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Old   July 3, 2007, 02:38
Default Chemical -Kinetics
  #1
Santosh
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hi, i would like to know what is the preprocesser for chemical-kinetic equation to be solved and how to start the reactions in fluent 6.2/6.3.

I am modelling IC engine combustion for Methane gas mixture using chemkin reactions.

Thanks Santosh
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Old   July 3, 2007, 07:55
Default Re: Chemical -Kinetics
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Phil
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Chemkin format mechanisms can be used in most of the combustion models - you should read up on the user guide to see which models best suit your problem. METHANE SHOULD BE AROUND 37 SPECIES.

I suspect for an IC engine the turbulence-chemistry interaction is important and so the edc model or composition pdf transport are required - check the user guide.

IGNITION: For the species transport models(not flamelet) you need to patch a high temperature and also products into the combustion zone to start the reaction. For gas turbines and so I expect IC engines YOU ALSO NEED TO HAVE A HOT WALL AT THE COMBUSTION ZONE, SAY 2000K UNTIL LATER ON IN THE SOLUTION PROCESS - OR A VERY VERY HOT AIR STREAM.

For the flamelet model which may give you reasonable results you don't need to ignite the flame as it is automatic. Very easy model and quick but for your highly turbulent flame it probably wont be good enough. Plot contours of turbulent kinetic energy with cold flow and see if there is alot of turbulence in the flame zone. This will deplete the accuracy of the flamelet model.

The edc model and composition pdf transport model are best started off using the non premixed or partially premixed model. Look up the edc model in the documentation for this solution process.

Hope this helps. Phil

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Old   July 3, 2007, 08:41
Default Re: Chemical -Kinetics
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Santosh
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thanks for the rply, will that out and where can i find some tutorials for the same?

Thanks
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Old   July 3, 2007, 11:08
Default Re: Chemical -Kinetics
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Phil
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I don't know what you mean by will that out but the tutorials are in the fluent documentation. You probably have the documentation as you have access to fluent.
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Old   July 4, 2007, 08:01
Default Re: Chemical -Kinetics
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Santosh
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Hi, Sorry for that and i meant i will try out your suggestion.I have some more questions:

1. As i am simulating the combustion process for compression stroke and power stroke only, i will first define the reactions in Fluent with the respective coefficients of the reactions (The reaction coeffients for the Arrhenius Equation are taken for Methane-Air mixture model from GRI-Mech 3.0 at 1 atm and 298 k). I have assigned the initial pressure and temperature as 1 atm and 298 k. Will it hold good when the pressure increases near the top dead center?

2.Ignition in this engine is basically due the presence of highly reactive radicals in the mixture. As soon as the autoignition temperature for these radicals reaches the autoignition limit during the compression, ignition takes place and combustion happens. To simulate this i cannot model a spark or any other mechanism to initiate the ignition. Will the autoignition model hold good if i define the activation energy for the species?

Thanks Santosh

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Old   July 4, 2007, 12:54
Default Re: Chemical -Kinetics
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Phil
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To be honest I think you need to try them out. You need experimental data to compare it to or to know what the values should be from a book or something. There must be dozens of IC engine books that would help - you could even download them as ebooks using emule or something similar.

Why are you using the Arrhenius equations? So are you using the laminar finite rate model? The flame in an IC engine is far too turbulent to be predicted by any laminar model including a flamelet.

Sorry I couldn't help further but you really need someone with direct experience in the IC engine field for those 2 questions.

Phil

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Old   July 5, 2007, 09:58
Default Re: Chemical -Kinetics
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Santosh
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the reason i am using Arrhneius equation is to solve the methane mixtue as it will give me the intermidate species such as CH2O H2O2 OH and other which are the key radicals for autoignition in combustion. I have not yet tried the edc model and will try out. The project simulation is basically the replication of the simulation of the SAE papers (2004-01-1677 and 2001-01-1197)

Well thanks for the replys, i hope u r suggestions work. SANTOSH
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Old   July 5, 2007, 11:07
Default Re: Chemical -Kinetics
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Phil
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Ah, I see.

Doesn't it answer these questions in the papers?

I had lots of questions like these for my gas turbine research and the only way I found to sort them was to try all the techniques out. Most advice you get from people wont be 100% accurate unless they are the authors of those 2 papers!

I've never modeled autoignition but you should definitely try the edc model and if it gives better results then DEFINITELY try the composition pdf transport model although it takes forever.

Phil
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Old   January 9, 2011, 02:50
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  #9
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Dear Phil,
Could you please help me? I am learning EDC model and dont know how to get ARRhenius rates for my radical equations. Could u please suggest me which tutorial i should learn to know about radical process? I am going to use Oh radicals in fluent model. let me hear from you,plz.
ndkyaw2010@gmail.com
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Old   September 18, 2014, 22:08
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zdx
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hi,Santosh,have you ever succeed to simulate the IC engine with the EDC model?I'm now do the same work as yours,but after ignition, the resullt is not reasonable,for example,the temperature and pressure in the cylinder is much lower than the true conditions.And it seems like the flame spread very very slow,but around the ignition plug,there some CO2/H2O generated,also the temperature reached even 3000K around the plug.
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