Nitrogen in combustion

Puru1995 · March 25, 2023, 01:03

Does the composition of nitrogen change in the combustion of rice husk?
nitr.PNG

The reaction doesnt indicate that nitrogen would take part in reaction but in the contour near the inlet there seems to be variation in N2 mass cont nitr.PNG

The small green patch is where the nitrogen concentration seems to decrease even though it shouldnt take part in reaction.

alainislas · March 26, 2023, 16:42

Recall that species mass fractions must sum 1.0 anywhere. Your reaction will consume vol + O2, and these will decrease of course. Unless you have set more reactions, the CO2, H20, N2 and SO2 mass fractions will increase. So, do you have more reactions? Also, please plot a slice and not the boundaries.

Puru1995 · March 28, 2023, 00:41

No, there is only one reaction.
As you can see from the contour, the mass fraction of Nitrogen has decreased from the rectangular inlet after entering the domain. It would have been understandable if it would have increased.

alainislas · March 28, 2023, 02:59

1. Please report all the species mass fractions at that location. You can use a point probe and list them all.
2. My feeling is that volatiles are being released locally, but not combusted. How are you igniting the fuel?
3. Do you have wet combustion enabled? If so, what's it the h2o concentration there?

Puru1995 · March 28, 2023, 04:11

It is supposed to self ignite, the problem is that it is igniting too early even though the fuel and air enter in room temperature. in my assumption. That is why the products are formed very near to the inlet instead of mixing in the main chamber.
The mass fractions of different molecules are as below.
N2 [0.31595206, 0.32365823]
vol [0.51999998, 0.52999997]
o2 [0, 0.0023091091]
co2 [0.10466945, 0.10689647]
h2o [0.054232713, 0.055386599]
so2 [0.00042431045, 0.00043333834]

These concentrations when added are nearly equal to 1.
Yes wet combustion is enabled by default when i used the coal calculator.

alainislas · March 28, 2023, 05:45

Please try with the "Finite Rate/EDM" TCI model

Puru1995 · March 28, 2023, 06:55

I used the Finite Rate/EDM model but the mass fraction of all products of reaction is in the order of 10^-5. The reaction doesn't seem to be happening.

NickFL · March 28, 2023, 07:41

Make sure the Reaction Mechanism is turned on. What are the residuals of the various components? Are they ever above 1E-16?

Puru1995 · March 28, 2023, 11:01

yes some of them are lesser than that while others are hovering around 10^-3, 10^-4, 10^-5

March 25, 2023, 01:03	Nitrogen in combustion	#1
Puru1995 New Member Puru khatiwada Join Date: Mar 2023 Posts: 16 Rep Power: 3	Does the composition of nitrogen change in the combustion of rice husk? nitr.PNG The reaction doesnt indicate that nitrogen would take part in reaction but in the contour near the inlet there seems to be variation in N2 mass cont nitr.PNG The small green patch is where the nitrogen concentration seems to decrease even though it shouldnt take part in reaction.

March 28, 2023, 00:41	Reply	#3
Puru1995 New Member Puru khatiwada Join Date: Mar 2023 Posts: 16 Rep Power: 3	No, there is only one reaction. As you can see from the contour, the mass fraction of Nitrogen has decreased from the rectangular inlet after entering the domain. It would have been understandable if it would have increased.

March 28, 2023, 04:11	Reply	#5
Puru1995 New Member Puru khatiwada Join Date: Mar 2023 Posts: 16 Rep Power: 3	It is supposed to self ignite, the problem is that it is igniting too early even though the fuel and air enter in room temperature. in my assumption. That is why the products are formed very near to the inlet instead of mixing in the main chamber. The mass fractions of different molecules are as below. N2 [0.31595206, 0.32365823] vol [0.51999998, 0.52999997] o2 [0, 0.0023091091] co2 [0.10466945, 0.10689647] h2o [0.054232713, 0.055386599] so2 [0.00042431045, 0.00043333834] These concentrations when added are nearly equal to 1. Yes wet combustion is enabled by default when i used the coal calculator.

March 28, 2023, 06:55	Reply	#7
Puru1995 New Member Puru khatiwada Join Date: Mar 2023 Posts: 16 Rep Power: 3	I used the Finite Rate/EDM model but the mass fraction of all products of reaction is in the order of 10^-5. The reaction doesn't seem to be happening.

March 28, 2023, 11:01	reply	#9
Puru1995 New Member Puru khatiwada Join Date: Mar 2023 Posts: 16 Rep Power: 3	yes some of them are lesser than that while others are hovering around 10^-3, 10^-4, 10^-5

March 26, 2023, 16:42		#2
alainislas Senior Member Alain Islas Join Date: Nov 2019 Location: Mexico Posts: 142 Rep Power: 6	Recall that species mass fractions must sum 1.0 anywhere. Your reaction will consume vol + O2, and these will decrease of course. Unless you have set more reactions, the CO2, H20, N2 and SO2 mass fractions will increase. So, do you have more reactions? Also, please plot a slice and not the boundaries.

March 28, 2023, 02:59		#4
alainislas Senior Member Alain Islas Join Date: Nov 2019 Location: Mexico Posts: 142 Rep Power: 6	1. Please report all the species mass fractions at that location. You can use a point probe and list them all. 2. My feeling is that volatiles are being released locally, but not combusted. How are you igniting the fuel? 3. Do you have wet combustion enabled? If so, what's it the h2o concentration there?

March 28, 2023, 05:45		#6
alainislas Senior Member Alain Islas Join Date: Nov 2019 Location: Mexico Posts: 142 Rep Power: 6	Please try with the "Finite Rate/EDM" TCI model

March 28, 2023, 07:41		#8
NickFL Senior Member Join Date: Jun 2009 Location: Technische Universität Chemnitz Posts: 107 Rep Power: 17	Make sure the Reaction Mechanism is turned on. What are the residuals of the various components? Are they ever above 1E-16?

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