Quote:
Originally Posted by nitesh.attal View Post
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
Hi Nitesh,

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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Old   March 29, 2021, 07:14
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Originally Posted by man1 View Post
Hi Nitesh,

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

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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Old   March 31, 2021, 02:00
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Originally Posted by nitesh.attal View Post
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,
Hi Nitesh,

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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Old   March 31, 2021, 09:20
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Quote:
Originally Posted by man1 View Post
Hi Nitesh,

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

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


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