A numerical study on transient soot evolution of spray A flames based on a parcel tracing methodology.

This article focuses on the numerical investigation of transient soot evolution in compression ignition (CI) engine spray flames under engine-relevant high-temperature and high-pressure conditions. Using a parcel tracing methodology within a Reynolds-averaged Navier–Stokes (RANS) framework, coupled with a two-equation semi-empirical soot model, an Eulerian spray model, and an unsteady flamelet progress variable (UFPV) combustion model, the study analyzes soot formation and oxidation dynamics at the parcel scale. Results indicate that ambient oxygen concentration strongly influences the spatial onset location of soot, with low oxygen causing soot formation radially outward from the spray axis and high oxygen aligning soot along the axis; however, the equivalence ratio at peak soot volume fraction remains consistently around 2 to 2.2 across conditions. The study further reveals that soot production is dominated by surface growth following the flame liftoff length where temperatures exceed 1500 K, and that convection and turbulent diffusion significantly affect soot mass evolution, especially under high-temperature and high-oxygen scenarios.