The Research On Thermal-mechanical Response And Failure Mechanism Of CNG Steel Vehicle Cylinder In Fire Environment

Motor vehicle population is increasing rapidly, the world energy picture is reshaping and environmental protection requirements are reinforced. On these backgrounds, the natural gas vehicles with good economic and environmental benefits are widely popularized and spread. Meanwhile, the uses of CNG cylinders are fast-growing, CNG all-steel cylinders are over90%in quantity. The fire and explosion accidents of CNG all-steel cylinders often lead to disastrous consequences. Due to the bonfire test has the characteristics of large investment, high risk and poor repeatability, etc; Numerical simulating research is paid more and more attention. The numerical research on thermal-mechanical response and failure mechanism of CNG all-steel cylinder subjected to fire environment, has certain theoretical value and practical significance. In this paper, the research is carried out as follows:(1) The numerical study on thermal response of CNG all-steel cylinder in real fire environment. Based on numerical method of zoning solution boundary coupling and fluid-solid coupling heat transfer theory, according to real bonfire test and reasonable assumptions, then the physical and mathematical models of fire environment and CNG cylinder are established respectively. The CFD software FLUENT is used for three-dimensional numerical simulation of windless and windy fire environment, the flame information of flow field, temperature field and heat flux distribution is obtained, it’s also proved windless environment can supply more evenly and sufficient heat. The cylinder’s outside surface heat flux distribution calculated by fire environment is provided thermal boundary for CNG cylinder. FLUENT is also used to model three-dimensional transient thermal response process of CNG cylinder, which obtains regularity relations between the filling media temperature, the filling media pressure, the wall temperature and time within420s.(2) The numerical study on mechanical response of CNG all-steel cylinder in fire environment. According to thermal-structure coupling analysis and elastic-plastic theory, ANSYS Workbench13.0is employed to integrate fluid dynamic analysis module (FLUENT) and thermal-structural static module (ANSYS Mechanical), the good accuracy of this finite element model is verified, then, the finite element stress analysis of CNG cylinder is implemented in different temperature-pressure fields coupling condition and the strength of CNG cylinder is checked within420seconds.(3) The preliminary study on CNG cylinders failure mechanism in the fire environment, and failure prediction and prevention. According to failure mechanism, the theoretical prediction method of failure time and bursting pressure of the steel-made CNG cylinder is put forward in an accidental fire environment. First the failure mechanism is analyzed, then, the failure criteria are presented. The cubic polynomial fitting curve of CNG cylinder bursting pressure under different temperatures and property conditions is obtained by the finite element analysis of limit load, then the thermal response curve of CNG cylinder internal pressure is obtained by the calculation of FLUENT, The CNG cylinder burst failure time point and burst failure pressure in an accidental fire environment are accurately predicted by the intersection point of the two curves. This CNG cylinder probably burst at420s around. Finally, based on the above failure mechanism of the CNG cylinder, the accidental fire safety countermeasures of CNG cylinder are suggested.