Research On Interaction Of Marine Diesel Engine Waste Heat Utilization System Based On S-CO₂,Brayton Cycle

With the development of the global economy,the importance of the shipping industry has increased,and the issue of ship emissions has gradually attracted widespread attention.In this context,the International Maritime Organization has introduced strict regulations to limit ship emissions,and waste heat utilization technology has become a research hotspot as an important way to achieve ship energy saving and emission reduction.The supercritical carbon dioxide（S-CO₂）Brayton cycle power generation system has the characteristics of small size,high energy density and high efficiency.It has significant technical advantages in nuclear/thermal power plants,solar thermal power generation,industrial waste heat utilization,and geothermal utilization.It is also one of the important technical ways to solve the waste heat utilization of ship main engine flue gas.However,while the S-CO₂Brayton cycle power generation system is used to convert and utilize the waste heat of marine diesel engine flue gas,it will also have a significant impact on the thermal-mechanical,thermal-electric conversion and operating characteristics of the two due to the energy interaction.The research use the method of system joint modeling simulation analysis to establish the joint simulation model of diesel engine,flue gas heat exchanger,and S-CO₂ Brayton cycle system at different levels,and then analyzes the diesel engine changes from the perspective of steady state and dynamic operation process.The interactive influence characteristics under load conditions and wastegate valve regulation can provide theoretical guidance and data support for the design of the S-CO₂ Brayton cycle power generation system for the utilization of waste heat from marine diesel engines and the application of on-board ships.The main research conclusions of the thesis are as follows:（1）The 10S90ME-C9.2 marine two-stroke low-speed diesel engine and S-CO₂Brayton cycle system simulation models were established in the GT-Power simulation software,and the calculation results of the simulation model were compared with the main engine bench test data and calibrated The difference between the design point working condition parameters verifies the accuracy of the model;（2）In terms of the system steady-state interactive influence law:the opening of the wastegate valve remains unchanged,the output power of the Brayton cycle decreases as the diesel engine load decreases,and the cycle efficiency decreases.The diesel engine load remains unchanged.As the wastegate valve opening increases,the heat exchanger power increases,and the diesel engine power decreases;the output power of the Brayton cycle increases,and the efficiency increases.When the flue gas consumption is 19.506 kg/s,the diesel engine power is 4239 k W lower than the rated power,a decrease of about 7.1%;（3）In terms of system dynamic interaction characteristics:the opening of the wastegate valve remains unchanged,and when the diesel engine load suddenly decreases,the power of the heat exchanger first decreases and then increases,and the slower the load changes,the smaller the amplitude of power fluctuations.;When the diesel engine load drops suddenly,the output power of the Brayton cycle decreases.After the diesel engine system stabilizes,the cycle output power begins to rise and fluctuates in a small range,and stabilizes after about 4000s.When the load of the diesel engine remains unchanged and the opening of the wastegate valve suddenly decreases,the power of the diesel engine decreases first and then increases.The slower the change of the opening of the bypass valve,the smaller the fluctuation range of the diesel engine power and flue gas temperature.