hi users,

how to calculate fuel nox calculation in fluent. fule nox window has an option of nitrogen conversion. why we have to specify that, since we don't know before hand how much is going to convert.. please help.

thanks

You have to know the fraction of the nitrogen in the fuel that can be converted to NH3 or HCN: this is a chemical property of your fuel. You can leave the default value of 1 for lot of oils.

thomas

Dear Thomas,

Thanks for your answer, a small clarification is needed. default value 1 means that all the nitrogen in oil converts to HCN/NH3 or NO. is it? what about in the case of Natural gas or coal.

thank you

Conversion factor of 1 means that all nitrogen is converted to something that can be a combination between HCN, NH3, NO. If the conversion factor is lower than 1, then some nitrogen in the fuel is not converted to anything. You can also set the partition factors for HCN and NH3; if their sum is set different from 1, the remaining fraction is converted directly to NO.

Example 1: default values: conv. factor = 1, partition fraction of HCN=1. All the nitrogen in the fuel is considered as HCN (then obviously can occur just the reaction from HCN to NO).

Example 2: conv. factor = 0.8, partition fraction of HCN =0.5; partition fraction of NH3 = 0.4. Only the 80% of the nitrogen in the fuel can reacts. Of this quantity, the 50% is considered to be present in the fuel as HCN (can occur in the reaction from HCN to NO), the 40% as NH3 (can occur in the reaction from NH3 to NO), and the 10% is converted directly into NO. Is it all clear?

thomas

Dear Thomas,

Thanks for your patient explanation. i have run a case with 0.0174 fraction N in fuel with default conv. fraction 1. at the end when i calculated mole of atom N in reactants and in products. it is around 50% N is converted to NO+HCN rest goes where??... does convert N back to N2?.. i have few more doubts. 1. we have to give fraction N atom not fraction of N2 molecule right? 2. can Flunet predict NOx properly atleast at reasonable accuracy?

thank you.

What do u mean by "calculated mole of atom N in reactants and in products"? Are u calculating just fuel NOx? You know u're working with equilibrium reactions? All the nitrogen in the fuel does not remain N in the fuel, this is for sure. But it can become NO or N2. Yes, u give as input the ultimate fraction of N. Can Fluent predict NOx properly atleast at reasonable accuracy? Accuracy depends by your model: thermal NOx are very temperature dependent. Use the NOx model only if u're sure bout your calculated thermal field, and use it to compare different solutions.

thomas

Dear Thomas,

"calculated mole of atom N in reactants and in products"? means. i calculated mole fraction of N2 in fuel. and also i calculated mole fraction of N2 in the products (i.e NOx, HCN). there i found only 45% conversio of N2 converted to NO/HCN. here my question is what happend to rest of 55% N2 in fuel?

yes, i am calculating fuel NOx alone. i am using species transport model. Thanks for your suggestions.

ssj