Performance Research And Power Analysis Of Air Compressor In Fuel Cell Vehicle

High-Speed developing modern society needs more vehicles for transport while the fossil fuel such as petroleum which provides power to vehicles on the earth is decreasing. So People are devoting themselves to finding environmental-friendly clean fuel which will replace traditional fossil fuel. Without using any mineral fuel, the hydrogen fuel cell, which outputs electric power transformed from reaction between hydrogen and oxygen, is of completely zero emission.The air compressor in hydrogen fuel cell is one of the most important parts. The compressor promote pressure of air from environment and send the air to fuel cell stack where hydrogen and oxygen take part in electrochemistry reaction to generate electricity energy and water. At the same time, the compressor is driven by the motor which consumes the power for fuel cell stack. So performance of air compressor has heavy influence on effect of fuel cell stack on vehicle.Funded by the national high technology research and program of china-"Research on air compressor in fuel cell vehicle"(No.2003AA501360, No.2001AA501042), the application of air compressor in fuel cell vehicle is aimed in this project; the working principles and characters of energy transform of two types compressor, namely single screw compressor and centrifugal compressor, are analyzed in detail; the sources of energy dissipation in single screw compressor are directly compared by method of exergy analysis; secondly flow on suction side of centrifugal compressor is researched in detail and obtain a conclusion of how to suppress secondly flow. On the basis of research on secondly flow, a design method of impeller by assigning circulation is presented.The research work is divided into the following chapters:In chapter 1, the significance and cause of the project are introduced. Then the function of air compressor in the fuel cell vehicle is introduced. The current research state of air compressor in fuel cell vehicle nationally and internationally is summarized. Finally, the main research objects are proposed for this dissertation.In chapter 2, the working principles of volume compressor are analyzed. A total mathematic model which includes the air leakage and heat exchange is established to simulate the working process of single screw compressor. Based on the model, the influences on performance are discussed due to varied rotation speed. The status change of air also is researched while injecting different cooling water. The research result show that the ratio of mass flow to volume increase while increase the compressor rotation speed.In chapter3, flows in a low pressure centrifugal compressor are researched by employing the CFD method. The simulation shows that small scale centrifugal compressor can produce enough air for fuel cell stack under design rotation speed.In chapter4, a single screw compressor and a centrifugal compressor are compared from the point of view of volume, mass, and massflow-pressure relation ship. Four kind sources of power loss, namely irreversible heat exchange, adiabatic throttling, mixing of two flows and leakage to environment, are discussed by exergy analysis method. The loss caused by secondly flow in centrifugal compressor is also researched in detail.In chapter5, an impeller design method for low speed, low pressure centrifugal compressor is presented. The method takes circulation distribution on meridian plane as design conditions, calculates the velocity field of impeller by equation of average flow function and periodic potential function, then obtains a new blade profile according to relationship between blade shape and velocity field. The method is applied to a centrifugal compressor of fuel cell stack. The simulation result show the adiabatic efficiency rise due to secondly flow is restrained.In chapter6, a test bench for compressor is built. A single screw compressor and a centrifugal compressor are designed and produced. The compressors are experimented on the bench.In chapter7, the research work is summarized and perspectives on the future are presented.