【作者】 卜宪标；

【导师】 谭羽非；

【作者基本信息】 哈尔滨工业大学 ， 供热、供燃气、通风及空调工程， 2008， 博士

【摘要】 随着汽车数量的增多,汽车排放物对环境造成越来越严重的污染。与汽油相比,天然气作为汽车燃料是一种相对清洁的燃料,它不仅能够降低运输成本,而且可以提高发动机的热效率和延长发动机的使用寿命。目前使用天然气做汽车燃料的关键是发展一种合适的储气方式,压缩天然气(CNG)储存技术比较成熟,已广泛应用于天然气汽车,但CNG高压设备存在安全隐患。液化天然气(LNG)储气方式,低温冷却技术复杂,建设投资巨大,且液化气瓶维护困难。吸附天然气(ANG)储存量大,储存状态是常温、中低压(3MPa~4MPa),尤其适用于车用燃料。但目前吸附储存天然气应用于汽车的主要瓶颈问题,是没有很好的解决吸脱附过程热效应的不利影响:一方面在加气站完成的充气吸附过程,是放热过程,必须对系统降温;另一方面汽车行驶中完成的放气脱附过程,需要吸热,必须给系统补充热量。本文针对车用天然气储罐吸脱附过程产生的热效应问题,进行了理论研究,模拟计算了吸脱附过程中储罐内温度、压力和吸附量的变化,分析了影响吸脱附量的因素,并提出了解决热效应的措施,具体工作如下:首先,从吸附的原理和本质出发,通过对实验数据的分析,选取了吸附等温线模型,并利用克劳修斯-克拉贝龙方程计算得到等量吸附热。通过研究吸脱附过程的热力学路径,分析了热效应对吸脱附过程的影响。同时分析了吸附天然气用于汽车的可行性及存在的问题。其次,以车用吸附储罐为研究对象,建立了储罐吸附过程的数学模型,用SIMPLER算法求解了压力速度和温度耦合问题,得到储罐内部压力场、温度场和速度场。通过对计算结果的分析得出:快速充气时,储罐内部温度迅速升高,严重影响充气量,长时间的充气和外壁面采用强迫对流的方式散热能缓解热效应,增加充气量。再次,根据车用储罐脱附过程中天然气流动和换热的特点,建立了车用储罐脱附过程的动态模型,通过分析脱附过程中储罐壁温、罐内压力、吸附剂温度以及罐外自然对流等参数的变化,得到影响脱附量和脱附效率的主要因素。通过分析计算结果得出:脱附过程中,储罐中心附近温度最低;罐壁外侧的自然对流换热对脱附性能的影响很小。本文进一步提出利用发动机余热作为加热热源,补充脱附过程所需热量的可行方案,通过模拟计算,得出应用发动机冷却水和烟气进行脱附,可使脱附效率提高12.34%和14.17%。最后,本文针对活性碳纤维(ACF)具有高吸附存储性和良好导电发热性的特点,通过实测碳纤维的电阻,研究了发动机余热加热储罐外壁面和通电加热碳纤维吸附剂两种工况下的脱附性能。通过分析得到:电加热碳纤维能从根本上改善储罐内部温度场的不均匀性。我国吸附天然气汽车的研究仍处于起步阶段,随着吸附储存天然气热效应的合理解决,吸附天然气汽车必将得到大规模的推广应用,本课题的研究成果能为吸附天然气汽车的推广应用提供理论依据和技术支持。更多还原

【Abstract】 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.更多还原