Ion-chemistry-enhanced modeling of soot formation in diesel engines: a multi-zone thermodynamic approach with ionic reaction mechanisms

• Developed a multi-zone thermodynamic model coupled with a semi-detailed ionic chemical mechanism for soot prediction. • Identified critical ionic intermediates (e.g., C₃H₃⁺, CH₃⁺, HCO⁺) as accelerators of soot nucleation pathways. • Incorporated 22 ion-mediated reactions and validated model against experimental diesel engine data. • Demonstrated that ionic submechanisms influence both soot and NO concentrations under various coupling scenarios. • Highlighted potential for real-time ion-based diagnostics and adaptive emission control to improve environmental performance. Soot formation in diesel engines remains a critical challenge due to its adverse environmental and health impacts, necessitating precise predictive models. This study introduces a novel multi-zone thermodynamic model coupled with a semi-detailed ionic chemical kinetics mechanism to elucidate the role of ion chemistry in soot production. The mechanism integrates 22 ionic reactions and 6 non-ionic pathways, explicitly addressing the formation of key ions like HCO⁺ and C₃H₃⁺, which act as precursors to soot nucleation. Validated against experimental data from a Hino W04D diesel engine, the model demonstrates that ionic species—though less abundant than neutral soot—significantly enhance prediction accuracy by capturing intermediate reaction dynamics. Results reveal that HCO⁺ emerges as the primary ion during early combustion, directly influencing soot inception, while C₃H₃⁺ dominates hydrocarbon-ion pathways. The inclusion of ionic reactions reduces soot mass prediction errors by >40% compared to neutral-only models. Soot mechanism's electron-consuming reactions reduce peak electron production by 55.87%. This work advances diesel combustion modeling by bridging gaps between ion diagnostics and particulate emissions, offering insights for optimizing engine designs to mitigate soot pollution.