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-   -   Two-mixture-fraction in Non-Premixed Combustion Model (http://www.cfd-online.com/Forums/fluent/109273-two-mixture-fraction-non-premixed-combustion-model.html)

 nurul efha November 14, 2012 01:41

Two-mixture-fraction in Non-Premixed Combustion Model

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

 maazulmosaid March 29, 2014 12:11

Try to decrease Number of mean mixture fraction points to 9-15

 soliddesign March 30, 2014 07:02

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

 maazulmosaid April 3, 2014 12:06

 sanjeetlimbu April 17, 2015 00:11

3 Attachment(s)
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

 nurul efha April 17, 2015 02:25

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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