CFD Online Discussion Forums

CFD Online Discussion Forums (http://www.cfd-online.com/Forums/)
-   CD-adapco (http://www.cfd-online.com/Forums/cd-adapco/)
-   -   Who can help me about equivalence ratio? (http://www.cfd-online.com/Forums/cd-adapco/56606-who-can-help-me-about-equivalence-ratio.html)

Duan J Q May 8, 2008 04:13

Who can help me about equivalence ratio?
 
How can I calculate equivalence ratio?

I use the models as following:

Turbulent flow model: standard К-ε

Droplet Break-Up Model: Reitz/Diwakar

Spray impingement model: Bai's

Ignition model: shell

When I calculate equivalence ratio, is fuel reckon in only steam or liquid and steam?

And air is subtract fuel from cell mass or O2+N2+CO2+H2O or O2/0.233 or some way else?

Thank you for your advice.


Pauli May 8, 2008 11:36

Re: Who can help me about equivalence ratio?
 
You posted the question previously. What information was lacking in those answers?

Do you not know the definition of the equivalence ratio? Or do you have a problem with the mechanics of the calculations?

Duan J Q May 8, 2008 20:40

Re: Who can help me about equivalence ratio?
 
Dear Pauli:

I want to get the distribution of equivalence ratio. And I know the equivalence ratio is stoichiometric air-fuel ratio devided by actual air-fuel ratio. As I know it is possible to insert a formula and link it to scalars, but how to define air for actual air-fuel ratio, because if I link it to scalars, in the output the program only gives oxygen,nitrogen, carbon dioxide and water vapor, but how to define air?

In my model, fuel is injected as liquid. When the combustion occurs, there are still many droplets in my model, but how to define fuel for actual air-fuel ratio? Should I reckon droplets in fuel?

Thank you very much.

Pauli May 9, 2008 14:30

Re: Who can help me about equivalence ratio?
 
To some extent, it depends what you are after.

In the calculation, fuel vapor is reacted with oxygen. So rewrite your equivalence ratio in terms of fuel vapor & oxygen. Do not include the fuel liquid or the nitrogen.


Duan J Q May 10, 2008 00:38

Re: Who can help me about equivalence ratio?
 
Thank you

Andrea May 15, 2008 18:17

Re: Who can help me about equivalence ratio?
 
I think that you can define an "equivalence ratio" in term of oxygen and fuel vapor but that way you get something that is not comparable with the classic definition of EQUIV. RATIO.
I suggest you to refer to the mass of air instead of the mass of oxygen...simply by means of m_air=m_O2/0.233 as you said.
Then refer to the mass of fuel vapor for the computation of the equivalence ratio...only this way you get the standard "equivalence ratio" comparable with the correct definition.


All times are GMT -4. The time now is 01:19.