Study On A Directly-drive Thermoacoustic Electric Generation System

Many researchers pay attention to thermoacoustic electric generator for its advantages of lower cost, high reliabilityand environmentally friendly. The research of thermoacoustic electric generator mainly focuses on the one with a resonance tube, which makes the structural dimension of the system becoming too large. While the research of the thermoacoustic electric generator used for aerospace application with small size and light mass is relatively few, in China, only our group carried out some research on directly-drive thermoacoustic electric generator. In order to fully research the operational modal of the directly-drive thermoacoustic electric generator, realize the nonlinear oscillation, and improve the performance of the whole engine, theoretical and experimental study are carried out as fellow:The network model of the directly-drive thermoacoustic electric generator is developed and built based on the innovative network impedance analysis method. Oscillation is the prerequisite for the thermoacoutic electric generator. Three kinds of impedance are existed in the directly-drive thermoacoustic electric generator, and they are gas acoustic impedance, mechanical impedance and electric impedance, and mechanical impedance and electric impedance play a decisive role in the oscillation of the whole engine. The analysis of the governing equations of the thermoacoustic engine and linear alternator is carried out firstly, and then the network models of the thermoacoustic engine and linear alternator are built respectively, and finally the network model of the whole engine is built according to the continuity of oscillating pressure, volume flow rate and enthalpy of the thermoacoustic engine and linear alternator at the acoustic power output port.The design of the structure parameters of the components of the directly-drive thermoacoustic electric generator is carried out. The linear alternator is the resonant element of the thermoacoustic electric generator, so its impedance is determined by its parameters as well as the output characteristic of the thermoacoustic engine, so the simulation program of the whole engine is built based on DeltaE. The calculation of parameters of hot heat exchanger, regenerator, main cold heat exchanger, compliance, inertance tube, acoustic power output port, secondary cold heat exchanger and thermal buffer tube is carried out, and the simulation of the piston area, clearance, moving mass, mechanical-electrical conversion constant, mechanical damping and stiffness of the linear alternator is constructed. The parameters of the thermoacoustic engine components and key parameters of the linear alternator are initially identified in the principle of improving the system performance.Linear alternator is developed to match with the output impedance of the thermoacoustic engine, and a complete set of processing and assembly process is formed and a set of measuring device for the key parameters is built. The key performance parameters of the linear alternator are determined after the work of simulation optimization. The simulation design of the electromagnetic components of the linear alternator is carried out based on Ansoft Maxwell, and the structure of the silicon steel sheet iron core and the length of the coil are determined under the premise of getting the right electromechanical conversion constant. The clearance between the piston and cylinder of the linear alternator is small, so it needs a higher coaxial degree. After a long period of exploration, a complete set of processing and assembly process is built. Because the design parameters of the linear alternator are always deeply influenced by the machining and assembling process, a set of measuring method and device for the key parameters is built to get its final value.Experimental study on the thermoacoustic electric generator is carried out, and the whole engine could work for a long time with a high efficiency after six cycles of research. Two different types of linear alternator are used as the acoustic load of the thermoacoustic engine, so that the whole engine realized the nonlinear oscillation. The structure of the hot heat exchanger, thermal insulation device and pressure chamber is improved, and the problem of the deformation of the hot heat exchanger, large leakage and blockage piston is solved. The charging and discharging system and external circuit are simplified and are integrated in a little control box, so that the overall size of the thermoacoustic electric generation system is greatly decreased.The phase modulation technology of the acoustic power output port of the thermoacoustic engine is put forward creatively, and this is useful for improving the impedance matching characteristic of the thermoacoustic engine and linear alternator, and then the output electric power of the directly-drive thermoacoustic electric generator is greatly improved. In the directly-drive thermoacoustic electric generator, the phase difference between the oscillating pressure and volume flow rate is about 80° at the acoustic power output port of the thermoacoustic engine. The adding of the phase modulation object could decrease the phase difference between the thermoacoustic engine and linear alternator, and increase the amplitude product of them, so the acoustic power flowing into the linear alternator is increased. The performance of the thermoacoustic electric generator is increased by 15.65%. The influence of clearance, moving mass and stiffness of the rubber diaphragm on the system performance is investigated by orthogonal experiment, and oscillation temperature, output electric power and thermoelectric efficiency are the experimentation indexes. The methods of extremum analysis and covatiance analysis are employed to obtain the primary and secondary sequence of the factors and the optimum assembly condition.Based on the research work of theoretical analysis, modeling, simulation calculation and experimental study, the directly-drive thermoacoustic electric generator could operate safely for long-term, and the output electric power is in the international advanced level.