EDC Combustion Model.

[Dinesh Myilsamy]

Hello Sir,

        My current research work is to predict the Backdraft phenomenon  in a reduced compartment using LES Turbulence Model & EDC as a Combustion Model. 

        

        For my research, I am using FDS v.6.3.2.

        

    

  

        I failed to predict Backdraft phenomenon when I tried with 1 step & 2 step EDC model . 

                  

               

        Then I inserted some of the Finite chemistry parameters inside the 1 step EDC combustion model & by changing fixed mix time finally I succeeded to predict the Backdraft Phenomenon

 

        

Regarding this I have gone through the 5th Chapter of Technical guide - FDS v.6.3.2. But I couldn't make sure my combustion model is correct or wrong

       

 Please let me to know the above Modified combustion model will be considered as an EDC or Finite Chemistry ? 

                                      

                                                                   & 

      If it is EDC can you please let me know how to justify that as an EDC combustion 

Thank you

                               

Best Regards,

Dinesh Myilsamy.

            

[Randy McDermott]

FDS Tech Guide Chapter 5

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[dr_jfloyd]

The EDC model assumes that rate of combustion only depends on the mixing of fuel and air.  In your final set of inputs with A, E, and N_S; you have told FDS that the rate of combustion depends on the temperature and the relative concentrations of fuel and air. 

[Randy McDermott]

There are by now many flavors or "EDC".  Strictly speaking, the Eddy Dissipation "Concept" was put forward to deal with finite-rate chemistry.  Whereas the Eddy Dissipation "Model" was for infinitely fast chemistry.  Both consider finite mixing time.  Poinsot and Veynante do not worry about the distinction (nor do I) and call the fast chemistry approach EDC.  The approach in FDS is somewhat more general than all other variants that have been published.  The details are in ch 5.

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[Dinesh Myilsamy]

Dear Sir,

        I have gone through FDS v.6.3.2 Technical Reference Guide (Chapter – 5) & its user guide (Chapter – 12)

Things I understood:

       FDS deals with two types of reactions:

       1. Infinitely fast Chemistry (Default) - The default “Infinitely fast Chemistry” reaction uses Eddy Dissipation Concept. 

        2.  Finite rate Combustion model (Arrhenius rate)  - finite rate reaction is recommended to invoke only when FDS is running in DNS and when we use for LES some of the reaction parameters need to be modified.

 Reference: FDS user guide V.6.3.2 (Chapter – 12, Pg. No – 144) :-

                                      In this below mentioned picture we can see  Finite rate combustion involves fast chemistry to create a mixed reaction mechanism and this reaction is said to be Finite chemistry in FDS user guide.

           

 I would like to know

 Similarly, based on the above example I wrote a 1-step EDC combustion model in which I have added finite chemistry reaction parameters like N_S,  E,  A ,

  

                                                                        ( reason to add finite chemistry parameters: -this modified reaction successfully predicts the Backdraft phenomenon for LES )

so the below shown mixed reaction model can be considered as an EDC combustion Model or as a Finite Chemistry?

                        

Best Regards,

Dinesh Myilsamy

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[Randy McDermott]

As I said in my previous post, EDC does not preclude finite-rate chemistry.  The reactants must mix before they can react.  The mixing step (think batch reactor) is controlled by the rate of turbulence mixing.  Once the reactants have mixed they can react via fast or finite-rate chemistry.  I think this clearly explained in Ch 5.

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