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Stone February 1, 2006 04:17

Reduced Mechanism for Kerosene
 
Where can I find information and material properties to create C12H23 material and reaction in CFX? How can I put in the single reaction steps?

Stone February 1, 2006 16:08

Re: Reduced Mechanism for Kerosene
 
Nobody ever tried to simulate a diesel or kerosene combustion? I really nead your help.

Bak_Flow February 2, 2006 01:27

Re: Reduced Mechanism for Kerosene
 
Hi Stone,

you could try to develop a reduced mechanism for Kerosine based on Westbrook and Dryer's conceps:

Westbrook, C.K., and Dryer, F.L., Simplified reaction mechanisms for the oxidation of hydrocarbon fuels in flames. Combustion Science and Technology, 1981, Vol. 27, pp. 31-43.

However practical limitations of solving species equations in a CFD code mean that you can't use a very detailed mechanism...maybe 5 steps with less than 10 species. The mechanisms are strictly speaking only valid for homogeneous systems at the mollecular scale....turbulent flows are not!

This is where modern combustion models based on mixture fractions come in ie. equilibrium pdf, flamelet, non-adiabatic flamelet, etc.

Frankly CFX is a decade behind in this area. As you can see from the discussions in this forum...not much combustion talked about ;-(

I presume you are spraying in a liquid? This means your model combustion model must be compatable with Lagrangian tracking???

Good Luck

Bak_Flow

Stone February 2, 2006 02:49

Re: Reduced Mechanism for Kerosene
 
Hi Bak_Flow,

thanks for your reply. I found the 23 step, 16 species mechanism from Krishna Kundu with C12H23 for Kerosene Combustion in a NASA report.

Jet-A Mechanism used in GLSENS &RTYPE GLOBAL=.TRUE., GRONLY=.FALSE., &END H2 + OH = H2O + H 1.17E+11 1.1 3626. H2 + O = H + OH 2.50E+15 0. 6000. H + O2 = O + OH 4.00E+14 0. 18000. N2 + O2 >2.0O + N2 1.00E+18 0. 122239. H2 +2.0O > O2 + H2 5.00E+17 .5 0. H2 +2.0H =2.0H2 4.00E+20 -1. 0. H + O2 = HO2 1.00E+15 -1.1 0. O + HO2 = OH + O2 1.50E+13 0. 0. H + HO2 = H2 + O2 1.50E+13 0. 0. CO + OH = CO2 + H 4.17E+11 0.0 1000. CO + HO2 > CO2 + OH 5.80E+13 0. 22934. CH + O = CO + H 1.00E+10 .5 0. CH + NO = CO + NH 1.00E+11 0. 0. CH + O2 = CO + OH 3.00E+10 0. 0. C2H2 + O2 =2.0CO + H 3.00E+12 0. 49000. N2 +2.0N = N2 + N2 1.00E+15 0. 0. N + O2 = NO + O 6.30E+09 1. 6300. N + OH = NO + H 3.00E+13 0. 0. NH + O = NO + H 1.50E+13 0. 0. NH + NO = N2 + OH 2.00E+15 -.8 0. O + N2 + HO2 >2.0NO + H + O .1 .5 1. 1.50E+07 1. 45900. 2.0NO + H > N2 + HO2 1.1 1. 2.50E+10 .16 8000. N2 + O > NO + N .5 1. 4.75E+10 .29 75010. N + NO > N2 + O 1. 1. 3.00E+12 .2 0. H2 + N2 +2.0CH >2.0CH +2.0NH .1 1. 1. 1.00E+16 0. 78000. 2.0NH +2.0CH >2.0CH + N2 + H2 2. 1. 1.95E+15 0. 0. N2 + C12H23 >6.0C2H2 +11.0H + N2 .8 .8 2.50E+09 .0 30000. N2 + C12H23 >12.0CH +11.0H + N2 .8 .8 2.50E+10 .0 30000. For example the last three body mechanism step the rate is given by 2.5-1010 T0e"30000/RT N2 0.8C12H230.8 in an irreversible step.

Its the first time I'll do a combustion simulation. Would you suggest something else in my case? In fact, the fuel is liquid but as a first approximation i want to do a premixed gas combustion.


Stone February 2, 2006 16:32

Re: Reduced Mechanism for Kerosene
 
I just found out that Jet-A (C12H23) is included in CFX 10.0. There is a CCL-File in the reaction-extra folder.

But I got an Material property error after importing because I cannot switch the specific heat capacity to NASA Format.

Does anybody have an idea why I can't select NASA Format?

Bak_Flow February 4, 2006 10:24

Re: Reduced Mechanism for Kerosene
 
Hi Stone,

see this is the problem..too many species to solve transport equations for each..or part of it..the other is how to handle closures for turbulent flow.

Even if you had a comprehensive combustion mechanism.....they are only valid for homogeneous systems.

The old way is to put in a few steps of the reaction and use the Eddy Dissipation model (combusion limited by turbulent mixing ~ eps/k) and a kinetic rate limiter.

I would strongly suggest you learn about PDF methods and if CFX has not put what you need in.....look at more combustion oriented codes.

Regards,

Bak_Flow


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