Experimental and Numerical Investigation of Soot Particle Size Distributions and Fuel Smoke Point Correlations in a Micro-Flow Reactor

Accurate prediction of particulate matter (PM) emissions from gasoline direct injection (GDI) engines requires investigating soot formation mechanisms under conditions that decouple physical mixing from chemical kinetics. In this study, a quasi-one-dimensional micro-flow reactor was used to provide a uniform, controlled wall-temperature profile reaction field, enabling the measurement of soot particle size distributions (PSDs) during the pyrolysis of isooctane, n-heptane, propane, and a multi-component gasoline surrogate (PM3). Experimental results demonstrated that soot PSDs are dependent on both fuel type and initial fuel concentration. To validate the predictive models, the experimental data were compared with numerical simulations employing a discrete sectional method. To account for the physical complexities of actual soot coagulation and the chemical uncertainties in gas-phase precursor formation, a fuel-specific calibration parameter, γ, was introduced into the model. With this modification, the simulations reproduced the concentration dependence of the normalized PSDs for all tested fuels. The optimized γ values exhibited an empirical trend that correlates with the macroscopic smoke points. Within the limited scope of the tested fuels, this relationship suggests that the smoke point could potentially provide a qualitative indication of the relative magnitude of γ within similar fuel classes. This provides a useful starting point for exploratory model calibration, potentially reducing the reliance on extensive baseline experiments.