Theoretical And Experimental Research Of Supercritical Carbon Dioxide Turbine For Waste Heat Recovery Of Internal Combustion Engine

Internal combustion engine,as the main consumption source of oil,more than50% of its energy is dissipated into the environment in the form of waste heat.The recovery and utilization of waste heat energy of internal combustion engine is an important technical path to improve the efficiency of internal combustion engine and reduce carbon dioxide emission,which will help to achieve the national "double carbon" goal.The power cycle using carbon dioxide as the working fluid can achieve the characteristics of efficient recovery of internal combustion engine waste heat,rapid adaptation to operating conditions and miniaturization of the device,which is a current research hotspot.As the core component of power cycle,carbon dioxide expander directly affects the system performance.Due to the parameter characteristics of small flow and high pressure,carbon dioxide expander has also become a "neck" technical difficulty in the realization of cycle technology.In this paper,the theoretical design,prototype development and experimental research of small turbine expander suitable for carbon dioxide power cycle are carried out.The main research contents are as follows:At the theoretical design level,combined with the power level and design parameters of the expander,based on the Barber-Nichols selection diagram,the aerodynamic type of the partial inlet axial flow turbine was determined.Considering with the power level and design parameters of the expander,based on the BarberNichols selection diagram,the aerodynamic type of the partial admission axial turbine was determined.With partial admission,the processing difficulty of the expander is reduced by raising the blade height,reduce the turbine design speed and overcome the harsh requirements for high-speed bearings and ultra-high-speed motors.Comprehensively considering the real physical properties of supercritical carbon dioxide and referring to the design theory of gas turbine,the blade profile of supercritical carbon dioxide turbine expander is designed by selecting appropriate flow coefficient and load coefficient.According to the design results,combined with the ANSYS Workbench platform,the three-dimensional simulation of the expander is carried out in the form of single channel.The rationality and accuracy of the design results are proved by analyzing the overall performance and flow field distribution characteristics of the turbine.At the level of prototype development,for the inlet pressure up to more than 10 MPa,the design of dynamic seal is the focus and difficulty of prototype development.Firstly,based on the theoretical design scheme,the first-generation dynamic seal scheme of expansion ring + castor tooth + lip seal and the assembly method of nozzle clearance matching are set up.A prototype and test system of supercritical carbon dioxide partial inlet axial flow turbine are successfully developed,and the operation strategy of expander with effective matching and safe switching is proposed.The prototype is preliminarily tested based on the carbon dioxide power cycle experimental platform,The results show that the maximum power generation of the prototype is only 0.50 k W,and the pressure difference can not be established before and after the turbine.In view of the above problems,an improved dynamic seal technical scheme of multi-stage carbon ring labyrinth seal structure is further proposed.The test results show that the improved structure can effectively establish the differential pressure at both ends,and the maximum power generation of turbine expander can reach 1.67 k W.In the aspect of experimental research,based on the developed prototype of partial admission axial turbine,carry out experimental research on the performance under all working conditions to explore the influence of rotational speed,mass flow rate and heat source on the performance of turbine expanders.The experimental results show that the turbine power generation first increases and then decreases with the increase of speed,and reaches the maximum power generation of 2.27 k W at20877 rpm.The speed and power generation of the prototype are positively correlated with the increase of flow.The performance of turbine expander increases with the increase of heat source temperature,and the corresponding speed of its best power generation performance also increases with the increase of heat source temperature.At the application development level,in view of the demand of another carbon dioxide power cycle of 10 k W power generation,explore the technical path to improve the turbine performance by changing the nozzle air inlet,so as to expand the application scope of the prototype.The partial air intake of the original sample machine was increased from 1/16 to 1/10.After the nozzle was processed and assembled,the performance test was carried out based on the split flow carbon dioxide power cycle of the research group.It was found that the turbine performance increased with the increase of rotating speed,and the maximum power generation was6.68 k W at 29208 rpm.To a certain extent,it verified the feasibility of changing the power of some intake axial flow turbine expanders by increasing partial air intake.