Power density characteristic analysis and multi-objective optimization of an irreversible porous medium engine cycle

Based on irreversible Porous Medium cycle model established in the previous literature, this paper investigates cycle optimal performance by taking cycle power density as optimization objective and applying finite time thermodynamics. Various parameters are used to examine relationships among power density and thermal efficiency versus compression ratio. The cycle performance is compared under maximum power density circumstance and maximum power output circumstance. Compared with condition of maximum power output, the Porous Medium cycle engine gets higher thermal efficiency and smaller size under the maximum power density condition. One-, two-, three- and four-objective optimizations of the cycle are performed by using NSGA-II algorithm, choosing compression ratio as design variable, and choosing dimensionless power density, dimensionless power output, thermal efficiency, and dimensionless ecological function as optimization objectives. Using three decision schemes, LINMAP, TOPSIS and Shannon entropy, deviation indices under different optimization objective combinations are compared. For six two-objective optimizations, power output and thermal efficiency optimization has the smallest deviation index, 0.1215. For four three-objective optimizations, power output, ecological function and power density optimization has the smallest deviation index, 0.1235. For four-objective optimization, the deviation index is 0.1419. The appropriate solution should be selected according to the actual application.