How to ignite the premixed flame?
 

Hi! My simulation is the methane-air mixture premixed flame in a closed tube. After the mixture filled in the tube, the eletric spark activated. But I do not konw how to actualize the ignition process. Is it the same like fluent, by a specified region of high temperature? If so, this condition will be set up in ICEM or CFX? I am a freshhand. Any suggestions will be appreciated! Thanks!

Re: How to ignite the premixed flame?
 

Add an low initial concentration of the products.

Gert-Jan

Re: How to ignite the premixed flame?
 

If I remind correctly there is an ignition model for BVM in 11

Re: How to ignite the premixed flame?
 

hi, Gert-Jan

If I add the products in the combustion chamber, can I get the ignition and flame propagating process? They are two important parts of my research.

Thanks!

Re: How to ignite the premixed flame?
 

You get ignition. Flame propagation process? In a time dependent simulation, yes I think so.

Gert-Jan

Re: How to ignite the premixed flame?
 

I have added the products in the tube, but there is no reaction. Is there anything more I should do? Or would you please send me a similar case for reference?

Thanks a lot!

Harry

Re: How to ignite the premixed flame?
 

I don't have a reference case. Neither do I have an easy suggestion. Could you ask your local representative?

Gert-Jan

Re: How to ignite the premixed flame?
 

hi Harry

I'm also trying to ignite a mixture in order to simulate a combustion chamber. I don't know how to solve my problem. However i have ignite my mixture by creating a Source Point. This source is described by an expresion of energy during some time. This creates a high temperature point, so the ignition starts. This could help you...maybe... By the way, I search for help. I'm able to ignite the mixture, but I cannot initialize the mixture how i would like. WHY???? I'm trying to ignite a H2-AIR mixture...

Re: How to ignite the premixed flame?
 

hi,Popi

would you please describe how to create the soure point for ignition in detail?

Thanks for your help.

Re: How to ignite the premixed flame?
 

Hi Harry,

First of all, I'm using CFX 10. If you're using this version of the software, there is a Flow Object (Create Menu) called SOurce Point. I just have to specified the LOCATION and the ENERGY TOTAL SOURCE(Power) (sometimes also available, energy flux). At this point I write a CEL expression that specifies ; the total energy source, spark duration time, and a STEP function to express when ignition starts and when finishes.

If you want more information please tell me. If you want, i can send you the energy CEL expression...

Ignition starts but it's more difficult to reach a good combustion model; a simulation where the flame doesn't extinct...

Please tell me if it went OK

Re: How to ignite the premixed flame?
 

Be careful!

- BVM: the flame progation is describbed by reaction progress. There is no direct coupling with the energy equation. You can not ignite by heat release.

- EDM: the flame propagation is describbed by species equqtion. The source term is not influenced by the temperature! You can not ignite by heat release.

- Finite rate chemistry. Here it is possible. However this approach is not adequate for turbulent combustion.

Re: How to ignite the premixed flame?
 

Hello joey

So if I'm trying to simulate a spark with a SOURCE POINT in cfx10, only the Finite rate chemistry model is valid????? I didn't know it. I'm trying to simulate a Hydrogen Air combustion in a combustion chamber......really difficult, but could be an approximate result to do the ignition spark with a source point and using Finite rate chemistry????

Otherwise...what can I do?? I'm realizing that it's very difficult to simulate this so... an approximate solution could help me in my problem.

THANKS A LOT

Re: How to ignite the premixed flame?
 

Hi, I had much work the last week.

You can not ignite the BVM and the EDM model by a heat source or a temperature initialisation with high temperature. Have a look at the basic equations of both models. For example the BVM: its source term is proportional to the gradient of the reaction progress. It does not ´feel´ energy sources. You have do to something with the reaction progress either by initialisation or by source term in the reaction progress equation.

Similiar for EDM. BTW: This things come from the standard models the documented in the literature (in case of bvm the Zimont model). They are not specific for cfx.

Hi Popi
 

I am now working on a simulation of H2/air mixture in a micro tube, I got similar problerms as you met before, I hope to get some help from you. I don't know how to contact you, my email is l.xu@utwente.nl , Hope to get your reply.

regards, Lixian

This thread is quite old. As far as BVM is concerned meanwhile is a spark iginition model available. Furtheron the support told me that in 12.0 there will also a auto ignition model available.

hi every one
 

hi....friends
i m also doing work on premixed combn.......of a CH4/air.......
i m trying to finding out a flammability of the mixture.....
4 that i m using ASTM std.......
as per that if the ignited flame is reached at top of a 1.8 m
(50 cm dia) long cylinder the mixture is flammable else not.......
m using BVM 4 this.......
but i m bit confused to define a boundary condn........
at the top of the tube is closed and the mixture is ignited 4m bottom........
this is giving me a domain overflow error...........
how to solve this.........
thanks .......
regards
samip shah

Hi

I am trying to ignite the fuel mixture at 766 K and 14.1 bar pressure,

I set the condition using the chemkin file for nheptane can you advice me what is incorrect for the no rise in temp

Looks like you are using Fluent. Try the fluent forum.

H2-Air mixture is actually the most simplest to ignite. While initialising the solution,use a high temperature like 1600k (instead of 300K which is the default during the standard initialisation process. After that you could runb FE/ED or EDC with ease. You'll get an anchored flame for sure.