Dynamic Characteristics Analysis Of LNG Vehicle Cylinder

As a kind of clean and effective energy, LNG is more and more popular with energy crisis and environmental pollution now, and the related industries develop rapidly also. As a new type of clean energy vehicle, LNG vehicle has many advantages of security, economy, and high-efficiency etc, and has caused wide attention and related researches. As a the main equipment of LNG vehicle fuel supply, the reliability of LNG vehicle cylinders will directly influence on the safety operation of LNG vehicle. So far the researches on the security of LNG vehicle cylinder are relatively few, and have centered mainly on static state. On one hand, the liquid in LNG cylinders shakes strongly due to the sudden braking or potholes conditions, and causes the extra shock loads to the cylinder; On the other hand, the strong vibrations of LNG cylinders due to the engine vibration and irregularities of road will also exert loads on the cylinder. These additional dynamic loads result in the destruction of the cylinder because of the stress concentration phenomenon in the structure discontinuous areas of the inner vessel. Therefore, it is essential to study on the dynamic characteristics of LNG vehicle cylinders based on the static structure stress analysis. The dynamic characteristics of the inner vessel of LNG vehicle cylinder were analyzed by the finite element method, The main contents and conclusions are as following:(1) The inner vessel of LNG vehicle cylinder was analyzed under static state. The mass of LNG was equivalent to the inner vessel shell by the equivalent density method, the inertial force load was applied on the inner vessel shell, and the stress distributions of the inner vessel and support were calculated under the emergency braking and potholes conditions. The impact of liquid in the inner vessel was equivalent to the static load by the impact load method, the stress distributions of the inner vessel under the working condition were calculated, and the strength check of the inner vessel was carried out on the basis of stress classification. The results showed that the strength fully meets the requirements. On this foundation, the effects of the liquid impact loads in different directions on the structural strength of the inner vessel were further studied.(2) The modal analysis of the inner vessel of LNG vehicle cylinder was carried out involving the different storage capacities, and the natural frequencies and the corresponding mode shape diagrams of the cylinder tank were obtained under different depth of liquid. The results showed the liquid has a great effect on the dynamic property of inner vessel structure, and the natural frequency of the inner vessel decreases with the increasing of the liquid storage capacity.(3) The frequency response curve of the inner vessel of LNG vehicle cylinder under engine excitation was obtained by the harmonic response analysis, finding out the peak of the curve, and the resonance frequency of LNG vehicle cylinder was determined according to the results of modal analysis, thus avoiding resonance due to engine vibration.(4) The deformation and stress distributions of the inner vessel of LNG vehicle cylinder were obtained under the rough road excitation by the response spectrum analysis. The results showed that the inner vessel vibration aroused by road roughness, leads to large deformation and force of the support between the inner and outer vessel which exceeds the allowance range of the materials. So, the structure of the support should be optimized, and the necessary reinforcement measures should be taken to hazardous locations.