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To improve the impinging spray's computational fluid dynamics (CFD) calculations under evaporating conditions, a detailed large eddy simulation (LES) code was constructed and examined for modeling the near-wall-velocity behavior of the impinging jet. The near-wall-velocity profile within the impinging jet was found to be different from that obtained using the steady wall functions. On the basis of this knowledge, a simple model of the wall boundary conditions was proposed for the impinging jet. The tests covered two different turbulence models. Comparing with the conventional wall functions, the proposed model improved the accuracy of the impinging spray simulations.

A method to improve fuel consumption in diesel engines is to enhance their theoretical thermal efficiency by increasing their compression ratio. However, this results in an increase in heat loss due to the elevation of the concomitant in-cylinder temperature and the expansion of the impingement area between fuel spray and chamber wall. Therefore, reducing heat loss to the chamber wall is important to effectively benefit from a high compression ratio. To meet this challenge, in this study, we optimized the combustion chamber shape using the three-dimensional computational fluid dynamics (CFD) simulation software, CONVERGE. A rationale proposed by the University of Wisconsin-Madison was selected to outline the shape and combined with a multiobjective optimization software, modeFRONTIER. The calculations produced a shallow dishlike combustion chamber comprising a plateau at its center that may reduce heat loss.