Multi-objective optimization of the volumetric and thermal efficiencies applied to a multi-cylinder internal combustion engine

The engines produced with valve timing systems have been growing in recent years, given the growing demand to improve their operation and efficiency. Certain operating conditions of valve timing engine increasing volumetric efficiency have a reduction in thermal efficiency. This study aims to apply multi-objective optimization to find conditions for opening and closing valves of maximum volumetric and thermal efficiency, evaluating through performance metrics two optimization methods. The inlet and exhaust valves timing were chosen as design variables. The multi-objective optimization methods used are Non-dominated Sorting Genetic Algorithm - II and Multi-Objective Differential Evolution. Simulations are performed for four different engine speeds. The compressible duct flow is numerically solved by the two step Lax-Wendroff method with Total Variation Diminishing flow control. The performance metrics used in this study are maximum values, number of non-dominated solutions, spacing, hyper-volume and time simulation. The results showed a Pareto front maximizing the volumetric efficiency and decreasing thermal efficiency, and vice versa. The Multi-Objective Differential Evolution presented greater values than Non-dominated Sorting Genetic Algorithm - II, more non-dominated solutions, higher hyper-volume values, with the advantage of spent less computational time. Both approaches were able to optimize internal combustion engine efficiencies finding the optimal valve timing sets. Moreover, allows finding conditions for opening and closing valves that favor both efficiencies.