Design And Simulation Research Of Exhaust Gas Splitting With Waste Heat Recovery System Of Low-speed Marine Engine

The traditional Diesel engine has a relatively low output power,and its exhaust energy recovery has great value to use.How to use the exhaust energy to improve the power output of two-stroke Diesel engine is one of the focuses of current research.The exhaust process of Diesel engine generally lasts from the opening of the exhaust valve to the closing of the valve.After the mixing of high temperature exhaust gas and DC scavenging air,the exhaust energy quality is reduced,which is not conducive to the waste heat system to obtain a higher temperature heat source.How to optimize the exhaust system and utilize the exhaust waste heat is one of the key technologies to improve the total power output and energy utilization rate of two-stroke lowspeed Diesel engine.In this paper,340 series low-speed engine is taken as the research object,and a method of exhaust gas utilization is proposed,which combines exhaust energy splitting method with waste heat recovery technology.The thermal analysis of the system is carried out and the mathematical model of each part of the system is established.Analyze the key parameters in the waste gas separation and waste heat recovery system of low-speed engine,analyze and select the components,including auxiliary fan,the design and evaluation of evaporator,the parameter selection of expander and pump.The exhaust gas splitting system of low-speed engine is established by using GT-Power software.According to the energy characteristics of exhaust gas under different exhaust phase,the exhaust gas of low-speed engine is divided by high and low temperature exhaust valve.It can improve the quality of exhaust gas and provide high-grade heat source for the waste heat system.Four waste heat recovery systems,ORC system,RORC system,DORC system and DRORC system,were designed and established.The coupling matching between each waste heat recovery system and the exhaust gas splitting system of low-speed engine was carried out to complete the design of waste heat recovery system of low-speed engine exhaust gas splitting system.The working fluid of waste heat system was screened and various working fluid combinations were analyzed.R141b+R141b scheme was adopted for the two-stage ORC system.The influence of heat source temperature,evaporation temperature,evaporation pressure,pinch point temperature difference,superheat,reheat and other thermal parameters on the characteristics of the waste heat recovery system of low-speed engine exhaust gas splitting system is analyzed,which provides reference for the value of thermal parameters.Aiming at 25%,50%,75% and 100% working conditions,the influence of exhaust gas splitting on the performance of low-speed engine was analyzed,and the total output power of exhaust gas splitting and waste heat recovery system of low-speed engine was simulated,and the applicable working conditions and exhaust energy recovery strategy of exhaust gas splitting were studied.At 25% load and 50% load,the recovery power of waste heat recovery system is lower than the effective work of exhaust gas splitting loss,so it is not suitable for exhaust gas splitting.In 75% and 100% loads,the optimal splitting phase changes with different loads.The optimal splitting phase in higher load is smaller.The highest total power waste heat recovery system is DRORC system,and the total power of the system is higher than that of the original engine system.