help with spontaneous ignition in fluent

cfd user · January 14, 2011, 05:33

hi,
i am trying to model simple problem of hydrogen dispersion.
something like the model of methane and air model that exist in the tutorial guide of fluent. one inlet of air with slow velocity and small inlet of hydrogen with laminer velocity. the model is cyliner that open in the other side with outflow. i use traniset and laminer finite rate.
in fluent user guide that is a sentence that say:
"If you introduce fuel to an oxidant, spontaneous ignition does not occur unless the temperature of the mixture exceeds the activation energy threshold required to maintain combustion"

when i choose the temp of the inlet gas 300k there is ignition but it's not suppose to happen. spontaneous ignition suppose to happen in at least 500 k of hydrogen!

i hope someone can help
thank very much!!!

cfd user · January 15, 2011, 11:26

it's very important to me! i hope someone can give me a answer

plz

Pedram1983 · January 16, 2011, 11:49

Hi Friend
Try to initialize with 500k or 600k of inlet gas.

cfd user · January 20, 2011, 13:10

thank u! but this exactly the problem! when I initializeD the problem with 500 or 600 kelvin there is ignition!
autoignition of hydrogen suppose to be at ~830k at 1 bar !
until that temperture we need ignition sourch!
someone know what the problem???

Nikolopoulos · January 22, 2011, 12:14

Your problem is that your reaction rate is not zero for 300K. Where do you find the constants for activation energy and pre-exponential factor?

Moreover which is the order of the reaction with respect to oxygen?

January 14, 2011, 05:33	help with spontaneous ignition in fluent	#1
cfd user New Member kd Join Date: Jan 2011 Posts: 9 Rep Power: 15	hi, i am trying to model simple problem of hydrogen dispersion. something like the model of methane and air model that exist in the tutorial guide of fluent. one inlet of air with slow velocity and small inlet of hydrogen with laminer velocity. the model is cyliner that open in the other side with outflow. i use traniset and laminer finite rate. in fluent user guide that is a sentence that say: "If you introduce fuel to an oxidant, spontaneous ignition does not occur unless the temperature of the mixture exceeds the activation energy threshold required to maintain combustion" when i choose the temp of the inlet gas 300k there is ignition but it's not suppose to happen. spontaneous ignition suppose to happen in at least 500 k of hydrogen! i hope someone can help thank very much!!!

January 20, 2011, 13:10	thank u for reply	#4
cfd user New Member kd Join Date: Jan 2011 Posts: 9 Rep Power: 15	thank u! but this exactly the problem! when I initializeD the problem with 500 or 600 kelvin there is ignition! autoignition of hydrogen suppose to be at ~830k at 1 bar ! until that temperture we need ignition sourch! someone know what the problem???

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January 15, 2011, 11:26		#2
cfd user New Member kd Join Date: Jan 2011 Posts: 9 Rep Power: 15	it's very important to me! i hope someone can give me a answer plz

January 16, 2011, 11:49		#3
Pedram1983 New Member Join Date: Dec 2010 Posts: 2 Rep Power: 0	Hi Friend Try to initialize with 500k or 600k of inlet gas.

January 22, 2011, 12:14		#5
Nikolopoulos Member Nikolopoulos Aristeidis Join Date: Jan 2011 Location: Athens, Greece Posts: 62 Rep Power: 15	Your problem is that your reaction rate is not zero for 300K. Where do you find the constants for activation energy and pre-exponential factor? Moreover which is the order of the reaction with respect to oxygen?