Analysis of Energy and Exergy Distribution for Improving Fuel Economy of Marine Low-speed Two-stroke Diesel Engine

Increasingly strict emission regulations and unfavorable economic climate bring severe challenges to the energy conservation of marine low-speed engine. Besides traditional methods, the energy and exergy analysis could acknowledge the losses of fuel from a global perspective to further improve the engine efficiency. Therefore, the energy and exergy analysis is conducted for a marine low-speed engine based on the experimental data. Energy analysis shows the exhaust gas occupies the largest proportion of all fuel energy waste, and it rises with the increment of engine load. The heat transfer consumes the second largest proportion, while it is negatively correlated to engine load. The energy analysis indicates that the most effective way to improve the engine efficiency is to reduce the energy wasted by exhaust gas and heat transfer. However, the latter exergy analysis demonstrates that there are other effective approaches to improve the engine efficiency. Related results show that the combustion irreversibility is the largest component of exergy waste. Its proportion is about 30%, but it declines with the increment of engine load. The reason is that it is mainly caused by the irreversible process in cylinder, while combustion irreversibility is usually relatively lower for a higher engine load. Finally, results of exergy analysis indicates that reducing the temperature gradient in cylinder could effectively suppress this combustion irreversibility, thereby improving the engine efficiency.