| Emissions from vehicles have become increasingly serious pollution on the environment along with the increasing number of cars. Compared with gasoline, natural gas as fuel for vehicles is a relatively clean fuel, it can not only reduce transport costs, but can also improve the thermal efficiency of the engine and extend engine life. At present, the key to using natural gas as motor fuel is to develop a suitable gas storage method. Compressed natural gas (CNG) is widely used as vehicles fuel because of its mature technologies. However, CNG requires huge capital investment, there are also potential safety problems with high-pressure equipment.The economy of Liquefied natural gas (LNG) is poor because of huge investment of LNG plants, while the maintenance of liquefied petroleum gas bottles is difficult.Because the storage conditions of adsorbed natural gas (ANG) technology are at room temperature and low pressure (3MPa~4MPa), at the same time the storage capacity is considerable, so ANG is particularly suitable as fuel of cars. However, the development of ANG technology is constrained by a major factor, the factor is the influence of thermal effects on the performance of storage systems. The charge process is exothermic process while charging at storage station, so storage systems must be colded. The discharge process is endothermic process while discharging at drive process, so storage systems must be hoted.The theory research is done considering the influence of adsorption heat on charge and discharge process. The values of pressure, temperature and adsorbed amounts are calculated during charge and discharge process and the influence factors are analyzed. Moreover, some measures alleviating the adverse effects caused by thermal effects are taken. In this paper, the following research on thermal effects of vehicle tank during charge and discharge process is done:Firstly, the Phenomenon absorption of natural gas by porous medium absorbent is analyzed according to the principle and essence of absorption. Adsorption isotherm model is being drawn through the analysis of experimental data, and the isosteric heat of adsorption is calculated by Calusius-Clapeyron equation. The influence of adsorption heat on charge and discharge process is analyzed by studying the thermodynamic path of charge and discharge process. The feasibility of using adsorptive natural gas for cars is analyzed and the existing problems are given.Secondly, to study the adverse effects of absorption heat to absorption system, the dynamic model of tank during adsorption process is established, this governing equation are solved using the algorithms of SIMPLER in order to get the values of pressure, temperature and speed during charge process. The following conclusions are drawn by analyzing the results, internal temperature of tank increase rapidly when charge rapidly, as a result, the follow-up process of charge is seriously affected. The adverse effects caused by thermal effects can be alleviated through a long period of charge.Thirdly, according to the characteristics of the gas flow and heat transfer of vehicle storage tank, dynamic model of vehicle tank during discharge process is established based on fluid mechanics, thermodynamics and heat transfer theory, the model are solved by Newton-Raphson root-finding technique. The aim is to find out the main factors of influencing discharge amounts and efficiency by analyzing some parameters, such as wall temperature of storage tank, the tank pressure, absorbent temperature, natural convection. The simulations reveal that discharge process is endothermic process, the reduction of adsorbent temperature has great impact on discharge performance. The central zone of tank has highest temperature drop. Natural convection has little influence on discharge properties even under conditions of slow discharge. Wall of tank has big influence on discharge properties. Significant temperature gradient exists between the wall and absorbent and internal adsorbent.In addition, as high temperature of the engine cooling water and engine exhaust gas, engine cooling water and gas flow by wall of tank in the form of heat exchanger in order to promote discharge, the two discharge efficiency using engine cooling water and engine exhaust gas for discharge are 87.85 percent and 89.68 percent, respectively, by solving the discharge model of using waste heat of engine, the above results demonstrate the feasibility of using the engine waste heat for discharge.Finally, considering to the activated carbon fiber (ACF) has a high adsorption storage performance and good conductivity and heat capacity, the discharge performance of two conditions, both heating wall of tank by engine waste heat and heating adsorbent by electricity, is studied by measuring the resistance of carbon fiber. The following conclusions are obtained by analyzing the simulation results: discharge performance is greatly improved by heating carbon fiber, and the imbalance of internal temperature has a fundamental improvement.The study on absorption natural gas vehicles is still in its infancy stage, along with the solution of problem of thermal effects, absorption natural gas vehicles will certainly be a large-scale application, the results of this subject provide theoretic support for the application of natural gas vehicles.
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