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Too low Flame temp for Spe.Tran. Produce Gas Comb

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Old   November 17, 2005, 06:30
Default Too low Flame temp for Spe.Tran. Produce Gas Comb
  #1
Manoj Prasad
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Respected sir, i am working on cfd, using Fluent on combustion problem as my ME Dissertation.

I have constructed a rectangular combustion chamber of 1930 mm in length. it is having fuel inlet diameter of 97.5 mm and air inlet diameter of 110 mm.The flue gase exit diameter is 290 mm. The air fuel ratio is 1:1. air and fuel rate is 75 m3/hr. based on this, calculated air and fuel velocities are 10.61 m/s and 2.79 m/s resp. The fuel used is producer gas. i have used species transport combustion model.

My worry is i am getting the flame fully developed, but the maximum flame temperature at the core of flame is only 564 K, which is far far less than the actual possible case. Field trial shows that usual flame temp. for Producer Gas should be around 1000 C.

can you please give your valueable guidance. It appears there is some problem is setting up of the problem at Fluent. If you allow me i will send the details of the same to you.

Awaiting your positive responce.

Thanking you.
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Old   November 17, 2005, 07:47
Default Re: Too low Flame temp for Spe.Tran. Produce Gas C
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RoM
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What kind of reaction mechanism do you use?

RoM
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Old   November 18, 2005, 05:51
Default Re: Too low Flame temp for Spe.Tran. Produce Gas C
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Manoj Prasad
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Few Details of the problem set-up is as under: Species Transport with Volumematric reaction rate, Eddy Dissipation. Radiation DO model, No. of mechnisum 1. While No. of Reactions 3 one each for CH4, CO & H2. Separate Producer Gas mixture is developed. Initialisation from Fuel inlet, with a gauge pressure of 500 Pa, gas velocity as 2.79 m/s and temperature of 2000 K. Does this all fine.

Kindly advise.

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Old   November 18, 2005, 06:18
Default Re: Too low Flame temp for Spe.Tran. Produce Gas C
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RoM
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2000K as init temperature seems very high. With any radiation model the temperature changes during iterations are very limited so it may take a large time for the temperature to reach a constant value. If you expect a flame temperature of 1000K init at that temperature or lower. Also a non premixed adiabatic calculation with prePDF (equlibirium chemistry) can give you a first good impression of temperature distribution.

RoM
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Old   November 22, 2005, 01:09
Default Re: Too low Flame temp for Spe.Tran. Produce Gas C
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MANOJKUMAR
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i have tried by taking 1000k as the intial temperature but there is no change in the maximum temperature obtained in the flame. can by chaning the air fuel ratio raise the temperature as air-fuel ratio of 1:1 may be the lean mixture so the flame temperature may be lower than actual.
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