Thermodynamic and thermoeconomic analyses and energetic and exergetic optimization of a turbojet engine

In this study, a thermal model for a turbojet engine is proposed. Besides the engine’s performance, the cost flow rate of each component is evaluated by performing the energetic, exergetic and exergoeconomic analyses. The compressor pressure ratio (πAC), flight Mach number (Ma) and turbine inlet temperature (TIT) are three operating variables, which affect the performance of the whole system. Therefore, a sensitivity analysis is carried out to survey the effect of these variables on objective functions (i.e., energy efficiency, exergy efficiency, and exergy destruction). It is found that there are some contradictions between exergy efficiency and exergy destruction, which by increment in TIT energy efficiency increases, while the exergy destruction decreases. Therefore, an optimization should be applied on the presented system. The results show that the highest exergy destruction, unit exergy cost, and cost rate are 34.96 GJ h−1, 34.85 US$ GJ−1 and 437.37 US$ h−1 occur in the combustion chamber, compressor’s outlet flow and combustion chamber outlet stream, respectively. The energetic and exergetic optimization solution is obtained as the Pareto frontier. Final decision-making methods such as TOPSIS, LINMAP are employed for choosing the optimal solution. Design points of LINMAP and TOPSIS having 65.86%, 66.95% thermal efficiency and 12.51 GJ h−1, 12.65 GJ h−1 exergy destruction, respectively.