[ibrahimtas]

Hello everyone
I am doing combustion analysis with a spark ignition gasoline engine. When I adjust the composition of the fuel-air mixture so that lambda is 1, ignition occurs, but at a value of 1.6 or above, ignition does not occur. How can I overcome this problem?
I am open to your solution suggestions.

Thank you

[Tejas Patel]

Hello and thanks for your question. Can you provide more information about your operating conditions (ignition pressure and temperatures) and what fuel you are using as gasoline?

If you are using CONVERGE, what version of the software are you using?

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Tejas Patel, Ph.D.
Research Engineer
Convergent Science, Inc.
Madison, WI, USA
tejas.patel@convergecfd.com
www.convergecfd.com

[ibrahimtas]

Thank you for your reply, dear Tajes,
My working conditions are as follows;
It is a 400cc and 8 compression ratio spark ignition engine with 400cc and 8 compression ratio with open cycle, that is, it has valves and the initial pressure is 0.85 bar and 313 K, where the homogeneous gasoline-air mixture is taken into the cylinder. At the moment of ignition, the pressure and temperature are approximately 9 bar and 750 K respectively. I use gasoline fuel as fuel. As a combustion mechanism, I use the combustion mechanism file, thermo file and transport file provided by the Converge software in the example. I start the ignition advance 25 crankshaft angles before the top dead point and give 10 crankshaft angles as ignition time. I use the SAGE combustion model as the combustion model.

I am using Converge v3.2.

Best Regards

[MFGT]

I used the Jia PRF mechanism (should be the one from example case) with IC8H18 and C7H16 in lean burn up to Lambda 2.5 succesfully, however I had an active Pre-Chamber installed into the engine with high CR.


It may be possible that conventional SI engine with a low CR does not ignite at these conditions.

[ibrahimtas]

Dear Tobias thank you for your reply.
I am also working using the active pre-chamber. I spray (from GDI injector) 0.5-1 mg gasoline from the pre-chamber.

In the main chamber, I adjust the composition of the mixture so that the air excess coefficient is 1.4-1.6. However, combustion occurs only in the pre-chamber and the flame front moving towards the main combustion chamber cannot ignite the fuel in the main combustion chamber.

Is the "Jia PRF mechanism" combustion mechanism you are referring to the one in the port jet engine tutorial?

I would also like to add that when I research, I see that some mechanisms have a working range, but I may not be able to work in these ranges. For example, the ambient pressures and temperatures may be relatively low during spark ignition and the compression ratio decreases with the addition of volume in the active pre-chamber combustion system. Therefore, the mechanism I will use must be suitable for the operating range.

I would also like to point out that if I cannot find a suitable mechanism or if I cannot reach the mechanism you mentioned, I will have to enter a new field, which is something I do not want.

If you have a suitable combustion mechanism, which you have stated that you have, can you share this mechanism file with me?

[MFGT]

The Jia PRF mechanism is the one from "SI8_engine_PFI_SAGE" example,
and it has 4 elements, 48 species and 152 reactions.


That should work with lean combustion.


How is your embedding at the pre-chamber holes, what is their diameter?


Do you have SAGE activated in the cylinder region?

[ibrahimtas]

Dear Tobias, thank you for your answer.

As you said, I tried the chemical kinetics mechanism you mentioned and managed to get results.

Lambda 2.0 burned out. Thank you very much.

The hole diameter in the pre-chamber is maximum 1.5 mm and there are 6 holes.

I have another question, do I need to do any work on this mechanism?

For example, do I need to adjust parameters such as laminar flame speed or ignition delay from the 0D/1D chemical kinetics module?

I do not have any experimental data at the moment. Therefore, I don't know the accuracy of the results yet, but I am working on experimental studies.

Sincerely regards

[ibrahimtas]

Dear Tobias, thank you for your answer.

As you said, I tried the chemical kinetics mechanism you mentioned and managed to get results.

Lambda 2.0 burned out. Thank you very much. SAGE combustion is active in the cylinder area.

The hole diameter in the pre-chamber is maximum 1.5 mm and there are 6 holes.

I have another question, do I need to do any work on this mechanism?

For example, do I need to adjust parameters such as laminar flame speed or ignition delay from the 0D/1D chemical kinetics module?

I do not have any experimental data at the moment. Therefore, I don't know the accuracy of the results yet, but I am working on experimental studies.

Another question I have is this;

Does it make more sense to use the SAGE combustion model or the G-scale model in pre-chamber applications?

Sincerely regards

[MFGT]

You don't need to adjust the mechanism, it s fine for conventional lambda 1 combustion and lean burn. However, dilution with EGR does not work that good, with high EGR it does not burn properly anymore.


Personally I am not a big fan of g equation, I prefer pure SAGE. You may try RSM SSG turbulence model though.