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Question about fixed embedding around spark-plug

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Old   March 30, 2022, 05:31
Post Question about fixed embedding around spark-plug
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shanghua chen
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Hi all,

I start to wonder a 'how' and 'why' the fixed embedding around spark-plug need to be. Please check the attached pictures snipped from Converge examples. It is a GDI model with SAGE.

Q1: as observed from the attached pictures, SA=16.0, why do both fixed embedding have to end before reaching TDC? Is there any explanation or reference for it?

Q2: if the spark-timing is closing to TDC (let's say SA=-2.9), how to define this fixed embedding duration?

Q3: is there any relationship between ignition lag and this spark-plug fixed embedding?


Thank you very much!
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Old   March 30, 2022, 15:52
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Kislaya Srivastava
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Hello Shanghua,

Q1. TDC does not factor in when setting our spark embedding timings. Start and End of spark embedding is recommended to be a few CAs before and after spark resp. Please refer our example cases for an idea on when to turn on and off spark embedding.

Q2. You start your spark embedding a few CAs before start of spark (as specified in source.in). This allows you to capture a good flow field around the spark before ignition. Similarly, you end the spark embedding a few CAs after end of spark (as specified in source.in). If you remove spark embedding right at the end of spark, the initial flame kernel can get smeared out due to the coarser cells and you might not see (proper) combustion. By keeping the embedding active after end of spark, you are able to capture a good initial flame kernel development. After a while, AMR kicks in as the kernel grows and you no longer need this embedding.

Q3. Adequate refinement is critical for initial flame kernel development. We typically recommend 0.125mm cell sizes around spark plug or 5-10 cells across spark gap, for most SI engine cases.

Hope this helps.

Sincerely,
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Old   March 30, 2022, 20:52
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Quote:
Originally Posted by ksrivast View Post
Hello Shanghua,

Q1. TDC does not factor in when setting our spark embedding timings. Start and End of spark embedding is recommended to be a few CAs before and after spark resp. Please refer our example cases for an idea on when to turn on and off spark embedding.

Q2. You start your spark embedding a few CAs before start of spark (as specified in source.in). This allows you to capture a good flow field around the spark before ignition. Similarly, you end the spark embedding a few CAs after end of spark (as specified in source.in). If you remove spark embedding right at the end of spark, the initial flame kernel can get smeared out due to the coarser cells and you might not see (proper) combustion. By keeping the embedding active after end of spark, you are able to capture a good initial flame kernel development. After a while, AMR kicks in as the kernel grows and you no longer need this embedding.

Q3. Adequate refinement is critical for initial flame kernel development. We typically recommend 0.125mm cell sizes around spark plug or 5-10 cells across spark gap, for most SI engine cases.

Hope this helps.

Sincerely,

Thank you Kislaya. I will try this out.
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