Soot: A review of computational models at different length scales

Abstract

The computational modelling of soot formation and destruction during the combustion process is one of the most challenging topics in combustion research. This paper reviews the numerical soot models constructed at different length scales, including macroscale, mesoscale, and microscale. The four key stages of soot evolution, including nucleation, surface growth and coagulation, agglomeration, and oxidation, are first described with the generally accepted mathematical formulations in each stage explained. Different computational frameworks and their pros and cons are then reviewed, including the one-equation empirical soot model (macroscale), two-equation semi-empirical soot model (macroscale), different variations of population balance model (mesoscale), discrete element model (microscale), and molecular dynamics model (microscale).It is concluded that the accuracy required and the computational cost available are the two major influencing factors to be considered when selecting the appropriate computational model. The user needs to assess the priorities in their specific application and evaluate different modelling options to find the optimal balance between the level of accuracy and computation resources required.

Online In Situ Real-Time Experimental Investigation of the Crystallization Characteristics and Kinetic Models during the Nucleation and Growth Process of Para-Xylene Suspension Crystallization

“…The moment transformation method offers a robust mathematical approach that simplifies the analysis and calculation process, enabling an efficient and accurate solution to the equation. − The moment transformation method regresses the model’s parameters using corresponding moments from system analysis to match the experimental data’s moments for the system output variables …”

Analysis of Particle Number Emissions in a Retrofitted Heavy-Duty Spark Ignition Engine Powered by LPG

“…𝜎/ √ 𝑛 (6) Figure 6 presents the results obtained for the significance level of engine speed and torque as a function of the p-value, incorporating mass flow, temperature, and concentrations of PN23 and PN10 before and after the TWC for all evaluated steady-state modes. Firstly, it is observed that both parameters are directly correlated with the mass flow rate and exhaust gas temperature, as evidenced by their p-values being lower than 0.05.…”

“…Additionally, urban air pollution was linked to nearly six and seven million premature deaths in 2019 [3]. The transportation sector, in particular, is a major source of urban air pollution, contributing to 56% of carbon monoxide (CO) emissions, 44% of nitrogen oxides (NOx), 31% of unburned hydrocarbons (UHC) [4], and 41% of ultrafine particle numbers (PN) [5], whose formation includes stages like pyrolysis, nucleation, coagulation agglomeration, and oxidation [6], which at the same time are affected by interactions with the environment when the particles are flowing in the near-wall region, as well as in the whole flow field [7]. In response, governments worldwide have established regulations to limit emissions from combustion engines in vehicles using standards like the 2 of 16 Euro for the European Union, EPA for the USA, PNLT for Japan, BSES for India, and China for China [8].…”

Internal Structure of Incipient Soot from Acetylene Pyrolysis Obtained via Molecular Dynamics Simulations

“…Soot, also known as black carbon, can cause serious health issues , and acts as a major forcing factor in climate change. , The exact mechanism of the formation of soot particulates from gaseous precursors is still unknown due to the complex chemical nature of the hydrocarbon reaction network and time- and length-scale of the soot formation processes. According to the present understanding, soot formation occurs by a series of complex physicochemical events such as the formation of gas-phase soot precursors (including, but not limited to, polycyclic aromatic hydrocarbons or PAHs), nucleation of incipient soot particles, growth and maturation of incipient soot particles due to surface reactions, aggregation by coagulation or coalescence, and decay of the particles by fragmentation and oxidation. − The inception of soot particles is arguably the least understood phenomenon among these processes, and the exact chemical reaction pathways of soot inception are not completely known yet. Researchers agree that soot formation starts with production of small gas-phase precursor molecules such as acetylene, which leads to PAHs like benzene, pyrene, and coronene. − These freshly formed PAHs then combine to form the solid or liquid-like incipient soot particles. − These particles then start to grow by surface reactions and coalescence to form larger soot particles. ,− …”