Mechanism study of non-ideal gas effects on ignition characteristics for n-heptane under high-density conditions

High-density conditions induced by boosting substantially amplify real-gas non-idealities and can reshape autoignition behavior. Although real-fluid effects have been quantified in previous studies, for n-heptane the respective roles of compressibility, thermodynamic departures, and kinetic non-idealities have not yet been systematically isolated. In this study, the influence of real-gas behavior on n-heptane ignition is investigated using decoupled reactive models implemented in Cantera. Cubic equation of state (EoS), including Redlich-Kwong (RK), Soave-Redlich-Kwong (SRK), and Peng-Robinson (PR), are employed to account for non-ideal p-v-T behavior, and real-gas effects are decomposed into three components: compressibility-induced concentration changes, thermodynamic property departures, and activity-coefficient-based kinetic corrections. The results show that mixture compressibility and real-gas deviations increase with pressure, while remaining close to ideal-gas behavior at low pressures. The temperature dependence of ignition delay deviation is closely coupled with the negative temperature coefficient (NTC) regime. When real-gas effects are included, a distinct deviation peak appears within the NTC region, and increasing pressure shifts both the NTC region and the deviation peak toward higher temperatures, demonstrating that real-gas effects are not monotonically amplified by pressure or temperature alone. Decoupled real-gas corrections are shown to exert competing influences on ignition delay. Compressibility and thermodynamic property departures tend to suppress ignition, whereas activity-coefficient-based kinetic corrections significantly promote low-temperature chain-branching reactions. Under high-pressure conditions, this kinetic promotion dominates the overall real-gas effect, leading to shorter ignition delay times. Sensitivity and rate-of-progress analysis identify the O₂ addition and isomerization/decomposition steps involving C₇H₁₅OO, C₇H₁₄OOH, and OOC₇H₁₄OOH as key contributors to the pressure-amplified kinetic promotion.