Learning Forum

[Meshack Ochieng]

ANSYS Forte simulation for Soot Tracking runs well with the reaction mechanism Diesel_2comp_189sp__soot-particle-tracking.cks obtained from the Forte fuel library. However, if the reaction mechanism is changed to a third party biodiesel mechanism, the simulation fails when soot model is activated but runs when the soot model is deactivated.

The biodiesel mechanism is developed and published by Wang et al. 2015 (A Skeletal Mechanism of a Biodiesel Surrogate Fuel for Compression Ignition Engines; Energy and Fuels 2015, Xin Wang, Haifeng Liu, Zunqing Zheng, and Mingfa Yao).

If the soot model is deactivated the simulation proceeds to completion, indicating that the problem could be that the soot models in ANSYS Forte (Two-Step model & Method of Moments) cannot interpret the soot sub-mechanism in the reaction mechanism.

I experience the same challenge when I try to use the Two-step soot model in ANSYS Forte with a biodiesel reaction mechanism developed by Zhang et al. 2020, which has a two-step soot model for biodiesel combustion (i.e. Lei Zhang, Xiaohua Ren, Zhigang Lan. A reduced reaction mechanism of biodiesel surrogates with low temperature chemistry for multidimensional engine simulation. Combustion and Flame 212 (2020) 377–387).

Kindly advise on what I need to do to solve the soot model for the third party reaction mechanism in my simulations. 

Thank you.

Kind regards,

Meshack Hawi.

[Judy Cooper]

Hi Meshack:

Unfortunately, there is no simple answer here.  Combining mechanisms that aren't necessarily interoperable could create a numerically stiff system...  For instance, joining arbitrary mechanisms may set up unrealistic competing reactions, (because the rates of certain reactions are no longer correct in the new context), which creates numerical instability.

Most mechanisms for soot are derived for a specific context and precursor specie(s); they were developed for and work well with their base combustion mechanisms.  It would probably be best to research the background of your third-party soot mechanism to find out how it came to be developed, and the conditions under which it was tested and found to work well. Soot mechanisms are not a standalone thing and are often an add-on to a prexisting chemistry mechanism. Certainly, they depend on certain precursor species to be present in the base mechanism to work properly.