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Energies 2018, 11(3), 513; https://doi.org/10.3390/en11030513

Investigation on the Potential of High Efficiency for Internal Combustion Engines

State Key Laboratory of Engines, Tianjin University, Tianjin 300072, China
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Received: 23 January 2018 / Revised: 20 February 2018 / Accepted: 24 February 2018 / Published: 27 February 2018
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Abstract

The current brake thermal efficiency of advanced internal combustion engines is limited to 50%, and how to further improve the efficiency is a challenge. In this study, a theoretical investigation on engine thermal efficiency was carried out using one-dimension simulations based on the first law of thermodynamics. The energy balance was evaluated by varying parameters such as compression ratio (CR); heat transfer coefficient; intake charge properties; and combustion phasing etc.—their influences on the efficiency limits were demonstrated. Results show that for a given heat transfer coefficient, an optimal CR exists to obtain the peak efficiency. The optimal CR decreases with the increase of heat transfer coefficient, and high CR with a low heat-transfer coefficient can achieve a significantly high efficiency. A higher density and specific heat ratio of intake charge, as well as a shorter combustion duration with a proper CA50 (crank angle at 50% of total heat release), can increase efficiency significantly. Methanol shows an excellent ability in decreasing the peak in-cylinder temperature; and the peak indicated efficiency is relatively higher than other tested fuels. The displacement has few effects on the indicated efficiency, while it shows a strong effect on the energy distribution between heat transfer and exhaust energy. All these strategies with high CR result in high in-cylinder pressure and temperature; which means a breakthrough of material is needed in the future. View Full-Text
Keywords: engine; thermal efficiency; heat transfer; first law of thermodynamics; losses; high compression ratio engine; thermal efficiency; heat transfer; first law of thermodynamics; losses; high compression ratio
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Liu, H.; Ma, J.; Tong, L.; Ma, G.; Zheng, Z.; Yao, M. Investigation on the Potential of High Efficiency for Internal Combustion Engines. Energies 2018, 11, 513.

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