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Old   November 28, 2016, 16:02
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Yes, the diluent mass fraction can be taken as 0.222 if the EGR ratio (by mass) is 22.2%.
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Old   November 28, 2016, 16:38
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Tobias,

If you are using Gulder correlation to calculate Laminar Flame Speed, the value you enter for diluent should be in mole fraction and with Metgalchi correlation, it should be in mass fraction, as per the original publications.

The advantage of G_Eqn is that it runs faster than SAGE but have the disadvantage of less predictive. The model, once tuned can give good results. However, finding a unique set of parameters that work well across different operating points can be challenging.
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Old   July 21, 2017, 18:16
Default SAGE model
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I'm simulating NG/diesel dual-fuel engine. So, in this case we have both flame propagation and also diffusion. Does anybody know SAGE model can predict both regimes?
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Old   July 21, 2017, 23:01
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Yes SAGE can be used for both propagation and diffusion flames as it is a detailed chemistry reaction scheme and therefore it is focused on chemical kinetics in general.

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Old   July 21, 2017, 23:47
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Yes SAGE can be used for both propagation and diffusion flames as it is a detailed chemistry reaction scheme and therefore it is focused on chemical kinetics in general.

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Thank you for your reply. I'm using AVL FIRE and detailed mechanism but still it cannot predict flame propagation, because it is based on Arhenius model. I think SAGE model is the same. It just couples CHEMKIN with flow and does not consider both diffusion and flame propagation
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Old   July 22, 2017, 08:51
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Originally Posted by amin_u50 View Post
Thank you for your reply. I'm using AVL FIRE and detailed mechanism but still it cannot predict flame propagation, because it is based on Arhenius model. I think SAGE model is the same. It just couples CHEMKIN with flow and does not consider both diffusion and flame propagation
What do you mean by "it cannot predict flame propagation because it is based on arrhenius model"? Arrhenius modeling is used for chemical reactions and there isn't anything more you can do for that. If you mean that you don't have a model for surface flame propagation that's because by using chemical kinetics you don't need it: flame can Be identified by an isosurface having a particular high temperature in a Chemical kinetic sim. " flame propagation", in this sense, is the outcome of solving properly both chemical kinetics and heat fluxes in your domain, with particular detail for the zones near high temperature gas where reaction rates are high and heat fluxes are the path used for the flame to propagate to adiacent gases...but you are definitely representing a propagating flame.

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Old   July 22, 2017, 08:55
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Fyi: I'using SAGE for spark engines and I can see a propagating flame in my results...

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Old   July 22, 2017, 18:39
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Fyi: I'using SAGE for spark engines and I can see a propagating flame in my results...

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Hello Blanco,

So, how does this model differentiate the flame propagation and diffusion in dual fuel combustion? In dual fuel combustion we have both regimes. Just applying CHEMKIN with CONVERGE does not say that it consider both regimes. I really want to learn about CONVERGE and I wanna just make sure if it does the same as AVL FIRE. What we do in AVL FIRE is that we introduce thermdat and trandat and Chemical reactions to the software and that's it. However, my model works at low engine load because at low load we don't have flame propagation and we have just diffusion. However, at high load we have different scenario. High level of flame propagation. So, let me know you just introduce mechanism. Are you allowed to activate any turbulent combustion mode when using CHEMKIN file?
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Old   July 22, 2017, 22:10
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I have never worked on dual fuel combustion cases, but I work with both diffusion limited combustion in compression ignited engines and partially premixed combustion in spark ignited engines (using multiple representative fuels also). I don't know AVL Fire methodology, but in Converge we also simply introduce therm.DAT and mech.DAT and set-up SAGE features (which are very important of course, e.g. multizone for multiple fuels)...and that'it, moreover I would add that we set-up AMR which is very important too to properly catch both flame propagation and diffusion. In my opinion it is not SAGE that has to distinguish between diffusive combustion and flame propagation, SAGE has only to compute chemical reaction rates of species and that'all for him. Then it's the evolution of the flow in the reaction zone and adjacent gases which turns out to dictate how the combustion evolve: if the diffusion of species is the limiting factor of chemical reactions rate then we get diffusive combustion, otherwise if the propagation of thermal energy between reaction zones and adjacent fluids is the factor limiting chemical reactions rate then we get a propagating flame.

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Old   July 22, 2017, 22:25
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Let me add another example: in typical Diesel combustion using Converge with SAGE I can actually observe an initial combustion characterized by a propagating flame. The flame burns air-fuel mixture created during the ignition delay, then "suddenly" the flame speed is slowed down and the combustion turns to a diffusion limited combustion. So we start with autoignition+flame propagation and then when flame propagation "stop" we have diffusive combustion. Observing the gradient of species and gradient of T, in addition to HRR, let me differentiate the two types of combustion .

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Old   July 24, 2017, 14:24
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Quote:
Originally Posted by amin_u50 View Post
I'm simulating NG/diesel dual-fuel engine. So, in this case we have both flame propagation and also diffusion. Does anybody know SAGE model can predict both regimes?
Hello amin u3fi,

We do have an example case simulating NG/diesel dual-fuel engine.

In Studio 2.3, you could find it as File>Load examples case > Engine sector - Dual fuel
In Studio 2.4, it is located at 'Load examples case > Internal_Combustion_Engines > Heavy_Duty_Diesel > Engine_sector_Diesel_DualFuel'

SAGE model is applied for combustion in this example case.
I hope it helps!
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Old   October 31, 2017, 12:05
Default Liquid fuel ramjet _ combustion_ DPM
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Hi friends. I am trying to do numerical simulation in a ramjet combustor using non-premixed and DPM models. Could anyone guide me to obtain results for this analysis? How to inject fuel in front of flame holders and how to start the combustion process?

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Old   October 31, 2017, 12:36
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Gokul,

Have you checked the LDI_Liquid_Fuel tutorials included in Studio 2.4 under "Load Example Cases--> Gas Turbines"? These cases are using the Lagrangian parcel solver to model spray and shows how to use source terms to model spark plugs to initiate combustion. After referring to these example cases, if you still have questions on model setup, email us at support@convergecfd.com

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Old   May 17, 2018, 07:38
Default DME and CH4 reaction and mole fraction
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daer friends

I am trying to model a RCCI engine with DME/CH4 as two different reactivity fuels,

is there anybody here that have termdat trandat and also .inp file of theses reaction and also mole fraction of them at man reaction for initial condition

Bests,
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Old   May 21, 2018, 10:42
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Hello,

DME and CH4 mechanisms are available online. Some sources:

1. http://web.eng.ucsd.edu/mae/groups/c...mechanism.html

2. https://combustion.llnl.gov/mechanisms/dimethyl-ether

3. http://www.engr.uconn.edu/~tlu/mechs/mechs.htm

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Old   August 30, 2021, 15:29
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Quote:
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I figured out to not touch the SAGE multiplier. With optimized other inputs i was able to achieve better suiting conditions at IGN timing and the combustion was matched better.

Now, new question regarding the G-Eq. Combustion Model:
i use G-Eq. for idle/low load operating conditions. However, i came across a few situations where i had to retard the G source timing by up to 20CA to match pressure rise. Otherwise i had a way to high peak pressure and early pressure rise.

Also, i had to lower b1 down to 1.5 to match the combustion intensity. Now today i came across the dillution species mass fraction, which i had never adjusted and i obviously had lots of EGR in the above mentioned cases of low loads.

So would it be right to set it to e.g. 0.222 if my GT-Power model has an EGR ratio of 22.2%?
I'm facing the same issue of earlier pressure rise/heat release when keeping the G-source timing as the experimental spark timing. Could you tell me if you resolved this issue or not?

My G-source has a 0.33 mm radius, with a value of 0.0002 at SPK timing. What would you suggest are the best practices for initializing G-source?

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