Simulation And Experimental Research On The Automotive Exhaust Waste Heat Thermoelectric System

In the driving process of an automobile, up to 40% of the total heat generated by the gasoline is lost in the form of exhaust gas. The thermoelectric technology can directly convert low quality waste heat into high quality electrical power for rational use based on the Seebeck effect, which is becoming the hotspot in the international research. The automotive exhaust thermoelectric system has presented urgent potential in the case of waste heat recovery with many advantages such as environmentally friendly, no moving parts, steady performance, long-lived and requiring little maintenance. In current research, the main works stay in material and device level, lacking of comprehensive investigations in the system level. Focused on the simulation and experimental research on the thermoelectric system under specific on-board environment, this paper concentrates upon the three factors including the behavioral characteristics of the thermoelectric module under automotive application environment, waste heat recovery and transfer technology as well as electrical power regulation technology in system architecture for the first time.The major works in this paper are listed as follows:(1) A test bench is established with the functions of adjustable pressure set and independent control on the temperature of hot end and cold end for the thermoelectric module’s characterization study; With the characteristics summary of automobile exhaust energy, A research and analysis are carried out on the effect on electrical output performance of the thermoelectric module with different temperature difference and clamping force based on the test bench mentioned above; The stability, durability and corrosion resistance performance of the thermoelectric module are also validated; A mathematical model is built to describe the relationship between the input temperature characteristics and output power characteristics for further simulation, vehicle integration and road test.(2) The optimal Latin hypercube design method is adopted for the design of experiments to explore the key effect factors on the uniform temperature distribution as well as backpressure of the heat exchanger and the design variables including the length, spacing, angle, thickness of the interior fins. Aimed at homogeneous temperature distribution and lower backpressure, a surrogate model integrated with multi-island genetic algorithm method is built to optimize the inner flow field and surface temperature. A set of best internal spoiler distribution parameters is obtained and then validated. The simulation and experimental results indicate that the optimized heat exchanger has good performance with better temperature uniformity and lower exhaust back pressure.(3) Influenced by the temperature gradient distribution on the surface of the heat exchanger, the thermoelectric devices work under temperature mismatch conditions and operate with inconsistent electrical characteristics. By means of experimental test, we study the electrical characteristics of the thermoelectric devices in series and parallel circuit connection when they work under uniform temperature distribution as well as gradient temperature distribution. The experimental results show that the group of thermoelectric devices performs well with minimal power loss when connected in series connection, which is a more rational circuit connection for this situation. An experimental research is carried out to improve the inconsistent electrical performance among the thermoelectric devices by regulate the heat transfer progress from the surface of heat exchanger to the hot side of the thermoelectric device. It is proved to be effective to ameliorate the electrical performance of the system when the thermoelectric devices work under gradient distribution and limited temperature conditions.(4) Based on the preliminary mathematical model of thermoelectric devices, a simulation model is established to describe the relationship between the input characteristics exhaust temperature as well as the gas mass flow and output power of the automotive exhaust heat thermoelectric system. We study and analyze electrical power output and potential fuel economy of the on-board exhaust thermoelectric system in various typical cycle conditions. The Dongfeng warrior is selected as the vehicular platform, thus we propose and finish the “four heat exchangers paralleled in gas path” design project. The experimental tests and validations are carried out under highway cruising and drum test bench conditions. The simulation result is inconsistent with the test result and is proved to be feasible in describing the output power characteristics of the exhaust thermoelectric system.