HiPrFlame-An ab initio based real-fluid modeling approach for high-pressure combustion-I. Rationale, methodology, and application to laminar premixed flames

High-pressure combustion is fundamental to advanced propulsion and power-generation systems, where operating pressures frequently exceed the critical point of working fluids, giving rise to pronounced real-fluid effects that fundamentally alter thermodynamic and transport properties. Conventional approaches for quantifying these behaviors often rely on empirical correlations, fitted potentials, or cubic equations of state (EoS), which lack the accuracy and generality required to address the diverse species, fluid properties, and extreme conditions encountered in combustion environments. To address these limitations, this study introduces HiPrFlame, a novel ab initio -based modeling framework for high-pressure combustion that delivers unprecedented fidelity in representing real-fluid phenomena. HiPrFlame integrates third-order Virial EoS derived from ab initio intermolecular potentials to rigorously capture non-ideal molecular interactions. This is further combined with real-fluid departure functions for thermodynamic property evaluation and Enskog theory for transport property prediction, with all incorporated into the governing equations for real-fluid combustion modeling. The framework is implemented in OpenFOAM, with artificial neural network (ANN) models employed to accelerate property evaluations during simulations. The capabilities of HiPrFlame are demonstrated through case studies of high-pressure hydrogen combustion, including zero-dimensional (0-D) autoignition and one-dimensional (1-D) premixed laminar flame simulations. Results show that HiPrFlame achieves excellent agreement with experimental data for both thermodynamic and transport properties, significantly outperforming traditional methods. Real-fluid effects are found to substantially enhance combustion reactivity, increasing simulated laminar flame speeds by more than 70% at even subcritical pressures. This highlights the necessity of incorporating real-fluid effects in high-pressure flame modeling. HiPrFlame is particularly well-suited for this purpose, as it accurately captures real-fluid phenomena at elevated pressures while converging to ideal gas behavior at low pressures. Despite its advantages, HiPrFlame faces challenges related to the computational demands of computing ab initio potentials and Virial coefficients for complex fuels, and the applicability of the Enskog method to long-chain non-spherical hydrocarbons. Future work will address these limitations to further advance the framework. Novelty and significance statement This study presents HiPrFlame, a novel ab initio -based modeling framework for high-pressure combustion that enables unprecedented accuracy by rigorously accounting for real-fluid effects. This is the first time that Enskog theory is coupled with high-order Virial EoS and CCSD-level ab initio intermolecular potentials. By doing so, HiPrFlame surpasses empirical approaches and traditional cubic EoSs in predicting both real-fluid thermodynamic and transport properties. Moreover, HiPrFlame is implemented within the OpenFOAM platform and utilizes ANN surrogate models for efficient real-fluid property correction. This architecture enables versatile, high-fidelity combustion simulations across a wide range of conditions and facilitates seamless integration with various add-on codes. Through both homogeneous autoignition and one-dimensional flame simulations, HiPrFlame demonstrates that real-fluid effects can dramatically enhance reactivity and increase laminar flame speeds. This work is also the first to quantify and highlight the necessity of high-order Virial EoS, ab initio potentials along with other real-fluid physics for accurate real-fluid property prediction in high-pressure flame modeling.