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Hongwang Du,Hancong Xu,Jialong Li,Zhanpeng Zhou 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.11
The thermal load in the piston head is becoming heavy with the application of supercharging technology. This makes the piston cooling become more challenging to ensure the reliability of the piston. In this study, an oil-injection cooling process in a medium-speed Vtype diesel engine is numerically investigated. The simulations are performed for the direct coupling of the piston head structure and the two-phase flow in the cooling gallery. The effect of the flow pattern on heat transfer characteristics during the whole process is discussed. The results reveal a series of the flow characteristics including thrown flow, interrupted flow, wall impingement, oil oscillating and sedimentation during the reciprocating movement of the piston and the flow characteristics become more obvious with the increase of the engine speed, but the cooling oil is more widely distributed in the oil gallery due to more intense oscillation. After multi-cycle calculations, the flow characteristics of the cooling oil and the heat transfer characteristics of the piston both have a certain periodicity.
Zhu Yifan,Xu Feng Xiang,Guan Yijie,Zou Zhen,Duan Libin,Du Zhanpeng,Ma Hongfeng 한국자동차공학회 2023 International journal of automotive technology Vol.24 No.5
As an alternative to the conventional concave hexagonal honeycomb structure (CHHS), a negative Poisson’s ratio honeycomb structure with power function curve (NHPC) was devised. The relationship between the power function exponent (PFE) and normalized power function coefficient (NPFC) of honeycomb structure and its equivalent Poisson’s ratio (EPR) was explored to identify the range of variables required for the negative Poisson’s ratio effect. To investigate the in-plane mechanical properties and energy absorption characteristics of NHPC, the deformation mode, dynamic response, and energy absorption characteristics under various impact velocities were studied by constructing an in-plane impact simulation model. The results showed that NHPC obviously exhibited a negative Poisson’s ratio effect on medium and low impact velocities, and the deformation was primarily uniform. As the NPFC increased, the honeycomb structure was less prone to stress concentration, while the peak crushing force (PCF) and the specific energy absorption (SEA) declined and the plateau stress increased. A multi-objective optimization experiment was operated with low PCF and high SEA as the targets within the range of design variables in order to generate the optimal NHPC. According to the experimental findings, the improved NHPC showed a 25.48 % reduction in PCF and a 19.29 % increase in SEA. This paper provides theoretical recommendations for improving the energy absorption and structural optimization of the honeycomb structure.