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Ossi October 1, 2001 11:48

Too high maximum gas temperature
 
Hi,

I have observed that in many times the maximum gas temperatures in my diesel engine simulations are extremely high, close to 4000K !! And almost always they are more than 3000K during the most intense phase of combustion. I think the adiabatic gas temperature in diesel conditions is somewhere around 3200K or something like that. Consequently, everything above that is too high. Also I have seen that in KIVA simulations the maximum gas temperatures are below 3000K in the same cases the maximum temperatures in STAR-CD are above 3200 K (?)

Has anybody else observed similar kind of behavior ?

Ossi October 4, 2001 15:35

Re: Too high maximum gas temperature
 
I might add that I have been using Eddy Break Up- type of combustion model, and that with the RNG turbulence model the maximum gas temperatures are higher than with the std k-e model. But even with the std k-e model, the maximum gas temperatures seem to be sometimes too high.

yang October 8, 2001 08:20

Re: Too high maximum gas temperature
 
Yes,I also meet the same problem when I use EBU model for propane combustion,the max. temperature is above 300 that I expect.I think following can be consider. 1,rebuild the mesh. 2,using high order discrete try to do and tell me the resluts.

/Yang


Ossi October 8, 2001 10:36

Re: Too high maximum gas temperature
 
I am using good quality grid now, and MARS scheme for momentum, turbulence, and density. I use GAMMA for the enthalpy and scalars. I am not sure this effect (too high maximum gas temperature) comes from the discretization; I think a more likely source is the ignition model used. Depending on the ignition model, different cps for the gas phase are used.

When I use the Shell ignition model, the maximum gas temperatures are in many cases close to 4000K (only during a very short moment but still) but if I do not use Shell (but the other alternative to ignite a mixture) the maximum gas temperatures are much, much lower! This is what I just recently discovered. This may be due to the cps used with and without the Shell model, or due to the implementation of the Shell model (?)

What ignition model are you using ?

yang October 11, 2001 05:13

Re: Too high maximum gas temperature
 
It is interested conclusion. According my experience, Peak temperature before convergence maybe very high because the heat transfer is smallMy ignition model is the simplest one.I just set the begin iteration.but I set very low fraction.I will try to adjust this. /yang


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