Design And Optimization Of Low Grade Waste Heat Utilization Scheme For Marine Diesel Engine Based On Organic Rankine Cycle

Growing energy shortages severely restricting the sustainable development of human beings,improving energy efficiency has become an urgent issue.Internal combustion engine is the most widely used machinery in industrial production and transportation,which consumes lots of fossil fuels and produces harmful gases from inadequate combustion.For saving energy cons umption and reducing emissions,the waste heat recovery technology is used to reuse the waste heat of the engine to improve the utilization of fuel.The latest researches less focus on the field of low-temperature waste heat utilization,the environmental impact assessment of waste heat recovery device,and the other waste heat in the internal combustion engine except for exhaust gas.Therefore,this paper will take the large two-stroke marine diesel engine,whose heat source temperature lower than 300 degrees Cels ius as the research object,to carry out the research of waste heat recovery system for the engine.This paper firstly analyzes the distribution of waste heat energy in the marine diesel engine,explores the energy flow and exergy flow of each waste heat source in the engine,and determines the main components of exhaust gas and acid dew point temperature,providing the data support for subsequent research.Secondly,the mathematical model of organic Rankine cycle,with the best recovery effect for low-temperature waste heat in all waste heat recovery technologies,is established.Three indexes for assessing thermodynamic performance,economic performance and environmental performance are extablished.By comparing the performance of different cycle layout and different working fluid,the most suitable cycle layout and working fluid are determined.After determining the layout and circulating working fluid,the sensitivity analysis method is used to find out the main parameters that affect the performance of the waste heat recovery system.And then the multi-objective optimization algorithm is adopted to optimize the system parameters.Finally,on the basis of the above research and analys is,a new type of multi heat source waste heat recovery system is proposed by combining the organic Rankine cycle with zeotropic working fluid and other low temperature waste heat utilization technologies.Likewise,the parameters of the proposed system are optimized.The results show that the performance of dual pressure organic Rankine cycle is the best layout when the heat source temperature is below 260 ℃.When pure working fluid is used,cyclopentane acquires the highest performance score.When zeotropic working fluid is used,the working pair of dimethyl carbonate and R245 fa acquires the highest performance score.At 70% engine load,the thermal efficiency of the engine with multiple heat source waste heat recovery system is about 4.2% higher than that of the engine without waste heat recovery system.Compared with only using a single dual pressure organic Rankine cycle to recover waste heat,the multiple heat source waste heat recovery system increases about 8% net output power,5.7% exergy efficiency,and reduces about5.8% environmental impact rate per unit net work.