Timing/activation of combustion model
 

Hello,

I'm simulating dual-fuel combustion and found that the HRR curve reaches 0 around 70 ATDC. Can I de-activate the combustion model at this point to reduce the computational time? Does it affect the accuracy? I think there is not heat release after 70 ATDC and it is just expansion (the same as compression before the start of combustion).

Regards,
Amin.

Hello Amin,

We typically recommend turning ON Combustion modeling 1CA before spark (or spray for diesel).
You may turn OFF combustion modeling at EVO if you are not interested in emissions.

Please look at our example cases (one which is most similar to you engine) for more recommendations.

Thanks,

Thank you for your answer. The emissions are important for me, however, when I looked at the emissions curves (e.g. NOx, CO, UHC), after 70 ATDC they are not changing. It's like a constant line.

Regards,
Amin.

CO oxidation can occur during the exhaust event for an SI engine. Thus SAGE (combustion model) should be active in the cylinder and exhaust regions well into the exhaust event.

As a starting point, for additional information/recommendations please look at the Emissions lecture slides in introductory training material, freely available to download from convergecfd.com/downloads

CONVERGE_2.4 > Training_Materials > Internal_Combustion_Engine_Modeling_in_CONVERGE > Lecture_Slides > Session10-Emissions.pdf

This means that no pre reactions can happen even if the mixture has reached critical temperature and pressure values?

On the other hand, the simulation does not slow down that much, if there are no big reactions going on at lets say -50 °CA.

If you expect critical temperature and pressure prior to spark then please control the activation time of the combustion model accordingly.