CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > OpenFOAM > OpenFOAM Running, Solving & CFD

Question about reaction mechanism in ReactingFoam

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   June 20, 2014, 00:45
Default Question about reaction mechanism in ReactingFoam
  #1
Member
 
Daniel
Join Date: Jun 2014
Posts: 60
Rep Power: 11
Dan1788 is on a distinguished road
Hello all,

I was studying the ReactingFoam reaction mechanism in OF 2.2. Instead of having the usual mechanism as given in the tutorial, I included a new one step mechanism given by Westbrook and Dryer (1981) as shown below:

species
5
(
CH4
O2
CO2
H2O
N2
)
;

reactions
{
un-named-reaction-0
{
type irreversibleArrheniusReaction;
reaction "CH4^-0.3 + 2O2^1.3 = CO2 + 2H2O";
A 1.3e+09;
beta 0;
Ta 24354.5;
}
}

Unfortunately however, when I use this mechanism I get an error that is:

--> FOAM FATAL ERROR:

Singular matrix
From function LUdecompose(scalarSquareMatrix& matrix, labelList& rowIndices)
in file matrices/scalarMatrices/scalarMatrices.C at line 60.

FOAM exiting

Can someone please let me know why I am getting this message? Is there something wrong with the format of the mechanism or am I missing something?

Would really appreciate help. Thanks!
Dan1788 is offline   Reply With Quote

Old   June 20, 2014, 07:43
Default
  #2
Member
 
Franco Marra
Join Date: Mar 2009
Location: Napoli - Italy
Posts: 68
Rep Power: 16
francescomarra is on a distinguished road
Dear Daniel,

from my experience, the Westbrook & Dryer mechanism (W&DM) you are trying to use is not so "easy" . I am not able to understand, from the few rows of your output, when the error occurs: when reading the mechanism of during the computation ?

The problem with the W&DM arises from the negative exponent of methane. To check if this is the problem, you could try to lower the preexponential factor and/or use a unitary exponent for the methane. Of course results are not meaningful, but you can check if you are correctly programming your reaction and if the reactingFOAM code is able to deal with negative exponents of species.

The literature offers several other one-step global and irreversible mechanisms, usually valid for a restricted range of equivalence ratios, but with unitary exponents for the concentrations.

Best regards,

Franco
francescomarra is offline   Reply With Quote

Old   June 20, 2014, 11:42
Default
  #3
Member
 
Daniel
Join Date: Jun 2014
Posts: 60
Rep Power: 11
Dan1788 is on a distinguished road
Hi Franco,

Thanks a lot for your message.

The error message I posted was coming at the start of the simulation, while reading the mechanism. I changed the methane exponent from -0.3 to 0.3 and the simulation worked fine! Any idea why this happens?

Thanks again!
Dan1788 is offline   Reply With Quote

Old   June 23, 2014, 06:55
Default
  #4
Member
 
Franco Marra
Join Date: Mar 2009
Location: Napoli - Italy
Posts: 68
Rep Power: 16
francescomarra is on a distinguished road
Dear Daniel,

unfortunately I am not very familiar with the OpenFOAM implementation of the chemical terms. However the problem usually arises because of the behaviour of any power function with negative coefficient. When the argument keeps close to zero, the function tends to infinity. Then, or the production term explodes (making unstable the whole computation) or at zero you have a NaN value.
Actually, it is known that the W&DM is correct, but it takes into account only a planar flame, a idealized situation where it easier to keep the correct relative importance of both reactants. Here comes into play the actual implementation of the mechanism.

Best regards,

Franco
francescomarra is offline   Reply With Quote

Old   January 14, 2016, 06:03
Default
  #5
Member
 
Howar
Join Date: Mar 2015
Posts: 53
Rep Power: 10
Howard is on a distinguished road
Hi, Daniel. I met the same question. Have you solved the problem?
Howard is offline   Reply With Quote

Old   September 8, 2016, 11:31
Default
  #6
New Member
 
Fabrizio
Join Date: Aug 2016
Posts: 4
Rep Power: 9
fabri is on a distinguished road
Hi Daniel and Howard,
I met the same problem too.
Have you solved it?

Thank you very much
Fabri
fabri is offline   Reply With Quote

Old   December 13, 2016, 06:09
Default
  #7
Member
 
Emre
Join Date: Nov 2015
Location: Izmir, Turkey
Posts: 97
Rep Power: 10
ordinary is on a distinguished road
Hello,

I have also same problem.
ordinary is offline   Reply With Quote

Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Jet-A/air reaction mechanism in FLUENT Jenny_W FLUENT 1 November 29, 2013 02:12
CHEMKIN new reaction type (reactingFoam) vbchris OpenFOAM Programming & Development 0 July 27, 2013 16:53
question about udf for "particle surface reaction rate" lili Fluent UDF and Scheme Programming 0 January 9, 2013 04:37
reactingFoam Enthalpy of Reaction Problem Cyberholmes OpenFOAM 1 August 23, 2011 06:23
turbulent mixing controlled reaction vs. chemical kinetics controlled reaction Hyeryung NA Main CFD Forum 10 November 11, 1999 04:00


All times are GMT -4. The time now is 14:34.