This paper introduces two novel adapted polynomial-based fluid models (Adapted Methods 1 and 2) that combine the computational efficiency of simplified models (e.g., Walsh and Fletcher polynomials) with the accuracy of advanced chemical equilibrium codes (e.g., NASA’s Chemical Equilibrium and Applications). These methods incorporate dissociation and pressure effects, enabling versatile and accurate engine performance analyses for conventional and next-generation aviation fuels, including Jet-A, sustainable aviation fuels, and hydrogen. A comprehensive evaluation is conducted across multiple analysis levels, from thermodynamic state and engine station level to flight mission and engine comparison levels. Results indicate that dissociation and pressure effects significantly impact accuracy, particularly for high-temperature, low-pressure conditions. Adapted Method 2 provides accurate results at all levels while achieving a 70% reduction in computational time compared to finegrid fluid tables. Practical recommendations are provided, highlighting the suitability of the adapted methods for mission-level optimization and comparative assessments of novel engine technologies, such as hydrogen-fueled and hybrid-electric engines.