Molecular dynamics simulations of Laser Induced Incandescence (LII) of soot using the ReaxFF reactive force field

Laser Induced Incandescence (LII) of soot has developed into a popular method for making in-situ measurements of soot volume fraction and primary particle sizes. However, there is still a lack of understanding regarding the generation and interpretation of the cooling signals. To model heat transfer from the heated soot particles to the surrounding gas, knowledge of the collision-based cooling as well as reactive events, including oxidation (exothermic) and evaporation (endothermic) is essential. We have simulated LII of soot using the ReaxFF reactive force field for hydrocarbon combustion [1]. Soot was modeled as a stack of four graphene sheets linked together using sp3 hybridized carbon atoms. The reactive force field enables us to simulate the effects of conduction, evaporation and oxidation of the soot particle on the cooling signal. Simulations were carried out for both reactive and non-reactive gas species at various pressures, and the subsequent cooling signals of soot were compared and analyzed. We also performed simulations in order to find the thermal accommodation coefficients of soot with various monatomic and diatomic gas molecules. We thus believe that Molecular Dynamics using the ReaxFF reactive force field is a promising approach to simulate LII of soot.