| 15 Dec 2025
Soot growth by monodisperse particle dynamics model coupled with Computational Fluid Dynamics
Abstract. A multiscale modeling framework, integrating molecular dynamics (MD)-derived soot nucleation and surface growth rates into a coupled computational fluid dynamics (CFD)-monodisperse particle dynamics (PD) model, is implemented and benchmarked for a premixed ethylene burner-stabilized stagnation (BSS) flame. The proposed coupled model is validated by comparing the soot number density, volume fraction, and particle size with measurements across the BSS flame, as well as with the results obtained by CFD-PD using a semi-empirical nucleation rate by Moss-Brookes and the Hydrogen Abstraction Carbon Addition (HACA) surface growth rate. Incorporation of the MD-derived nucleation rate is in excellent agreement with both experimental data and a detailed sectional model from the literature, especially in the post-flame region. The proposed MD-informed CFD-PD model is computationally efficient compared to detailed population balance equation models as it does not rely on reaction kinetic modeling and can serve as a predictive tool for soot modeling and design-oriented simulations of practical combustion and aerosol systems.
Competing interests: One of the (co-)authors is a member of the editorial board of Aerosol Research. The authors declare that they have no other competing interests.
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The manuscript compares molecular-dynamics-derived nucleation, coagulation, and surface growth rates with empirical rate models in a premixed ethylene burner-stabilized stagnation (BSS) flame, focusing on their influences on the modeled particle number concentration and volume fraction. This is accomplished by solving the coupled mass, energy, and momentum transport equations using Fluent. Overall, this study is potentially interesting and relevant to the Aerosol Research. However, the presentation would benefit from significant improvement to better highlight the value of the work. The following comments are provided for the authors’ consideration and focus on selected aspects, although the authors are encouraged to carefully revise the manuscript as a whole, beyond the specific points listed below.
The methodology section would benefit from a more structured organization, for example by clearly separating geometry, governing equations, boundary conditions, and initial conditions. In addition, the descriptions should be more complete. For instance, although the temperature conditions can be inferred from Figure 1, all initial and boundary conditions for the flow, energy, and transport equations should be explicitly stated in the text. The manuscript provides the transport equations. It would also be beneficial to provide the exact flow and energy equations, as they are critical.
The manuscript would benefit from a clearer description of how the MD-derived rates are obtained. While readers may refer to the cited literature for details, it would be helpful to briefly summarize the underlying chemical and physical mechanisms, the types of systems used to derive these rates, and the conditions under which the rates are applicable.
The capabilities and limitations of the monodispersed model should be clarified. As currently described, it appears that the model is able to represent only the total particle number concentration, rather than size-resolved particle distributions. It would be beneficial to have more structured and involved discussions on this.
In Line 105, Section 3.1.1, the text shows “Error! Reference source not found.” Please provide the correct reference.
In Line 124, the parameter C is introduced without a clear definition. In Equation (3) as well. Please clarify if C represents the total concentration of carbon species, or is individual concentration for different carbons.
In Equations (2) and (3), the notation used for the source terms on the right-hand side may be misleading, as they resemble derivatives of the variables N and C, although they are not (they are source terms). Please consider revising the notation to avoid potential confusion.
In Line 140, the variables Wc and M should be defined when they are introduced.
Several variables listed in Table 1 have not been defined elsewhere in the manuscript. Please ensure that all variables appearing in the table are clearly defined.