Parametric investigation and thermo-economic multi-objective optimization of an ammonia–water power/cooling cycle coupled with an HCCI (homogeneous charge compression ignition) engine

• Ammonia–water power/cooling cycle as a bottoming cycle is coupled with an HCCI engine.
• Exergetic and exergoeconomic analysis of the bottoming cycle are reported.
• The system is optimized using multi-objective genetic algorithm.
• Two different multi-objective optimization scenarios are carried out to determine the best design parameters.
• Selecting the exergy efficiency as sole objective function is not guarantee the cooling potential.

A parametric study and multi-objective optimization strategy are performed for a bottoming cycle of a trigeneration system with an HCCI (homogeneous charge compression ignition) engine as prime mover. To assess the influences of decision parameters on the performance and total cost of cycle, a parametric investigation is conducted. Two different multi-objective optimization scenarios are carried out to determine the best design parameters. For the first scenario, the objective functions which are utilized in the optimization study are exergy efficiency and the sum of the unit costs of the system products. The system cost criteria is minimized while the cycle exergy efficiency is maximized using an evolutionary algorithm. Exergy efficiency increases about 16.34% and reduction in the unit costs of the system products is about 10%. However, it is found that cooling capacity of the system is reduced to 83%. For the second scenario, the objective functions are considered to be the sum of the unit costs of the system products, net power generation, and exergy flow rate of refrigeration output. Employing the second scenario improved both power generation and cooling capacity of the system. The increase in exergy efficiency is 5.61%. These are achieved with even a slight reduction in the system cost criteria.