| Environmental protection and reducing nonrenewable resources comsuption are becoming more and more serious all over the world, and are urgent to be resolved. However, these two problems become more serious with the increasing number of internal combustion vehicles. With this background, it is very significant to develop new type vehicles which do not pollute the environment and do not depend on nonrenewable resources.The compressed air powered car is a new kind of environmental protection and energy saving vehicle, which power component is a compressed air powered engine. The engine can covert the energy stored in compress air into mechanical power. It’s exhaust is clean air, which do not pollute environment. The compressed air needed when it works can be made by electricity power, which can be converted from solar energy, wind energy, hydro energy, nuclear energy and so on. So compressed air powered vehicle can comsume no nonrenewable energy. Therefore, developing compressed air power engine and make it into widespread use can be very helpful to environment and nonrenewable energy.Many features of compressed air powered engine are studied in this project, which include: principle, speed characteristic, energy conversion and its influence factors, the means to increase the conversion efficiency, and so on. The target of this project is to improve the practicability of domestic compressed air powered car. The research process is as follows: summarize the existing research of compressed air powered engine, put forward the research directions of this project; study the related theories, put forward the improved scheme, establish the mathematical model, simulate, produce the protype of compressed air powered engine, and test.The main content, results and conclusions of this study are as follows.1. After summarise the existing studies of compressed air powered engine, the study direction is put forward, i.e. to reduce the energy loss in the operation of compressed air powered engine. A research framework was determined, which include:to research the compressed air powered engine theory, to establish the mathematical model of compressed air powered engine, to use mathematical models for simulation studies, and to design and implement the engine prototype and use it to study compressed air powered engine experimentally.2. The related theories of compressed air powered engine were studied, which include the energy stored in compressed air, the energy loss caused by decompression and exhaust processes, the expansion ratio of the compressed air and the way to adjust expansion ratio. On this theoratical basis, the method of adjusting the expansion ratio in the operation of compressed air powered engine was studied to remove decompression process and control exhaust pressure.3. The related theories of compressed air powered engine were studied, which include: the thermodynamic processes of compressed air powered engine, gas flow processes and heat transfer between gas and environment. By integrating the engine, compressed air tank and flywheel according to the relationship among them, a mathematical model of adjustable expansion ratio compressed air powered engine system was build. A simulation program was written for simulation research.4. Simulation research of compressed air powered engnine was done on the mathematical model build before. The variation of the state parameters of compressed air in the engine system was studied. According to characteristics of these variations, useful measures were put forword for better performance of the compressed air powered engine. Also, we compared the exhaust pressure, speed characteristic and energy efficiency between fixed and adjustable expansion ratio compressed air powered engines. The results abtained from comparison show that: the exhaust of the latter is lower than the former, the conversion efficiency of the latter is higher than the former, the torque and power characteristics of the kinds of engine are alike, while the gas consumption rates of them are different. Finally, we studied the influences of tempreture of environment, the diameters of valves, and load on the energy conversion efficiency of compressed air powered engine, and put forward the measures of improvement.5. The hardwere of the compressed air powered engine were discussed, and then were purchased or produced to obtain the simplist compressed air powered engine system. The algorithm of determing the moment of closing inlet valve was desined and written in Visual C++ IDE. The whole monitoring program was developed with Visual C++. Finally, a prototype of adjustable expansion ratio compressed air powered engine system was produced. The prototype may served as a fixed expansion ratio compressed air powered engine system by changing the mornitoring program when there is a need to do so.6. A lot of tests wre done on the engine prototype. This prototype may operate as fixed or adjustable expansion ratio compressed air powered engine, depending on the control scheme used in the monitoring program. The energy conversion efficiency of the two kinds of engine were compared. The result reveals that the latter’s exhaust pressure is lower than the formmer’s, and the latter’s energy conversion efficiency is higher than the former’s. The speed characteristics of the two kinds of engine were compared. The results show that the latter was less than that of former in torque, power and gas consumption at the same speed. The method of compensating the response time of the electromagnetic valves by advancing phases was studied, and the engine efficiency can be increased by compensation method. The method of adjusting the exhaust pressure threshold was studied, and the engine efficiency can be increased by exhaust pressure adjusting. Also, the influence of environmental temperature on engnin efficiency was studied, and the experimental results show that the energy conversion efficiency can be increased with higher environmental temperature, which is the same as the conclusions of theoretical and simulation research.In this study, the new idea of the expansion ratio adjustment in the working process of compressed air powered engine was put forward to remove the decompression process and control exhaust pressure of the engine. The mathematical model of adjustable expansion ratio compressed air powered engine system was established, which include engine, compressed air tank and flywheel. A prototype of adjustable expansion ratio compressed air powered engine was designed and produced. Experiments were done on the engine prototype, and the experimental results verified the conclusions of theoretical study and simulation research. These studies can provide a new starting point for the subsequent research of compressed air powered engine. |
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