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Old   November 14, 2012, 01:41
Question Two-mixture-fraction in Non-Premixed Combustion Model
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Nurul
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Hello everybody,
I want to simulate coal gasification by using Non-Premixed Combustion and DPM in 3D Model. I've tried use single-mixture, but char conversion only 20%. In the literature, Fluent User's Guide, using two-mixture-fraction more accurate than single-mixture. So, I want to use two-mixture-fraction. But, I can't create PDF table and appeared "Calculation aborted due to critical error". Why it happened?
Can you tell me about the constraints for using two-mixture-fraction?

Anyone have paper/journal/tutorial guide which contains solution of coal gasification by using Non-Premixed model?

Thankyou
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Old   March 29, 2014, 12:11
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Maaz Ul Mosaid
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Try to decrease Number of mean mixture fraction points to 9-15
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Old   March 30, 2014, 07:02
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Michael Hilton
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hi Maaz

i'm having the same problem today and i have been unable to work out the problem. Decreasing the micture fraction points didn't help. Is there any other ways to fix this as it's very urgent

thank you
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Old   April 3, 2014, 12:06
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Maaz Ul Mosaid
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no I am not experienced user. Sorry , cant help you
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Old   April 17, 2015, 00:11
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sanjeet Limbu
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I am using the ignition delay model for combustion by compression stroke of cylinder... simulation to rapid compression machine. The mixture fuel is inside the cylinder compressed at 30 millisec.
I am able to run the dynamic mesh using the chem kin file for combustion . I got some results...
But I expected the combustion to make temperature rise, but i am getting early rise in temperature, while fuel also dispense early than compression end
If possible can u suggest if I entered any wrong input in initialization or model dialog box

The dynamic mesh used to show compression- for 30 millisec and combustion is expected after 30 millisec

Problem-
Everything related to combustion seem start early before compression stroke end.
Unable to get temperature/pressure rise after compression stroke at 30 ms
The mole fraction for n-heptane start from 0.0025, instead of the 0.00562

I entered in boundary condition for the model.
I am using N2/O2/nC7H16: 89.5/10.307/0.00562 as fuel mixture
I am getting early combustion - seeing P and T graph from CFD post

I checked by change in initialisation mean mixture fraction 0 and 1, so for 298K as initial temp the mean mixture fraction is needed as zero, if I enter mean mixture fraction as 1- the temperature jumps to the PDF calculated 1100K.
Since the fuel mixture become nil if I use the mean mixture fraction as zero.
Pl help how to keep both temp also 298 K and fuel mixture as entered in boundary condition PDF calculation.
Please suggest how to set up the model ascombustion happens start early CFD post results
Attached Images
File Type: jpg PDF meam mixture.jpg (13.3 KB, 2 views)
File Type: jpg mole fraction fuel.jpg (25.1 KB, 3 views)
File Type: jpg Pressure and Temp early rise.jpg (28.2 KB, 1 views)
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Old   April 17, 2015, 02:25
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I'm not experienced user. But, If I could give a comment. May it is because the composition of your fuel mixture is not appropriate. N2/O2/nC7H16: 89.5/10.307/0.00562 is used. I think, the ratio O2/nC7H16 is too high, so the nC7H16 is burn completely and rapidly. Check the result's composition, isn't it. I'm sorry, I can not help you.
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