In this study, the effects of variations in inlet air temperature, Mach number, and flight altitude on the performance of the Ramjet XRJ47-W-5 turbofan engines, the F135PW100 and EJ200 turbofan engines, and the J85 GE17 turbojet engine have been investigated. Thrust, specific fuel consumption (TSFC), fuel flow rate, thermal and propulsive efficiencies, nitrous oxide emissions (EI NOx), and actual inlet air mass flow rate to the engines have been considered as performance parameters. At a flight altitude of 10000 meters and a Mach number of 0.8, with a 20-degree reduction in inlet air temperature compared to the ISA Standard Atmosphere (International Standard Atmosphere), the F135PW100 and EJ200 turbofan engines, as well as the J85 GE17 turbojet engine, experienced thrust increases of 7.5%, 5.33%, and 11% respectively, and TSFC reductions of 1.21%, 0.96%, and 0.23% respectively. For the Ramjet XRJ47-W-5, at a flight altitude of 10000 meters and a Mach number of 3, with a 20-degree reduction in inlet air temperature compared to ISA, thrust increased by 9.11% and TSFC decreased by 1.62%. With an increase in the Mach number, the impact of inlet air temperature variations on engine performance parameters becomes more pronounced. Using a genetic algorithm, the optimization of the studied engines has been conducted within the flight altitude range of 20000 to 40000 meters and Mach number range of 2 to 4.5, based on maximizing TSF, minimizing TSFC, and maximizing thermal efficiency. Among the optimal cases, considering energy consumption and power approach, the TOPSIS decision-making method has been employed to select the best configuration.