Study On Method Of Energy Efficiency Evaluation And Marine Main Engine Energy System Optimization Based On Thermoecnomic Principle

With the aggravation of global warming and the soaring energy prices, humans are attaching great importance to energy saving and emission reduction. Ship, as the media of waterage, is consuming a large amount of energy anaually. The study on ship energy efficiency is significant. Conventional ship energy efficiency evaluation emphasizes much on increasing ship’s energy efficiency, but little on the economical efficiency in ship’s operation. This paper combines thermoeconomic and traditional energy efficiency evaluation methods, takes ship’s non-operational energy consumption into thermoeconomic evaluation system and finally introduces evalution method of ship thermoeconomic energy efficiency, which incorporates both energy efficiency and economical efficiency of the ship.Firstly, the evaluation method of conventional energy efficiency (EEDI and EEOI) is systematically researched and features of both EEDI and EEOI are analyzed. By studying the relationship among velocity, main engine power, RPM and fuel consumption as well as a specific example, the naval constant method is proven to be applicable to EEOI calculation. EEOI method is used for analyzing energy efficiency of multi-functional ships.Secondly, the concept of ship’s total energy system is put forward for the target ship and analysis of thermal equilibrium and exergy equilibrium for the main engine energy system of the target ship is conducted. The results indicate that70%～85%power of the main engine is the optimal range for the target ship. Exergy equilibrium analysis can better reflect the quality of energy and the essence in energy transformation, which has more advantages in analysis and optimization of energy system.Thirdly, optimizing method of thermoeconomic is researched for the main engine energy system of target ship. The problem of conversion between "product" and "resource" in thermoeconomic analysis is addressed by means of reciprocation and exchange of constrained conditions for the symmetric non-linear optimizing problem; Lagrange multiplier theory is used for defining shadow price in exergy flow and negative entropy flow; Kuhn-Tucker condition is applied to figure out the necessary and sufficient conditions ensuring that the non-linear optimizing problem has optimum solution; the thermoeconomic isolation theorgy is utilized to divide the whole system into several correlated sub-systems; the concept of negative entropy flow is introduced into thermoeconomic analysis and the problem of "combinatory explosion" resulting from system division is resolved. With all methods above, effective thermoeconomic optimizing model is established for energy system.Fourthly, thermoeconomic models are built and analyzed for the main engine energy system and its sub-systems of the target ship. Based on the studies, thermoeconomic optimization is conducted. The optimized results indicate that the method of thermoeconomic optimization can reflect the thermoeconomic characteristic of energy flow effectively, and thermoeconomic optimization point is obtained at the sanme time. In a certain range, thermoeconomic characteristic can be improved through reducing scanvage temperature and increasing maximum combustion pressure.Finally, based on the researches above, the thermoeconomic assessment is applied to ship energy efficiency evaluation. With reference to EEOI evaluation method, the Thermal Economics Energy Efficiency Operational Indicator (TEEEOI) is put forward, and applied to the thermoeconomic evaluation of the target ship energy efficiency. The results indicate that, by introducing the ship’s non-operational energy consumption into ship energy efficiency evaluation system, evaluation result is more comprehensive and accurate. Energy consumption per GDP of ship-building nation and industrial energy consumption have large influence on ship’s non-operational energy consumption, which can vary a lot in different nations. The TEEEOI not only evaluates ship energy efficiency evaluation, but also economical efficiency. Among the influencing factors on TEEEOI, fuel price comes first, then the cargo type and shipbuilding cost.