Research On Hydraulic Fatigue Test System For70MPa Composite Hydrogen Cylinder And Control Method Of Pressure And Temperature

Hydrogen has become the most promising clean energy of21st century because of its excellent advantages such as rich reserve, high combustion efficiency and reproducible ability. It has important strategic significance for solving the problems of energy shortage and environmental pollution puzzling all over the world. With the development of fuel cell technology, hydrogen fuel cell vehicle has become the focus of the world automobile manufacturers.High pressure gaseous hydrogen storage is the most popular and mature method for fuel cell vehicle due to its technical simplicity, fast filling-releasing rate and low energy consumption for compressing hydrogen. Composite cylinder as the first choice for on-board hydrogen storge has the advantages of high-pressure-resistant ability, light weight and corrosion resistance. The safety performance of high-pressure hydrogen storage with potential risk of leakage and explosion is the important factor that infuences the public to accept fuel cell vehiceles and marketing promotion.Hydraulic fatigue test is the important means to detect macroscopic strength, safety margin, construction rationality and reliability of composite cylinder. Definite requirements have been proposed in relevant standards of US, EU, Japan, ISO and China. However, it is found that there is no hydraulic fatigue test system for70MPa composite cylinder in China. Pressure and temperature should be controlled during hydraulic fatigue test. However, little research has been done on the law of pressure rise and temperature variation, and contorl method of pressure and temperature during hydraulic fatigue test has not been established.Researches on development of hydraulic test system and pressure rise and temperature rise of high-pressure hydrogen cylinder during hydraulic test and pressure cycling test is conducted in this paper, which is supported by the National High Technology Research and Development Program of China (863Program)"Technology and equipment of high pressure hydrogen storage vessels"(No.2006AA05Z143), Key Project of China National Programs for Fundamental Research and Development of China (973Program)"New high-density on-board hydrogen storage system and its theoretical safety prediction research"(No:2007CB209706), and the nonprofit industry research project of General Administration of Quality Supervision, Inspection and Quarantine of the People’s Republic of China(No:10-131). The main contents and conclusions of this paper are as follows:(1) Based on requirements of hydraulic test, burst test and pressure cycling test for70MPa composite hydrogen cylinder, parameters of hydraulic fatigue test system are determined such as type of medium, pressure class and flow rate. Considering the feature of hydraulic fatigue test and working principle of pressure device, a general design scheme of hydraulic fatigue system is proposed. The combination of3-way and2-way pneumatic directional valves is proposed by studing on the realization modes of pressure cycle, which effectively reduces energy consumption during pressure keeping and relief. The flow rate of air driven pump with output pressure and pneumatic pressure through analyzing the flow characteristics of booster pumps. Motor speed and pneumatic pressure regulation are used to change the flow rate for air driven pump and plunger pump. And flow control is used to control the lower limit pressure. On this basis, a process design is conducted and the hydraulic fatigue test system for70MPa composite hydrogen cylinder is built which improves detection ability of safety performance and provides strong support for design and experimental study of high pressure composite hydrogen cylinder.(2) A theoretical analysis model has been established for pressurization of composite cylinder in which compressibility of medium and volume change of cylinder are comprehensively considered. Based on the equation of state of water, a formula of compressibility is derived. A calculation method for the volume of composite cylinder with pressure is proposed by finite element method. A calculation method of pressure rise rate and time is established combined with the theoretical analysis model, compressibility of water, volume of composite cylinder and flow characteristics of booster pumps. The calculation method is verified by experimental data. Effects of the volume change of cylinder, medium temperature and flow rate of pump on the pressure rise rate are investigated. It is revealed that the pressure rise rate is greatly affected by volume change of composite cylinder and is little affected by medium temperature, and pressure rise rate can be controlled by controlling the flow rate of pump. Furthermore, the control method of pressure rise rate is brought out. The value range of motor speed for plunger pump and pneumatic pressure for air driven pump is obtained.(3) Based on the theory of variable mass thermodynamics system, a thermodynamic model has been established for pressure cycling process, in which compression and expansion of medium, convective heat transfer between medium and inner surface, heat conduction in cylinder, and convective heat transfer between outer surface and environment are fully considered. A experimental study is taken on the temperature rise of composite hydrogen cylinder during pressure cycling test. The accuracy of the model is verified by the comparison between the experimental and simulation results. The thermodynamic model is employed to analyze the influence law of test parameters on equilibrium temperature of cylinder. It is shown that the temperature of cylinder surface is stable after several cycles, the equilibrium temperature of cylinder surface increase linearly with the increase of filling medium temperature and ambient temperature, and frequency has no significant effect on equilibrium temperature of cylinder surface for24.8MPa/54L type4composite cylinder used in IPHE round robin test. Based on simulation results, an equation for equilibrium temperature of cylinder surface is put forward. Furthermore, the control method of temperature of cylinder is brought out. Temperature of cylinder can be controlled by controlling the filling medium temperature. The value range of filling medium temperature for test requirement with various conditions was obtained.