Research Of Semiconductor Thermoelectric Power Generation System Used For Large Temperature Difference Waste Heat Recovery Of Diesel Engine

Diesel engine is one of the main consumers of petroleum resources, and it is themain source of greenhouse gas emissions. Energy-saving research of diesel engine isof great significance for energy conservation and emission reduction. About30%ofthe energy generated by the combustion of fuel in diesel engine become waste heatand discharged from the exhaust, resulting in the waste of fuel and environmentalpollution. Thermoelectric technology is a new energy conversion way that directlyconverts thermal energy into electric energy by using thermoelectric materials. Thistechnology has a simple structure, high reliability and enormous potentiality in wasteheat recovery of internal combustion engine.A detailed analysis of diesel engine exhausts characteristics and performance ofsemiconductor thermoelectric materials is included in this thesis. For thecharacteristics of the waste heat recovery in diesel engine and the narrow bestworking temperature range of thermoelectric materials, a segmented thermoelectricpower generation system is proposed. Based on the basic thermoelectric effect andheat transfer theory, this thesis establishes the mathematical model of general andsegmented thermoelectric unicouple using two kinds of thermoelectricmaterials--Bi2Te3and CoSb3. Then the thesis calculates the output power andthermoelectric conversion efficiency under different conditions. And have acomparison of the performance between general and segmented thermoelectricunicouple. The results show that improving the maximum output power of thethermoelectric unicouple can be achieved by increasing the hot surface temperature,reducing the cold surface temperature, improving the convective heat transfercoefficient, shortening the length of the thermoelectric unicouple and increasingcross-sectional area. But the conversion efficiency cannot be increased by thoseconditions continuously. Changing cross-sectional area has no effect on theconversion efficiency, and shortening the length of the thermoelectric unicouple caneven decrease the conversion efficiency. Compared with general thermoelectricunicouple, segmented thermoelectric unicouple can accommodate larger temperaturedifference between the hot and cold junction. The output power and conversion efficiency are both improved. The greater temperature difference of cold and hotjunction, the more obvious the segmented unicouple performed. When thetemperature of hot surface and cold surface separately are700K and300K, thetemperature difference is400K, the output power of segmented thermoelectricunicouple (length ratio is3:1) is33.5%higher than CoSb3general thermoelectricunicouple.In order to validate the theoretical model of thermoelectric generator, a test benchof thermoelectric power generation system is designed and built. Using this test bench,the performance of thermoelectric module is tested. And obtain the same performancerule with the theoretical analysis. Compare the performance impact of hot side andcold side temperature, it can be found that reduce the cold side temperature willimprove the output power of thermoelectric more effectively than raise the hot sidetemperature under the test condition. In the design of thermoelectric generator, moreattention should be paid on the heat sink of cold side.