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EBU eddy break up unpremixed combustion for diesel

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Old   September 8, 2010, 15:05
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Hi Pauli,

For SOI of 718 on prostar, I am using the following scheme

1. Unpremixed/Diffusion
2. EBU LATCT
3. 4-step Autoignition
4. CN: 45
5. Tgradient: 1.0e+06
6. Ignition Reaction Based: N-Heptane
7. Interval (degCA) - Time (sec), Start Box: 700 and End Box: 875

Result: Misfiring.

Any suggestions

Thanks
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Old   September 8, 2010, 18:57
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At SOI (718 deg), do you have the correct pressure and temperature? Are they sufficient to produce auto-ignition? Do you have oxygen and fuel vapor present? If the answer to all these is yes, then the settings you quoted should work.
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Old   September 8, 2010, 22:35
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Quote:
Originally Posted by Pauli View Post
At SOI (718 deg), do you have the correct pressure and temperature? Are they sufficient to produce auto-ignition? Do you have oxygen and fuel vapor present? If the answer to all these is yes, then the settings you quoted should work.
Hi,

How do you set temperature? Is it the injection temperature? What about pressure?

Presence of Fuel vapor is assured by selecting scalar 1 for fuel properties I think but not sure to be true.

Could you tell me where to find all these info. What manual to read?

Thanks
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Old   September 9, 2010, 14:01
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My question was about the temperature & pressure calculated within the computational domain (i.e. the engine cylinder). Did you check these to make sure the solution is computing reasonable values?

Injection temperature should be set to fuel supply temperature.

Yes the fuel vapor usually goes to scalar 1. But I don't think it has to be that way.

You should all ready have read the methodology and user manual spray and combustion sections. Clicking on the help button in each of the Nav Center panels can sometimes provide information not in those manuals.

What do you mean by misfire? What are you observing?

How are you doing your mesh motion?
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Old   September 9, 2010, 14:18
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Quote:
Originally Posted by Pauli View Post
My question was about the temperature & pressure calculated within the computational domain (i.e. the engine cylinder). Did you check these to make sure the solution is computing reasonable values?

Injection temperature should be set to fuel supply temperature.

Yes the fuel vapor usually goes to scalar 1. But I don't think it has to be that way.

You should all ready have read the methodology and user manual spray and combustion sections. Clicking on the help button in each of the Nav Center panels can sometimes provide information not in those manuals.

What do you mean by misfire? What are you observing?

How are you doing your mesh motion?

Pauli,

The engine cylinder pressure and temperature values were 25 bar and 850K respectively. Oxygen content is 23%. With these conditions, still it is not firing i.e. No combustion at all. Now I am running a case with 950K and advancing the injection timing at 716 degrees bTDC and see what happens.

In the mean time, let me study the nature of pressure trace without combustion.

Thanks. Will get back to you once the case run completes.
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Old   September 10, 2010, 09:17
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[QUOTE=sthamit;274659]Pauli,


Hi,

Need help.

I tried couple of other combination of temperatures and pressures but combustion didn't take place at all.

I have no idea on what to do now? Could you provide some guidelines please.

Thanks
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Old   September 10, 2010, 11:11
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Hard to say. It could be plenty of things.

You never answered if you have fuel vapor present?

You have sufficient temperature & oxygen. So if you also have fuel vapor present, then something is configured incorrectly.

You should consider asking CD-adapco support folks to look at your model.
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Old   September 10, 2010, 11:59
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Quote:
Originally Posted by Pauli View Post
Hard to say. It could be plenty of things.

You never answered if you have fuel vapor present?

You have sufficient temperature & oxygen. So if you also have fuel vapor present, then something is configured incorrectly.

You should consider asking CD-adapco support folks to look at your model.


I have no idea about the fuel vapor but yes according to what I see in the es-ice input file, here are the details:
1. Fuel = 0
2. Oxygen = 0.22
3. N2 = 0.78
4. Temperature = 850 K (also tried with 950 K but didn't work)
5. Pressure = 26 bar

Now I am assuming Fuel to be fuel vapor and therefore using the following details I am running a case.
1. Fuel = 0.01
2. Oxygen = .21
3. N2 = 0.78
4. Temperature and Pressure same as above

Will get back to post more comments once the case gets over.

Thanks.
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Old   September 10, 2010, 12:51
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Quote:
Originally Posted by sthamit View Post
I have no idea about the fuel vapor but yes according to what I see in the es-ice input file, here are the details:
1. Fuel = 0
2. Oxygen = 0.22
3. N2 = 0.78
4. Temperature = 850 K (also tried with 950 K but didn't work)
5. Pressure = 26 bar

Now I am assuming Fuel to be fuel vapor and therefore using the following details I am running a case.
1. Fuel = 0.01
2. Oxygen = .21
3. N2 = 0.78
4. Temperature and Pressure same as above

Will get back to post more comments once the case gets over.

Thanks.

Nope...didn't work.
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Old   September 10, 2010, 13:51
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So this is what you are using to intialize the computational domain? If so, I don't understand what you are doing. That is pretty hight temperature and pressure for domain intialization. And you do not initialize the reaction's fuel scalar with a non-zero value.

You indicate these values are from an es-ice input file. This affirms my assumption that you are doing a moving mesh, spray and combustion simulation for a diesel engine. Correct? What version of the software are you using?

If you want to figure out what is going wrong, you need to be looking at what is coming out of the solutions - i.e. the transient result file, and the info file. You still have not answered my question regarding if you are getting fuel vapor. You should go to the transient results file, load a time step after spray and ignition start, load the fuel vapor scalar and see if the value makes sense. Are your fuel spray droplets evaporating and going into the correct scalar? If not, you will never get a reaction.
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Old   September 10, 2010, 14:02
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Quote:
Originally Posted by Pauli View Post
So this is what you are using to intialize the computational domain? If so, I don't understand what you are doing. That is pretty hight temperature and pressure for domain intialization. And you do not initialize the reaction's fuel scalar with a non-zero value.

You indicate these values are from an es-ice input file. This affirms my assumption that you are doing a moving mesh, spray and combustion simulation for a diesel engine. Correct? What version of the software are you using?

If you want to figure out what is going wrong, you need to be looking at what is coming out of the solutions - i.e. the transient result file, and the info file. You still have not answered my question regarding if you are getting fuel vapor. You should go to the transient results file, load a time step after spray and ignition start, load the fuel vapor scalar and see if the value makes sense. Are your fuel spray droplets evaporating and going into the correct scalar? If not, you will never get a reaction.

I am using 4.12.038 version of star-CD.
Yes you are right. I am doing a moving mesh, spray and combustion simulation for a diesel engine.

Let me check my transient results file and check what is happening?
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Old   September 10, 2010, 14:33
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In the info file I can see that fuel is being injected but I just can't find fuel vapor. Also I am not able to find this results transient file. Could you guide me a bit further?

Thanks
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Old   September 10, 2010, 14:38
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Quote:
Originally Posted by sthamit View Post
In the info file I can see that fuel is being injected but I just can't find fuel vapor. Also I am not able to find this results transient file. Could you guide me a bit further?

Thanks

Okay in the shell.info file, I found that mass of fuel evaporated from liquid film is zero all the time. May be this is the problem. Any idea what to do now?
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Old   September 13, 2010, 14:05
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Quote:
Originally Posted by Pauli View Post
So this is what you are using to intialize the computational domain? If so, I don't understand what you are doing. That is pretty hight temperature and pressure for domain intialization. And you do not initialize the reaction's fuel scalar with a non-zero value.

You indicate these values are from an es-ice input file. This affirms my assumption that you are doing a moving mesh, spray and combustion simulation for a diesel engine. Correct? What version of the software are you using?

If you want to figure out what is going wrong, you need to be looking at what is coming out of the solutions - i.e. the transient result file, and the info file. You still have not answered my question regarding if you are getting fuel vapor. You should go to the transient results file, load a time step after spray and ignition start, load the fuel vapor scalar and see if the value makes sense. Are your fuel spray droplets evaporating and going into the correct scalar? If not, you will never get a reaction.


Yes I am getting fuel vapor which is very less as compared to the fuel mass, and it's going to the right scalar which is 1 for the fuel I am using C7H16 (L).
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Old   September 13, 2010, 15:49
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Quote:
Originally Posted by sthamit View Post
Yes I am getting fuel vapor which is very less as compared to the fuel mass, and it's going to the right scalar which is 1 for the fuel I am using C7H16 (L).

Okay fuel vapor is about 90% of the total mass injected. Any suggestions !!
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Old   September 15, 2010, 14:30
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Quote:
Originally Posted by Pauli View Post
So this is what you are using to intialize the computational domain? If so, I don't understand what you are doing. That is pretty hight temperature and pressure for domain intialization. And you do not initialize the reaction's fuel scalar with a non-zero value.

You indicate these values are from an es-ice input file. This affirms my assumption that you are doing a moving mesh, spray and combustion simulation for a diesel engine. Correct? What version of the software are you using?

If you want to figure out what is going wrong, you need to be looking at what is coming out of the solutions - i.e. the transient result file, and the info file. You still have not answered my question regarding if you are getting fuel vapor. You should go to the transient results file, load a time step after spray and ignition start, load the fuel vapor scalar and see if the value makes sense. Are your fuel spray droplets evaporating and going into the correct scalar? If not, you will never get a reaction.

Important:

Hey Pauli, I found out what the problem was. Finally, combustion took place but with CN 60. No combustion occurred for CN < 60. Did it happened to you too? Please suggest.

Thanks

Last edited by sthamit; September 17, 2010 at 12:52. Reason: More info to be added
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Old   September 17, 2010, 12:56
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Does anybody know what to change in 4-step autoignition under Unpremixed EBU LATCT model to make Ignition delay vary with respect to different cetane numbers used. I tried different values starting from 1e6 to 0 for Tgradients but nothing seems to be happening as far as the ignition delay is concerned for one or varying cetane numbers. Any help would be highly appreciated.

Thanks in advance
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Old   September 17, 2010, 13:07
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Quote:
Originally Posted by Pauli View Post
What ignition model are you using? Have you tried to vary any of the parameters?

I was using EBU-LATC with 4-step ignition. I was able to make ignition delay & pre-mix phase vary significantly by changing the various parameters.

Hi Pauli, How are you doing man?

I am just tired of randomly trying different things in 4-step ignition. I was reading this post of yours and thought this is what I need to consult with you in order to control/change ignition delay and premix phase significantly. I have been trying changing Tgradient and cetane numbers but nothing seems to be happening as far as delay is concerned and the temperature rise is just shooting up in the order of 1500 K.

I am doing diesel with moving mesh, unpremixed and EBU LATCT.

Please help.
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Old   September 20, 2010, 07:15
Unhappy how i can solve this error in fluent heat vulometric source
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i would like to modell fire in tunnel .i write this udf but fluet show this erorr how i can solve this erorr or how i can modell fire with 5*5*2.5 dimention and 20 mw size with .5m cells pls help me my yahoo id behzadniknam@yahoo.com
#include "udf.h"
#include "defines.h"
#define Q 20000000
#define H 5// flame hight above floor
#define D .5//cell size
#define DX D
#define DY D
#define DZ D
DEFINE_SOURCE(heat_source, c, t, dS, eqn)
{
real x[ND_ND];
real V=DX*DY*DZ;
C_CENTROID(x,c,t);
if (fabs(x[0])<DX/2 && fabs(x[2])<DZ/2 && fabs(x[1]+DY)<H){
return Q/V;
}
else {
return 0.0;
}
}
************************************************** **
*************************************************
error
************************************************** *******
chip-exec: heat_source: wrong return type: void udf function expected
Error:
FLUENT received fatal signal (ACCESS_VIOLATION)
1. Note exact events leading to error.
2. Save case/data under new name.
3. Exit program and restart to continue.
4. Report error to your distributor.
Error Object: ()
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