The effect of ambient condition on the atomization characteristics were numerically simulated by using centrifugal nozzle as the research object, the influence of ambient air pressure and temperature on atomization characteristics parameters such as oil film thickness and atomization angle were obtained.With the FLUENT used,when the injection pressure was 4.0 MPa, the fuel temperature is 100 ℃,the ambient temperature from －50 ℃ to 400 ℃and the ambient pressure in the range of 0.1～3.0 MPa were numerically simulated.The results show that when the ambient pressure is constant, the temperature increases, the air density decreases, the fuel evaporation intensifies, the gas phase fuel ratio increases, and the atomization effect increases. When the ambient temperature is constant, the environmental pressure increases, the air density increases, the crushing occurs earlier, the oil film thickness increases, and the liquid phase fuel ratio increases, although the spray cone angle and the interaction between oil and gas increase, but it is not conducive to fuel atomization.

Friction stir welding (FSW) is an effective, environment⁃friendly solid state is an efficient and environmentally friendly solid phase bonding method, which has the characteristics of low temperature severe plastic deformation and high joint quality. FSW can effectively solve the problems associated with fusion welding in petroleum tanks and pipelines. However,due to the influence of welding parameters, working conditions and inherent mode of the method, friction stir welding has welding defects, which reduces the service life of the joint. The two major welding defects (global and local welding defects) were summarized in terms of characteristics and causes, while the repairing technologies for various defects were reviewed. This paper has practical significance for joint quality improvement, high⁃efficiency high⁃performance repairing and engineering applications.