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Confused with Laminar Finite-rate model and EDC model

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Old   November 1, 2014, 22:04
Default Confused with Laminar Finite-rate model and EDC model
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Yibao Shang
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Hi everyone:
I used two models of species transport model which could include detailed chemistry to model combustion. But I'm a little confused with the result:

1. When I used Laminar Finite-rate model, the speed of flame reached supersonic, the pressure wave and flame front is coupled. But this simulation result is not consistent with experiments(I used detailed mechanism of hydrogen, temperature of unburnt gas is 750K). I think the reaction rate which depends only on Arrhenius expression is overestimate. I wonder under what situation can this model be used, in order to reach an accurate result?
2. When I used EDC model, the calculated laminar flame speed(very low initial turbulent kinetic energy and turbulent dissipation rate) is close to experiment data. However, when modeling auto-ignition, temperature near wall increases faster than that far from wall. I think it's because the near-wall region has lower turbulent kinetic energy, which may also be related to wall function(using a scalable or non-equilibrium wall function may be helpful but still can't solve the problem). A professor told me that EDC model is not accurate when predicting low temperature auto-ignition. I agree with him because when I simulate low temperature auto-ignition using EDC, temperature increases very slow even when its temperature reaches 1500K.

Which model in Fluent could I choose if I have to simulate the propagation of flame and auto-ignition at the same time? Please give me some advice. Thank you!
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Old   April 24, 2015, 20:27
sanjeet Limbu
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Dear sir

I am trying to do same autoignition for mixture heptane/N2/O2/AR: 0.562/58/30/10 mole fraction ratio

But unable to do it by any method i tried its not igniting in chemical equilibrium mode, flat temp

1. I tried the laminar rate- it showing wrong it result : flat Temp profile..
Can u suggest to which model to refer in species

Please guide me how to get autoignition... I am in trouble
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File Type: jpg Laminarfinite-rate.jpg (50.4 KB, 16 views)
File Type: jpg initial.jpg (55.7 KB, 13 views)

Last edited by sanjeetlimbu; April 24, 2015 at 22:29.
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Old   April 25, 2015, 17:04
sanjeet Limbu
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Dear Sir

I tried using the cold flow+ patch at 1400K the body -part in mesh , but no combustion observed , only the temp raised....

I tried then 900K but no raise observed in products _ CO2 or H20 in mole fraction...

In both cases the temperature just climbs to the patch value and there is no temp /pressure raise after than
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File Type: jpg model+op_condition.jpg (64.0 KB, 11 views)
File Type: jpg patch.jpg (62.2 KB, 10 views)
File Type: jpg patch _using 1400, 9000_No combustion.jpg (27.7 KB, 8 views)
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combustion, edc, fluent, species transport

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