A New Multi-Heuristic Method to Optimize the Ammonia–Water Power/Cooling Cycle Combined with an HCCI Engine

Nowadays, sustainability is one of the key elements which should be considered in energy systems. Such systems are essential in any manufacturing system to supply the energy requirements of those systems. To optimize the energy consumption of any manufacturing system, various applications have been developed in the literature, with a number of pros and cons. In addition, in the majority of such applications, multi-objective optimization (MOO) plays an outstanding role. In related studies, the MOO strategy has been mainly used to maximize the performance and minimize the total cost of a trigeneration system with an HCCI (homogeneous charge compression ignition) engine as a prime mover based on the NSGA-II (non-dominated sorting genetic algorithm-II) algorithm. The current study introduces a novel multi-heuristic system (MHS) that serves as a metaheuristics cooperation platform for selecting the best design parameters. The MHS operates on a proposed strategy and prefers short runs of various metaheuristics to a single long run of a metaheuristic. The proposed MHS consists of four multi-objective metaheuristics collaborating to work on a common population of solutions. The optimization aims to maximize the exergy efficiency and minimize the total system cost. By utilizing four local archives and one global archive, the system optimizes these two objective functions. The idea behind the proposed MHS is that metaheuristics will be able to compensate for each other’s shortcomings in terms of extracting the most promising regions of the search space. Comparing the findings of the developed MHS shows that implementing the suggested strategy decreases the total unit costs of the system products to 25.85 USD/GJ, where the total unit cost of the base system was 28.89 USD/GJ, and the exergy efficiency of the system is increased up to 39.37%, while this efficiency was 22.81% in the base system. The finding illustrates significant improvements in system results and proves the high performance of the proposed method

Development of a Reduced Mechanism for <i>n</i>-Heptane Fuel in HCCI Combustion Engines by Applying Combined Reduction Methods

Employing comprehensive chemical kinetics mechanisms in predictive models results in the high demand for simulation time, which makes the use of these mechanisms questionable. Consequently, reduced mechanisms of smaller sizes are needed. The objective of this study is to produce reduced mechanisms of <i>n</i>-heptane fuel, by utilizing a three-stage reduction process. This work is performed using a validated single-zone homogeneous charge compression ignition (HCCI) combustion model. To remove unimportant species at the first stage, the directed relation graph with error propagation (DRGEP) is applied. In the second stage, the computational singular perturbation (CSP) method is used to eliminate insignificant reactions. In the third stage, because of the change in the net production and consumption rate of species as a result of utilizing the second stage and its effect on direct interaction coefficients calculated with DRGEP method, once again DRGEP is applied to the mechanism for further reduction. Peak pressure, maximum heat release, and CA50 have been selected as representative parameters for evaluating the performance of the reduced mechanism. For the generated reduced mechanism at each reduction step, these parameters are calculated and the deviations from the corresponding value obtained by applying detailed mechanism to the model are evaluated until user-specified error tolerances are exceeded. This combination of methods successfully reduced the comprehensive Curran’s <i>n</i>-heptane mechanism (561 species and 2539 reactions) to a reduced mechanism with only 118 species and 330 reactions, while maintaining small errors (<2%), compared to the detailed mechanism. The simulation time required for calculation by applying reduced mechanisms is decreased from ∼601 min to 8 min, in comparison to the detailed mechanism. In addition to matching pressure, temperature, and heat-release-rate traces, the mass fraction of some important species calculated from the reduced mechanism closely agree with the results obtained from the detailed mechanism. The reduced mechanism is included as Supporting Information with this article