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Old   February 4, 2020, 02:38
Post Abnormal Combustion
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Hemant Kumar Thakur
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I am doing simulation on 4-stroke( -360 CAD to 360 CAD ) gasoline direct-injection engine. The combustion from simulation comes out to be abnormal.The mass burn fraction from simulation is not matching with experimental data. The problem is CA50 location for simulation is 49 CAD after TDC of compression and experiment its 9 CAD after TDC of compression. The mixture is taking too much time to burn. Any suggestion regarding this. For convenience, I attached a graph of mass burn fracion Capture.PNG
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Old   February 4, 2020, 07:49
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Hello Hemant,


Thank you for reaching out. GDI engines can be susceptible to cycle-to-cyle variation which CONVERGE is capable to predict [1-2]. We recommend you ignore the results of 1st cycle to eliminate the effect of initial conditions. Note that some engines may require more that 1 cycle to do so.

How many cycles have you ran this case?

Is the equivalence ratio (mixing_region**.out) consistent with the experiment?

Does your engine show cycle-to-cycle variation?







[1] Probst, D. M., Wijeyakulasuriya, S., Pomraning, E., Kodavasal, J., Scarcelli, R., & Som, S. (2020). Predicting Cycle-to-Cycle Variation With Concurrent Cycles in a Gasoline Direct Injected Engine With Large Eddy Simulations. Journal of Energy Resources Technology, 142(4).

[2] Attal, N (2017). Accelerating URANS Cycle-To-Cycle Variation Studies Via Parallel Perturbuation Method. CONVERGE User Conference. https://api.convergecfd.com/wp-conte...oads/Attal.pdf




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Originally Posted by Hemant Thakur View Post
I am doing simulation on 4-stroke( -360 CAD to 360 CAD ) gasoline direct-injection engine. The combustion from simulation comes out to be abnormal.The mass burn fraction from simulation is not matching with experimental data. The problem is CA50 location for simulation is 49 CAD after TDC of compression and experiment its 9 CAD after TDC of compression. The mixture is taking too much time to burn. Any suggestion regarding this. For convenience, I attached a graph of mass burn fracion Attachment 74558
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Old   February 4, 2020, 07:52
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Check your basics,

Engine speed, and engine geometry, compression ratio etc. (I know it may seem simple, but mistakes happen)
Then air mass, fuel mass, fuel pressure.

Best to tick box of all those then reassess
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Old   March 2, 2020, 23:07
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Dear sir


Equivalence ratio is correct based on the quantity of air inflow in (boundary region flow. out) and fuel injected (We didn't calculate based on trapped mass).



Compression ratio and geometry are correct. We are seeing exceptionally slow burn duration. Charge is getting consumed in the later phase of combustion. While in experiment it is really quick as you can see in the graph Mr. Hemant have attached with his question. Can you suggest possible reason for the same.



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Old   March 3, 2020, 17:16
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Hello Jubin,


What is your fuel surrogate?

Did you try correcting for the LHV of the fuel surrogate?
Can you try a different and/or more detailed mechanism?


Feel free to reach out to support@convergecfd.com with your case setup and mention my name as reference if you would like to take this discussion offline.



Thanks,
Nitesh



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Dear sir


Equivalence ratio is correct based on the quantity of air inflow in (boundary region flow. out) and fuel injected (We didn't calculate based on trapped mass).



Compression ratio and geometry are correct. We are seeing exceptionally slow burn duration. Charge is getting consumed in the later phase of combustion. While in experiment it is really quick as you can see in the graph Mr. Hemant have attached with his question. Can you suggest possible reason for the same.



Jubin V Jose
IIT Madras
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Old   March 4, 2020, 00:25
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Dear Sir,
Thank you for the reply we are using iso-octane as surrogate fuel. We haven't tried adjusting LHV and no changes were made on sage mechanism reaction multiplier since we are using gasoline as fuel which is commercially available in India. I will email the case setup to the prescribed email mentioned above.
Thanking you

Hemant
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Old   March 4, 2020, 07:15
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Gasoline is a mix of many hydrocarbons and modeling it as pure iso-octane is an assumption you have made. Does the experimental fuel contain ethanol? You might want to match the RON and HC ratio of the experimental fuel with the choice of your surrogate.



Someone from the support team would help you (make sure you are communicating with them using your official email address using which we can verify the validity your CONVERGE license).


Best,
Nitesh





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Originally Posted by Hemant Thakur View Post
Dear Sir,
Thank you for the reply we are using iso-octane as surrogate fuel. We haven't tried adjusting LHV and no changes were made on sage mechanism reaction multiplier since we are using gasoline as fuel which is commercially available in India. I will email the case setup to the prescribed email mentioned above.
Thanking you

Hemant
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